Genetic Requirements for PIE-1 Localization and Inhibition of Gene Expression in the Embryonic Germ Lineage ofCaenorhabditis elegans

Abstract

In early Caenorhabditis elegans embryos, production of new mRNAs is inhibited in the germ lineage. This inhibition requires the germline factor PIE-1, and correlates with the absence in germline blastomeres of a phosphoepitope on RNA polymerase II (RNAPII-H5). We show that PIE-1 is uniformly distributed in oocytes and newly fertilized eggs, and becomes localized asymmetrically in the late one-cell stage. To begin to dissect the mechanisms required for PIE-1 localization and inhibition of RNAPII-H5 expression, we have examined the distribution of PIE-1 and RNAPII-H5 in maternal-effect mutants that disrupt embryonic development. We find that mutants that disrupt the asymmetric divisions of germline blastomeres mislocalize PIE-1, and activate RNAPII-H5 expression in the germ lineage. In contrast, mutants that alter somatic cell identities do not affect PIE-1 localization or RNAPII-H5 expression. Our observations suggest that PIE-1 represses mRNA transcription in each germline blastomere in a concentration-dependent manner. We also show that in wild-type, and in mutants where PIE-1 is mislocalized, the cellular and subcellular distribution of PIE-1 remarkably parallels that of the P granules, suggesting that the localizations of these two germline components are coordinately regulated.

Polarization of theC. eleganszygote proceeds via distinct establishment and maintenance phases

“…PAR-1 regulates the localization of cytoplasmic proteins, including MEX-5 and PIE-1 (Schubert et al, 2000;Tenenhaus et al, 1998). We confirmed these observations and extended them to MEX-6, by following GFP:MEX-5, GFP:MEX-6 and PIE-1:GFP dynamics in par-1(RNAi) embryos.…”

emb-4Is a Conserved Gene Required for Efficient Germline-Specific Chromatin Remodeling DuringCaenorhabditis elegansEmbryogenesis

“…Similar mechanisms degrade PIE-1 in the soma and in Z2/Z3: During the asymmetric divisions of the P-lineage, PIE-1 is actively moved to the posterior half of the cell prior to cytokinesis for enriched deposition into the posterior (germline) daughter (Tenenhaus et al 1998;Reese et al 2000). PIE-1 that is retained or left behind in the anterior (somatic) daughter is quickly degraded by a mechanism involving an E3 ubiquitin ligase complex that includes CUL-2 and ZIF-1 (DeRenzo et al 2003).…”

“…It also suggests that fast degradation of PIE-1 at the birth of Z2/Z3 may be a redundant process and supports previous findings that a highly concentrated level of PIE-1 is required for its full effect. Indeed, dilution of PIE-1 at the symmetric P 4 cell division may lead to insufficient PIE-1 for complete repression, allowing some transcription elongation to occur (Tenenhaus et al 1998). One early product could be ZIF-1, which could then quickly direct degradation of the remaining PIE-1.…”

cdk-7 is required for mRNA transcription and cell cycle progression in Caenorhabditis elegans embryos

“…mAbH5, mAbH14, and mAb8WG16 immunostaining of embryos was performed as described (36). For Western blotting with mAbH5 and mAbH14, embryonic protein extracts were prepared as described (37), and extracts were run on SDS͞10% PAGE.…”