Studies on fertilization in the teleost. I. Dynamic responses of fertilized medaka eggs

Abstract

In order to understand the mechanisms of fertilization in the teleost, the movements of the egg cortex, cytoplasmic inclusions and pronuclei were observed in detail in fertilized medaka Oryzias latipes eggs. The first cortical contraction occurred toward the animal pole region following the onset of exocytosis of cortical alveoli. The cortical contraction caused movement of oil droplets toward the animal pole where the germinal vesicle had broken down during oocyte maturation. The movement of oil droplets toward the animal pole region was frequently twisted in the right or left direction. The direction of the twisting movement has been correlated with the unilateral bending of non-attaching filaments on the chorion. The female pronucleus, which approached the male pronucleus from the vicinity of the second polar body, took a course to the right, left or straight along the s-p axis connecting the male pronucleus and the second polar body. The course of approach by the female pronucleus correlated with the bending direction of the non-attaching filaments that had been determined by rotation of the oocyte around the animal-vegetal axis during oogenesis. The first cleavage furrow also very frequently coincided with the axis. These observations suggest that dynamic responses of medaka eggs from fertilization to the first cleavage reflect the architecture dynamically constructed during oogenesis.

Electron microscopic observations of karyogamy in the fish egg

“…At the time of their migration and association, the female and male pronuclei are similar in size in Spisula (Longo & Anderson 1970), while the female pronucleus is larger than the male pronucleus in Arbacia (Longo & Anderson 1968). Our present and previous observations (Iwamatsu 1998; Iwamatsu et al . 1999) of pronuclear behavior during migration revealed that the male pronucleus is larger than the female pronucleus in Oryzias as reported in rat (Austin 1951, 1952) and rabbit eggs (Thibault et al .…”

Generation of a transgenic medaka (Oryzias latipes) strain for visualization of nuclear dynamics in early developmental stages

“…This is the first report demonstrating nuclear dynamics immediately after fertilization, using live fluorescence imaging in medaka. Previous studies reported the pronuclear migration under a bright field or phase contrast microscopy (Iwamatsu ). For a fluorescent nuclear observation, the marker proteins should be expressed in fertilized eggs before the zygotic gene activation.…”

“…Small fish have been used as convenient models for vertebrates in analysis of the pronuclear dynamics. Previous studies reported a profile of pronuclear dynamics in medaka eggs, its molecular mechanism in zebrafish (Iwamatsu 1998;Abrams et al 2012;Lindeman & Pelegri 2012). However, live imaging methods have not been established in the pronuclear research.…”

cDNA cloning, characterization and expression of cytochrome P450 family 1 (CYP1A) from Javanese medaka, Oryzias javanicus by environmental conditions

“…Javanese medaka (Oryzias javanicus) is one of more than 14 species belonging to the genus Oryzias distributed in the estuarine regions of East and Southeast Asia (Iwamatsu, 1998;Kinoshita et al, 2009). Medaka has been used as an experimental test fish because it has several advantages, including its ability to adapt to different environmental conditions.…”