The PGL Family Proteins Associate With Germ Granules and Function Redundantly in Caenorhabditis elegans Germline Development

Abstract

PGL-1 is a constitutive protein component of C. elegans germ granules, also known as P granules. Maternally supplied PGL-1 is essential for germline development but only at elevated temperature, raising the possibility that redundant factors provide sufficient function at lower temperatures. We have identified two PGL-1-related proteins, PGL-2 and PGL-3, by sequence analysis of the C. elegans genome and by a yeast two-hybrid screen for proteins that interact with PGL-1. PGL-3 is associated with P granules at all stages of development, while PGL-2 is associated with P granules only during postembryonic development. All three PGL proteins interact with each other in vitro. Furthermore, PGL-1 and PGL-3 are co-immunoprecipitated from embryo extracts, indicating that they are indeed in the same protein complex in vivo. Nevertheless, each PGL protein localizes to P granules independently of the other two. pgl-2 or pgl-3 singlemutant worms do not show obvious defects in germline development. However, pgl-1; pgl-3 (but not pgl-2; pgl-1) double-mutant hermaphrodites and males show significantly enhanced sterility at all temperatures, compared to pgl-1 alone. Mutant hermaphrodites show defects in germline proliferation and in production of healthy gametes and viable embryos. Our findings demonstrate that both PGL-2 and PGL-3 are components of P granules, both interact with PGL-1, and at least PGL-3 functions redundantly with PGL-1 to ensure fertility in both sexes of C. elegans.

PGL germ granule assembly protein is a base-specific, single-stranded RNase

“…These granules possess common components across phyla (5) but use unique scaffold proteins, such as Drosophila Oskar (6), zebrafish Bucky Ball (7), and Caenorhabditis elegans paralogs PGL-1 and PGL-3 (8,9), called PGL collectively. Germ granule scaffold proteins from different phyla have distinct amino acid sequences with no conserved domains.…”

“…P-granules are required for germ-line survival (8,9) and germline totipotency (14). A recent model proposes that P-granules capture selected mRNAs exiting the nucleus (15), an idea based on the finding that untranslated mRNAs are enriched in P-granules, but translated mRNAs are absent (15,16).…”

“…PGL-1 and PGL-3 are required for adult germ cell development but the function of PGL-2 is unknown (8). All three PGL proteins interact with each other in vitro (8), but thus far only PGL-1 and PGL-3 are known to self-assemble into granules when expressed in nematode somatic cells or in mammalian cell culture (17,18). By primary sequence prediction, PGLs have only one recognizable region, C-terminal RGG repeats (Fig.…”

A twist of fate: How a meiotic protein is providing new perspectives on germ cell development

“…7 During this stage, zygotic expression initiates for a handful of germline genes that play key roles in germ cell differentiation, including transcripts for Pgranules components (pgl-1) and the nanos ortholog, nos-1. 8,9 Zygotic gene activation and resumption of the cell cycle occurs post-hatching in response to feeding. However, the X chromosome remains transcriptionally silenced in oocytes, a repression that is required for normal germ cell development.…”

Standing guard: Perinuclear localization of an RNA-dependent RNA polymerase

“…P granules have been proposed to function in mRNA transport, translation control, and͞or as carriers of maternal factors during assembly and asymmetric distribution of ''germ plasm'' during embryogenesis (24,25). P granule distribution in adult meiotic cells is abnormal in ego-1 RdRP mutant animals, which may be an indirect effect, but is interesting in light of the study by Shiu et al (26).…”