P Granules in the Germ Cells of Caenorhabditis elegans Adults Are Associated with Clusters of Nuclear Pores and Contain RNA

Abstract

The germ cells, and germ cell precursors, in the nematode Caenorhabditis elegans contain distinctive granules called P granules. During early embryogenesis, P granules are segregated asymmetrically into those blastomeres that eventually produce the germ line. Because of the correlation between P granule distribution and the development of the germ line, P granules are widely thought to function in some aspect of germ line specification or differentiation. Most of the analysis of P granule structure and localization has focused on the early embryo, when P granules are located in the cytoplasm. However, during most of development P granules are associated with germ cell nuclei. We report here an ultrastructural analysis of the nuclear-associated P granules in the germ cells of the adult hermaphrodite gonad. We show that P granules are tightly associated with nuclear pores and that the positions of certain structures within the P granules correspond to the positions of pores on the nuclear envelope. We present immunocytochemical and ultrastructural data suggesting that P granules can associate, or remain associated, with pore-like structures even after they detach from the nuclear envelope during oogenesis. Finally, we show that nuclear-associated P granules in the gonad contain RNA, complementing previous studies showing that cytoplasmic P granules in embryos contain RNA.

Essential Roles forCaenorhabditis elegansLamin Gene in Nuclear Organization, Cell Cycle Progression, and Spatial Organization of Nuclear Pore Complexes

“…As expected, both MAb414 and Ce-lamin brightly stained the nuclear envelope. However, only Ce-lamin showed intranuclear location (top panels in Figure 3), while MAb414 gave a higher cytoplasmic background, as described (Pitt et al, 2000). The internal staining disappeared as well as the nuclear envelope staining in lmn-1(RNAi) embryos (Figure 3).…”

“…In order to verify that the internal lamin staining was specific, embryonic and adult tissues were stained with both Ce-lamin antibodies and monoclonal antibody mAb414 (Davis and Blobel, 1987), which recognizes the nuclear pores in many eukaryotes, including C. elegans (Pitt et al, 2000). As expected, both MAb414 and Ce-lamin brightly stained the nuclear envelope.…”

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

“…In contrast to the perinuclear association of PGL-1 in the more than four-cell stage wild-type embryos, most PGL-1-containing granules in embryos depleted for nuclear pore components remained detached from the nuclear envelope ( Figure 5A). The finding that .75% of nuclear pores are overlaid by P granules in the adult germ line (Pitt et al 2000) predicted that loss of nuclear pore components might compromise association of P granules with the nuclear periphery.…”

Germ Granules Prevent Accumulation of Somatic Transcripts in the AdultCaenorhabditis elegansGermline

“…The mechanism by which P granules perform these functions remains to be determined. P granules reside on the outer periphery of germ cell nuclei and overlie nuclear pores (Pitt et al 2000;Sheth et al 2010;Updike et al 2011). It has been proposed that as mRNAs exit the nucleus, P granules intercept and perhaps process these transcripts, thus influencing the transcriptome and proteome of the germline (Kasper et al 2014; Figure 8).…”