Junichi Komiyama

Oocyte growth-dependent progression of maternal imprinting in mice.

In mammals, some genes categorized as imprinted genes are exclusively expressed either from maternal or paternal allele. This parental‐origin‐specific gene expression is regulated by epigenetic modification of DNA methylation in differentially methylated region (DMR), which is independently imposed during oogenesis and spermatogenesis. It is known that methylation of DMR in the female germ line is established during oocyte growth phase. However, the cause of the progression of methylation on DMR, due to either aging of mice or growth‐size of oocyte was unclear up to now. Here, we analyzed the methylation of DMR for each eight imprinted genes (Igf2r, Lit1, Zac1, Snrpn, Peg1/Mest, Impact, Meg1/Grb10, and H19) by bisulfite sequencing methylation assay, using oocytes from 10 dpp (days post partum), 15 dpp, 20 dpp, and adult mice. To find whether the size of oocytes is the cause of methylation, above oocytes were classified into seven groups (each oocyte diameter ranging from 40 to 75 µm with intervals of 5 µm). The results from juvenile mice oocytes showed that DMR methylation progressed according to oocyte growth each imprinted gene. More than 85% of DMR methylation was achieved for both Igf2r, Zac1 & Lit1 with oocyte size of reaching 55 µm and Snrpn, Peg1/Mest, Impact, and Meg1/Grb10 with oocyte size of reaching 60 µm. Preferential methylation of maternal allele was observed in Zac1 and Peg1/Mest of juvenile oocytes and in Snrpn of juvenile and adult oocytes. The oocyte size‐dependent‐methylation progressed equally for all three different‐age juvenile mice. The size‐dependent‐methylation was also recognized in the growing oocytes collected from adult mice, although the progress is slightly slower than that of juvenile mice. From these results, we concluded that DNA methylation is established with oocyte size dependent manner, not with aging of mice.

Lysophosphatic acid modulates prostaglandin secretion in the bovine uterus.

Lysophosphatidic acid (LPA) modulates prostaglandin (PG) synthesis via LPA receptor 3 (LPAR3) in the murine endometrium. The lack of functional LPAR3 in mice may lead to embryo mortality. In the present study, we examined the role of LPA in the bovine uterus. We confirmed that LPA is locally produced and released from the bovine endometrium. Moreover, there are enzymes involved in LPA synthesis (phospholipase (PL) D(2) and PLA2G1B) in the bovine endometrium during estrous cycle and early pregnancy. Expression of the receptor for LPA (LPAR1) was positively correlated with the expression of PGE(2) synthase (PGES) and negatively correlated with the expression of PGF(2alpha) synthase (aldose reductase with 20 alpha-hydroxysteroid dehydrogenase activity - PGFS) during early pregnancy. In vivo LPA induced P4 and PGE(2) secretion was inhibited by LPAR1 antagonist (Ki16425). The overall results indicate that LPA is locally produced and released from the bovine endometrium. Moreover, LPAR1 gene expression in the endometrium during the estrous cycle and early pregnancy indicates that LPA may play autocrine and/or paracrine roles in the bovine uterus. LPAR1 gene expression is positively correlated with the expression of the enzyme responsible for luteotropic PGE(2) production (PGES) in endometrium. In cow, LPA stimulates P4 and PGE(2) secretion. Thus, LPA in the bovine reproductive tract may indirectly (via endometrium) or directly support corpus luteum action via the increase of P4 synthesis and the increase of PGE(2)/PGF(2)(alpha) ratio. It suggests that LPA may serve as an important factor in the maintenance of early pregnancy in cow.

Cortisol Is a Suppressor of Apoptosis in Bovine Corpus Luteum

Glucocorticoid (GC) acts as a modulator of physiological functions in several organs. In the present study, we examined whether GC suppresses luteolysis in bovine corpus luteum (CL). Cortisol (an active GC) reduced the mRNA expression of caspase 8 (CASP8) and caspase 3 (CASP3) and reduced the enzymatic activity of CASP3 and cell death induced by tumor necrosis factor (TNF) and interferon gamma (IFNG) in cultured bovine luteal cells. mRNAs and proteins of GC receptor (NR3C1), 11beta-hydroxysteroid dehydrogenase type 1 (HSD11B1), and HSD11B2 were expressed in CL throughout the estrous cycle. Moreover, the protein expression and the enzymatic activity of HSD11B1 were high at the early and the midluteal stages compared to the regressed luteal stage. These results suggest that cortisol suppresses TNF-IFNG-induced apoptosis in vitro by reducing apoptosis signals via CASP8 and CASP3 in bovine CL and that the local increase in cortisol production resulting from increased HSD11B1 at the early and midluteal stages helps to maintain CL function by suppressing apoptosis of luteal cells.

Disruption of parental‐specific expression of imprinted genes in uniparental fetuses

In mammals, imprinted genes show parental origin‐dependent expression based on epigenetic modifications called genomic imprinting (GI), which are established independently during spermatogenesis or oogenesis. Due to GI, uniparental fetuses never develop to term. To determine whether such expression of imprinted genes is maintained in uniparental mouse fetuses, we analyzed the expression of 20 paternally and 11 maternally expressed genes in androgenetic and parthenogenetic fetuses. Four genes of each type were expressed in both groups of fetuses. Furthermore, quantitative analysis showed that expression levels deviated from the presumed levels for some imprinted genes. These results suggest that mechanisms acting in trans between paternal and maternal alleles are involved in the appropriate expression of some imprinted genes.

