Genetic Analysis of theCaenorhabditis elegansGLH Family of P-Granule Proteins

Abstract

The Vasa DEAD-box helicases are widespread markers of germ cells across species, and in some organisms have been shown to be essential for germ-cell formation and development. In contrast to the single Vasa gene in most systems analyzed, Caenorhabditis elegans has four Vasa family members, the germline helicases GLH-1, GLH-2, GLH-3, and GLH-4. Our analysis of deletion alleles of each glh gene demonstrates that GLH-1 is the key member of the family: loss of GLH-1 function causes sterility that is mainly maternal effect, is manifested predominantly at elevated temperature, and is due to reduced germcell proliferation and impaired formation of both sperm and oocytes. The other GLHs are not essential. However, GLH-4 serves redundant roles with GLH-1: loss of both genes' function causes glh-1-like sterility at all temperatures. Molecular epistasis analysis demonstrates that GLH-1 and GLH-4 are required for proper association of the PGL family of proteins with P granules, suggesting a pathway of P-granule assembly in which the GLHs are upstream of the PGL proteins and the mRNA cap-binding protein IFE-1. While loss of some P-granule components causes worms to be defective in RNA interference, loss of GLH-1 and GLH-4 does not compromise RNAi. Thus, RNAi likely does not require intact P granules but instead relies on particular P-granule factors. We discuss the evolution of the Vasa/GLH genes and current views of their functions and the assembly and roles of germ granules among species.

A Genomewide RNAi Screen for Genes That Affect the Stability, Distribution and Function of P Granules in Caenorhabditis elegans

“…Identification of genes whose loss alters the level and/or distribution of PGL-1 offers an avenue to identify other P-granule components and components that regulate P-granule assembly and stability. For example, the C. elegans VASA homolog GLH-1, another constitutive P-granule component, acts ''upstream'' of PGL-1; in glh-1 loss-of-function mutants, PGL-1 is not properly localized to P granules and instead a significant portion of PGL-1 is diffusely distributed in the germ-line cytoplasm (Kawasaki et al 1998;Spike et al 2008a). More recently another constitutive P-granule component, DEPS-1, was identified in a forward genetic screen for mutants that display PGL-1 localization defects similar to those seen in glh-1(lf) mutants (Spike et al 2008b).…”

Germ Granules Prevent Accumulation of Somatic Transcripts in the AdultCaenorhabditis elegansGermline

“…C. elegans germ granules or "P granules" are necessary for germline development and fertility (Kawasaki et al 1998(Kawasaki et al , 2004Spike et al 2008) and protect the germline from expressing somatic fate markers (Updike et al 2014). In this study, we analyzed the progressive transcript changes that occur in PG(2) germlines.…”

“…The two most important PGL proteins, PGL-1 and PGL-3, contain a predicted RNA-binding motif at their C terminus called an RGG (Arg-Gly-Gly) box (Kawasaki et al 1998(Kawasaki et al , 2004. The four GLH proteins are homologs of the highly conserved Vasa protein and contain DEAD-box helicase domains, which may also bind and modulate RNAs (Gruidl et al 1996;Kuznicki et al 2000;Spike et al 2008). The most important GLH protein, GLH-1, is necessary for P-granule retention at the nuclear periphery (Updike et al 2011).…”

C. elegans meg‐1 and meg‐2 differentially interact with nanos family members to either promote or inhibit germ cell proliferation and survival

“…glh-1 and pgl-1 mutants, as well as many other P granule components, have under-proliferated gonads (Kawasaki et al, 1998;Spike et al, 2008). Further examination of other components might reveal how necessary P granules themselves are for germ cell proliferation relative to other roles in gamete differentiation.…”

“…glh-1; meg-1 mutant animals display a synergistic increase in the penetrance of sterility. In nematodes, GLH-1 is required for the proper localization to P granules of the PGL family of RNA binding proteins, including PGL-1 (Spike et al, 2008). Intriguingly, while glh-1 is synergistic with meg-1, pgl-1 appears to be antagonistic.…”