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The presence and localization of α- and β-spectrins and of the spectrin cross-linking protein actin were investigated, in previtellogenic oocytes of three species of Antarctic teleosts: the two red-blooded nototheniids, Trematomus bernacchii and Trematomus newnesi, and the channichthyid, the ice fish Chionodraco hamatus. Analyses by western blotting indicated that these species had an unusual abundance of spectrin isoforms and that they were characterized by rather low molecular masses. The immunocytochemistry in situ demonstrated that α- and β-spectrins showed a variable pattern of localization that clearly depended on both the species considered and the stage of oocyte differentiation. In particular, the two Trematomus spp. showed a distribution of spectrins absolutely comparable and rather different from that of C. hamatus. The evidences collected confirmed that channichthyids have isolated early from the group of red-blooded species and suggest that in notothenioids significant changes might have occurred in spectrin genes and in their protein products.

Cytochemical analyses was used to study the organization and content of cortical alveoli in eight species of Antarctic teleosts belonging to three different families of notothenioids: nototheniids, bathydraconids and channichthyids. Results indicated differences existed among the various species in alveolar size and distribution and in their content. In nototheniids, in particular, typical nucleoids were formed that could be large and single or small and multiple, according to the species considered. As demonstrated by the affinity to periodic acid-Schiff (PAS) and lectin staining, these nucleoids were rich in glycoconjugates, whose nature was extremely varied in the different species, but not in lipo- or acidic proteins as indicated by Sudan Black B and silver salts staining. Protein extracts, electrophoresed and stained with Sudan, PAS and two lectins demonstrated that the alveoli in the two species, Trematomus bernacchii and Trematomus newnesi, contained c. 80 kDa protein rich in N-acetylglucosamine groups. By contrast, the typical hyosophorins, described as the major alveolar content in other fishes, were apparently present only in T. newnesi.

To determine whether oogonial proliferation and oocyte recruitment are under control of hypophyseal and/or ovarian factors, we carried out a series of investigations using Podarcis sicula, a lizard inhabiting the temperate lowlands of Europe in which oocyte recruitment occurs throughout the year, as animal model. Germinal beds containing oogonia and oocytes in prefollicular stages were cocultured with different ovarian compartments in presence/absence of FSH, and the effects of different treatments were evaluated by counting the number of prelepto-leptotene oocytes. Results revealed that oocyte recruitment from the pool of oogonia is under the control of a factor released by follicle cells while FSH has an indirect effect on modulating oogonial proliferation. SDS-PAGE analyses carried out on media conditioned by follicles suggest that the factor involved in the control of oocyte recruitment may be a small protein (about 21 kDa) and that its release is dependent on the period of the ovarian cycle but apparently not on the circulating levels of FSH.

The present work was carried out to clarify the nature and origin of the yolk DNA present in vitellogenic oocytes of the lizard Podarcis sicula. Morphological and biochemical evidences indicate that it has an intrafollicular origin, from the apoptotic bodies resulting from follicle cells regression at the end of previtellogenesis. This conclusion is reinforced by the observation that the oocyte membrane, in in vitro experiments, is unpermeable to exogenous DNA. Biochemical evidences reveal that the yolk DNA has a low (200bp) molecular weight and this suggests that it is produced by the endonucleases typically involved in apoptotic DNA laddering. Indeed, immunocytochemical analyses demonstrate that follicle cells contain significant amounts of DNAse I. In immunoblots, carried out during different periods of the ovarian cycle, the enzyme shows a MW of about 33, 66 or 100 kDa thus indicating that its activity in the follicle of Podarcis is modulated by dimerization and/or binding to regulatory factors. Mol. Reprod. Dev. 59: 422–430, 2001. © 2001 Wiley-Liss, Inc.

