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netrin 1-deficient mice develop massive aberrant innervation of the ipsilateral septum. Coronal sections. (A-C) Pattern of DiI labeling in control mice following DiI injections in the hippocampus. (A) Section illustrating the injected hippocampus (left) and the resulting labeling in the contralateral hippocampus (h), with many labeled fibers and retrogradely labeled neurons in CA3. (B) At rostral levels labeled fibers cross the midline through the hippocampal commissure (arrow) to innervate the contralateral side. (C) Pattern of hippocampo-septal innervation in control mice. Hippocampo-septal axons innervate the dorsolateral septal (dls) area forming a projection which is a mainly ipsilateral (arrowhead). A few axons form a contralateral hippocampo-septal innervation (arrow). In addition, a band of retrogradely labeled neurons is observed in the medial septum/diagonal band complex (mdb). (D-I) Pattern of labeling following DiI injections in the hippocampus of netrin 1-mutant mice. (D) After DiI injection in the hippocampus (left) no labeled fibers are seen in the contralateral hippocampus (h). (E) At rostral levels labeled fibers do not cross the midline but turn ventrally (arrow) towards the septum (s). (F) Pattern of hippocampo-septal innervation in netrin 1-mutant mice, illustrating many fascicles of fibers (arrows) extending into the septum. (G-I) Adjacent sections from the same animal as in F ordered from caudal (G) to rostral (I), illustrating that anterogradely labeled hippocampal axons (arrow) innervate the entire rostrocaudal extent of the septum. Retrogradely labeled neurons in the medial septum/diagonal band complex (mdb) are also observed. (J,K) Photomicrographs of the fimbria in control and mutant mice showing the disorganization of fiber tracts in the netrin 1-deficient fimbria. CA1-CA3, hippocampal fields; cc, corpus callosum; DG, dentate gyrus; h, hippocampus; nc, neocortex; s, septum; t, thalamus. Broken lines indicate the midline. Scale bar in A: 500 µm in A,B,D,E. Scale bar in C: 175 µm in C,F-I. Scale bar in J: 50 µm in J,K.
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Diffusible factors, including netrins and semaphorins, are believed to be important cues for the formation of neural circuits in the forebrain. Here we have examined the role of netrin 1 in the development of hippocampal connections. We show that netrin 1 and its receptor, Dcc, are expressed in the developing fimbria and in projection neurons, resp...
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... examine whether commissural axons that normally terminate in the contralateral hippocampus may aberrantly innervate the septum in the absence of netrin 1, injections of the lipophilic tracer DiI were performed in the hippocampus. Injections of DiI in control mice yielded the typical pattern of anterograde commissural labeling ( Supèr and Soriano, 1994;Supèr et al., 1998), in which most fibers crossed the hippocampal commissure and innervated the contralateral hippocampus (Fig. 4A,B). In addition, some fibers curved ventrally before crossing to form the hippocampo-septal pathway. Consistent with previous studies (Supèr and Soriano, 1994), hippocampo-septal axons terminated in a restricted area of the dorsal septum (Fig. 4C). This projection was essentially ipsilateral, although a few contralateral fibers were observed (Fig. 4C). In addition, many retrogradely labeled neurons were present in the medial septum/diagonal band complex (Fig. 4C), which forms the reciprocal septo-hippocampal pathway (Amaral and Witter, 1995;Supèr and Soriano, 1994). No fiber fascicles were detected in the septum of control ...
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... examine whether commissural axons that normally terminate in the contralateral hippocampus may aberrantly innervate the septum in the absence of netrin 1, injections of the lipophilic tracer DiI were performed in the hippocampus. Injections of DiI in control mice yielded the typical pattern of anterograde commissural labeling ( Supèr and Soriano, 1994;Supèr et al., 1998), in which most fibers crossed the hippocampal commissure and innervated the contralateral hippocampus (Fig. 4A,B). In addition, some fibers curved ventrally before crossing to form the hippocampo-septal pathway. Consistent with previous studies (Supèr and Soriano, 1994), hippocampo-septal axons terminated in a restricted area of the dorsal septum (Fig. 4C). This projection was essentially ipsilateral, although a few contralateral fibers were observed (Fig. 4C). In addition, many retrogradely labeled neurons were present in the medial septum/diagonal band complex (Fig. 4C), which forms the reciprocal septo-hippocampal pathway (Amaral and Witter, 1995;Supèr and Soriano, 1994). No fiber fascicles were detected in the septum of control ...
