FIGURE 31 - uploaded by Jonathan Benito-Sipos
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1 The early neuroectoderm is patterned by segment-polarity, columnar, and Hox cues. This results in a positional grid. When NB selection commences, by the process of lateral inhibition, the positional grid provides each NB with a unique identity.
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Citations
... For example, the nervous system of flies and mammals is patterned along the anteroposterior (A-P) axis by Hox genes (Tümpel et al., 2009;Philippidou and Dasen, 2013;Estacio-Gómez and Díaz-Benjumea, 2014;Jung et al., 2014; Figure 1B). Within each segment along the A-P axis, neural progenitors are further patterned on the A-P and dorsoventral (D-V) axis, forming non-intermingling progenitor populations that will generate distinct neuronal types (Jessell, 2000;Briscoe and Ericson, 2001;Karlsson et al., 2010;Benito-Sipos et al., 2013;Birkholz et al., 2013; Figure 1C). ...
The nervous system is one of the most sophisticated animal tissues, consisting of thousands of interconnected cell types. How the nervous system develops its diversity from a few neural stem cells remains a challenging question. Spatial and temporal patterning mechanisms provide an efficient model through which diversity can be generated. The molecular mechanism of spatiotemporal patterning has been studied extensively in Drosophila melanogaster, where distinct sets of transcription factors define the spatial domains and temporal windows that give rise to different cell types. Similarly, in vertebrates, spatial domains defined by transcription factors produce different types of neurons in the brain and neural tube. At the same time, different cortical neuronal types are generated within the same cell lineage with a specific birth order. However, we still do not understand how the orthogonal information of spatial and temporal patterning is integrated into the progenitor and post-mitotic cells to combinatorially give rise to different neurons. In this review, after introducing spatial and temporal patterning in Drosophila and mice, we discuss possible mechanisms that neural progenitors may use to integrate spatial and temporal information. We finally review the functional implications of spatial and temporal patterning and conclude envisaging how small alterations of these mechanisms can lead to the evolution of new neuronal cell types.
... Dissecting organ scaling is complicated by the diverse range of organ formation processes and morphologies. For example, in Drosophila, muscle growth occurs through myoblast fusion and elongation (32), the hindgut grows by chiral reorientation of cells (33), the ventral nerve cord (VNC) undergoes large-scale elongation followed by condensation (34,35), and the heart forms from a fixed number of cells (31,36). ...
... For example, under starvation, growth of the ovaries is delayed in the Drosophila larvae (58), whereas the brain continues to develop similarly to healthy conditions for a substantially longer period (59)(60)(61). The VNC is constructed of a highly stereotypic repetition of specific neurons and connections (34,62). Larvae from TjGal4>fat2RNAi embryos quickly reach similar absolute size and morphology to larvae from control embryos. ...
Many species show a diverse range of sizes; for example, domestic dogs have large variation in body mass. Yet, the internal structure of the organism remains similar, i.e. the system scales to organism size. Drosophila melanogaster has been a powerful model system for exploring scaling mechanisms. In the early embryo, gene expression boundaries scale very precisely to embryo length. Later in development, the adult wings grow with remarkable symmetry and scale well with animal size. Yet, our knowledge of whether internal organs initially scale to embryo size remains largely unknown. Here, we utilise artificially small Drosophila embryos to explore how three critical internal organs – the heart, hindgut and ventral nerve cord (VNC) – adapt to changes in embryo morphology. We find that the heart scales precisely with embryo length. Intriguingly, reduction in cardiac cell length, rather than number, appears to be important in controlling heart length. The hindgut – which is the first chiral organ to form – displays scaling with embryo size under large-scale changes in the artificially smaller embryos but shows few hallmarks of scaling within wild-type size variation. Finally, the VNC only displays weak scaling behaviour; even large changes in embryo geometry result in only small shifts in VNC length. This suggests that the VNC may have an intrinsic minimal length, which is largely independent of embryo length. Overall, our work shows that internal organs can adapt to embryo size changes in Drosophila. but the extent to which they scale varies significantly between organs.
Many species show a diverse range of sizes; for example, domestic dogs have large variation in body mass. Yet, the internal structure of the organism remains similar, i.e. the system scales to organism size. Drosophila melanogaster has been a powerful model system for exploring scaling mechanisms. In the early embryo, gene expression boundaries scale very precisely to embryo length. Later in development, the adult wings grow with remarkable symmetry and scale well with animal size. Yet, our knowledge of whether internal organs initially scale to embryo size remains largely unknown. Here, we utilise artificially small Drosophila embryos to explore how three critical internal organs - the heart, hindgut and ventral nerve cord (VNC) - adapt to changes in embryo morphology. We find that the heart scales precisely with embryo length. Intriguingly, reduction in cardiac cell length, rather than number, appears to be important in controlling heart length. The hindgut - which is the first chiral organ to form - displays scaling with embryo size under large-scale changes in the artificially smaller embryos but shows few hallmarks of scaling within wild-type size variation. Finally, the VNC only displays weak scaling behaviour; even large changes in embryo geometry result in only small shifts in VNC length. This suggests that the VNC may have an intrinsic minimal length, which is largely independent of embryo length. Overall, our work shows that internal organs can adapt to embryo size changes in Drosophila. but the extent to which they scale varies significantly between organs.
