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C Pieau

Publications and source records attributed to C Pieau.

At least 37 records · Page 2Linked to original sources
PubMed1994

Early development of GABA-like immunoreactive cells in the retina of turtle embryos.

Gamma aminobutyric acid (GABA) is one of the earliest neuroactive substances appearing in the developing central nervous system. The distribution and the time course of the appearance of GABA-like immunoreactivity in the retina of the turtle Emys orbicularis were investigated from embryonic stage 13 to hatching. The first GABA-like immunoreactive cells were observed at stage 14. These cells were located in both the scleral third of the neuroblastic layer and the inner layers of the retina. They were identified as presumptive immature horizontal cells and amacrine cells, respectively. The observation of numerous labelled fibers in the nerve fiber layer suggests that some of the GABA-like immunoreactive cells in the layers were ganglion cells. The development of GABA-like immunoreactive cells followed a gradient of maturation from central to peripheral retina. At hatching, the central retina appeared nearly morphologically mature. In conclusion, GABA is present before the morphofunctional maturation of the retina and this precocious existence supports the idea of its involvement in a neurotrophic role preceding the establishment of synaptic connections and neurotransmitter function.

Animals↗
PubMed1993

Sensitive stages for the effects of temperature on gonadal aromatase activity in embryos of the marine turtle Dermochelys coriacea.

Many data suggest an involvement of estrogens in gonadal differentiation in reptiles with temperature-dependent sex determination (TSD). However, the site of estrogen synthesis in two species of freshwater turtles is unclear. In Emys orbicularis, estrogens were shown to be produced by the gonads, whereas in Trachemys scripta, gonadal steroids were not detected. The marine turtle Dermochelys coriacea exhibits TSD but in gonadal development, ovarian differentiation is delayed. Gonadal aromatase activity and estrogen content in this species were measured in embryos incubated at 27 degrees and in embryos incubated at 30.5 degrees, respectively, masculinizing and feminizing temperatures within the range of temperatures found in natural nests. At all stages studied, aromatase activity was present and found to be higher at 30.5 degrees than at 27 degrees. Estrogens were only found at 30.5 degrees. The effects of temperature shifts on gonadal aromatase activity were then examined. Eggs were shifted from 27 to 35 degrees (feminizing temperature) at different embryonic stages and exposed to 35 degrees for 6 days. An increase in gonadal aromatase activity, although with significant individual variations, was seen only when eggs were shifted between stages 23 and 27. These stages are in the range of the thermosensitive stages for sexual differentiation of the gonads determined in other turtles. These results are similar to those previously obtained in E. orbicularis and agree with a key role for endogenous estrogens in gonadal differentiation of reptiles with TSD.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The embryological development of primary visual centres in the turtle Emys orbicularis.

The development of the primary visual centres was studied in a series of embryos of the turtle, Emys orbicularis, incubated at 25 degrees C. The differentiation of both visual and nonvisual diencephalic and mesencephalic structures takes place entirely within the 2nd quarter of the period of incubation; this finding appears to be consistent with previous descriptions of the embryology of 2 other chelonian species, Lepidochelys and Chelydra. Two successive waves of migration, each dividing into internal and external sheaves, are involved in the formation of the structures of the diencephalon and mesencephalon. The primary visual centres, which comprise 2 hypothalamic, 5 thalamic and 5 pretectal zones of retinal projections, together with the 2 superficial layers of the tectum and a single tegmental projection zone, all have their origin in the external sheaf of the 1st wave of migration. The finding that the adult nucleus geniculatus lateralis dorsalis, pars ventralis arises from one of the migrations of the dorsal thalamus is discussed in the context of the debate over the possible homologues of the mammalian geniculostriate visual pathway.

Animals↗
PubMed1992

Aromatase activity in gonads of turtle embryos as a function of the incubation temperature of eggs.

