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The retinotectal projection in the esrom mutant. (A-D) Optic tectum of 4-day-old zebrafish, with retinal axons labeled using DiI (red) or DiD (blue). Insets show lateral view of the injected eye. (A) Axons from the anterior region of the eye (red) project to the posterior tectum in wild type. Axons from the posterior (blue) arborize in the anterior tectum. (B) In the esrom mutant, anterior axons defasciculate and arborize anteriorly. (C) Axons from the ventral (red) and dorsal (blue) regions of the eye are well separated in a wild type. (D) In the mutant, there is some overlap between two populations. (E,F) Dorsal view of the pretectal region of 3-day-old fish, in which retinal axons are labeled with GFP under the sonic hedgehog promoter. The pretectal target AF7 (yellow arrowhead) is more innervated in the mutant (F) compared with the wild type (G). AF9 (arrow), by contrast, is less innervated in the mutant. (G,H) The optic nerve exiting from the eye in 7-day-old fish. Only dorsal neurons have been labeled with DiI. In the wild type (G), axons remain closely associated with one another in the optic nerve (arrow). In the mutant (H), axons have formed two separate bundles (arrows). Scale bar: 50 µm. Anterior is towards the left. r, retina; the broken white line in G,H indicates the margin of the eye. (E,F) Single optical planes; other panels are projections of z-stacks.
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Visual system development is dependent on correct interpretation of cues that direct growth cone migration and axon branching. Mutations in the zebrafish esrom gene disrupt bundling and targeting of retinal axons, and also cause ectopic arborization. By positional cloning, we establish that esrom encodes a very large protein orthologous to PAM (pro...
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... most prominent defect in the esrom mutant is a failure of anterior axons to map to the posterior tectum. In wild types, retinal axons from the anterior eye remain unbranched and are fasciculated until reaching the posterior tectum (Fig. 1A). In mutants, however, anterior axons branch in the anterior tectum (Fig. 1B). The posterior tectum is very sparsely innervated. Defects are also detectable in the dorsoventral axis of mutants. Axons from the ventral eye normally branch in the dorsal tectum, whereas those from the dorsal eye branch in the ventral tectum (Fig. 1C). In ...
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... most prominent defect in the esrom mutant is a failure of anterior axons to map to the posterior tectum. In wild types, retinal axons from the anterior eye remain unbranched and are fasciculated until reaching the posterior tectum (Fig. 1A). In mutants, however, anterior axons branch in the anterior tectum (Fig. 1B). The posterior tectum is very sparsely innervated. Defects are also detectable in the dorsoventral axis of mutants. Axons from the ventral eye normally branch in the dorsal tectum, whereas those from the dorsal eye branch in the ventral tectum (Fig. 1C). In esrom mutants, this segregation is not strictly followed (Fig. 1D). In addition ...
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... posterior tectum (Fig. 1A). In mutants, however, anterior axons branch in the anterior tectum (Fig. 1B). The posterior tectum is very sparsely innervated. Defects are also detectable in the dorsoventral axis of mutants. Axons from the ventral eye normally branch in the dorsal tectum, whereas those from the dorsal eye branch in the ventral tectum (Fig. 1C). In esrom mutants, this segregation is not strictly followed (Fig. 1D). In addition to these mapping errors, the pre- tectal target AF7 ( Burrill and Easter, 1994) is excessively innervated in mutants, whereas fewer axons terminate in AF9 (Fig. 1E,F). Furthermore, axons are not bundled correctly in the optic nerve: axons that originate ...
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... in the anterior tectum (Fig. 1B). The posterior tectum is very sparsely innervated. Defects are also detectable in the dorsoventral axis of mutants. Axons from the ventral eye normally branch in the dorsal tectum, whereas those from the dorsal eye branch in the ventral tectum (Fig. 1C). In esrom mutants, this segregation is not strictly followed (Fig. 1D). In addition to these mapping errors, the pre- tectal target AF7 ( Burrill and Easter, 1994) is excessively innervated in mutants, whereas fewer axons terminate in AF9 (Fig. 1E,F). Furthermore, axons are not bundled correctly in the optic nerve: axons that originate from one region of the eye and should therefore remain close together, ...