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... examine whether commissural axons that normally terminate in the contralateral hippocampus may aberrantly innervate the septum in the absence of netrin 1, injections of the lipophilic tracer DiI were performed in the hippocampus. Injections of DiI in control mice yielded the typical pattern of anterograde commissural labeling ( Supèr and Soriano, 1994;Supèr et al., 1998), in which most fibers crossed the hippocampal commissure and innervated the contralateral hippocampus (Fig. 4A,B). In addition, some fibers curved ventrally before crossing to form the hippocampo-septal pathway. Consistent with previous studies (Supèr and Soriano, 1994), hippocampo-septal axons terminated in a restricted area of the dorsal septum (Fig. 4C). This projection was essentially ipsilateral, although a few contralateral fibers were observed (Fig. 4C). In addition, many retrogradely labeled neurons were present in the medial septum/diagonal band complex (Fig. 4C), which forms the reciprocal septo-hippocampal pathway (Amaral and Witter, 1995;Supèr and Soriano, 1994). No fiber fascicles were detected in the septum of control ...
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... examine whether commissural axons that normally terminate in the contralateral hippocampus may aberrantly innervate the septum in the absence of netrin 1, injections of the lipophilic tracer DiI were performed in the hippocampus. Injections of DiI in control mice yielded the typical pattern of anterograde commissural labeling ( Supèr and Soriano, 1994;Supèr et al., 1998), in which most fibers crossed the hippocampal commissure and innervated the contralateral hippocampus (Fig. 4A,B). In addition, some fibers curved ventrally before crossing to form the hippocampo-septal pathway. Consistent with previous studies (Supèr and Soriano, 1994), hippocampo-septal axons terminated in a restricted area of the dorsal septum (Fig. 4C). This projection was essentially ipsilateral, although a few contralateral fibers were observed (Fig. 4C). In addition, many retrogradely labeled neurons were present in the medial septum/diagonal band complex (Fig. 4C), which forms the reciprocal septo-hippocampal pathway (Amaral and Witter, 1995;Supèr and Soriano, 1994). No fiber fascicles were detected in the septum of control ...
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... of DiI in the hippocampus of mutant mice showed no labeled fiber in the contralateral hippocampus (Fig. 4D). Moreover, the pattern of anterograde labeling in the septum differed greatly from that in control mice. First, the hippocampo-septal innervation was exclusively ipsilateral (Fig. 4E,F), indicating that netrin 1 is necessary for the formation of the crossed hippocampo-septal pathway. More importantly, the septum ipsilateral to the injection was occupied by thick fiber bundles that descended from the fimbria towards medial and ventral levels, filling most of the dorsoventral extent of the septum (Fig. 4F). In some cases, these bundles defasciculated and gave rise to fibers terminating in growth cones. Serial sections showed that this massive hippocampo-septal innervation was present in all the rostrocaudal levels of the septum (Fig. 4G-I). Single axons were also close to the olfatory tubercle, but no labeled fibers were detected in other nearby forebrain areas, including the neocortex and the ...
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... of DiI in the hippocampus of mutant mice showed no labeled fiber in the contralateral hippocampus (Fig. 4D). Moreover, the pattern of anterograde labeling in the septum differed greatly from that in control mice. First, the hippocampo-septal innervation was exclusively ipsilateral (Fig. 4E,F), indicating that netrin 1 is necessary for the formation of the crossed hippocampo-septal pathway. More importantly, the septum ipsilateral to the injection was occupied by thick fiber bundles that descended from the fimbria towards medial and ventral levels, filling most of the dorsoventral extent of the septum (Fig. 4F). In some cases, these bundles defasciculated and gave rise to fibers terminating in growth cones. Serial sections showed that this massive hippocampo-septal innervation was present in all the rostrocaudal levels of the septum (Fig. 4G-I). Single axons were also close to the olfatory tubercle, but no labeled fibers were detected in other nearby forebrain areas, including the neocortex and the ...