In embryos of the European pond turtle, sexual differentiation of gonads is temperature-dependent. Production of oestrogens appears to play a key role in this phenomenon. Gonadal aromatase activity was measured in embryos incubated at 25 degrees C (masculinizing temperature) and at 30 degrees C (feminizing temperature). At the beginning of the thermosensitive period, the aromatase activity was low at both temperatures but was somewhat higher at 30 than at 25 degrees C. Afterwards, it remained low in differentiating testes at 25 degrees C, whereas it increased in differentiating ovaries at 30 degrees C to form a marked peak when germ cells underwent meiotic prophase. Eggs were shifted either from 25 to 30 degrees C (highly feminizing) or from 30 to 35 degrees C for 6 days at different stages of embryonic development. The 25-35 degrees C shifts performed during the thermosensitive period strongly increased the aromatase activity but were ineffective after this period. The 30-35 degrees C shifts increased the aromatase activity at all stages. Altogether, results indicate that, in differentiating gonads of turtle embryos, temperature acts on the regulation of synthesis (and therefore activity) of cytochrome P-450 aromatase (P-450-aro). The expression of the P-450-aro gene itself could be temperature-dependent. However, temperature could also act upon the expression of another gene involved in P-450-aro regulation.

Animals↗
PubMed1992

A quantitative and interspecific test for biological activity of anti-müllerian hormone: the fetal ovary aromatase assay.

Anti-Müllerian hormone (AMH), also known as Müllerian-inhibiting substance or factor, has previously been shown to sex-reverse the steroidogenic pattern of fetal mammalian ovaries through repression of aromatase biosynthesis. Study of the ontogeny of the response of cyclic AMP-stimulated aromatase activity of rat fetal ovaries to AMH has allowed us to develop a quantitative bioassay for the hormone. Linear responses as a function of the logarithm of AMH concentration were observed over ranges of 0.2-7.5 micrograms/ml for the bovine protein and 0.15-2 micrograms/ml for the human protein, with a maximal decrease in aromatase activity of 90% for both proteins. Under the same in vitro conditions, AMH treatment did not affect cyclic AMP-stimulated fetal rat testicular aromatase activity. Partially purified chick AMH also decreased rat ovarian aromatase activity, allowing us to use this test to study AMH ontogeny in chick gonads. Analysis of the species specificity of AMH repression of ovarian aromatase activity indicated that turtle and rat fetal ovaries responded to AMH of other vertebrate classes, whereas aromatase activity of chick embryo ovaries could be repressed only by the homospecific hormone.

Animals↗
PubMed1991

Steroid metabolism in gonads of turtle embryos as a function of the incubation temperature of eggs.

In embryos of many reptiles, the sexual differentiation of gonads is temperature-dependent. In the turtle Emys orbicularis, all individuals become phenotypic males at 25 degrees C, whereas 100% phenotypic females are obtained at 30 degrees C. Steroid metabolism in embryonic gonads was studied at both temperatures, during and after the thermosensitive period for sexual differentiation. Pools of gonads were incubated for various times, with 3 beta-hydroxy-5-pregnen-20-one (pregnenolone), progesterone, dehydroepiandrosterone or 4-androstene-3,17- dione as substrates. The analysis of metabolites combined two successive chromatographies (HPLC and TLC) and autoradiography. Conversion of pregnenolone to progesterone and of dehydroepiandrosterone to 4-androstene-3,17-dione was more important in testes at 25 degrees C than in ovaries at 30 degrees C. In ovaries, a large amount of 5-pregnene- 3 beta,20 beta-diol was formed from pregnenolone, and 5-androstene-3 beta,17 beta-diol was produced from dehydroepiandrosterone. In both testes and ovaries, 5 alpha-pregnane and 5 alpha-androstane derivatives were the main metabolites obtained from progesterone and 4-androstene-3,17-dione, respectively. Progesterone was also converted to 20 beta-hydroxy-4-pregnen-3-one. Dehydroepiandrosterone and 4-androstene-3,17-dione were also metabolized into 11 beta-hydroxy-4-androstene-3,17-dione (only in testes), testosterone, 11 beta,17 beta-dihydroxy-4-androstene-3-one, 17 beta-hydroxy-4-androstene-3,11-dione (low amounts in testes, traces in ovaries), 17 alpha-hydroxy-4-androstene-3-one, estrone and estradiol-17 beta (traces).

Androstenedione↗
PubMed1990

Temperature sex-reversal in amphibians and reptiles.