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... branch in the dorsal tectum, whereas those from the dorsal eye branch in the ventral tectum (Fig. 1C). In esrom mutants, this segregation is not strictly followed (Fig. 1D). In addition to these mapping errors, the pre- tectal target AF7 ( Burrill and Easter, 1994) is excessively innervated in mutants, whereas fewer axons terminate in AF9 (Fig. 1E,F). Furthermore, axons are not bundled correctly in the optic nerve: axons that originate from one region of the eye and should therefore remain close together, are separated in mutants ( Fig. 1G,H; split seen in all mutants, n>50, and in no wild types, n>50). The esrom gene is thus required for bundling, target selection and topographic ...
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... these mapping errors, the pre- tectal target AF7 ( Burrill and Easter, 1994) is excessively innervated in mutants, whereas fewer axons terminate in AF9 (Fig. 1E,F). Furthermore, axons are not bundled correctly in the optic nerve: axons that originate from one region of the eye and should therefore remain close together, are separated in mutants ( Fig. 1G,H; split seen in all mutants, n>50, and in no wild types, n>50). The esrom gene is thus required for bundling, target selection and topographic ...
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... Several studies described the roles of the PHR proteins as key regulators of presynaptic differentiation and function, thereby fundamentally affecting neuronal development [88][89][90]. Among the PHR proteins, the Regulator of Presynaptic Morphology (RPM)-1 has been shown to negatively regulate DLK-1 as part of an ubiquitin ligase complex in C. elegans [91,92]. ...
The dual leucine zipper kinase (DLK) alias mitogen-activated protein 3 kinase 12 (MAP3K12) has gained much attention in recent years. DLK belongs to the mixed lineage kinases, characterized by homology to serine/threonine and tyrosine kinase, but exerts serine/threonine kinase activity. DLK has been implicated in many diseases, including several neurodegenerative diseases, glaucoma, and diabetes mellitus. As a MAP3K, it is generally assumed that DLK becomes phosphorylated and activated by upstream signals and phosphorylates and activates itself, the downstream serine/threonine MAP2K, and, ultimately, MAPK. In addition, other mechanisms such as protein–protein interactions, proteasomal degradation, dephosphorylation by various phosphatases, palmitoylation, and subcellular localization have been shown to be involved in the regulation of DLK activity or its fine-tuning. In the present review, the diverse mechanisms regulating DLK activity will be summarized to provide better insights into DLK action and, possibly, new targets to modulate DLK function.
... This is also supported by the striking similarity of MYCBP2 and EPHB2 loss-offunction phenotypes in the mouse nervous system. In the context of developing neuronal connections, EphB2 and Mycbp2/Phr1 mouse mutants display similar axon guidance phenotypes such as abnormal limb nerve trajectories by motor axons, defective growth cone crossing of the midline at the level of the optic chiasm and decreased connectivity between the two cortical hemispheres through the corpus callosum (Lewcock et al., 2007;Luria et al., 2008;Williams et al., 2003;Henkemeyer et al., 1996;D'Souza et al., 2005). Both proteins also function in synaptic development and their loss of function leads to decreased numbers of synapses and altered synapse morphology (Wan et al., 2000;Bloom et al., 2007;Dalva et al., 2000;Zhen et al., 2000). ...
