Gametes and fertilization in the Chinese hamster

Abstract

Freshly ovulated eggs are each surrounded by a compact cumulus oophorus. The overall diameter of the normal egg (including the zona pellucida) is about 100 μm. Cumulus cells, particularly those near the egg, are arranged redially in a viscous noncellular matrix. The spermatozoon is about 250 μm in length. The head a large acrosome, changes in which can be readily examined with the light (phase‐ contrast) microsope. When exposed to physiological salt solutions, testicular spermatozoa either were motionless or flexed the posterior half of their tails slowly. Spermatozoa from the caput epididymis were highly motile, flexing the entire tail. A few of them moved progressively. Mature spermatozoa from the vas deferens were highly motile and moved either straightforward or in a circle. They vibrated their tails stiffly without flexing them. In normally mated females, fertilization began sometime between 2 and 3 h after ovulation and was completed within the next 4 to 5 h. Spermatozoa swimming in the ampullary fluid or within the cumulus oophorus about the time of fertilization flexed the anterior half (which roughly corresponds to the midpieac region) of their tails. This peculiar movement may be homologous to the so‐called “hyperactivation” of spermatozoa as reported in several other mammalian species. Actively motile spermatozoa within the cumulus or no the zona pellucida had either modified (“collapsed”) or no acrosomal caps. The sperm head usually passed verticually or nearly through the zona, but the path was oblique in some instances. In 54% of the recently fertilized eggs examined, the entire length of the sperm tail was within the perivitelline space; in the other 46% of the eggs varying lenghts of the tail remined the perivitelline space, the tails were extruded from the vitellus of many eggs even before the eggs began their first cleavage. When unfertilized eggs in the cumulus oophorus were inseminated with vas deferens spermatozoa in a modified Tyrode's solution (m‐TALP), about 80% of them were ferrtilized by 4–6 h after insemination. The vast majority were monospermic. When eggs were freed from the cumulus prior to insemination, none were fertilized, suggesting that the cumulus cells or their matrix assisted capacitation and/or the acrosome reaction of the spermatozoa under the in vitro conditions employed. No eggs were fertilized by the testicular or caput epididymal spermatozoa regardless of the presence or absence of cumulus oophorus around the eggs at the time of insemination.

Mammalian gamete interactions: What can be gained from observations on living eggs?

“…Austin and Braden (1956) had earlier suggested, from observing the angle of penetration slits in zonae, that the orientation was usually vertical (or nearly so) in the mouse, rat, and hamster. Similar conclusions have been reached for the Chinese hamster by Yanagimachi et al (1983).…”

“…First, there may be genuine differences between species in this regard. In the Chinese hamster, for example, penetration is nearly always perpendicular, whereas in the Syrian (or golden) hamster it is oblique (Yanagimachi, 1981;Yanagimachi et al, 1983). Secondly, the in vitro conditions under which observations are made may actually influence the angle of zona penetration.…”

Sperm penetration through oocyte investments in mammals

“…The release of hyaluronidase at this time would facilitate and may be necessary for penetration to the zona. Indeed many of the sperm that have been seen in both ultrastructural studies of the rabbit (Bedford, 1972) and hamster (Yanagimachi and Noda, 1970a) and phase-contrast microscopic studies of rodents (Austin and Bishop, 195813;Yanagimachi and Phillips, 1984;Yanagimachi et al, 1983) do appear to be undergoing acrosome reactions in the cumulus and the corona radiata. Moreover, synthetic inhibitors of hyaluronidase will block in vitro fertilization of cumulus-intact, but not cumulusfree, mouse oocytes (Reddy et al, 1979).…”

Molecules that initiate or help stimulate the acrosome reaction by their interaction with the mammalian sperm surface

“…Suarez et al (1983) reported that all six rabbit sperm detected in the cumuli flushed from oviducts of mated animals were "apparently unreacted." Yanagimachi et al (1983) removed the freshly ovulated cumulus-egg mass from mated Chinese hamsters by flushing or puncturing the oviducts 2-8 hr after ovulation, examined those oviductal contents by phasecontrast microscopy, and found that all five cumuli sperm detected either had undergone or were undergoing the AR. They also found that cumulus-intact but not cumulus-free eggs were fertilized in vitro by vas deferens sperm.…”