Assembly of RNP granules in stressed and aging oocytes requires nucleoporins and is coordinated with nuclear membrane blebbing

Abstract

Protective cellular responses to stress and aging in the germ line are essential for perpetuation of a species; however, relatively few studies have focused on how germ cells respond to stress and aging. We have previously shown that large ribonucleoprotein (RNP) complexes assemble in oocytes of Caenorhabditis during extended meiotic arrest or after environmental stress. Here we explore the regulation of these dynamic RNPs and demonstrate their assembly is coordinated with dramatic, nuclear membrane blebbing in oocytes. Our ultrastructural analyses reveal distinct changes in the endoplasmic reticulum, and the first evidence for the assembly of stacked annulate lamellae in Caenorhabditis. We further show several nucleoporins are required for the complete assembly of RNP granules, and a disruption in RNP granule assembly coupled with a low frequency of nuclear blebbing in arrested oocytes negatively impacts embryonic viability. Our observations support a model where nuclear membrane blebbing is required to increase the trafficking of nucleoporins to the cell cortex in stressed or meiotically-arrested cells and to facilitate the recruitment of RNA and protein components of RNPs into large complexes. These new insights may have general implications for better understanding how germ cells preserve their integrity when fertilization is delayed and how cells respond to stress.

RNA Granules in Germ Cells

“…These granules become larger in arrested oocytes and may correspond to the membraneassociated, sponge body-like structures characterized by electron microscopy (Jud et al 2008;Patterson et al 2011). Loss of the P-body protein CAR1/Tral/RAP55 disrupts grP bodies, and causes ectopic translation of glp-1 mRNA in oocytes, as is observed upon loss of PUF-5 and related PUFs (Noble et al 2008).…”

“…Consistent with a role for FG-repeats, three C. elegans VASA family members, GLH-1, 2, and 4, contain FG repeats (Kuznicki et al 2000), and the FG-containing nucleoporin Nup98 and mRNA export factor DDX-19 colocalize with germ granules (Sheth et al 2010;Voronina and Seydoux 2010). RNAi screens have also identified several nucleoporins required for germ granule integrity in embryos (Updike and Strome 2009a;Voronina and Seydoux 2010) and for the assembly of sponge body-like aggregates in stressed oocytes (Patterson et al 2011).…”

“…During the oocyte growth phase, the perinuclear germ granules detach from the nuclear envelope, apparently taking with them membrane fragments containing clusters of nuclear pores (Pitt et al 2000). Stressed and aging oocytes assemble even larger cytoplasmic RNP complexes, whose formation has been correlated with dramatic nuclear membrane blebbing (Jud et al 2008;Patterson et al 2011). Drosophila sponge bodies also change morphology under different environmental conditions (Snee and McDonald 2009), suggesting a role for these membranous structures in protecting oocytes from stress.…”

T-cell internal antigen 1 counteracts somatic RNA degradation during early Xenopus embryogenesis

“…Thus, localization RNPs and stress granules appear to contain overlapping components. C. elegans oocytes form large RNP granules in response to stress that contain Tia1 (Jud et al, 2008;Patterson et al, 2011), whereas, to our best knowledge, the presence of stress granules in Xenopus oocytes has not been reported to date. Nevertheless, Tia1 might promote multimerization of localization RNPs.…”

Endoplasmic Reticulum-Derived Multilamellar Bodies in Oocytes of Mouse Follicle Cultures under Oxidized Low-Density Lipoprotein Treatment

“…Annulate lamellae are largely restricted to oocytes and implicated in pronuclear formation after fertilization in mammalian oocytes [Sutovsky et al, 1998]. Recently, stacks of annulate lamellae assembled with ribonucleoproteins into large complexes were described as a protective cellular response against stress and ageing in insect oocytes [Patterson et al, 2011]. The annulate lamellae differ from multilamellar bodies, which are surrounded by smooth ER membranes without nuclear pore complexes [Snapp et al, 2003;Korkhov et al, 2008Korkhov et al, , 2009.…”