Eph receptor tyrosine kinases participate in a variety of normal and pathogenic processes during development and throughout adulthood. This versatility is likely facilitated by the ability of Eph receptors to signal through diverse cellular signalling pathways: primarily by controlling cytoskeletal dynamics, but also by regulating cellular growth, proliferation, and survival. Despite many proteins linked to these signalling pathways interacting with Eph receptors, the specific mechanisms behind such links and their coordination remain to be elucidated. In a proteomics screen for novel EPHB2 multi-effector proteins, we identified human MYC binding protein 2 (MYCBP2 or PAM or Phr1). MYCBP2 is a large signalling hub involved in diverse processes such as neuronal connectivity, synaptic growth, cell division, neuronal survival, and protein ubiquitination. Our biochemical experiments demonstrate that the formation of a complex containing EPHB2 and MYCBP2 is facilitated by FBXO45, a protein known to select substrates for MYCBP2 ubiquitin ligase activity. Formation of the MYCBP2-EPHB2 complex does not require EPHB2 tyrosine kinase activity and is destabilised by binding of ephrin-B ligands, suggesting that the MYCBP2-EPHB2 association is a prelude to EPHB2 signalling. Paradoxically, the loss of MYCBP2 results in increased ubiquitination of EPHB2 and a decrease of its protein levels suggesting that MYCBP2 stabilises EPHB2. Commensurate with this effect, our cellular experiments reveal that MYCBP2 is essential for efficient EPHB2 signalling responses in cell lines and primary neurons. Finally, our genetic studies in Caenorhabditis elegans provide in vivo evidence that the ephrin receptor VAB-1 displays genetic interactions with known MYCBP2 binding proteins. Together, our results align with the similarity of neurodevelopmental phenotypes caused by MYCBP2 and EPHB2 loss of function, and couple EPHB2 to a signalling effector that controls diverse cellular functions.
... Several studies described the role of the PHR proteins as key regulators of presynaptic differentiation and function, thereby fundamentally affecting neuronal development [58][59][60]. Among the PHR proteins, the Regulator of Presynaptic Morphology (RPM)-1 has been shown to negatively regulate DLK-1 as part of an ubiquitin ligase complex in C. elegans [61,62]. ...
The dual leucine zipper kinase (DLK) alias mitogen-activated protein 3 kinase 12 (MAP3K12) has gained much attention in recent years. DLK belongs to the mixed lineage kinases, characterized by homology to serine/threonine and tyrosine kinase but exerts serine/threonine kinase activity. DLK has been implicated in many diseases including several neurodegenerative diseases, glaucoma, and diabetes mellitus. As a MAP3K, it is generally assumed that DLK becomes phosphorylated and activated by upstream signals and phosphorylates and activates itself, the downstream serine/threonine MAP2K, and ultimately MAPK. In addition, other mechanisms such as protein-protein interactions, proteasomal degradation, dephosphorylation by various phosphatases, palmitoylation, and subcellular localization have been shown to be involved in the regulation of DLK activity or its fine-tuning. In the present review, the diverse mechanisms regulating DLK activity will be summarized to provide a better insight into DLK action and possibly new targets to modulate DLK function.
... This is also supported by the striking similarity of MYCBP2 and EPHB2 loss of function phenotypes in the mouse nervous system. In the context of developing neuronal connections, EphB2 and Mycbp2/Phr1 mouse mutants display similar axon guidance phenotypes such as abnormal limb nerve trajectories by motor axons, defective growth cone crossing of the midline at the level of the optic chiasm and decreased connectivity between the two cortical hemispheres through the corpus callosum (Lewcock et al., 2007 ;Luria et al., 2008 ;Williams et al., 2003 ;Henkemeyer et al., 1996 ;D'Souza et al., 2005 ). Both proteins also function in synaptic development and their loss of function leads to decreased numbers of synapses and altered synapse morphology (Wan et al., 2000 ;Bloom et al., 2007 ;Dalva et al., 2000 ;Zhen et al., 2000 ). ...
