Dcp1-Bodies in Mouse Oocytes

Abstract

Processing bodies (P-bodies) are cytoplasmic granules involved in the storage and degradation of mRNAs. In somatic cells, their formation involves miRNA-mediated mRNA silencing. Many P-body protein components are also found in germ cell granules, such as in mammalian spermatocytes. In fully grown mammalian oocytes, where changes in gene expression depend entirely on translational control, RNA granules have not as yet been characterized. Here we show the presence of P-body-like foci in mouse oocytes, as revealed by the presence of Dcp1a and the colocalization of RNAassociated protein 55 (RAP55) and the DEAD box RNA helicase Rck/p54, two proteins associated with P-bodies and translational control. These P-body-like structures have been called Dcp1-bodies and in meiotically arrested primary oocytes, two types can be distinguished based on their size. They also have different protein partners and sensitivities to the depletion of endogenous siRNA/miRNA and translational inhibitors. However, both type progressively disappear during in vitro meiotic maturation and are virtually absent in metaphase II-arrested secondary oocytes. Moreover, this disassembly of hDcp1a-bodies is concomitant with the posttranslational modification of EGFP-hDcp1a. INTRODUCTIONGene expression flows from DNA to protein using mRNA as an intermediate. Transcripts can either be used immediately as template for protein synthesis or translationally silenced and stored for later translation. A subset of silenced mRNAs is packaged into microscopically visible RNP granules that lack a limiting lipid membrane (Kedersha and Anderson, 2007). In mammals, processing bodies (P-bodies) RNA granules are present in a broad range of somatic cell types, including highly specialized cells such as neurons. Initially, P-bodies were discovered as 5Ј-3Ј mRNA decay centers in mammalian somatic cells (Bashkirov et al., 1997;Eystathioy et al., 2003;Cougot et al., 2004), and were found to be conserved in yeast (Sheth and Parker, 2003); because of the systematic localization of the decapping protein Dcp1a in P-bodies, they were also called Dcp1-bodies. Subsequently, P-bodies were shown to be involved in mRNA surveillance (Chen and Shyu, 2003;Couttet and Grange, 2004), RNAmediated silencing (Rehwinkel et al., 2005;Jakymiw et al., 2005;Liu et al., 2005a), and translational control Liu et al., 2005b;Bhattacharyya et al., 2006b).A role for P-bodies in translational control was first highlighted in yeast cells. It was shown that the entry of an mRNA into P-bodies does not automatically lead to its degradation: upon glucose starvation mRNAs can be temporarily stored in P-bodies, which increase in size and number, and then exit the foci upon refeeding to reenter polysomes (Brengues et al., 2005). In mammals, this reversibility of mRNA localization has been observed for miRNA-mediated mRNA repression in Huh7 cells (Pillai, 2005;Pillai et al., 2005;Bhattacharyya et al., 2006a). Although such a shuttling of mRNAs between polysomes and P-bodies has not been described for other mecha...

Small RNAs in early mammalian development: from gametes to gastrulation

“…Together, these surprising results show that miRNA function is suppressed in fully grown oocytes even though miRNA biogenesis is unaffected and miRNA targets are present. Although the mechanism of suppression is unknown, one hint comes from the finding that P-bodies (processing bodies, see Box 1), in which miRNA destabilization normally occurs (Parker and Sheth, 2007), are lost in maturing oocytes and only reform at the blastocyst stage Swetloff et al, 2009). Whether the loss of P-bodies is a primary or secondary consequence of miRNA functional loss is unclear.…”

Distinct functions of maternal and somatic Pat1 protein paralogs

“…Many of the protein components found in the CPEB maternal RNP are also found in cytoplasmic RNP complexes variously called germinal granules, P-granules, Balbianibodies, neuronal RNP granules, and P(rocessing)-bodies in fly, worms, and mammalian germline as well as somatic cells (Kotaja et al 2006;Roper 2007;Boag et al 2008;Noble et al 2008;Swetloff et al 2009;Flemr et al 2010). The conservation of components across species emphasizes the importance of these RNP complexes in translational control.…”

RNA Processing During Early Embryogenesis: Managing Storage, Utilisation and Destruction

“…Flemr and colleagues reported components that include "unidentified 18033 antibodyinteracting protein", DDX6, YBX2 (previously termed MSY2 in the mouse and FRGY2 in xenopus), CPEB, and the exon junction complex or EJC, which is a variable complex based around 5 proteins (SRm160, DEK, RNPS1, Y14 and REF) that have a number of other interactions and are involved in enhancing nucleocytoplasmic shuttling of mRNAs (Le Hir et al 2001). In a similar fashion to the storage mechanisms described in other cell types, two DCP1 containing bodies were proposed to be active in the mouse oocyte (Swetloff et al 2009). Likewise, responsiveness to chemical treatments like cycloheximide and RNase A treatments (Lin et al 2008) also helps to define the different granule types, with p-bodies being sensitive to the chemicals, unlike decapping bodies.…”