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).
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.
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.
公開日: 2010/10/20 | 42 巻 6 号 p. j143-j150
公開日: 2010/10/20 | 44 巻 6 号 p. j47-j52
公開日: 2010/10/20 | 43 巻 6 号 p. j19-j25
岡部 勝, 伊川 正人, 山田 秀一, 中西 友子, 馬場 忠
Infectious Causes of Reproductive Disorders in Cattle
公開日: 2010/08/10 | 56 巻 S 号 p. S53-S60
Han Sang YOO
Monitoring Metabolic Health of Dairy Cattle in the Transition Period
公開日: 2010/08/10 | 56 巻 S 号 p. S29-S35