Further experimental evidence for the involvement of ecdysone in the control of meiotic reinitiation in oocytes of Locusta migratoria (Insecta, Orthoptera).

Ecdysone has recently been shown to be able to trigger meiotic reinitiation in vitro in submature oocytes of Locusta. In the present study we have experimentally depressed (by 60-70%) ecdysone biosynthesis in the ovaries of adult females by rearing them on a diet with a modified sterol profile. Mature oocytes from such females fail to undergo normal reinitiation, but when incubated in vitro, can be induced to break their meiotic arrest by the addition of exogenous ecdysone. These results lend further support to the hypothesis that in Locusta, ovarian ecdysone is involved in the control of meiotic reinitiation.

Growth stimulation of the immature chick oviduct by androgens: the vagina as a new target tissue.

Testosterone when injected alone stimulates growth of the vagina but is inactive upon the other segments of the oviduct of the immature chicken. This action of testosterone can already be detected in embryos: it is expressed by the beginning of differentiation of the vaginal mesenchyme cells into smooth muscle cells. In the treated immature chicken, stimulation of growth is considerable and is specifically caused by androgens (testosterone and 5-alpha-dihydrotestosterone); the vaginal mesenchyme differentiates into two smooth muscular layers and vaginal epithelium cells differentiate into ciliated cells and goblets cells. [3H]testosterone binding has been found in the vagina of the immature chicken (data not shown). The characteristics of testosterone binding to cytoplasmic components of the chick vagina are consistent with its identity as a testosterone receptor.

[Feminizing action of dehydroepiandrosterone on the left testis of the chick embryo: ultrastructural aspect]. / Action féminisante de la déhydroépiandrostérone sur le testicule gauche de l'embryon de poulet: aspect ultrastructural.

Chick embryos were injected with 4 X 0.5 mg of dehydroepiandrosterone from day 4 onwards and the ultrastructure of the 20-day old hormone-treated male gonads was studied. The cortex was well-developed and some oocytes had reached the meiotic prophase stage. The prefollicular cells did not seem to be stimulated by the androgenic hormone. We especially studied the seminiferous cords with Sertoli cells. Dense core granules, which might be related to secretory activity, were observed in the basal part of the Sertoli cells. The extensive development of smooth endoplasmic reticulum vesicles suggested that some Sertoli cells might have a steroidogenic function. The interstitial cells did not show an important steroidogenic synthesis. The action of dehydroepiandrosterone, which could induce the development of an ovarian-like cortex in intersexual gonads, is discussed.

[Current findings on the asymmetric growth of the mullerian tract in female chick embryos]. / Nouvelles données sur la croissance asymétrique du tractus müllérien chez l'embryon de poulet femelle.

Shape and orientation of the mesothelial cells were examined in the mullerian ducts of 8, 13 and 15 day female chick embryos with the scanning electron microscope. The observed evolution in the pattern of these cells likely reflects the mechanical conditions to which these organs are subjected during embryonic development: stretching for the left duct, slackening for the right duct. These observations, together with data concerning growth of these organs, suggest that topographical relationships between cells, which in this system result from mechanical factors, play an important role in controlling cell proliferation.

Cell division and cytodifferentiation of odontoblasts.

The chronological delay of overt cytodifferentiation of odontoblasts in isochronal and heterochronal associations between inner dental epithelium and preameloblasts was analysed. The in vitro action of FUdR of tooth germs was summarised. The respective role of cell interaction and specific cell cycle was discussed.