Identification of Regulatory Relationships of hnd-1 in Muscle Differentiation and of elt-1 in Hypodermal Differentiation in the Caenorhabditis elegans Embryo

The Caenorhabditis elegans transcription factors hnd-1 and elt-1 are members of conserved transcription factor families that serve important roles in tissue differentiation. Previous studies have identified hnd-1 as a part of a trio of genes that are necessary and sufficient for myogenesis and elt-1 as a gene required for most hypodermal differentiation. However, we do not fully understand how these transcription factors influence tissue differentiation as all of their downstream effectors have not been identified. Automated cell lineage analysis studies lead us to hypothesize that hnd-1 and elt-1 regulate expression of members of other conserved transcription factor families involved in embryogenesis and differentiation. These factors include members of the HOX factors, nuclear receptors, and targets of the conserved WNT signaling pathway, all of which are critical in cell fate specification. We hypothesize that hnd-1 regulates expression of the HOX factor egl-5 and the WNT target cwn-1, as each have muscle-specific expression, while elt-1 regulates expression of the nuclear receptor transcription factor nhr-25, the HOX factor lin-39, and the WNT target tlp-1, as each have hypodermal-specific expression. To address our hypothesis, we will test whether knock-outs of hnd-1 or elt-1 influence the expression of these putative downstream factors using fluorescent reporter proteins in conjunction with 3D and time-lapse imaging and automated cell lineage tracing. Our results will clarify the respective functions of hnd-1 and elt-1 in muscle and hypodermal tissue differentiation.