Journal of Reproduction and Development
Online ISSN : 1348-4400
Print ISSN : 0916-8818
ISSN-L : 0916-8818
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  • Volume 66 (2020) Issue 2 Pages 105-113
    Increased supply from blood vessels promotes the activation of dormant primordial follicles in mouse ovaries Read more
    Editor’s picks

    Cover Story:
    Most primordial follicles present in ovaries are dormant and only a few of them are activated in every estrus cycle. However, the mechanism controlling the activation of dormant primordial follicles in vivo remains unclear. In this study, Komatsu et al. found that almost all the activated primordial follicles (black arrows) made contact with blood vessels (red arrows) in mouse ovaries (Komatsu et al. Increased supply from blood vessels promotes the activation of dormant primordial follicles in mouse ovaries. pp. 105–113). To confirm the hypothesis that angiogenesis is crucial for activation of the dormant primordial follicles in vivo, Komatsu et al. induced angiogenesis using recombinant VEGF. They found that the activation of dormant primordial follicles was promoted by an increase in the number of blood vessels in the ovaries. Furthermore, the number of activated follicles increased in cultured ovarian tissues depending on the serum concentration in the medium. These results confirm that the supply of serum components through new blood vessels formed via angiogenesis is a cue for the activation of dormant primordial follicles in the ovaries.

  • Volume 66 (2020) Issue 1 Pages 67-73
    Production of mouse offspring from inactivated spermatozoa using horse PLCζ mRNA Read more
    Editor’s picks

    Cover Story:
    Improving artificial oocyte activation is essential for animal biotechnology, to obtain healthy offspring with a high success rate. Yamamoto et al. investigated whether the equine sperm-specific phospholipase C zeta (ePLCζ) mRNA, which has the strongest oocyte activation potential in mammals, could improve the mouse oocyte activation rate and subsequent embryonic development using inactivated spermatozoa (Yamamoto et al. Production of mouse offspring from inactivated spermatozoa using horse PLCζ mRNA. pp. 67–73). The activation potential of ePLCζ was ten times greater than that of murine (m) PLCζ and normal blastocysts were obtained. However, the birth rate was slightly, but significantly, decreased in oocytes activated by ePLCζ compared to those activated by mPLCζ. These results suggest that activation rate does not always correlate birth rate.

  • Volume 65 (2019) Issue 6 Pages 485-489
    Functional consequences of mitochondrial mismatch in reconstituted embryos and offspring Read more
    Editor’s picks

    Cover Story:
    The oocyte is the only cell that can reprogram a somatic nucleus to totipotency. The process of reprogramming is, however, only partially understood, and is accompanied by both epigenetic and structural changes in the somatic nucleus. The oocyte components that are necessary for a successful reprogramming and remodeling are unknown. In this issue, Fulka H et al. demonstrate that rather than the insoluble nuclear envelope, together with chromatin-bound factors, or the cytoplasm alone, it is the soluble nuclear fraction that has a major effect upon the somatic nucleus (Fulka H, et al.: Dissecting the role of the germinal vesicle nuclear envelope and soluble content in the process of somatic cell remodeling and reprogramming. pp. 433-441). This fraction is essential for altering the size of the somatic nucleus as well as transcriptional silencing and efficient histone H3.3 incorporation.

  • Volume 65 (2019) Issue 5 Pages 433-441
    Dissecting the role of the germinal vesicle nuclear envelope and soluble content in the process of somatic cell remodelling and reprogramming Read more
    Editor’s picks

    Cover Story:
    The oocyte is the only cell that can reprogram a somatic nucleus to totipotency. The process of reprogramming is, however, only partially understood, and is accompanied by both epigenetic and structural changes in the somatic nucleus. The oocyte components that are necessary for a successful reprogramming and remodeling are unknown. In this issue, Fulka H et al. demonstrate that rather than the insoluble nuclear envelope, together with chromatin-bound factors, or the cytoplasm alone, it is the soluble nuclear fraction that has a major effect upon the somatic nucleus (Fulka H, et al.: Dissecting the role of the germinal vesicle nuclear envelope and soluble content in the process of somatic cell remodeling and reprogramming. pp. 433-441). This fraction is essential for altering the size of the somatic nucleus as well as transcriptional silencing and efficient histone H3.3 incorporation.