The sexual differentiation of gonads has been shown to be temperature-sensitive in many species of amphibians and reptiles. In two close species of salamanders, Pleurodeles poireti and P. waltl, both displaying a ZZ/ZW mechanism of genotypic sex determination (GSD), the rearing of larvae at high temperatures (30 degrees-32 degrees C) produces opposite effects: ZZ genotypic males of Pleurodeles poireti become phenotypic females whereas ZW genotypic females of P. waltl become phenotypic males. Sex-reversal of these individuals has been irrefutably demonstrated through genetic, cytogenetic, enzymatic and immunological studies. In many turtles, both sexes differentiate only within a critical range of temperature: above this range, all the individuals become phenotypic females, whereas below it, 100% become phenotypic males. The inverse occurs in some crocodiles and lizards. In many species of these three orders of reptiles, females are obtained at low and high temperatures, and males at intermediate ones. Preliminary studies in turtles (Emys orbicularis) indicate that within the critical range of temperature, sexual phenotype conforms with GSD, but that above and below this range, GSD is overriden. Temperature shifts during larval development in salamanders and during embryonic development in reptiles allowed the determination of thermosensitive stages for gonadal differentiation. Estrogens synthesized in the gonads at these stages appear to be involved in their sexual differentiation, higher levels being produced at feminizing temperatures than at masculinizing ones. The phenomenon of temperature sensitivity of gonadal differentiation occurs in species showing a very early stage in the evolution of sex chromosomes. Its adaptive value, chiefly in reptiles, remains an open question.

Amphibians↗
PubMed1988

Temperature-dependent gonadal differentiation in the turtle Emys orbicularis: concordance between sexual phenotype and serological H-Y antigen expression at threshold temperature.

As in many other turtles, the sexual differentiation of gonads in embryos of Emys orbicularis is temperature-sensitive, 100% phenotypic males being obtained below 27.5 degrees C and 100% phenotypic females above 29.5 degrees C. The expression of the serologically defined H-Y (SD-H-Y) antigen at both low and high temperatures has been shown to be different in gonads and in blood : in gonads, it is closely associated with ovarian structure, whereas in blood it is independent of sexual phenotype and appears to indicate sexual genotype. Both sexes differentiate at 28.5 degrees C, suggesting that at this intermediate (threshold) temperature, sexual differentiation of gonads conforms with sexual genotype. To test this hypothesis, the expression of SD-H-Y antigen has been carried out in blood cells of Emys individuals raised from eggs incubated at the threshold temperature (28.5 degrees C). All phenotypic males typed SD-H-Y negative, whereas most phenotypic females typed SD-H-Y positive. From this concordance between sexual phenotype of gonads and SD-H-Y phenotype of blood, we postulate that a ZZ male/ZW female mechanism of genotypic sex determination is revealed at the threshold temperature for gonad differentiation in Emys.

Animals↗
PubMed1986

Neurogenesis in reptilian cortical structures: 3H-thymidine autoradiographic analysis.

Histogenesis was studied in forebrain cortical areas of two reptiles, Emys orbicularis and Lacerta trilineata, by using tritiated thymidine autoradiography. Four areas were considered: the dorsomedial, the general (dorsal), and the lateral cortices, and the dorsal ventricular ridge (DVR). The bulk of neurogenesis in these four pallial fields proceeds within a short period of 8-9 days, between developmental stages 15 and 18 in Emys and stages 32-34 in Lacerta. Lateral-to-medial as well as anterior-to-posterior tangential gradients of histogenesis are present in both species. Radial neurogenetic gradients are directed from outside to inside, except in the medial cortex of lizards, where no radial gradient is seen. This pattern of histogenesis in the cortex of turtles and lizards is comparable to that in mammals in terms of timing and tangential, areal variations. It might represent a "common denominator" of cortical histogenesis. However, in contrast to the mammalian cortex, which develops according to an inside to outside, "inverted" pattern, radial neurogenesis in the cortex of turtles and lizards follows an outside-to-inside gradient. These observations suggest that the inside-out gradient of cortical neurogenesis has been acquired during evolution of the synapsid radiation from stem reptiles to mammals, and that it may be related to the development of radial cortical architectonics.

Animals↗
PubMed1982

H-Y antigen expression in temperature sex-reversed turtles (Emys orbicularis).