Eph receptor tyrosine kinases participate in a variety of normal and pathogenic processes during development and throughout adulthood. This versatility is likely facilitated by the ability of Eph receptors to signal through diverse cellular signalling pathways: primarily by controlling cytoskeletal dynamics, but also by regulating cellular growth, proliferation, and survival. Despite many proteins linked to these signalling pathways interacting with Eph receptors, the specific mechanisms behind such links and their coordination remain to be elucidated. In a proteomics screen for novel EPHB2 multi-effector proteins, we identified human MYC binding protein 2 (MYCBP2 or PAM or Phr1). MYCBP2 is a large signalling hub involved in diverse processes such as neuronal connectivity, synaptic growth, cell division, neuronal survival, and protein ubiquitination. Our biochemical experiments demonstrate that the formation of a complex containing EPHB2 and MYCBP2 is facilitated by FBXO45, a protein known to select substrates for MYCBP2 ubiquitin ligase activity. Formation of the MYCBP2-EPHB2 complex does not require EPHB2 tyrosine kinase activity and is destabilised by binding of ephrin-B ligands, suggesting that the MYCBP2-EPHB2 association is a prelude to EPHB2 signalling. Paradoxically, the loss of MYCBP2 results in increased ubiquitination of EPHB2 and a decrease of its protein levels suggesting that MYCBP2 stabilises EPHB2. Commensurate with this effect, our cellular experiments reveal that MYCBP2 is essential for efficient EPHB2 signalling responses in cell lines and primary neurons. Finally, our genetic studies in C. elegans provide in vivo evidence that the ephrin receptor VAB-1 displays genetic interactions with known MYCBP2 binding proteins. Together, our results align with the similarity of neurodevelopmental phenotypes caused by MYCBP2 and EPHB2 loss of function, and couple EPHB2 to a signaling effector that controls diverse cellular functions.
... This is also supported by the striking similarity of MYCBP2 and EPHB2 loss of function phenotypes in the mouse nervous system. In the context of developing neuronal connections, EphB2 and Mycbp2/Phr1 mouse mutants display similar axon guidance phenotypes such as abnormal limb nerve trajectories by motor axons, defective growth cone crossing of the midline at the level of the optic chiasm and decreased connectivity between the two cortical hemispheres through the corpus callosum (Lewcock et al., 2007 ;Luria et al., 2008 ;Williams et al., 2003 ;Henkemeyer et al., 1996 ;D'Souza et al., 2005 ). Both proteins also function in synaptic development and their loss of function leads to decreased numbers of synapses and altered synapse morphology (Wan et al., 2000 ;Bloom et al., 2007 ;Dalva et al., 2000 ;Zhen et al., 2000 ). ...
Eph receptor tyrosine kinases participate in a variety of normal and pathogenic processes during development and throughout adulthood. This versatility is likely facilitated by the ability of Eph receptors to signal through diverse cellular signalling pathways: primarily by controlling cytoskeletal dynamics, but also by regulating cellular growth, proliferation, and survival. Despite many proteins linked to these signalling pathways interacting with Eph receptors, the specific mechanisms behind such links and their coordination remain to be elucidated. In a proteomics screen for novel EPHB2 multi-effector proteins, we identified human MYC binding protein 2 (MYCBP2 or PAM or Phr1). MYCBP2 is a large signalling hub involved in diverse processes such as neuronal connectivity, synaptic growth, cell division, neuronal survival, and protein ubiquitination. Our biochemical experiments demonstrate that the formation of a complex containing EPHB2 and MYCBP2 is facilitated by FBXO45, a protein known to select substrates for MYCBP2 ubiquitin ligase activity. Formation of the MYCBP2-EPHB2 complex does not require EPHB2 tyrosine kinase activity and is destabilised by binding of ephrin-B ligands, suggesting that the MYCBP2-EPHB2 association is a prelude to EPHB2 signalling. Paradoxically, the loss of MYCBP2 results in increased ubiquitination of EPHB2 and a decrease of its protein levels suggesting that MYCBP2 stabilises EPHB2. Commensurate with this effect, our cellular experiments reveal that MYCBP2 is essential for efficient EPHB2 signalling responses in cell lines and primary neurons. Finally, our genetic studies in C. elegans provide in vivo evidence that the ephrin receptor VAB-1 displays genetic interactions with known MYCBP2 binding proteins. Together, our results align with the similarity of neurodevelopmental phenotypes caused by MYCBP2 and EPHB2 loss of function, and couple EPHB2 to a signaling effector that controls diverse cellular functions.