  • Volume 65 (2019) Issue 4 Pages 281-287
    A way for in vitro/ex vivo egg production in mammals Read more
    Editor’s picks

    Cover Story:
    In vitro/ex vivo egg production has been widely studied in various mammalian species over half of the century to utilize the majority of the immature oocytes stocked in the female ovaries. Recently, the first successful protocol of in vitro oogenesis from primordial germ cells (PGC) has been established by Morohaku K, et al., resulting in the live birth of offspring in mice. The protocol consists of two vital steps; 1) ex vivo organ culture of mouse PGC ovaries to complete the process of follicle formation, with successful incorporation of antagonists for the existing estrogen receptors, and 2) in vitro follicle culture of the growing follicles isolated from the cultured ovaries. The review in this issue introduces the current findings and aspects governing in vitro oogenesis, with a brief history (Morohaku K. A way for in vitro/ex vivo egg production in mammals. pp. 281–287).

  • Volume 65 (2019) Issue 3 Pages 195-201
    Acquisition of developmental competence and in vitro growth culture of bovine oocytes Read more
    Editor’s picks

    Cover Story:
    In cattle, small oocytes (group VII), included in small follicles, grow with follicular development, and the size and developmental competence of oocytes increase (groups I and II) (Nagano, Acquisition of developmental competence and in vitro growth culture of bovine oocytes, pp. 195-201).  Subsequently, only one follicle is selected to develop to a dominant follicle and ovulates, but the other follicles start to degenerate. During the degeneration process, an accumulation of lipid droplets and undulation of the nuclear membrane of germinal vesicle start, and the developmental competence of oocytes also increases (pseudomaturation-like change in group III). However, too many pseudomaturation-like changes impair the developmental competence of oocytes (groups V and VI).  If oocytes start to degenerate before pseudomaturation-like changes, the oocytes may become group IV.

  • Volume 65 (2019) Issue 2 Pages 155-162
    Glycerol kinase 2 is essential for proper arrangement of crescent-like mitochondria to form the mitochondrial sheath during mouse spermatogenesis Read more
    Editor’s picks

    Cover Story:
    The mitochondrial sheath is composed of mitochondria that coil tightly around the midpiece of the sperm flagellum. Mitochondria are recruited from the cytoplasm to the flagellum late in spermatogenesis. Recruited mitochondria are initially spherical, but then elongate laterally to become crescent-like in shape. Subsequently, these crescent-like mitochondria elongate continuously to coil tightly around the flagellum. Mitochondrial sheath development in glycerol kinase 2 (Gk2)-disrupted mice, which show abnormal mitochondrial sheath formation, was observed using freeze-fracturing coupled with scanning electron microscopy (Shimada et al., Glycerol kinase 2 is essential for proper arrangement of crescent-like mitochondria to form the mitochondrial sheath during mouse spermatogenesis, pp. 155–162). Gk2-disrupted spermatids show abnormal localization of crescent-like mitochondria, despite initially exhibiting proper alignment of spherical mitochondria around the flagellum. These results indicate that GK2 is essential for proper arrangement of crescent-like mitochondria during mitochondrial sheath formation in mouse spermatogenesis.