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... of DiI in the hippocampus of mutant mice showed no labeled fiber in the contralateral hippocampus (Fig. 4D). Moreover, the pattern of anterograde labeling in the septum differed greatly from that in control mice. First, the hippocampo-septal innervation was exclusively ipsilateral (Fig. 4E,F), indicating that netrin 1 is necessary for the formation of the crossed hippocampo-septal pathway. More importantly, the septum ipsilateral to the injection was occupied by thick fiber bundles that descended from the fimbria towards medial and ventral levels, filling most of the dorsoventral extent of the septum (Fig. 4F). In some cases, these bundles defasciculated and gave rise to fibers terminating in growth cones. Serial sections showed that this massive hippocampo-septal innervation was present in all the rostrocaudal levels of the septum (Fig. 4G-I). Single axons were also close to the olfatory tubercle, but no labeled fibers were detected in other nearby forebrain areas, including the neocortex and the ...
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... of DiI in the hippocampus of mutant mice showed no labeled fiber in the contralateral hippocampus (Fig. 4D). Moreover, the pattern of anterograde labeling in the septum differed greatly from that in control mice. First, the hippocampo-septal innervation was exclusively ipsilateral (Fig. 4E,F), indicating that netrin 1 is necessary for the formation of the crossed hippocampo-septal pathway. More importantly, the septum ipsilateral to the injection was occupied by thick fiber bundles that descended from the fimbria towards medial and ventral levels, filling most of the dorsoventral extent of the septum (Fig. 4F). In some cases, these bundles defasciculated and gave rise to fibers terminating in growth cones. Serial sections showed that this massive hippocampo-septal innervation was present in all the rostrocaudal levels of the septum (Fig. 4G-I). Single axons were also close to the olfatory tubercle, but no labeled fibers were detected in other nearby forebrain areas, including the neocortex and the ...
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Citations
... In particular, Map1b is required for commissure formation (Meixner et al., 2000) and homozygous Map1b knockout animals have similar phenotypes to Tuba1a ND/+ mice [ Figure 3 and (Meixner et al., 2000)]. Map1b is necessary for neuronal response to the guidance cue, Netrin1, a key player in commissural formation (Serafini et al., 1996;Barallobre et al., 2000;Finger et al., 2002;Lindwall et al., 2007;Fothergill et al., 2014;Arbeille and Bashaw, 2018). While our data show that Tuba1a ND/+ neurites grow faster in response to global application of Netrin-1 similar to wild type neurons in the time frame we measured, we cannot rule out impairment of turning in response to a localized source of Netrin-1 or response to other guidance cues. ...
Developing neurons undergo dramatic morphological changes to appropriately migrate and extend axons to make synaptic connections. The microtubule cytoskeleton, made of α/β-tubulin dimers, drives neurite outgrowth, promotes neuronal growth cone responses, and facilitates intracellular transport of critical cargoes during neurodevelopment. TUBA1A constitutes the majority of α-tubulin in the developing brain and mutations to TUBA1A in humans cause severe brain malformations accompanied by varying neurological defects, collectively termed tubulinopathies. Studies of TUBA1A function in mammalian cells have been limited by the presence of multiple genes encoding highly similar tubulin proteins, which leads to α-tubulin antibody promiscuity and makes genetic manipulation challenging. Here, we test mutant tubulin levels and assembly activity and analyze the impact of TUBA1A reduction on growth cone composition, neurite extension, and commissural axon architecture during brain development. We present a novel tagging method for studying and manipulating TUBA1A in cells without impairing tubulin function. Using this tool, we show that a TUBA1A loss-of-function mutation TUBA1AN102D (TUBA1AND), reduces TUBA1A protein levels and prevents incorporation of TUBA1A into microtubule polymers. Reduced Tuba1a α-tubulin in heterozygous Tuba1aND/+ mice leads to grossly normal brain formation except a significant impact on axon extension and impaired formation of forebrain commissures. Neurons with reduced Tuba1a as a result of the Tuba1aND mutation exhibit slower neuron outgrowth compared to controls. Neurons deficient in Tuba1a failed to localize microtubule associated protein-1b (Map1b) to the developing growth cone, likely impacting stabilization of microtubules. Overall, we show that reduced Tuba1a is sufficient to support neuronal migration and cortex development but not commissure formation, and provide mechanistic insight as to how TUBA1A tunes microtubule function to support neurodevelopment.
