Reciprocal epithelial–mesenchymal interactions and several signalling pathways regulate the development of the genital tubercle (GT), an embryonic primordium of external genitalia. The morphology of the adult male external genitalia of the Asian house musk shrew Suncus murinus (hereafter, laboratory name: suncus) belonging to the order Eulipotyphla (the former order Insectivora or Soricomorpha) differs from those of mice and humans. However, the developmental process of the suncus GT and its regulatory genes are unknown. In the present study, we explored the morphological changes and gene expression patterns during the development of the suncus GT. Morphological observations suggested the presence of common (during the initial outgrowth) and species-specific (during the sexual differentiation of GT) developmental processes of the suncus GT. In gene expression analysis, fibroblast growth factor 8 (Fgf8) and sonic hedgehog (Shh), an indicator and regulator of GT development in mice respectively, were found to be expressed in the cloacal epithelium and the developing urethral epithelium of the suncus GT. This pattern of expression specifically in GT epithelium is similar to that observed in the developing mouse GT. Our results indicate that the mechanism of GT formation regulated by the FGF and SHH signalling pathways is widely conserved in mammals.
Mami Miyado, Kenji Miyado, Akihiro Nakamura, Maki Fukami, Gen Yamada and Sen-ichi Oda
Chizuru Ito, Kenji Yamatoya, Keiichi Yoshida, Lisa Fujimura, Hajime Sugiyama, Akiko Suganami, Yutaka Tamura, Masahiko Hatano, Kenji Miyado and Kiyotaka Toshimori
A number of sperm proteins are involved in the processes from gamete adhesion to fusion, but the underlying mechanism is still unclear. Here, we established a mouse mutant, the EQUATORIN-knockout (EQTN-KO, Eqtn -/-) mouse model and found that the EQTN-KO males have reduced fertility and sperm-egg adhesion, while the EQTN-KO females are fertile. Eqtn -/- sperm were normal in morphology and motility. Eqtn -/--Tg (Acr-Egfp) sperm, which were produced as the acrosome reporter by crossing Eqtn -/- with Eqtn +/+-Tg(Acr-Egfp) mice, traveled to the oviduct ampulla and penetrated the egg zona pellucida of wild-type females. However, Eqtn -/- males mated with wild-type females showed significant reduction in both fertility and the number of sperm attached to the zona-free oocyte. Sperm IZUMO1 and egg CD9 behaved normally in Eqtn -/- sperm when they were fertilized with wild-type egg. Another acrosomal protein, SPESP1, behaved aberrantly in Eqtn -/- sperm during the acrosome reaction. The fertility impairment of EQTN/SPESP1-double KO males lacking Eqtn and Spesp1 (Eqtn/Spesp1 -/-) was more severe compared with that of Eqtn -/- males. Eqtn -/--Tg (Eqtn) males, which were generated to rescue Eqtn -/-males, restored the reduced fertility.
Naoya Araki, Natsuko Kawano, Woojin Kang, Kenji Miyado, Kaoru Yoshida and Manabu Yoshida
Mammalian spermatozoa acquire their fertilizing ability in the female reproductive tract (sperm capacitation). On the other hand, seminal vesicle secretion, which is a major component of seminal plasma, inhibits the initiation of sperm capacitation (capacitation inhibition) and reduces the fertility of the capacitated spermatozoa (decapacitation). There are seven major proteins involved in murine seminal vesicle secretion (SVS1-7), and we have previously shown that SVS2 acts as both a capacitation inhibitor and a decapacitation factor, and is indispensable for in vivo fertilization. However, the effects of SVSs other than SVS2 on the sperm have not been elucidated. Since mouse Svs2–Svs6 genes evolved by gene duplication belong to the same gene family, it is possible that SVSs other than SVS2 also have some effects on sperm capacitation. In this study, we examined the effects of SVS3 and SVS4 on sperm capacitation. Our results showed that both SVS3 and SVS4 are able to bind to spermatozoa, but SVS3 alone showed no effects on sperm capacitation. On the other hand, SVS4 acted as a capacitation inhibitor, although it did not show decapacitation abilities. Interestingly, SVS3 showed an affinity for SVS2 and it facilitated the effects of SVS2. Interaction of SVS2 and spermatozoa is mediated by the ganglioside GM1 in the sperm membrane; however, both SVS3 and SVS4 had weaker affinities for GM1 than SVS2. Therefore, we suggest that separate processes may cause capacitation inhibition and decapacitation, and SVS3 and SVS4 act on sperm capacitation cooperatively with SVS2.
Toshio Hamatani, Mitsutoshi Yamada, Hidenori Akutsu, Naoaki Kuji, Yoshiyuki Mochimaru, Mitsuko Takano, Masashi Toyoda, Kenji Miyado, Akihiro Umezawa and Yasunori Yoshimura
Mammalian ooplasm supports the preimplantation development and reprograms the introduced nucleus transferred from a somatic cell to confer pluripotency in a cloning experiment. However, the underlying molecular mechanisms of oocyte competence remain unknown. Recent advances in microarray technologies have allowed gene expression profiling of such tiny specimens as oocytes and preimplantation embryos, generating a flood of information about gene expressions. So, what can we learn from it? Here, we review the initiative global gene expression studies of mouse and/or human oocytes, focusing on the lists of maternal transcripts and their expression patterns during oogenesis and preimplantation development. Especially, the genes expressed exclusively in oocytes should contribute to the uniqueness of oocyte competence, driving mammalian development systems of oocytes and preimplantation embryos. Furthermore, we discuss future directions for oocyte gene expression profiling, including discovering biomarkers of oocyte quality and exploiting the microarray data for ‘making oocytes’.