The study of environmental factors affecting vertebrate reproduction has long interested both developmental and evolutionary biologists. Although photoperiod has been considered to be an important environmental parameter for vertebrates such as birds, temperature is probably a primary external factor responsible for reproductive cyclicity in reptiles. In spite of the progress made in the understanding of reptilian reproductive strategies and adaptations, much remains to be learned about the interplay between endocrine physiological factors, such as hormones, and environmental parameters. In this report, we have examined the effects of in vivo administered FSH on oocyte recruitment during the most significant periods of the reproductive cycle of the lizard, Podarcis sicula. The results show that when FSH is administered in proximity to the reproductive period, it stimulates oocyte growth and ovulation; when the hormone is administered at the beginning of the winter stasis it affects ovarian activity without inducing ovulation. Ovarian adenylate cyclase activity is moderately sensitive to in vitro FSH stimulation during the pre- and post-reproductive periods. The sensitivity to hormone stimulation increases significantly during the reproductive period and winter stasis. We have also tested the hypothesis that environmental temperature affects the responsiveness of ovarian adenylate cyclase to FSH stimulation. For such a purpose, we exposed animals to 28 degrees C or 4 degrees C in different periods of the ovarian cycle. The results show that, whenever the temperature applied mimics the thermal regime of the coming season, adenylate cyclase sensitivity to FSH shifts towards levels that anticipate the natural responsiveness.

The effects of follicle-stimulating hormone (FSH) on early meiotic oocytes were studied by cytological, autoradiographic, and photometric techniques. In addition to regulating oogonial proliferation, oogenesis, and folliculogenesis, the hormone influenced germ cell number and the time course of early meiosis. FSH did not affect the timing of DNA replication and amplification and did not change the amount of rDNA accumulated in the nucleus by amplification. A genetic control mechanism for these processes is suggested.

In order to clarify the role of follicle cells during growth of previtellogenic oocytes in lizards, an ultrastructural and autoradiographic investigation was carried out in Podarcis sicula. The evidence obtained clearly indicated that both intermediate and pyriform cells are actively involved in the synthesis of RNA that is then transferred to the oocyte, via intercellular bridges, apparently together with a variety of cytoplasmic organelles. At the end of the previtellogenic phase of growth, during the regression of the epithelium, the rate of synthesis of RNA in follicle cells is reduced, in particular in the nucleolus, but the flow of materials toward the oocyte continues. Thus, the intermediate and pyriform cells should be regarded as nurse cells even though they have characteristics rather different from those of the nurse cells described in other animals, such as insects. © 1995 Wiley-Liss, Inc.

This paper concerns the differentiation process of germ cells from oogonia to primary follicles in the lizard Podarcis sicula. The study was carried out at the morphological level and using a cytophotometric analysis for determining the number of differentiating germ cells undergoing degeneration. The progressive disorganization of the germ cell clusters during the early diplotene stage and the role played by the prefollicular cells during this process are described. Oocyte degeneration has been observed between the mid-zygotene and the early diplotene stages. When the primary follicle (oocyte plus follicular cells) is being formed, the degeneration process stops and the oocyte undergoes regular growth and ovulation.

Physiological adaptation of Antarctic teleosts to cold environment was studied with regard to the presence of regulatory peptides involved in (i) cardiac and ion‐water homeostasis, (ii) brain, (iii) intestine, and (iv) gonads. Immunoreactivity for different regions of the Atrial Natriuretic Peptide was detected in the heart of Trematomus bernacchii, Chionodraco hamatus, Cryodraco antarcticus, and Champsocephalus gunnari, while immunoreactivity for other regulatory peptides (i.e., endothelin‐1, somatostatin‐14, and galanin) appeared to be widely distributed in the cardio‐vascular system. Osmoregulatory peptides (somatostatin‐14, prolactin, atrial natriuretic peptide, galanin, and urotensin II) were localised by immunohistochemistry in the urinary bladder and gills. From studies on the distribution of the pituitary specific transcription factor 1 and adenohypophysial hormones (growth hormone, prolactin, and gonadotropin releasing hormone) in the brain and pituitary of Trematomus bernacchii and Pago...