... This is also supported by the striking similarity of MYCBP2 and EPHB2 loss of function phenotypes in the mouse nervous system. In the context of developing neuronal connections, EphB2 and Mycbp2/Phr1 mouse mutants display similar axon guidance phenotypes such as abnormal limb nerve trajectories by motor axons, defective growth cone crossing of the midline at the level of the optic chiasm and decreased connectivity between the two cortical hemispheres through the corpus callosum (D'Souza et al., 2005 ;Henkemeyer et al., 1996 ;Lewcock et al., 2007 ;Luria et al., 2008 ;Williams et al., 2003 ). Both proteins also function in synaptic development and their loss of function leads to decreased numbers of synapses and altered synapse morphology (Bloom et al., 2007 ;Dalva et al., 2000 ;Wan et al., 2000 ;Zhen et al., 2000 ). ...
Eph receptor tyrosine kinases participate in a variety of normal and pathogenic processes during development and throughout adulthood. This versatility is likely facilitated by the ability of Eph receptors to signal through diverse cellular signalling pathways: primarily by controlling cytoskeletal dynamics, but also by regulating cellular growth, proliferation, and survival. Despite many proteins linked to these signalling pathways interacting with Eph receptors, the specific mechanisms behind such links and their coordination remain to be elucidated. In a proteomics screen for novel EPHB2 multi-effector proteins, we identified human MYC binding protein 2 (MYCBP2 or PAM or Phr1). MYCBP2 is a large signalling hub involved in diverse processes such as neuronal connectivity, synaptic growth, cell division, neuronal survival, and protein ubiquitination. Our biochemical experiments demonstrate that the formation of a complex containing EPHB2 and MYCBP2 is facilitated by FBXO45, a protein known to select substrates for MYCBP2 ubiquitin ligase activity. Formation of the MYCBP2-EPHB2 complex does not require EPHB2 tyrosine kinase activity and is destabilised by binding of ephrin-B ligands, suggesting that the MYCBP2-EPHB2 association is a prelude to EPHB2 signalling. Paradoxically, the loss of MYCBP2 results in increased ubiquitination of EPHB2 and a decrease of its protein levels suggesting that MYCBP2 stabilises EPHB2. Commensurate with this effect, our cellular experiments reveal that MYCBP2 is essential for efficient EPHB2 signalling responses in cell lines and primary neurons. Finally, our genetic studies in C. elegans provide in vivo evidence that the ephrin receptor VAB-1 functions within the MYCBP2 signalling network. Together, our results align with the similarity of neurodevelopmental phenotypes caused by MYCBP2 and EPHB2 loss of function, and our findings couple EPHB2 to a signaling effector controlling diverse cellular functions.
... This is also supported by the striking similarity of MYCBP2 and EPHB2 loss-offunction phenotypes in the mouse nervous system. In the context of developing neuronal connections, EphB2 and Mycbp2/Phr1 mouse mutants display similar axon guidance phenotypes such as abnormal limb nerve trajectories by motor axons, defective growth cone crossing of the midline at the level of the optic chiasm and decreased connectivity between the two cortical hemispheres through the corpus callosum (Lewcock et al., 2007;Luria et al., 2008;Williams et al., 2003;Henkemeyer et al., 1996;D'Souza et al., 2005). Both proteins also function in synaptic development and their loss of function leads to decreased numbers of synapses and altered synapse morphology (Wan et al., 2000;Bloom et al., 2007;Dalva et al., 2000;Zhen et al., 2000). ...
