While it is generally well accepted that the ovarian follicular sites of estradiol-17β (E2) synthesis are restricted to somatic cells, the possible contribution of the germinal compartment has received little or no attention in teleosts. In order to demonstrate the expression of ovarian aromatase in the oocyte, cyp19a1a mRNA was studied in ovarian follicles by in situ hybridization. In addition, the expression of cyp19a1a was studied in both somatic and germinal compartments of the ovarian follicle in rainbow trout (Oncorhynchus mykiss) during final oocyte maturation (i.e., maturational competence acquisition and subsequent meiosis resumption) by real-time PCR. The enzymatic activity of ovarian aromatase was also studied in both somatic and germinal compartments of the ovarian follicle. Finally, E2 levels were monitored in follicle-enclosed oocytes throughout the pre-ovulatory period. We were able to demonstrate a significant ovarian aromatase expression and activity in the late vitellogenic oocyte. Furthermore, a dramatic decrease in aromatase expression and activity occurs in the oocyte during late oogenesis, concomitantly with the trend observed in surrounding follicular layers. We also report an unexpected increase of E2 levels in the oocyte during the pre-ovulatory period. To our knowledge, these observations are reported for the first time in any teleost species. Together, our data support the hypothesis of the participation of the germinal compartment in follicular estrogen synthesis and a biological role of E2 during oocyte and/or early embryo development.

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In contrast to the classical model describing the synthesis of androgens and estrogens as restricted to somatic cells, a previous study demonstrated that Xenopus laevis oocytes participate in androgen synthesis. The objective of our study was to determine whether Xenopus oocytes are also involved in estrogen synthesis. More precisely, we analyzed aromatase expression by in situ hybridization and RT-QPCR and measured aromatase activity. Aromatase, the enzyme responsible for estrogen synthesis, appears to be expressed and active not only in the follicular cells but also in the vitellogenic oocytes. During late oogenesis, aromatase oocyte expression and activity decreased concomitantly with the trend observed in surrounding follicular layers. In order to investigate the role of estradiol-17b (E 2 ), we studied its effect on oocyte meiotic resumption. It appears that, as in Rana pipiens, E 2 inhibited the follicle-enclosed maturation of Xenopus oocytes, likely through inhibition of LH-induced maturation-inducing steroid synthesis. In addition, E 2 exerted a slight enhancing action on denuded oocyte maturation whose biological significance remains unclear. Together, our results demonstrate that Xenopus oocyte significantly participates in ovarian E 2 synthesis and this may be a common feature of vitellogenic vertebrates.

Frozen animal tissues are thought to be appropriate for use as a donor for somatic cell nuclear transfer. This makes the freezing for long term storage a valuable tool for breeders needing to protect an animal population that is endangered by sanitary problems or for cryobanking of genetic resources. We report the successful cryopreservation of explants of skin derived from small biopsies from rabbit ear biopsies by using a protocol that can be easily performed by usual breeders, which are not equipped with cooling devices. By optimizing the procedure, we show that small biopsies can be kept at -20°C in a physiological solution containing 10% DMSO for up to 20 days before being deeply frozen in liquid nitrogen for long-term storage. After 10 days of storage at -20°C, the rate of viability of biopsies was similar to the control one (86 and 82% respectively). After 20 days of storage at -20°C, the rate of viability was dramatically lowered (39%), but it still allows to recover a significant population of viable cells from the preserved sample. Being appropriate to places lacking specific device, such a very simple technique may contribute to facilitate genome banking policies dedicated to the management of genetic resources in wild and domestic animals.

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