Analyse de la fécondation chez les Batraciens par l'hybridation et la polyspermie physiologique

Sans résumé     

Formation de la membrane de fécondation de l'oeuf d'Artemia salina

Résumé L'oeuf vierge d'Artemia salina n'est pas entouré de membranes exocellulaires. Le plasme sous-cortical ne contient pas d'organites spéciaux. Dès la fécondation, une membrane est secrétée par l'oeuf. La substance membranogène, contenue dans le reticulum endoplasmique lisse, passe par les éléments golgiens, où elle semble modifiée, et est expulsée dans des vésicules qui se détachent du Golgi. Retenue par un enduit granuleux, qui couvre le plasmolemme, et qui peut être un glycocoat ou du suc du tractus génital, elle s'étale en une membrane de fécondation, qui se soulève pour constituer l'espace périvitellin. Le processus est progressif et dure environ une heure et demi.

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Formation of the fertilization membrane of the egg inArtemia salina

Summary The unfertilized egg ofArtemia salina is not covered with any extracellular structure. No special organelles are found in the sub-cortical plasma. From the moment of fertilization, a membrane is progressively secreted by the egg. The membranogenous substance is first seen as large granules in the smooth endoplasmic reticulum, presumably transformed within Golgi elements and extruded in vesicles liberated from the Golgi apparatus. Retained by a glycocoat or by contact with the fluid of the genital tract, it spreads out into a fertilization membrane, soon surrounding a perivitelline space. The process lasts till 1 1/2 h after fertilization.

     

Étude ultrastructurale de la fécondation chez Grantia compressa F.

The fertilization of a calcareous sponge is studied by means of the electron microscope, in Grantia compressa F.. The mature oocyte lies beneath the choanoderm; the carrier cell is applied to its surface, and the spermiocyst enters its cytoplasm. The ultrastructural study demonstrates two formations in this spermiocyst: (i) the ‘head’, surrounded by a lamellar envelope, consists mainly of a nucleus with ring-shaped chromatin; (ii) a large area with a periodic structure corresponding to the modified ‘middle piece’ or ‘mitochondrial body’ of other authors.     

Analyse de la fécondation par la parthénogénèse expérimentale

Sans résumé     

Malladaites nov. gen. et Spinammatoceras (Hammatoceratidae,Ammonitina) de l'Aalénien de la zone subbétique,Sud de l'Espagne

The aim of this paper is to remark some morphologicaldifferences among the type-species of the genus ZurcheriaDouvillé and those species attributed to this genuf by Buckman & Brasil: the group of H. pugnaxVacek for which Schindewolf (1964) defined the genus Spinammatoceras, and the group of H. pertinaxVacek for which we propose Malladaites gen. nov.; new species of both genera are described. The stratigraphical range of these species is established in the Betic Cordillera.     

La respiration chez Drosophila melanogaster au cours de la métamorphose. Influence de la pupaison,de la mue nymphale et de l'émergence

With a new electrolytic respirometer, the evolution of respiratory rate is studied in single pupae. During metamorphosis oxygen consumption follows a classical U-shaped curve. Puparium formation, larval-nymphal moult (i.e. apolysis), and imaginal ecdysis are accompanied by increases in respiratory rate. Interpretation of these phenomena is discussed.     

Composition lipidique membranaire durant la préparation de spermatozoïdes à la fécondation

The final modifications that the spermatozoa undergo correspond with the destabilization of their plasma membrane. This indispensable step facilitates the fusion of membranes and primes the signal transduction during fertilization. This destabilization is composed of a series of changes and modulation of the lipids in membranes such as cholestérol, phospholipids and glycolipids. Several differences exist in the lipid composition of the plasma, acrosome, nuclear and mitochondrial membranes of spermatozoa. The principal membrane phospholipids are phosphatidyl choline, phosphatidyl ethanolamine and sphingomyelin. Plasma membrane of sperm is also rich in polyunsaturated fatty acids (PUFA) linked to phospholipids. Such as C₁₈∶2n?6, C₂₀∶4n?6 and large amounts of docosahexaenoic acid (C₂₂∶6n?6). The amount of membrane lipids in human sperm varies considerably between patients. This variation, could influence certain functional properties of the sperm cells such as their ability to undergo capacitation, the acrosome reaction and the fusion between sperm and oocyte membranes. The lipid composition of the human sperm cell can be altered during the process of freezing-thawing. A significant decrease in phospholipids (phosphatidyl choline, phosphatidyl ethanolamine), and PUFA in particular docosahexaenoic acid and arachidonic acid was observed. Human spermatozoa have a molar cholestérol/phopholipid ratio ≤1.0, and reduces during capacitation due to loss of cholestérol. In addition, the decrease in the levels of cholestérol and the methylation of phospholipids is involved in the modification of membrane fluidity and in the maturation of the sperm plasma membrane receptors. Therefore it seems that the methylation is important for the fusion between sperm and oocyte membranes. Intrinsic sperm phospholipase A2 also plays a role in the destabilization of the plasma membrane by producing of lysophospholipid. Therefore this enzyme and free fatty acids are believed to play a role in the acrosome reaction, an indispensable event facilitating the fusion between sperm and oocyte membranes.     

