In C.elegans, the heterochronic genes are responsible for specifying the timing of non-gonadal cell division patterns throughout larval development. Mutations in these genes cause developmental patterns to be skipped or repeated inappropriately.
lin-28,
lin-46, and
hbl-1 are three heterochronic genes that control evens of the L2 and L3. LIN-28 is an RNA binding protein that has at least two mechanisms of action, one of which is to block the maturation of the microRNA
let-7.LIN-46, a protein found only in Caenorhabditis species, and HBL-1, an Ikaros family zinc-finger transcription factor. Our goal is to define the relationships among these factors and determine how they control development in different tissues. To determine their regulatory relationships, we performed epistasis analysis between
lin-28,
lin-46 and
hbl-1. The creation of a double mutant containing a
lin-28 null allele and a hypomorphic allele of
hbl-1 lead to the discovery of a sterility defect, a novel phenotype with respect to heterochronic genes. Further analysis of this double mutant revealed gross morphological defects of the somatic gonad. The distal tip cells of the double mutant follow aberrant migration patterns causing the gonad arms to adopt atypical configurations. The double displays variant formation of spermatheca and of those developed, all are malformed. This is further observed by the irregular expression pattern of the spermatheca specific FKH-6::GFP marker in the double mutant. Due to the absence of developing embryos, pools of yoke are seen throughout the coelom of the animal. Our findings suggest for the first time a redundant role for these heterochronic genes in gonad development. We have previously found through a yeast-2-hybrid screen that LIN-46 physically interacts with the HBL-1 protein. Remarkably, removal of
lin-46 activity from the aforementioned double mutant resulted in the restoration of fertility. We plan to further explore this novel sterility phenotype in order to determine how these heterochronic genes effect somatic gonad development. We are also using the somatic gonad as a new tool to continue studying the relationships among these heterochronic genes and determine if their relationship is preserved in different tissues.