Fig. 6.3.

Translational control of the mitosis–meiosis decision in C. elegans. The LAG-2 ligand produced by the somatic cell called the distal tip cell (DTC) activates the GLP-1 receptor present on germ cells. This results in the transcriptional activation of the RBP FBF-2, which along with FBF-1 inhibits meiotic entry by suppressing the translation of gld-1, gld-3, gld-2, and cki-2 mRNAs. The RBPs PUF-8 and MEX-3 promote proliferation, possibly by regulating the translation of unknown mRNAs. Although a single proliferating cell is shown in this cartoon, the mitotic region extends to about 20-cell diameters from DTC. The entire proliferative zone comprises of a total of ~200 cells. The schematic on the right represents a cell from the transition zone. In the transition zone, GLP-1 activity and the levels of FBFs decrease, resulting in the expression of FBF targets such as GLD-1 and GLD-2. GLD-1 represses the translation of glp-1 and unknown mRNAs to promote meiotic entry. GLD-2 and GLD-4 (PAPs) promote GLD-1 expression. In addition, these two PAPs promote meiotic entry independently of GLD-1 by regulating the translation of unknown mRNAs. Furthermore, PUF-8 facilitates meiotic entry by repressing the translation of let-60, which encodes RAS, a well-known proliferation-promoting factor, in this zone