  • Volume 65 (2019) Issue 1 Pages 57-66
    Destabilization of spindle assembly checkpoint causes aneuploidy during meiosis II in murine post-ovulatory aged oocytes Read more
    Editor’s picks

    Cover Story:
    Mammalian oocyte quality degrades over time after in vitro ovulation. As various oocyte manipulations employed in assisted reproductive technology are time consuming, post-ovulatory aging is a serious problem in reproductive medicine and ova research. Shimoi et al. investigated the effects of post-ovulatory aging on the incidence of chromosomal aneuploidy during meiosis II (MII), with a focus on the expression of functional proteins from the spindle assembly checkpoint (SAC) (Shimoi G et al.: Destabilization of spindle assembly checkpoint causes aneuploidy during meiosis II in murine post-ovulatory aged oocytes. pp. 57–66). This study showed that post-ovulatory oocyte aging inhibits MAD2 localization to the sister kinetochore. Furthermore, oocyte aging prevented cohesin subunits from being appropriately maintained or degraded. These results suggest that destabilization of SAC signaling causes sister chromatid segregation errors in MII oocytes and consequently increases the incidence of aneuploidy in early embryos.

  • Volume 64 (2018) Issue 6 Pages 469-476
    The roles of kisspeptin in the mechanism underlying reproductive functions in mammals Read more
    Editor’s picks

    Cover Story:
    The review article by Uenoyama et al. describes the roles of hypothalamic kisspeptin in the central mechanism regulating puberty and subsequent reproductive functions in mammals. The schematic illustration shows a possible mechanism regulating the pubertal augmentation of Kiss1 expression in the arcuate nucleus (ARC) to trigger pulsatile GnRH/gonadotropin secretion in rodents. The authors suspect that estrogen strongly suppresses ARC Kiss1 expression during the prepubertal period via direct and indirect pathways and that the sensitivity to estrogen negative feedback action on ARC Kiss1 expression decreases during the pubertal transition. The resultant increase in secretion of kisspeptin would trigger GnRH/gonadotropin secretion at pubertal onset (Uenoyama et al. The role of kisspeptin in the mechanism underlying reproductive function in mammals. pp. 469–476).

  • Volume 64 (2018) Issue 5 Pages 393-400
    DNA fragmentation in epididymal freeze-dried ram spermatozoa impairs embryo development Read more
    Editor’s picks

    Cover Story:
    Dry biobanking has many advantages over the current paradigm of storing cryopreserved cells under liquid nitrogen. During drying, however, the cells become damaged. The highly condensed spermatozoa DNA has been shown in many desiccation studies to generally maintain its integrity. Using ram freeze-dried epididymal spermatozoa as a model, Palazzese et al. were the first to evaluate both single- and double-strand DNA breaks (SSBs and DSBs, respectively), showing that drying causes minimal DSBs but extensive SSBs (Palazzese L et al., 2018. DNA fragmentation in epididymal freeze-dried ram spermatozoa impairs embryo development, pp. 393–400). Furthermore, the authors also demonstrated that spermatozoa capable of directing embryo development to the blastocyst stage in vitro originated from rams with the least DNA damage Overall, the impact of sperm DNA damage on embryonic development depends on a balance between the extent of sperm DNA fragmentation, fragmentation type, and the oocyte’s repair capacity.

  • Volume 64 (2018) Issue 4 Pages 297-301
    Oocyte-specific gene Oog1 suppresses the expression of spermatogenesis-specific genes in oocytes Read more
    Editor’s picks

    Cover Story: Oog1, an oocyte-specific gene, encodes the protein belonging to the leucine-rich repeat (LRR) superfamily. LRR is a motif involved in protein-protein interactions. Complete knockout of Oog1 is challenging because five copies of the Oog1 gene are present on chromosomes 4 and 12. Honda et al. generated Oog1 RNA interference (RNAi)-transgenic mice to investigate the effects of Oog1 knockdown on gene expression in the oocytes (Honda et al. Oocyte-specific gene Oog1 suppresses the expression of spermatogenesis-specific genes in oocytes, pp. 297–301). The abundance of spermatogenesis-specific transcripts was elevated in the Oog1 knockdown ovaries. In addition, a few abnormal oocytes were observed in 6-month-old Oog1 knockdown mouse ovaries. These findings suggested that OOG1 suppresses the expression of spermatogenesis-specific genes in the oocytes and plays important roles during oogenesis.