... Mouse models have been increasingly employed for neurobiology research largely due to advances in genetic/molecular manipulation methods. The corpus callosum and hippocampal commissures were found to have inheritable defects in some inbred mouse strains (Schimanski et al., 2002;MacPherson et al., 2008;Bohlen et al., 2012) or were poorly developed in some transgenic models (Barallobre et al., 2000;Shu et al., 2003). To date, no study has examined bilateral hippocampal activities in a mouse model in vitro. ...
Bilateral interconnections through the hippocampal commissure play important roles in synchronizing or spreading hippocampal seizure activities. Intact hippocampi or bilateral hippocampal slices have been isolated from neonatal or immature rats (6–7 or 12–21 days old, respectively) and the mechanisms underlying the bilateral synchrony of hippocampal epileptiform activities have been investigated. However, the feasibility of examining bilateral epileptiform activities of more developed hippocampal circuitry in vitro remains to be explored. For this, we prepared bilateral hippocampal slices from C57 black mice, a strain commonly used in neuroscience and for genetic/molecular modifications. Young mice (21–24-day-old) were used in most experiments. A 600-μm-thick slice was obtained from each mouse by horizontal vibratome sectioning. Bilateral dorsal hippocampal and connecting dorsal hippocampal commissure (DHC) tissues were preserved in the slice and extrahippocampal tissues were removed. Slices were recorded in a submerged chamber mainly at a room temperature (21–22°C). Bilateral CA3 areas were monitored by extracellular recordings, and unilateral electrical stimulation was used to elicit CA3 synaptic field potentials. The unilateral stimulation could elicit population spikes in the contralateral CA3 area. These contralateral spikes were attenuated by inhibiting synaptic transmission with cobalt-containing medium and were abolished when a cut was made at the DHC. Self-sustained and bilaterally correlated epileptiform potentials were observed following application of 4-aminopyradine and became independent after the DHC cut. Bilateral hippocampal activities were detectable in some slices of adult mice and/or at 35–36°C, but with smaller amplitudes and variable waveforms compared to those observed from slices of young mice and at the room temperature. Together, these observations suggested that examining bilateral epileptiform activities in hippocampal slices of young mice is feasible. The weaknesses and limitations of this preparation and our experimentation are discussed.
... The imbalance can result from defects in spinal interneuronal circuits. It has been demonstrated previously that functioning of spinal interneuronal circuits is adversely affected in Netrin-1 and DCC-deficient mice (Barallobre et al., 2000;Deiner & Sretavan, 1999). Mutations in the axon-guidance pathway can also cause miswiring in the spinal cord, an idea supported by data from mice with DCC mutations. ...
Horizontal Gaze Palsy with Progressive Scoliosis‐2 with Impaired Intellectual Development (HGPPS2) is a rare congenital disorder characterized by absence of conjugate horizontal eye movements, and progressive scoliosis developing in childhood and adolescence. We report three new patients with HGPPS2 in a consanguineous Pakistani family, presenting varying degrees of progressive scoliosis, developmental delays, horizontal gaze palsy, agenesis of corpus callosum, and absence of cerebral commissures. Analysis of genotyping data identified shared loss of heterozygosity (LOH) region on chromosomes 5p15.33‐15.31, 6q11.2‐12, and 18q21.1‐21.3. A hypothesis‐free, unbiased exome data analysis detected an insertion of nucleotide A (c.2399dupA) in exon 16 of the DCC gene. The insertion is predicted to cause frameshift p.(Asn800Lysfs*11). Interestingly, DCC gene is present in the LOH region on chromosome 18. Variant (c.2399dupA) in the DCC gene is considered as the most probable candidate variant for HGPPS2 based on the presence of DCC in the LOH region, previously reported role of DCC in HGPPS2, perfect segregation of candidate variant with the disease, prediction of variant pathogenicity, and absence of variant in variation databases. Sanger Sequencing confirmed the presence of the novel homozygous mutation in all three patients; the parents were heterozygous carriers of the mutation, in accordance with an autosomal recessive inheritance pattern. DCC encodes a netrin‐1 receptor protein; its role in the development of the CNS has recently been established. Biallelic DCC mutations have previously been shown to cause HGPPS2. A novel homozygous variant in patients of the reported family extend the genotypic and phenotypic spectrum of HGPPS2.