Hypoxia Promotes Luteal Cell Death in Bovine Corpus Luteum

Abstract Low oxygen caused by a decreasing blood supply is known to induce various responses of cells, including apoptosis. The present study was conducted to examine whether low-oxygen conditions (hypoxia) induce luteal cell apoptosis in cattle. Bovine midluteal cells incubated under hypoxia (3% O2) showed significantly more cell death than did those incubated under normoxia (20% O2) at 24 and 48 h of culture, and had significantly lower progesterone (P4) levels starting at 8 h. Characteristic features of apoptosis, such as shrunken nuclei and DNA fragmentation, were observed in cells cultured under hypoxia for 48 h. Hypoxia increased the mRNA expressions of BNIP3 and caspase 3 at 24 and 48 h of culture. Hypoxia had no significant effect on the expressions of BCL2 and BAX mRNA. Hypoxia also increased BNIP3 protein, and activated capsase-3. Treatment of P4 attenuated cell death, caspase-3 mRNA expression, and caspase-3 activity under hypoxia. Overall results of the present study indicate that hypoxia induces luteal cell apoptosis by enhancing the expression of proapoptotic protein, BNIP3, and by activating caspase-3, and that the induction of apoptosis by hypoxia is partially caused by a decrease in P4 production. Because hypoxia suppresses P4 synthesis in bovine luteal cells, we suggest that oxygen deficiency caused by a decreasing blood supply in bovine corpus luteum is one of the major factors contributing to both functional and structural luteolysis.

DNA methylation imprints on the IG-DMR of the Dlk1-Gtl2 domain in mouse male germline.

Mouse genomes show a large cluster of imprinted genes at the Dlk1–Gtl2 domain in the distal region of chromosome 12. An intergenic‐differentially methylated region (IG‐DMR) located between Dlk1 and Gtl2 is specifically methylated in the male germline; IG‐DMR regulates the parental allele‐specific expression of imprinted genes. Here, we show the resetting of IG‐DMR methylation marks during male germ‐cell differentiation. For parental allele‐specific methylation analysis, polymorphisms were detected in a 2.6‐kb IG‐DMR in three mouse strains. Bisulfite methylation analysis showed erasure of the marks by E14 and re‐establishment before birth. The IG‐DMR methylation status was maintained in spermatogonia and spermatocytes of mature testes. The IG‐DMR methylation status established before birth is thus maintained throughout the lifetime in the male germline.

The expression of the nuclear receptors NR5A1 and NR5A2 and transcription factor GATA6 correlates with steroidogenic gene expression in the bovine corpus luteum

The corpus luteum (CL) is the major site of progesterone (P4) production during the luteal phase of the estrous cycle in cattle. To better understand the molecular mechanisms underlying P4 production, we compared the mRNA and protein expression profiles of key components of the steroidogenic pathway (StAR, CYP11A, and 3β‐HSD) during the bovine CL luteal phase with that of several transcription factors (NR5A1, NR5A2, GATA4, GATA6) known for their roles in the control of steroidogenic gene expression. In the bovine CL, StAR, CYP11A, and 3β‐HSD mRNA and protein levels remained constant at the mid and late luteal phases but markedly declined at the regressed luteal stage. NR5A1 and NR5A2 exhibited a similar pattern with a significant decrease in expression at the regressed luteal stage. Both GATA4 and GATA6 mRNA and proteins could be detected in bovine CL; GATA6 levels, however, were generally higher. Although GATA4 expression did not change during the luteal phase, GATA6 showed a marked decrease at the regressed luteal stage, like NR5A1, NR5A2, and the other steroidogenic markers. Thus, we suggest that NR5A1, NR5A2, and GATA6, but not GATA4, contribute to the transcriptional regulation of steroidogenic gene expression, and hence P4 production, in the bovine CL. Furthermore, we have demonstrated the association of NR5A1 and NR5A2 with the bovine StAR promoter in the mid‐luteal CL using chromatin immunoprecipitation, suggesting that these factors have definitive roles in the regulation of StAR gene transcription in vivo. Mol. Reprod. Dev. 76: 873–880, 2009.

Nuclei of Oocytes Derived from Mouse Parthenogenetic Embryos Are Competent to Support Development to Term

Abstract Mouse parthenotes result in embryonic death before 10 days of gestation, but parthenogenetic embryos (ng/fg PE) that contain haploid sets of genomes from nongrowing (ng) oocytes derived from newborn fetuses and fully grown (fg) oocytes derived from adults can develop into 13.5-day-old fetuses. This prolonged development is due to a lack of genomic imprinting in ng oocytes. Here, we show maternal genomes of oocytes derived from ng/fg PE are competent to support normal development. After 28 days of culture, the ovaries from ng/fg PE grew as well as the controls, forming vesicular follicles with follicular antrums. The oocytes collected from the developed follicles were the same size as those of the controls. To determine whether maternal primary imprinting had been established in the oocytes derived from ng/fg PE, we examined the DNA methylation status in differentially methylated regions of three imprinted genes, Igf2r, Lit1, and H19. The results showed that maternal-specific modifications were imposed in the oocytes derived from ng/fg PE. Further, to assess nuclear competence to support development, we constructed matured oocytes containing a haploid genome derived from ng/fg PE oocytes by serial nuclear transfer. After in vitro fertilization and culture and embryo transplantation into recipients, two live pups were obtained. One developed normally to a fertile adult. These results revealed that oocytes derived from ng/fg PE can be normally imprinted during oogenesis and acquire competence to participate in development as female genomes.