The diversity of an organism's nervous system underlies its ability to sense and react to its complex environment. In order to understand the mechanisms that underlie neuronal diversification we are dissecting the development of the chemosensory system of C. elegans. A number of factors that play a role in the development of the AWA olfactory neurons were identified previously, allowing us to propose a pathway by which the AWA neurons are formed and develop a distinct identity from their sister cells, the ASG chemosensory neurons. In this model, UNC-130, a forkhead transcription factor acts in the AWA/ASG precursors to restrict the AWA potential to the daughter cell that will become AWA (Sarafi-Reinach and Sengupta, 2000). LIN-11, a LIM homeodomain transcription factor, acts in AWA to initiate the expression of ODR-7, a nuclear hormone receptor transcription factor (Sarafi-Reinach et al., 2001).
odr-7 is necessary for the specification of the AWA neurons (Sengupta et al., 1994). Mutations in
lin-11 also affect the differentiation of the ASG neurons. Interestingly,
lin-11 is transiently expressed in AWA, while in ASG its expression is maintained throughout development, suggesting that differential temporal expression of
lin-11 may contribute to determining the distinct identities of these neurons. In a screen aimed at isolating additional genes involved in AWA specification, I identified
sns-10. In all alleles of
sns-10, expression of
odr-7 is lost in an incompletely penetrant manner. Animals lacking
odr-7 expression in the AWA neurons fail to respond to the AWA-sensed odorant diacetyl, indicating that
sns-10 is required for the correct functions of the AWA neurons.
sns-10 mutants also exhibit defects in ASG-specific gene expression. However, loss of gene expression in the AWA and ASG neurons are not correlated, suggesting that SNS-10 acts independently in these neurons. Accordingly, the interaction of SNS-10 with UNC-130 and LIN-11 appears to depend on the cell type. While in AWA, SNS-10 appears to function in parallel to UNC-130 and upstream of LIN-11, in ASG, SNS-10 may act in parallel to both.
sns-10 encodes a paired-like homeodomain transcription factor with high homology to the Drosophila gene Aristaless. Indeed, Drosophila Aristaless can substitute for SNS-10 function. Intriguingly, Aristaless has been shown to regulate the Drosophila dLim1, the Drosophila ortholog of
lin-11 in the development of the leg and aristae, suggesting a conservation of a genetic regulatory circuit . Thus, investigating how SNS-10 functions in the development of the C. elegans chemosenseory system could contribute not only to our understanding of the diversification of these sensory neurons but also to our understanding of other developmental processes.