... 1.10 | Molecular cues guiding the hippocampal-septal pathway during development 1.10.1 | Netrin-DCC signaling During development, the secreted guidance molecule, NTN1 is expressed between E14 and E18 in the fimbria, the midline, and the septum. NTN1 expression at the fimbria is required both by the hippocampal axons to exit the hippocampus and the septal axons to enter the hippocampus (Barallobre et al., 2000;Pascual et al., 2004). The receptor for NTN1, DCC (deleted in colorectal carcinoma) is expressed by hippocampal axons arising from all the hippocampal fields (Barallobre et al., 2000). ...
... NTN1 expression at the fimbria is required both by the hippocampal axons to exit the hippocampus and the septal axons to enter the hippocampus (Barallobre et al., 2000;Pascual et al., 2004). The receptor for NTN1, DCC (deleted in colorectal carcinoma) is expressed by hippocampal axons arising from all the hippocampal fields (Barallobre et al., 2000). NTN1 expression is further required for hippocampal axons to cross over to the contralateral side via the hippocampal commissure. ...
... A subset of hippocampal axons turn ventrally in the ipsilateral side and project to the lateral septum. In Ntn1 mutants, however, hippocampal axons fail to cross the commissure entirely and instead all of them turn ipsilateral to project within the septum in an aberrant manner (Barallobre et al., 2000). This suggests that NTN1-DCC-mediated signaling is critical for formation of the hippocampo-septal pathway. ...
A hallmark of the nervous system is the precision with which myriad cell types are integrated into functional networks that control complex behaviors. The limbic system governs evolutionarily conserved processes essential for survival. The septum and the hippocampus are central to the limbic system, and control not only emotion‐related behaviors but also learning and memory. Here, we provide a developmental and evolutionary perspective of the hippocampus and septum and highlight the neuronal diversity and circuitry that connects these two central components of the limbic system.
This article is categorized under:
Nervous System Development > Vertebrates: Regional Development
Nervous System Development > Vertebrates: General Principles
Comparative Development and Evolution > Regulation of Organ Diversity
... Research in this field during the last three decades has provided a large number of molecules implicated in axonal guidance processes, and four major families have been identified: the slits, ephrins, netrins, and semaphorins, as well as some morphogens such as Wnts, SHH, and BMPs [35][36][37]. Members of all of these families have been implicated in hippocampal axonal specification [30,[38][39][40] as we discuss later. Among these, great interest has been focused on the class 3 secreted semaphorins family; and different members and/or combinations of members have been described as playing roles in different hippocampal connections and their refinements. ...
... As mentioned above, the hippocampal formation presents a well-organized architecture: principal cells are located in single layers and afferents (entorhinal and commissural/associational axons) and intrinsic connections are distributed in a layer-specific termination [32][33][34]. Members of all four families of guidance factors have been involved in hippocampal axonal specification [38][39][40] with class 3 semaphorins being the most studied so far. The list of receptors and co-receptors that participate in this Sema3s-mediated signaling is continuously growing, and a great variety of combinations of receptor complexes can be assembled. ...
... In these animals, the perforant pathway is well developed and only a few axons are misrouted in stratum radiatum and hilus [83,85]. In addition, other guidance molecules such as Ephrin-A3, Netrin-1, and RGMa have been reported to be involved in the layer-specific termination of the perforant pathway in the SLM and OML [39,87,88]. Therefore, the molecules studied to date are not, themselves, essential for this pathway and other guidance factors; a combination of these or different signaling mechanisms should be implicated. ...
