Genetic Analysis of Pry-1/Axin Function in the Nematode Caenorhabditis Briggsae

Abstract

Evolutionary variations during vulval development in C. elegans and its related nematode species are well analyzed. The formation of C. elegans vulva involves many complex cell-cell interactions that are mediated through well conserved EGF/EGFR/RAS, LIN12/Notch and WNT signaling pathways. These pathways specify distinct cell fates of the six epidermal vulval precursor cells (VPCs), P(3-8).p. pry-1/Axin in C. elegans is identified as a part of destruction box complex that mediates (beta)-catenin degradation and is known to negatively regulate canonical Wnt signaling pathway during its development. I focused on the genetic analysis of pry-1 I Axin function in C. briggsae, sister species to C. elegans, to study inter-species comparisons of vulva formation. Three alleles, lin(sy5353), lin(sy5411) and lin(sy5270) were genetically mapped to LG I using standard genetic and in del mapping techniques. Interestingly, a unique simultaneous Multi vulva and Vulvaless (Muv-Vul) phenotype was observed during vulva formation in Cbr-pry-1 alleles, resulting from the varying induction potentials of the VPCs along the A/P axis, compared to Cel-pry-1 animals. In order to analyze these phenotypic differences between Cel-pry-1 and Cbr-pry-1 in greater detail, I dissected vulval development in sy5353 animals. VPC competence analysis was done through cell lineages and ablations studies, while the C. briggsae vulval cell fate markers were used for cell fate specification analysis. Cell ablations revealed that P7.p and P8.p in Cbr-pry-1 animals exhibited non-competence towards anchor cell signaling. Additionally, gonad-independent inductions was observed in P(3-8).p cells and they adopted 2° cell fate specifications. Using RNAi approach, Cbr-pry-1 interactions with other vulval pathway genes were dissected and it was observed that Cbr-lin-12 is involved in VPC competence of P7.p and Cbr-pop-1 exhibited different regulatory levels during vulval development compared to C. elegans. Thus, it can be inferred that the mechanisms of vulva formation in C. briggsae has evolved through changes in the competence of VPCs.