H-Y antigen has been used as a marker for the heterogametic sex and is assumed to be an organizing factor for the heterogametic gonad. In the turtle Emys orbicularis, H-Y antigen is restricted to the female cells, indicating a female heterogamety (ZZ/ZW) sex-determining mechanism. Moreover, the sexual differentiation of the gonads is temperature sensitive, and complete sex reversal can be obtained at will. In this framework the relationships between H-Y antigen, temperature, and gonadal phenotype were studied. Mouse H-Y antiserum was absorbed with blood and gonadal cells of control wild male and female adults, and with blood and gonadal cells from three lots of young turtles from eggs incubated at 25-26 degrees C (100% phenotypic males), at 30-30.5 degrees C (100% phenotypic females), or at 28.5-29 degrees C (majority of females with some males and intersexes). The residual activity of H-Y antiserum was then estimated using an immunobacterial rosette technique. In adults, both blood cells and gonadal cells were typed as H-Y negative in males and as H-Y positive in females. In each of the three lots of young, blood cells were H-Y negative in some individuals and H-Y positive in others. The proposed interpretation is that the H-Y negative individuals were genotypic males (ZZ) and the H-Y positive were genotypic females (ZW). The gonads of these animals were then pooled in different sets according to their sexual phenotype and to the presumed genotypic sex (i.e., blood H-Y phenotype). Testicular cells were typed as H-Y negative in genotypic males as well as in the presumed sex-reversed genotypic females; likewise, ovarian cells were typed as H-Y positive in genotypic females as well as in the presumed sex-reversed genotypic males. These results provide additional evidence that H-Y antigen expression is closely associated with ovarian structure in vertebrates displaying a ZZ/ZW sex-determining mechanism.

Animals↗
PubMed1979

Variation of DNA polymerase activities in chick neural retina as a function of age.

The activities of DNA polymerases alpha, beta, and gamma and of thymidine kinase were determined in the chick neural retina at different stages of embryonic development (starting at seven days) and after hatching (up to five years). Crude extracts of neural retinae were fractionated by centrifugation on sucrose gradients and the enzymatic activities measured using specific assays. The DNA polymerase alpha activity decreases greatly between 7 and 11 days of incubation. This decrease parallels the decline in mitotic activity. However, a constant residual activity remains after hatching, even in the oldest animals. DNA polymerase beta activity increases slightly between 7 and 14 days of incubation; it then decreases slowly until seven days after hatching and remains constant thereafter. DNA polymerase gamma activity is maximal between 7 and 14 days of incubation and then decreases until hatching. The activity of thymidine kinase increases slightly during the embryonic life until hatching and remains almost constant thereafter. The implication of these enzymes in DNA replication and repair processes is discussed.

Aging↗
PubMed1979

Changes of DNA ligases in chick neural retina as a function of age.

In the course of chick neural retina development, several forms of DNA ligase have been found. During embryonic life the major DNA ligase activity that is found at seven days is form I (8.2 S) which gradually decreases and disappears by 14 days after incubation, whereas form II (6.2 S) increases to reach a maximum at the time of hatching. Form II then decreases reaching a constant level by Day 7 and from that time new slow sedimenting forms also appear (forms III and IV). Form III(2 S) is first detectable at seven days and increases up to 90 days, whereas form IV (3 S) is the only form detected in the 17- and 18-month-old and also in the 5-year-old birds. These four forms display different elution patterns on phosphocellulose column chromatography. They also differ in their thermal stability and sensitivity towards N-ethylmaleimide.

Aging↗
PubMed1978

[Effects of raised and lowered incubation temperatures on the sexual differentiation in the embryos of Emys orbicularis L. (Chelonien)].

Eggs of Emys orbicularis L. were incubated at 18 and 19 degrees 5C during the period of sexual differentiation of the gonads of the embryos; genital glands of testicular structure and retrogressed Müllerian ducts were observed in all cases, like in the embryos issued from eggs incubated at 25 +/- 1 degrees C and 27,5 +/- 0,5 degrees C. On the contrary, the sexual phenotype is female in all the embryos which developed at 35 degrees C, as it is the case between 29 and 30 degrees C.

Animals↗