The Rb pathway in Caenorhabditis elegans is part of the SynMuv pathway, which is comprised of two groups of genes (A and B) with redundant functions for the inhibition of vulval induction. Members of the Rb complex consist of
lin-35 (Rb),
rba-2 (RbAp48 homolog),
hda-1(histone deacetylase),
dpl-1(DP like protein), and
efl-1(E2F like protein) (Lu and Horvitz, Cell 95(7):981-91, 1998), all of which were previously identified in mammalian cell studies as a transcriptional repressor complex in the G1-S transition of the cell cycle. Negative regulation of gene expression by pRb is largely mediated through physical interaction with EFL-1 and DPL-1, two predicted transcription regulators. pRB also recruits Rb-associated protein, RBA-2 and a histone deacetylase, HDA-1 to enhance its negative regulatory function. Positive signals for vulval induction come from RTK/Ras/Map kinase cascade, which overcomes the inhibitory effect by the Rb complex. The antagonistic signal by MAPK is required for induction of the appropriate vulval precursor cell (P6.p) to adopt vulval fate. We are interested in examining the relationship between these two pathways in a second tissue that produces a different fate from vulval induction. First, our germline gene expression study has identified that all the members of the Rb complex as germline enriched genes. Recent studies have also shown that four out of the five the Rb complex components gave germline phenotypes when mutated. Loss of function in HDA-1 (Dufourcq et al, MCB 22(9):3024-34, 2002), EFL-1, DPL-1(Craig and Horvitz, Mol Cell. 7(3):461-732001), and RBA-2 showed various germline phenotypes such as sterility, embryonic lethality, brood size reduction, and oocyte maturation defects. Interestingly, EFL-1 expression was found in the germline (Page et al, JR. Mol Cell, (3):451-60, 2001) specifically near where MAPK acts for meiotic progression (Church and Lambie, Development; 121(8):2525-35, 1995). Currently, it is unclear if any relationship between MAPK and the Rb pathway exists in the germline, and whether it is still antagonistic as in vulval development. The target genes in the two pathways may be the same or overlapping or completely distinct in the germline. We are performing microarray experiments to examine the effects of depleting each of the factors of the complex on gene expression in the germline, focusing first on the sequence specific transcription factors
efl-1 and
dpl-1. We hope to identify genes that are transcriptionally responsive to the Rb complex in the germline. We will then compare these genes to those regulated by MAPK in the germline to determine whether these pathways converge on common or distinct sets of target genes.