There is emerging evidence that molecules, receptors, and signaling mechanisms involved in vascular development also play crucial roles during the development of the nervous system. Among others, specific semaphorins and their receptors (neuropilins and plexins) have, in recent years, attracted the attention of researchers due to their pleiotropy of functions. Their functions, mainly associated with control of the cellular cytoskeleton, include control of cell migration, cell morphology, and synapse remodeling. Here, we will focus on their roles in the hippocampal formation that plays a crucial role in memory and learning as it is a prime target during neurodegeneration.
... Hippocampal explants were obtained from E15 brains, sectioned using a tissue chopper. Small tissue explants (300-400 µm thick) were obtained from the CA1/CA3 regions [77]. Hippocampal explants were cultured in Neurobasal medium (Gibco-BRL) plus 0.54% glucose, 0.032% NaH2CO3, L-glutamine, and 10% Horse Serum and supplemented with B27. ...
SNARE proteins are essential components of the machinery that regulates vesicle trafficking and exocytosis. Their role is critical for the membrane-fusion processes that occur during neurotransmitter release. However, research in the last decade has also unraveled the relevance of these proteins in membrane expansion and cytoskeletal rearrangements during developmental processes such as neuronal migration and growth cone extension and attraction. Neurotrophins are neurotrophic factors that are required for many cellular functions throughout the brain, including neurite outgrowth and guidance, synaptic formation, and plasticity. Here we show that neurotrophin Trk receptors form a specific protein complex with the t-SNARE protein Syntaxin 1, both in vivo and in vitro. We also demonstrate that blockade of Syntaxin 1 abolishes neurotrophin-dependent growth of axons in neuronal cultures and decreases exocytotic events at the tip of axonal growth cones. 25-kDa soluble N-ethylmaleimide-sensitive factor attachment protein and Vesicle-associated membrane protein 2 do not participate in the formation of this SNARE complex, while tetanus neurotoxin-insensitive vesicle-associated membrane protein interacts with Trk receptors; knockdown of this (v) SNARE impairs Trk-dependent outgrowth. Taken together, our results support the notion that an atypical SNARE complex comprising Syntaxin 1 and tetanus neurotoxin-insensitive vesicle-associated membrane protein is required for axonal neurotrophin function.
... Netrin-1, the most studied member of the family, was first shown to attract commissural neurons of the spinal cord to the ventral midline 21 ; subsequently, the expression of netrin-1 has been observed in other structures of the central nervous system, such as the ganglionic eminence, the fimbria, the lateral septum, the external germinal layer of the cerebellum, and the retina 22 . In the hippocampus, in particular, netrin-1 deficiency leads to aberrant projections of the hippocampal commissural axons, as well as alterations in the ipsilateral entorhino-hippocampal connections and CA3-to-CA1 associations 23 . Netrin-1 is a bi-functional molecule: it attracts axons of some classes of neurons, while it repels several others 24 . ...
High-throughput quantitative approaches to study axon growth behaviors have remained a challenge. We have developed a 1024-chamber microfluidic gradient generator array that enables large-scale investigations of axon guidance and growth dynamics from individual primary mammalian neurons, which are exposed to gradients of diffusible molecules. Our microfluidic method (a) generates statistically rich data sets, (b) produces a stable, reproducible gradient with negligible shear stresses on the culture surface, (c) is amenable to the long-term culture of primary neurons without any unconventional protocol, and (d) eliminates the confounding influence of cell-secreted factors. Using this platform, we demonstrate that hippocampal axon guidance in response to a netrin-1 gradient is concentration-dependent-attractive at higher concentrations and repulsive at lower concentrations. We also show that the turning of the growth cone depends on the angle of incidence of the gradient. Our study highlights the potential of microfluidic devices in producing large amounts of data from morphogen and chemokine gradients that play essential roles not only in axonal navigation but also in stem cell differentiation, cell migration, and immune response.
... Für Serafini et al., 1996) sowie von Axonen im Thalamus ( Braisted et al., 2000) und Hippocampus ( Barallobre et al., 2000). Es ist die Axonprojektion, aber nicht das Wachstum der Axone selbst betroffen ( Fazeli et al., 1997). ...
