The ultrastructure of the thecal cell of the teleost, Oryzias latipes, during ovulation in vitro

Abstract

Summary Ultrastructural examination of the follicular envelope of the teleost, Oryzias latipes, during ovulation in vitro showed that the follicle cell layer became increasingly dissociated. Microfilaments, measuring 50-70 \ l =A%o\ were sparse in the thecal cells at the start of incubation, but were organized into bands after 5 hr, and into bundles after 10 hr of incubation. It is suggested that these microfilaments are contractile and are involved in cell movement during ovulation.

The inhibition of in-vitro ovulation from follicles of the teleost, Oryzias latipes, by cytochalasin B

“…Despite the frequency with which cytochalasin has been reported to affect microfilaments mor¬ phologically, the microfilaments in the thecal cells of Oryzias were similar to, and as extensive as, those found in control follicles that are expected to ovulate (Pendergrass & Schroeder, 1976).…”

“…The follicular tissue of the trout, therefore, had probably been exposed to the normal preovulatory endocrine environment for a considerable period, allowing some of the preovulatory events in the follicle to occur in vivo before addition of cytochalasin in vitro. In the medaka experiments, however, the drug probably operated throughout the postulated period of morphogenesis of myoepithelial cells in the theca (Pendergrass & Schroeder, 1976).…”

“…After study of the ultrastructure of the follicular envelope and the constriction of the oocyte of Oryzias during ovulation in vitro, we concluded that, in this species, the discontinuous patches of follicular cells could not be the source of the constricting force (Pendergrass & Schroeder, 1976). Instead, we suggested that the bundles of 50-70 Â microfilaments which are abundant in the thecal layers after incubation for about 10 hr are involved in oocyte extrusion.…”

“…Fish were maintained and brought into breeding condition as described previously (Pendergrass & Schroeder, 1976); the lighting regimen was 18 hr light/24 hr.…”

“…Oocytes which had been incubated in M-199 with 1 µ DMSO/ml alone, with hormone, and with 2 µg hormone -f 1 µg cytochalasin B/ml were fixed for electron micro¬ scope examination after 0, 5,10 or 15 hr of incubation using the cacodylate buffer fixative previously described (Pendergrass & Schroeder, 1976). Silver sections were cut with a diamond knife, stained with methanolic uranyl acetate and lead citrate (Reynolds, 1963) and examined with an Hitachi HS-8 transmission electron microscope.…”