Biology subjects

Okuda, A.

Publications and source records attributed to Okuda, A..

3 recordsLinked to original sources

bioRxiv2020

Identification of germ cell-specific Mga variant mRNA that promotes meiotic entry via impediment of a non-canonical PRC1

Transition from mitosis to meiosis in cell division is a fundamental process of gametogenesis. This transition is thought to be largely controlled by the exchange of relative dominance between positive and negative regulation by the retinoic acid/Stra8 signal cascade and a non-canonical PRC1 (PRC1.6), respectively. We have previously demonstrated that germ cells have transcriptionally and/or post-translationally reduced levels of MAX, a component of PRC1.6, immediately prior to meiotic onset, leading to alleviation of the negative effect of PRC1.6 against meiotic onset. Here, we found that germ cells produced Mga variant mRNA bearing a premature termination codon (PTC) during meiosis as an additional mechanism to impede the function of PRC1.6. Our data indicated that spermatocytes and/or round spermatids produced an anomalous MGA protein lacking the bHLHZ domain from the variant mRNA and therefore functioned as a dominant negative regulator of PRC1.6 by exquisitely using their inefficient background of PTC-mediated nonsense-mediated mRNA decay. Thus, our data indicate that meiotic onset of male germ cells is controlled in a multi-layered manner in which both MAX and MGA, which constitute the core of PRC1.6 by their interaction, are at least used as targets to deteriorate the integrity of the complex to ensure initiation of meiosis. Significance StatementPRC1.6, a non-canonical PRC1, functions as a strong blocker of meiotic onset. Therefore, germ cells need to alleviate the function of the complex as a prerequisite for meiotic onset. The MGA/MAX heterodimer not only constitutes a core of PRC1.6, but also confers direct DNA-binding activity to the complex. We have previously demonstrated that germ cells reduce Max amounts prior to meiotic onset to inactivate PRC1.6. In this study, we explored the possibility of an additional molecular mechanism that promotes meiotic onset via impediment of PRC1.6 functions as a safeguard system. Here, we demonstrate that meiotic germ cells specifically generate variant Mga mRNA by alternative splicing, which leads to production of a dominant negative regulator of PRC1.6.

developmental biology↗

bioRxiv2020

Two DNA binding domains of Mga act in combination to suppress ectopic activation of meiosis-related genes in mouse embryonic stem cells

Mouse embryonic stem cells (ESCs) have high potential for meiotic entry, like germ cells. Although the physiological meaning of this potential is not known, it is certain that a rigid safeguarding system is required to prevent ectopic onset of meiosis. PRC1.6, a non-canonical PRC1, is known for its suppression of precocious and ectopic meiotic onset in germ cells and ESCs, respectively, in which MGA has important roles in DNA binding as well as in constructing the complex as a scaffolding component. As a salient feature, MGA bears two distinct DNA-binding domains termed bHLHZ and T-box. However, how these features contribute to the functions of PRC1.6, particularly in the repression of meiotic genes, remains largely obscure. Here, we demonstrated that both DNA binding domains of Mga repress distinct sets of genes in murine ESCs, and substantial numbers of meiosis-related genes are included in both gene sets. In addition, our data demonstrated that both DNA binding domains of Mga, in particular bHLHZ, are crucially involved in repressing the expression of Meiosin, which plays essential roles in meiotic entry in collaboration with Stra8, revealing at least part of the molecular mechanisms that link negative and positive regulation of meiotic onset.

cell biology↗

bioRxiv2020

Targeted disruption of Pparγ1 promotes trophoblast endoreplication in the murine placenta

In murine placentas, peroxisome proliferator-activated receptor (PPAR) {gamma}1, a nuclear receptor, is abundant at the late stage of pregnancy (E15-E16), but its functional roles are still elusive because PPAR{gamma}-full knockout embryos die early (E10). We generated mice disrupted in only Ppar{gamma}1, one of the two major mRNA splicing variants of PPAR{gamma}1. Ppar{gamma}1- knockout embryos developed normally until 15.5 dpc, but their growth was retarded thereafter and they did not survive. At 15.5 dpc, in the wild-type placentas, intense PPAR{gamma}-immunostaining was detected in sinusoidal trophoblast giant cells (sTGCs), a cell lineage that coordinates the maternal blood microcirculation in the labyrinth, whereas they were absent in the knockouts. Although Ppar{gamma}1-knockout placentas were normal in morphology, we observed severely dilated maternal blood sinuses in the labyrinth. The Ppar{gamma}1-knockout sTGCs had abnormally large nuclei, an enhanced endocycling phenotype, indicating insufficient differentiation. RNA-sequencing of the placentas showed increased expression of genes coding for nucleosome assembly factors. Labyrinthine gene expressions for atypical E2Fs and cyclin E, key drivers for endocycling, were increased >3-fold. These findings suggested that PPAR{gamma}1 plays a key role in endocycle termination.

developmental biology↗