[P158]: The bHLH gene NSCL1 in the vertebrate nervous system: expression and functional studies

Abstract

563that only a subset of ZII − Purkinje cells are ectopic in cdf and taken together this indicates that there are at least two classes of ZII − Purkinje cells.Interestingly, recent experiments examining the origins of ZII − cells during development also suggest that at least two immunologically distinct populations of Purkinje cells contribute to the ZII − population in the adult cerebellum -one that expresses neurogranin alone (NG+) and a second that expresses a combination of heat shock protein25, calbindin and neurogranin (HSP25+). Our data reveals that both Purkinje cell phenotypes are present in the cdf cerebellum. However, we observed that the overwhelming majority of ectopic Purkinje cells in the perinatal cdf cerebellum are represented by the HSP25+ subset. This observation supports the adult data because a population of cells predicted to contribute to the adult ZII − population is ectopic in the perinatal cerebellum. Finally, despite the ectopia present in the cdf cerebellum, overall, parasagittal patterning is very similar to wild type. Thus, our evidence indicates that mediolateral patterning is established prior to Purkinje cell dispersal and that this dispersal process is differentially regulated across Purkinje cell subclasses.The basic helix-loop-helix (bHLH) genes encode for a family of transcription factors involved in developmental processes such as neurogenesis, myogenesis, hematopoeisis and sex determination. NSCL1 is a bHLH transcription factor expressed in various populations of postmitotic neurons of the CNS and the PNS. In situ hybridization demonstrated expression of NSCL1 in the subependymal layer of the neuroepithelium throughout the CNS, in the dorsal root ganglia, trigeminal and other cranial ganglia, sensory nasal epithelium, sensory layer of the developing optic cup, in the forebrain, hippocampus, septum, tectum, hypothalamic nuclei, hindbrain and spinal cord both in mouse embryos, postnatal and adult animals.NSCL1 behaves as an initiator factor of cerebellar granule cell growth and differentiation. Expression in the cerebellum, spinal cord and dorsal root ganglia corresponds to the expression of the adhesion molecule TAG-1/axonin-1. NSCL1 is detected in rhombomere boundaries both in mouse and chick. NSCL1 expression in these structures is coincident with their formation and is maintained until these structures are gone at later stages of development. cNSCL1 expression is also observed during rhombomere boundary regeneration in chick embryos, after their microsurgical ablation. In addition, a stronger NSCL1 signal is observed in r4, corresponding to facial branchiomotor (fbm) and visceromotor neurons. The expression pattern of mNSCL1 in Hoxb1 −/− mice is strongly affected in r4 where migrating fbm neurons are located.To further investigate the role of NSCL-1 as a transcriptional activator or repressor, we performed luciferase assays using different truncated forms of cNSCL-1 fused to GAL-4, and a UAS luciferase reporter. In a complementary system, ME1a, a binding partner of NSCL-1 ...