Identification of spatial and temporal cues that regulate postembryonic expression of axon maintenance factors in the XXXX ventral nerve cord.

@entity71079 @entity2199 @entity58559 @entity44416
Patterns of gene expression are under precise spatial and temporal control. A particularly striking example is represented by several members of the zig gene family, which code for secreted immunoglobulin domain proteins required for maintaining ventral nerve cord organization in @entity2199 . These genes are coordinately expressed in a single interneuron in the ventral nerve cord, known as PVT. Their expression is initiated at a precise postembryonic stage, long after PVT has been generated in mid-embryogenesis. We define spatial and temporal cues that are required for the precise regulation of zig gene expression. We find that two LIM homeobox genes, the Lhx3-class gene @entity71079 and the Lmx-class gene @entity44416 are coordinately required for zig gene expression in PVT. Temporal control of zig gene expression is conferred by the heterochronic gene @entity58559 , a nuclear factor previously implicated in developmental timing in various contexts. Loss of the @entity44416 and @entity71079 transcription factors and the developmental timer @entity58559 cause not only a loss of zig gene expression but also lead to defects in the maintenance of ventral nerve cord architecture. Overriding the normal spatiotemporal control of zig gene expression through expression of one of the zig genes under control of heterologous promoters also causes axon patterning defects in the ventral nerve cord. Our findings illustrate the importance of spatial and temporal control of gene expression in the nervous system and, furthermore, implicate heterochronic genes in postmitotic neural patterning events.