Mikrotubuli-assoziierte Proteine (MAPs) modulieren die Stabilität und Dynamik von Mikrotubuli. Indem sie das Wachstum der Mikrotubuli regulieren, die den Hauptanteil des axonalen Zytoskeletts ausmachen, spielen MAPs eine entscheidende Rolle für die Elongation und Navigation von Axonen. Eines der fünf klassischen MAPs (MAP1–4 und Tau) ist MAP1B, ein axonales MAP, das als Erstes während der Embryonalentwicklung auftritt. In dieser Arbeit wurde die Rolle von MAP1B bei der Wegfindung von Axonen der retinalen Ganglienzellen (RGZ) in der sich entwickelnden Retina untersucht. Hierzu wurden Retinae von Mausembryonen, die kein MAP1B besitzen (Knockout), in der Phase des maximalen RGZ-Axonwachstums (E14,5) untersucht. Die k.o.-Neuroretina ist im Zentralbereich (um den Sehnervkopf herum) dünner als im Wildtyp. Dies ist jedoch nicht auf eine Reduktion der RGZ-Axone zurückzuführen, sondern auf eine Verminderung der Neuroepithelialzellschicht. RGZ-Axone zeigen auf ihrem Weg zum Sehnerv, auf dem sie sich zunehmend bündeln, in der k.o.-Retina ein abnormales Navigationsverhalten: Einzelne RGZ-Axone und dünne Axonbündel lösen sich häufiger aus ihren Faszikeln, wodurch die Anzahl dünner Faszikel erhöht ist. In vitro Experimente unter genauer definierten Bedingungen und an einzelnen RGZ-Axonen offenbarten, dass zwei Verhaltensweisen im k.o. häufiger auftraten: starke Seitwärtsbewegungen der Axonspitzen und starke Lateralexploration des Wachstumskegels an der Axonspitze. Sowohl in vivo als auch in vitro Befunde weisen also darauf hin, dass bei Fehlen von MAP1B die Feinregulation der Steuerungsbewegungen der Axone reduziert ist, was zu dem beobachteten Abwandern aus den Bündeln führen könnte. Dies bewirkt insbesondere am Sehnervkopf, wo die RGZ-Axone ein Abbiegemanöver durchführen, dramatische Fehlnavigationen im k.o.: Die Axone tauchen zwar in den Sehnervkopf ein, wachsen dann jedoch in die gegenüberliegende Neuroretina. Sie wachsen dabei nicht antiparallel entlang der RGZ-Axone, sondern in einer tieferen Neuroretinaschicht. Die Ergebnisse dieser Arbeit zeigen zum ersten Mal eine wichtige Rolle von MAP1B bei der Moderierung des Wachstumskegelverhaltens sowie der Weg- und Zielfindung navigierender Axone.
... Netrin-1 signaling promotes neuronal arborization and synaptogenesis in numerous neuronal systems, including cortical and hippocampal neurons (Barallobre et al., 2000;Winkle et al., 2014). TRIM9 interacts directly with multiple factors, such as vasodilator-stimulated phosphoprotein (VASP) and synaptosome-associated protein 25 kDa (SNAP25), to help mediate the neuronal response to Netrin-1 through ligase-dependent and -independent actions (Fig. 1). ...
... In addition to investigating TRIM9's role in dendritic arborization, Winkle, Olsen et al. (2016) examined how TRIM9 affects axon pathfinding. Because Netrin-1 signaling is required for establishing axonal projections between CA3 pyramidal cells and the septal nuclei (Barallobre et al., 2000), the authors investigated how conditional deletion of TRIM9 in excitatory cortical and hippocampal neurons affected CA3-to-septal projections in vivo. Because TRIM9 mediates Netrin-1 signaling in vitro and in cortical neurons (Winkle et al., 2014;Menon et al., 2015), the authors hypothesized that loss of TRIM9 would reduce the density of CA3-to-septal nuclei projections, as was observed after Netrin-1 deletion (Barallobre et al., 2000). ...