Eph receptor tyrosine kinases participate in a variety of normal and pathogenic processes during development and throughout adulthood. This versatility is likely facilitated by the ability of Eph receptors to signal through diverse cellular signalling pathways: primarily by controlling cytoskeletal dynamics, but also by regulating cellular growth, proliferation, and survival. Despite many proteins linked to these signalling pathways interacting with Eph receptors, the specific mechanisms behind such links and their coordination remain to be elucidated. In a proteomics screen for novel EPHB2 multi-effector proteins, we identified human MYC binding protein 2 (MYCBP2 or PAM or Phr1). MYCBP2 is a large signalling hub involved in diverse processes such as neuronal connectivity, synaptic growth, cell division, neuronal survival, and protein ubiquitination. Our biochemical experiments demonstrate that the formation of a complex containing EPHB2 and MYCBP2 is facilitated by FBXO45, a protein known to select substrates for MYCBP2 ubiquitin ligase activity. Formation of the MYCBP2-EPHB2 complex does not require EPHB2 tyrosine kinase activity and is destabilised by binding of ephrin-B ligands, suggesting that the MYCBP2-EPHB2 association is a prelude to EPHB2 signalling. Paradoxically, the loss of MYCBP2 results in increased ubiquitination of EPHB2 and a decrease of its protein levels suggesting that MYCBP2 stabilises EPHB2. Commensurate with this effect, our cellular experiments reveal that MYCBP2 is essential for efficient EPHB2 signalling responses in cell lines and primary neurons. Finally, our genetic studies in C. elegans provide in vivo evidence that the ephrin receptor VAB-1 functions within the MYCBP2 signalling network. Together, our results align with the similarity of neurodevelopmental phenotypes caused by MYCBP2 and EPHB2 loss of function, and our findings couple EPHB2 to a signaling effector controlling diverse cellular functions.
... Although the physiological significance of this interaction has not been elaborated, genetic screens in Drosophila and C. elegans identified Highwire and Rpm-1 as important regulators of synaptogenesis (Schaefer et al., 2000;Wan et al., 2000;Zhen et al., 2000). A conserved role in synaptic development was also found in vertebrates as nerve terminal morphology is severely disrupted in zebrafish and mice constitutively lacking Esrom and MYCBP2, respectively (Burgess et al., 2004;D'Souza et al., 2005;Bloom et al., 2007). In mice the phrenic nerve does not fully innervate the diaphragm resulting in perinatal lethality due to respiratory distress. ...
... relay and ensuing ester-linked ubiquitination is ablated. A striking reduction in neurite outgrowth was observed in superior cervical ganglion explants from this homozygous knock-in model, reminiscent of the phenotypes observed with MYCBP2 silencing in mammals (Burgess et al., 2004;D'Souza et al., 2005;Bloom et al., 2007). Indeed, loss of RCR ubiquitin ligase activity in late-stage embryos also resulted in a marked reduction in diaphragm innervation by the phrenic nerve (Mabbitt et al., 2020). ...
The degeneration of nerve fibres following injury was first described by Augustus Waller over 170 years ago. Initially assumed to be a passive process, it is now evident that axons respond to insult via regulated cellular signaling events resulting in their programmed degeneration. Pro-survival and pro-degenerative factors have been identified and their regulatory mechanisms are beginning to emerge. The ubiquitin system has been implicated in the pro-degenerative process and a key component is the ubiquitin E3 ligase MYCBP2 (also known as PHR1). Ubiquitin E3 ligases are tasked with the transfer of the small protein modifier ubiquitin to substrates and consist of hundreds of members. They can be classified as single subunit systems or as multi-subunit complexes. Their catalytic domains can also be assigned to three general architectures. Hints that MYCBP2 might not conform to these established formats came to light and it is now clear from biochemical and structural studies that MYCBP2 is indeed an outlier in terms of its modus operandi. Furthermore, the unconventional way in which MYCBP2 transfers ubiquitin to substrates has been linked to neurodevelopmental and pro-degenerative function. Herein, we will summarize these research developments relating to the unusual features of MYCBP2 and postulate therapeutic strategies that prevent Wallerian degeneration. These have exciting potential for providing relief from pathological neuropathies and neurodegenerative diseases.
