mab-22 is an important gene controlling male sensory ray assembly in C. elegans. By genetic mapping and RNAi data, it was confirmed that mab-22 encodes a T-box containing transcription factor, TBX-2. Within that coding region, a point mutation was found, which leads to a single amino acid substitution in the putative dimerization domain of TBX-2....[ Read more ]

mab-22 is an important gene controlling male sensory ray assembly in C. elegans. By genetic mapping and RNAi data, it was confirmed that mab-22 encodes a T-box containing transcription factor, TBX-2. Within that coding region, a point mutation was found, which leads to a single amino acid substitution in the putative dimerization domain of TBX-2.

In this thesis study, homodimerization of MAB-22 T-box domain was evaluated via a yeast two-hybrid assay. In addition, mab-22 expression profile was documented with a GFP-reporter. Reporter signal was observed in the structural cell of rays 1, 5, 7 in the wild type background and other rays under different genetic backgrounds. With bioinformatics prediction and genetic data, it was shown that mab-22 expression was subjected to a negative feedback regulation by itself. mab-22 expression level was elevated in the pharyngeal muscle and detected in more ray structural cells in the bx59 mutant. By candidate gene approach, I showed that mab-22 expression depends on wild type lin-32 and hlh-2 functions, and it was repressed by egl-5.

To decipher how mab-22 executes the ray assembly program, putative structural cell-specific genes and mab-22 downstream targets were identified. Immuno-pull down with poly-A binding (PAB) protein expressed in the structural cells uncovered 20 putative structural cell-specific genes. In the list, ram-5, ceh-43 and unc-62 were shown to be expressed in the structural cells using gfp reporters. Other genes in the list might participate in different cellular events of ray assembly, e.g. polarity formation, nucleocytoplasmic transport or nucleokinesis. Combining PAB pull down with mab-22(RNAi), 19 genes were found to be activated by mab-22 while two genes were indicated to be repressed by mab-22. I further showed that mab-22 is required for the activation of ram-5 acting in ray morphogenesis step. The delineation of how mab-22 controls its target gene will offer a better understanding of the coordinated transcriptional control of execution components in organ assembly.