Biomedical subjects

M Kentouri

Publications and source records attributed to M Kentouri.

6 recordsLinked to original sources

PubMed2006

Gonadal changes and blood sex steroids levels during natural sex inversion in the protogynous Mediterranean red porgy, Pagrus pagrus (Teleostei: Sparidae).

Changes in gonadal structure and serum levels of sex steroids were investigated during natural sex inversion from female to male in reared populations of the protogynous Mediterranean red porgy, Pagrus pagrus. Four developmental phases were identified by histological observation: female, early transitional (ETr), late transitional (LTr), and male phases. At female phase, a few nests of spermatogonia were observed at the posterior-ventral part of the gonad mainly in females out of the breeding season. At ETr phase, spermatogonial proliferation occurred while perinucleolar oocytes showed signs of degeneration. At LTr phase, seminiferous lobules were formed and spermatogonial proliferation expanded along the ovary which degenerated. All types of male germ cells could be found. At male phase, functional testis underwent active spermatogenesis while small ovarian remnants associated to fat tissue could be detected. Both 17beta-estradiol (E2) and estrone (E1) blood levels were significantly lower in fish at transitional and male phases in comparison to breeding females, while levels of 11-ketotestosterone (11-KT) and testosterone (T) gradually increased in the transitional and male phases. In conclusion, the protogynous P. pagrus possess a delimited type bisexual gonad with a medio-dorsal ovarian area and a latero-ventral testicular zone. Sex inversion starts mainly after the female breeding season with an active spermatogonial proliferation. The testis tissues develop while ovarian tissues regress to disappear completely in the functional male. This process is accompanied by a sharp decrease of estrogens levels and a progressive increase of androgens levels. The physiological significance of such endocrine changes is discussed.

Animals↗

PubMed2001

Cell genesis in the hypothalamus is associated to the sexual phase of a hermaphrodite teleost.

The present study aimed to define sex differences in the genesis of hypothalamic and telencephalic cells in the adult brain of male, female and under sex reversal teleosts (Sparus aurata). Application of 5-bromo-2-deoxyuridine immunocytochemistry and quantification of the newborn cells using the disector method, determined a statistically significant difference in the dorsal hypothalamic ventricular area between sexual phases. Female brain exhibited a higher number of newborn cells, suggesting that estrogens possibly influence higher mitotic activity. In contrast, paraventricular organ and ventral nucleus of the ventral telencephalon did not show any significant changes, while cell proliferation differences in the preoptic area were correlated with age. The sex-specific cell proliferation pattern in the hypothalamus adds important information on the cellular mechanisms that underlie sex change in a protandrous hermaphrodite teleost.

Analysis of Variance↗

PubMed2001

Temperature and myogenic factor transcript levels during early development determines muscle growth potential in rainbow trout (Oncorhynchus mykiss) and sea bass (Dicentrarchus labrax).

The influence of changes in environmental temperature on the mRNA levels of myogenic regulatory factors (MRFs), i.e. MyoD and myogenin, as well as myosin heavy chain (MyHC) were studied during early larval development in rainbow trout and sea bass. Phosphoimager analysis of northern blots indicated that there is an optimum temperature for the RNA transcript levels of MRF and MyHC RNA in trout and in sea bass larvae. In the trout strain studied, the highest concentration for MRF and MyHC transcripts was found at 8 degrees C rather than 4 degrees C or 20 degrees C. In European sea bass, the highest concentrations of MRF and MyHC mRNA were observed at 15-20 degrees C rather than 13 degrees C. Raising sea bass larvae at 15 degrees C was associated with higher MyHC gene expression as well as a trend towards an increase in total muscle fibre number and higher growth rates after transfer at ambient temperature. Results suggest that mRNA levels of MRF and MyHC can be used to optimise early development. An experiment in which the temperature was changed illustrates the consequence of precise temporal expression of MRF genes in specifying muscle fibre number at critical stages during early development.

Animals↗

PubMed2000

Evidence of temperature-dependent sex determination in the European sea bass (Dicentrarchus labrax L.).

To test the hypothesis that sex determination in the European sea bass (Dicentrarchus labrax L.) Can be affected by the incubating temperature during the very early developmental stages, eggs from the same batch of spontaneously spawned broodstock were divided at the stage of half-epiboly into three groups according to rearing temperature: G13 = 13 degrees C, G15 = 15 degrees C, and G20 = 20 degrees C. Temperature treatment lasted until the middle of metamorphosis (17-18 mm total length, [TL]), and, with the exclusion of water temperature, all biotic and abiotic conditions were identical for the three experimental groups. The on-growing phase was performed under ambient photoperiod and temperature conditions for all groups. Sex proportions were determined by histological examination of the gonads of fish at 308, 467, and 568 days posthatch (DPH). At 308 DPH (TL: 135-201 mm), 100% of the specimens had differentiated into males and females. A significantly higher (P < 0.01) proportion of females was found in groups G13 (72-74%) and G15 (67-73%) than in group G20 (24-28%). At the final sampling there was no statistically significant difference in body weight between the experimental groups. However, in all groups, female fish were larger than males (P < 0.001). Results provide for the first time clear evidence that temperature during the very early developmental stages is the crucial factor affecting the process of sex differentiation of the sea bass, with low rearing temperatures (13 or 15 degrees C) resulting in sex proportions consistently skewed in favor of females.

Animals↗

PubMed2000

Proliferation zones in the adult brain of a sequential hermaphrodite teleost species (Sparus aurata).

Teleost sex change is an important model to understand general principles of sexual differentiation and plasticity in the adult brain. The present study is the first to examine the proliferation zones in the adult brain of males, females and sex-changing individuals of a protandrous teleost species (Sparus aurata), by means of 5-bromo-2-deoxyuridine immunocytochemistry. Postnatal neurogenesis in the marine teleost brain was found in ventricular and subventricular areas of the brain that in most cases coincided with the embryonic proliferation zones. The molecular layer of corpus and valvula cerebelli exhibited the highest mitotic activity in the adult brain. High mitotic activity was observed in the hypothalamic, thalamic and telencephalic ventricular areas, as well as the dorsal and ventral rim of the optic tectum. Most of the labeled cells were elongated, indicating the initiation of migratory activity. There were no qualitative differences in the distribution of proliferation zones between the sex phases studied with the exception of the ventricular region of the dorsal hypothalamic area. Volume fraction analysis of the area occupied by the labeled cells suggested that this region included higher densities of newborn cells in the female animals. The proliferation pattern in the adult gilthead sea bream brain is in agreement with the hypothesis of the continuous generation of new cells in the teleost brain. Moreover, our data propose that cell proliferation differences possibly existing in the ventricular region of the dorsal hypothalamus between sexual phases, might be involved in central mechanisms of sexual plasticity in protandrous hermaphrodite teleosts.

Animals↗

PubMed1999

Unilateral eye abnormalities in reared Mediterranean gilthead sea bream.

Eye abnormalities in reared gilthead sea bream (Sparus aurata) were investigated clinically and by histological techniques. A significant number of fish had a cataract in one eye and ocular inflammation including gross exophthalmos. In a small number of fish gas bubbles were observed in the anterior chamber of the eye. Histological examination provided no evidence of an infectious process and a possible behavioural aetiology is discussed.

Animals↗