Role for PADI6 in securing the mRNA-MSY2 complex to the oocyte cytoplasmic lattices

Abstract

The oocyte cytoplasmic lattices (CPLs) have long been predicted to function as a storage form for the maternal contribution of ribosomes to the early embryo. Our previous studies have demonstrated that ribosomal component S6 is stored in the oocyte CPLs and peptidylarginine deiminase 6 (PADI6) is critical for CPLs formation. Additionally, we found that depletion of PADI6 reduced de novo protein synthesis prior to the maternal-to-embryonic transition, therefore causing embryos to arrest at the 2-cell stage. Here, we present evidence further supporting the association of ribosomes with the CPLs by demonstrating that rRNAs are dramatically decreased in Padi6 KO oocytes. We also show that the abundance and localization of mRNAs is affected upon PADI6 depletion, suggesting that mRNAs are very possibly associated with CPLs. Consistent with this observation, the amount of the major RNA binding protein, MSY2, that is associated with the insoluble fraction of the oocytes after Triton X-100 extraction is also markedly decreased in the Padi6 KO oocytes. Furthermore, treatment of the oocytes with RNase A followed by Triton X-100 extraction severely impairs the localization of PADI6 and MSY2 in oocytes. These results indicate that mRNAs, possibly in a complex with MSY2 and PADI6, are bound in the CPLs and may play a role in securing the mRNA-MSY2 complex to the CPLs.

ZAR1 and ZAR2 are required for oocyte meiotic maturation by regulating the maternal transcriptome and mRNA translational activation

“…Consistent with western blotting, the MSY2 immunofluorescent signal decreased in Zar1/2 –/– oocytes; however, its cortical enrichment persisted. Collectively, these results suggest that ZAR1/2 may function together with MSY2 and CPL, which have been reported to be involved in maternal mRNA stabilization and mobilization in oocytes (46–47,49).…”

“…Therefore we further investigated the possible causes for the maternal transcriptome change. MSY2 is an RNA-binding protein that maintains global mRNA stability in mammalian germ cells (46,47). Zar1/2 knockout caused phenotypes resembling Msy2 knockout; female Msy2 –/– mice are infertile as their MII oocytes are severely compromised due to aberrant spindle formation and chromosome alignment (48).…”

“…PADI6 anchors MSY2-mRNAs to oocyte cytoplasmic lattices (CPLs), which have a function in mRNA and ribosomes storage during MZT (46,49–50). CPLs contain several proteins encoded by Mater, Padi6, Floped, Tle6 and Filia , whose deficiency in oocytes cause CPL disassembly, abnormal subcellular structure clustering (mitochondria and Golgi apparatus) and zygotic arrest (51).…”

L-bodies are RNA–protein condensates driving RNA localization in Xenopus oocytes

“…4A), our results argue that L-bodies are distinct from stress granules, Pbodies, germ granules, and other cytoplasmic RNP granules such as RNase L Bodies (Burke et al, 2020), as more than a quarter (26.7%) of the identified L-body proteins are not found in these other RNP granule types. Proteins unique to L-bodies include a cytokeratin protein (Krt12), which could be involved in anchoring to the vegetal cortex, as cytokeratin proteins have been implicated in this process (Kloc et al, 2005), a Kinesin II subunit (Kif3a), which has been shown to play a role in vegetal RNA transport in Xenopus oocytes (Betley et al, 2004;Messitt et al, 2008), and a peptidyl arginine deiminase (Padi2), for which there is an oocyte-specific paralog (Padi6) in mouse (Liu et al, 2017). Our results also indicate that L-bodies are distinct from Xenopus germ granules, or Balbiani bodies.…”

Acquisition of oocyte competence to develop as an embryo: integrated nuclear and cytoplasmic events

“…This lattice is composed of fibrillary structures including intermediate filaments and other filamentous structures. It has been proposed that these structures function in the storage of ribosomes (Liu et al, 2017). Several genetic studies indicate that disruption of these structures leads to impaired developmental competence and defective embryo development.…”