... 16 MYCBP2 has prominent roles in nervous system development including important functions in axon development from C. elegans through mice. [19][20][21][22][23][24] In mice, Phr1 deficiency results in impaired axon development in the brain including partial agenesis of corpus callosum, and complete agenesis of the anterior commissure and internal capsule. 25 Impaired axon extension of motor neurons and overgrowth of peripheral sensory axons also occurs in Phr1 mutant mice. ...
... 16 Studies in mouse, zebrafish, Drosophila and C. elegans have shown that the respective orthologues Phr1, Phr/Esrom, Highwire and RPM-1 play conserved functions in axon and synapse development. 19,[21][22][23][24][25]54,56,57 In Phr1 loss of function mice, death occurs shortly after birth due to abnormal diaphragm innervation and impaired neuromuscular junction formation. 25 With regard to axon development, one principal defect observed in C. elegans rpm-1 mutants is impaired termination of axon growth. ...
The corpus callosum is a bundle of axon fibers that connects the two hemispheres of the brain. Neurodevelopmental disorders that feature dysgenesis of the corpus callosum as a core phenotype offer a valuable window into pathology derived from abnormal axon development. Here, we describe a cohort of eight patients with a neurodevelopmental disorder characterized by a range of deficits including corpus callosum abnormalities, developmental delay, intellectual disability, epilepsy, and autistic features. Each patient harbored a distinct de novo variant in MYCBP2, a gene encoding an atypical RING ubiquitin ligase and signaling hub with evolutionarily conserved functions in axon development.
We used CRISPR/Cas9 gene editing to introduce disease-associated variants into conserved residues in the C. elegans MYCBP2 ortholog, RPM-1, and evaluated functional outcomes in vivo. Consistent with variable phenotypes in patients with MYCBP2 variants, C. elegans carrying the corresponding human mutations in rpm-1 displayed axonal and behavioral abnormalities including altered habituation. Furthermore, abnormal axonal accumulation of the autophagy marker LGG-1/LC3 occurred in variants that affect RPM-1 ubiquitin ligase activity.
Functional genetic outcomes from anatomical, cell biological and behavioral readouts indicate that MYCBP2 variants are likely to result in loss of function.
Collectively, our results from multiple human patients and CRISPR gene editing with an in vivo animal model support a direct link between MYCBP2 and a human neurodevelopmental spectrum disorder that we term, MYCBP2-related developmental delay with corpus callosum defects (MDCD).
... MYCBP2 (also known as Phr1 (PAM-Highwire-Rpm-1)) is a conserved 0.5-MDa E3 with important roles in synaptogenesis and axon termination [17][18][19][20][21][22] . MYCBP2 has also been shown to ubiquitinate Fbxw7 and ULK1 kinase, thereby promoting chemotherapy resistance and inhibiting neuronal autophagy, respectively 23,24 . ...
MYCBP2 is a ubiquitin (Ub) E3 ligase (E3) that is essential for neurodevelopment and regulates axon maintenance. MYCBP2 transfers Ub to nonlysine substrates via a newly discovered RING-Cys-Relay (RCR) mechanism, where Ub is relayed from an upstream cysteine to a downstream substrate esterification site. The molecular bases for E2–E3 Ub transfer and Ub relay are unknown. Whether these activities are linked to the neural phenotypes is also unclear. We describe the crystal structure of a covalently trapped E2~Ub:MYCBP2 transfer intermediate revealing key structural rearrangements upon E2–E3 Ub transfer and Ub relay. Our data suggest that transfer to the dynamic upstream cysteine, whilst mitigating lysine activity, requires a closed-like E2~Ub conjugate with tempered reactivity, and Ub relay is facilitated by a helix–coil transition. Furthermore, neurodevelopmental defects and delayed injury-induced degeneration in RCR-defective knock-in mice suggest its requirement, and that of substrate esterification activity, for normal neural development and programmed axon degeneration.
