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SummaryThe formation of spinal sensory-motor circuits requires the diversification of proprioceptive sensory neurons (pSNs). During embryonic development, pSNs acquire molecular identities aligned with the limb muscle that they supply, but the extent of pSN “pool” diversity and how it is established are poorly understood. We find that the gene v-set transmembrane domain-2b (vstm2b) is preferentially expressed in pSN pools supplying dorsal limb muscle targets along the proximodistal extent of the limb. Genetic removal of muscle precursor cells from the developing limb greatly reduces the number of pSNs expressing vstm2b, demonstrating a requirement for limb muscle in specifying pSN pool identity. Comparison of dorsal and ventral muscle precursors identifies spatially restricted expression of the genes lumican (lum), decorin (dcn), and BMP binding endothelial regulator (bmper), demonstrating that dorsal and ventral muscle groups possess distinct molecular identities early in embryonic development. Together, these findings show that limb muscle is required for the specification of pSN pool identity and define early molecular correlates of dorsoventral muscle identity that are positioned to drive neuronal diversity.

Siamese fighting (betta) fish are among the most popular and morphologically diverse pet fish, but the genetic bases of their domestication and phenotypic diversification are largely unknown. We assembled de novo the genome of a wildBetta splendensand whole-genome sequenced 98 individuals across five closely related species. We find evidence of bidirectional hybridization between domesticated ornamental betta and other wildBettaspecies. We discoverdmrt1as the main sex determination gene in ornamental betta and that it has lower penetrance in wildB. splendens. Furthermore, we find genes with signatures of recent, strong selection that have large effects on color in specific parts of the body or on the shape of individual fins and that most are unlinked. Our results demonstrate how simple genetic architectures paired with anatomical modularity can lead to vast phenotypic diversity generated during animal domestication and launch betta as a powerful new system for evolutionary genetics.

During corticogenesis, pyramidal neurons (~80% of cortical neurons) arise from the ventricular zone (VZ) pass through a multipolar stage to become bipolar and attach to radial glia1, 3, and then migrate to their proper position within the cortex1, 2. As pyramidal neurons migrate radially, they remain attached to their glial substrate as they pass through the subventricular (SVZ) and intermediate (IZ) zones, regions rich in tangentially migrating interneurons and axon fiber tracts. We examined the role of Lamellipodin (Lpd), a homolog of a key regulator of neuronal migration and polarization in C. elegans, in corticogenesis. Lpd depletion caused bipolar pyramidal neurons to adopt a tangential, rather than radial-glial, migration mode without affecting cell fate. Mechanistically, Lpd depletion reduced the activity of SRF, a transcription factor regulated by changes in the ratio of polymerized to unpolymerized actin. Therefore, Lpd depletion exposes a role for SRF in directing pyramidal neurons to select a radial migration pathway along glia rather than a tangential migration mode.