... Because Netrin-1 signaling is required for establishing axonal projections between CA3 pyramidal cells and the septal nuclei (Barallobre et al., 2000), the authors investigated how conditional deletion of TRIM9 in excitatory cortical and hippocampal neurons affected CA3-to-septal projections in vivo. Because TRIM9 mediates Netrin-1 signaling in vitro and in cortical neurons (Winkle et al., 2014;Menon et al., 2015), the authors hypothesized that loss of TRIM9 would reduce the density of CA3-to-septal nuclei projections, as was observed after Netrin-1 deletion (Barallobre et al., 2000). In contrast to this hypothesis, the authors noted an increased density of fibers in the septal nuclei of Trim9 Ϫ/Ϫ mice. ...
... TRIM9 localizes to the somal compartment and proximal dendrites of hippocampal neurons (Tanji et al., 2010) and is a component of the postsynaptic density (Jordan et al., 2004), yet little is known regarding the role of TRIM9 in dendrites. Netrin-1 and DCC are present in the developing and adult hippocampus, and mice deficient in either genes exhibit neuroanatomical defects (Serafini et al., 1996;Fazeli et al., 1997;Bin et al., 2015;Yung et al., 2015) and altered spontaneous neural activity (Barallobre et al., 2000). TRIM9 mRNA is also enriched in maturing adult-born neurons (Chatzi et al., 2016). ...
... This revealed that Thy1-GFP/ Trim9 Ϫ/Ϫ hippocampal neurons had increased dendritic material compared with Thy1-GFP/Trim9 ϩ/ϩ littermates ( Fig. 5A; p Ͻ 0.05), with no changes in the percentage of GFP ϩ neurons (14.1 Ϯ 2.1% vs 15.4 Ϯ 0.8%). A subset of CA3 pyramidal cells project to the septal nuclei (Gaykema et al., 1991;Witter, 2007), and this projection is disrupted by netrin-1 deficiency (Barallobre et al., 2000). To determine whether deletion of Trim9 also disrupted this projection, we used NEX-Cre/Tau-LoxP-STOP-LoxP-mGFP mice (Goebbels et al., 2006) crossed with Trim9 fl/fl mice. ...
... The TRIM family of E3 ligases are implicated in multiple cellular processes, and mutations in TRIM genes occur in several human diseases (Hatakeyama, 2011;Napolitano and Meroni, 2012;Alloush and Weisleder, 2013;Mandell et al., 2014;Rajsbaum et al., 2014). Our findings identify a novel role for TRIM9 in the developing adult hippocampus, in which genetic loss of Trim9 exaggerates arbor complexity and is associated with severe deficits in spatial learning and memory. ...
Unlabelled:
During hippocampal development, newly born neurons migrate to appropriate destinations, extend axons, and ramify dendritic arbors to establish functional circuitry. These developmental stages are recapitulated in the dentate gyrus of the adult hippocampus, where neurons are continuously generated and subsequently incorporate into existing, local circuitry. Here we demonstrate that the E3 ubiquitin ligase TRIM9 regulates these developmental stages in embryonic and adult-born mouse hippocampal neurons in vitro and in vivo Embryonic hippocampal and adult-born dentate granule neurons lacking Trim9 exhibit several morphological defects, including excessive dendritic arborization. Although gross anatomy of the hippocampus was not detectably altered by Trim9 deletion, a significant number of Trim9(-/-) adult-born dentate neurons localized inappropriately. These morphological and localization defects of hippocampal neurons in Trim9(-/-) mice were associated with extreme deficits in spatial learning and memory, suggesting that TRIM9-directed neuronal morphogenesis may be involved in hippocampal-dependent behaviors.
Significance statement:
Appropriate generation and incorporation of adult-born neurons in the dentate gyrus are critical for spatial learning and memory and other hippocampal functions. Here we identify the brain-enriched E3 ubiquitin ligase TRIM9 as a novel regulator of embryonic and adult hippocampal neuron shape acquisition and hippocampal-dependent behaviors. Genetic deletion of Trim9 elevated dendritic arborization of hippocampal neurons in vitro and in vivo Adult-born dentate granule cells lacking Trim9 similarly exhibited excessive dendritic arborization and mislocalization of cell bodies in vivo These cellular defects were associated with severe deficits in spatial learning and memory.
