|M.Sc Student||Lilach Friedlander-Shani|
|Subject||Deciphering how the Zn-Finger Heterochronic Factor LIN-29|
Controls AFF-1-Dependent Fusion of the Seam Cells
in C. elegans
|Department||Department of Biology||Supervisor||Full Professor Podbilewicz Benjamin|
|Full Thesis text|
During the development of the nematode C. elegans about one third of its somatic cells undergo cell to cell fusion. The cell to cell fusion process in C. elegans was found to be under complex and diverse regulation. Both spatial regulation and the developmental timing of cell fusion events are important for proper development.
Heterochronic genes regulate the relative timing of specific developmental events in C. elegans. The epidermal seam cells terminal differentiation in the L4 to adult molt is controlled by the heterochronic gene pathway. The transcription factor LIN-29 is the most downstream known heterochronic regulator of the seam cells terminal differentiation. AFF-1 protein is the fusogen required for the fusion of the seam cells during their terminal differentiation. In lin-29 loss of function mutant worms the seam cells fail to fuse. In order to test whether lin-29 controls aff-1 expression in the seam cells, we generated strains carrying transcriptional aff-1promoter::GFP construct in lin-29 loss of function mutant background. We found that while in wild type worms aff-1promoter::GFP is expressed in the seam cells starting from the L4 stage, in lin-29(n546) loss of function mutant worms there is partial or no aff-1p::GFP expression in the seam cells during this stage. These results suggest that lin-29 activates aff-1 expression in the seam cells during the L4 to young adult transition by transcriptional regulation. Therefore, the heterochronic gene lin-29 controls the seam cells fusion via aff-1 expression in the seam cells.
Since we have shown that lin-29 is regulating aff-1 reporter expression in the seam cells, we examined whether lin-29 regulates aff-1 also in additional tissues in which both lin-29 and aff-1 are expressed. lin-29 is expressed in both the anchor cell and the vulva, which are tissues that undergo cell fusion events mediated by AFF-1. We found that while lin-29 is required for the fusion of the anchor cell it is not required for aff-1 expression in the anchor cell, thus lin-29 does not control aff-1 expression in the anchor cell. We also show preliminary results indicating that lin-29 is not required for the vulva A ring fusion. Thus, lin-29 is not necessary for aff-1 fusogenic activity and therefore does not control aff-1 expression in the vulva A ring. Taken together, our results show lin-29 regulation of aff-1 is specific to the seam cells tissue.