  • Volume 64 (2018) Issue 3 Pages 277-282
    Suberoylanilide hydroxamic acid during in vitro culture improves development of dog-pig interspecies cloned embryos but not dog cloned embryos Read more
    Editor’s picks

    Cover Story :
    Based on the results obtained for the studies of in vitro development of cloned embryos, epigenetic modifications have been widely used for cloning farm animals. However, such studies remain few in canids because of the lack of optimal in vitro oocyte maturation, embryo culture, and superovulation system. Kim et al. investigated whether a histone deacetylase inhibitor used in dog to pig interspecies somatic cell nuclear transfer (iSCNT), which improves nuclear reprogramming, could be used in dog cloning (Kim et al.: Suberoylanilide hydroxamic acid during in vitro culture improves development of dog-pig interspecies cloned embryos but not dog cloned embryos. p. 277–282). Porcine oocytes supported reprogramming of nuclei from dog fibroblasts up to early developmental stage of iSCNT embryos, and treating the embryos with suberoylanilide hydroxamic acid (SAHA) increased their developmental competence. However, unfortunately, SAHA treatment for dog to pig iSCNT embryos was not sufficient to improve their in vivo development because three and one clones were successfully produced from the control and SAHA treated groups, respectively.

  • Volume 64 (2018) Issue 2 Pages 153-160
    Macromolecular crowded conditions strengthen contacts between mouse oocytes and companion granulosa cells during in vitro growth Read more
    Editor’s picks

    Cover Story :
    Recently, the effects of macromolecular crowding on cultured cells have gathered increasing interest. Crowded culture medium prepared by the addition of polyvinylpyrrolidone (PVP; Mw 360,000) positively influences the viability of oocytes during in vitro growth. Mizumachi et al. found that crowding affects a wide range of factors, including oocyte viability, complex morphology, and intimate conjunction of oocytes with cumulus/granulosa cells across the zona pellucida (Mizumachi et al. Macromolecular crowded conditions strengthen contacts between mouse oocytes and companion granulosa cells during in vitro growth, pp. 153-160). Confocal laser scanning microscopy indicated a higher number of transzonal processes (TZPs) reaching the oocyte from cumulus cells in 2% PVP medium than in 0% PVP medium.

  • Volume 64 (2018) Issue 1 Pages 95-99
    Embryogenesis of vitrified mature bovine oocytes is improved in the presence of multi-layered cumulus cells Read more
    Editor’s picks

    Cover Story :
    Whether cumulus cells are required for the successful vitrification of mature oocytes in cattle is controversial. Ishii et al. re-evaluated the effects of the presence of multi-layered cumulus cells (MCCs) on the vitrification of mature bovine oocytes (Ishii et al., Embryogenesis of vitrified mature bovine oocytes is improved in the presence of multi-layered cumulus cells. pp. 95–99). In the presence of MCCs, there was no difference between the embryonic development of fresh and vitrified mature bovine oocytes. These results suggest that MCCs protect mature oocytes from freezing, and promote their survival and development after in vitro fertilization. Ishii et al. successfully produced calves using a small number of vitrified mature oocytes with MCCs collected from the ovaries of individual cows post-slaughter.

  • Volume 63 (2017) Issue 6 Pages 617-622
    A transvaginal endoscopy-based technique for performing ovarian examinations in sows Read more
    Editor’s picks

    Cover Story : 
    Okuyama et al. reported a transvaginal endoscopy-based technique for conducting ovarian examination in sows in a standing position. Sows were sedated in pig stalls, and their vaginal walls were punctured. Subsequently, a urethroscope was inserted into their abdomen, and an examination was conducted after their ovaries had moved towards the urethroscope camera via rectal palpation (Okuyama MW, et al. A transvaginal endoscopy-based technique for performing ovarian examinations in sows. pp. 617–622). This less invasive procedure without the use of general anesthesia may allow repeated ovarian examinations and increase our understanding of the ovarian dynamics in pigs.

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