Zebrafish CiA interneurons are late-born primary neurons

Generation of late-born neurons in the ventral spinal cord requires the coordination of retinoic acid and Notch signaling

Neural progenitor cells generate various types of neurons and glia in a tightly regulated manner. During primary neurogenesis, retinoic acid (RA) acts earlier than Notch signaling and regulates differentiation and proliferation by upregulating proneural and neurogenic genes in the neural plate. However, the relationship between Notch signaling and the retinoid pathway during late neurogenesis remains unclear. We investigated the role of Mindbomb (Mib)-mediated Notch signaling in the differentiation of neural progenitors during late neurogenesis by overexpressing Mib and administering RA to Tg[hsp70-Mib:EGFP]. The majority of cells in the p3 domain differentiated into GABAergic Kolmer-Agduhr (KA) cells in Tg[hsp70-mib:EGFP] embryos heat-shocked during late neurogenesis, whereas these phenotypes were suppressed by exogenous RA. Our observations suggest that Mib-mediated Notch signaling plays a critical role in the temporal differentiation of neural progenitors, and that the generation of late-born KA″ cells is regulated by the interplay between Mib and RA.

The Notch signalling system: recent insights into the complexity of a conserved pathway

Notch signalling links the fate of one cell to that of an immediate neighbour and consequently controls differentiation, proliferation and apoptotic events in multiple metazoan tissues. Perturbations in this pathway activity have been linked to several human genetic disorders and cancers. Recent genome-scale studies in Drosophila melanogaster have revealed an extraordinarily complex network of genes that can affect Notch activity. This highly interconnected network contrasts our traditional view of the Notch pathway as a simple linear sequence of events. Although we now have an unprecedented insight into the way in which such a fundamental signalling mechanism is controlled by the genome, we are faced with serious challenges in analysing the underlying molecular mechanisms of Notch signal control.

Essential genes for astroglial development and axon pathfinding during zebrafish embryogenesis

The formation of the central nervous system depends on the coordinated development of neural and glial cell types that arise from a common precursor. Using an existing group of zebrafish mutants generated by viral insertion, we performed a "shelf-screen" to identify genes necessary for astroglial development and axon scaffold formation. We screened 274 of 315 viral insertion lines using antibodies that label axons (anti-Acetylated Tubulin) and astroglia (anti-Gfap) and identified 25 mutants with defects in gliogenesis, glial patterning, neurogenesis, and axon guidance. We also identified a novel class of mutants affecting radial glial cell numbers. Defects in astroglial patterning were always associated with axon defects, supporting an important role for axon-glial interactions during axon scaffold development. The genes disrupted in these viral lines have all been identified, providing a powerful new resource for the study of axon guidance, glio- and neurogenesis, and neuron-glial interactions during development of the vertebrate CNS.