Bases génétiques de la spéciation et de la taxonomie chez les Babouins

This review gives a synthesis on the present knowledge on the use of several electrophoretic markers in examining speciation and taxonomy in baboons (genus Papio, Mendrillus and Theropithecus). In the various species studied, the amplitude of variation is small and the average rate of individual heterozygosity low; this seems partly due to the inbreeding which occurs within the groups. In these sub-populations, and when the frquencies are in equilibrium, it is possible to calculate the number of genetic migrants by generation between groups, which averages 3–18% according to species. The genetic distances between species allow one to establish in the genus Papio that the species P. hamadryas is the most differentiated and on the whole these species are comparable to geographical races of a polytypic species according to the measures obtained. Calculation of electrophoretic distances shows tht within Papio both P. papio and P. anubis are indistinguishable and that the three other species. P. cynocephalus, P. ursinus and P. hamadryas, diverge from this basic group. According to these criteria, both Mandrillus species diverge on the average of 30% of their genes, and according to the paleontological dates of divergence between Papio and Theropithacus, Papio would have appeared approximately 3.5 million years ago, a date in agreement with the information obtained from fossils. The electrophoretic study of inter-specific hybrids allows the intensity of the migratory flux betwen the different groups of Papio anubis and P. hanadryas in natural conditions to be calculated, and shows a partial inhibition of the paternal component of hybrids P. anubix × P. cynocephalus. It is concluded that two interesting research problems are the study of inbreeding in the different groups, and the influence of the genetic regulation in the evolution of various species. The evolution of different species within the group seems to constitute an excellent animal model from the diversification of fossils hominids during the Pleistocene epoch.     

La fécondation par injection d'une spermatide dans l'ovule

There was a recent large spreading of intracytoplasmic sperm injection (ICSI) to treat male infertility in most of in vitro fertilization (IVF) laboratories. The recent data confirm the efficacy of ICSI even by using testicular sperm or sperm with grossly abnormal phenotype (round head, absence of motility). Moreover it appears that ICSI could pass beyond the last events of spermatogenesis (i.e. spermiogenesis), since normal development follows fertilization with the male gamete, spermatid, recovered just after completion of meiosis. It is obvious that the natural properties of a mature spermatozoon (motility, ADN compaction, oocyte recognition and penetration) are only necessary to reach the site of fertilization (into the female tube) and to pass through the protective enveloppes around the oocyte (cumulus oophorus, zona pellucida, plasma membrane). The current view that spermatids lack genetic maturation comparing to eggs is not valid since eggs are only secondary oocytes at a meiotic stage equivalent to that of secondary spermatocytes. Moreover genetic imprinting occurs before meiosis, and cytoplasmic structures which seem necessary for embryo development are already present in spermatids. ICSI using spermatid cells is relevant to men suffering non obstructive azzospermia if spermatids are recovered from either the ejaculate or the testicular tubes. Several normal babies were born after injection of round spermatids. Since these spermatogenic cells are present in the ejaculate of most of the patients with non obstructive azoospermia (76% in our lab), one can estimate to 5–10% the proportion of sterile men potentially concerned by conception with spermatids. However certain of these men may have occasional sperm found with testicular sperm extraction and it is to early to know if such iatrogenic extraction is always preferable to ejaculate spermatid collection.     

Azoospermies non obstructives; facteurs prédictifs du prélèvement testiculaire et risques de la fécondation assistée

Surgical sperm retrieval has revolutionized the treatment of azoospermia. Intracytoplasmic sperm injection (ICSI) allows naturally infertile men to have children by allowing defective sperm cells to fertilize oocytes. These techniques, applied without any preliminary animal experimentation, raised an enormous enthusiasm and are performed on a large-scale. To increase the efficiency of these treatments, the clinicians are now trying, without success, to identify factors predictive of success allowing better patient selection and counselling of couples dependent on these techniques in order to avoid useless and harmful interventions. Animal research, conducted after introduction of these techniques, has raised serious doubts about the safety of ICSI and the legitimacy of using defective spermatozoa from genetically high-risk patients. Some studies have also emphasized the unusual frequency of obstetric and neonatal problems as well as rare diseases and malignancies in ICSI-born children and ART-born children. However, these disturbing findings are not specifically related to the ICSI procedure, as demonstrated by well-conducted large-scale follow-up studies in ICSI-born children. This paradox raises a lively debate. ICSI-children follow-up studies should continue until sound data taking into account the genetic and all other parental background are obtained. In conclusion, non obstructive azoospermic patients should be informed of the limits of sperm retrieval and genetic screening tools as well as all risks common to ICSI and ART.     

Paléoxylologie: Étude anatomique comparée de Scleromedulloxylon aveyronense nov. gen. nov. sp. du Permien de St-Affrique (Aveyron,France); considérations taxinomiques et stratigraphiques

The fossil woods studied in the present paper were collected by P. Béziat in the Permian Basin of St-Affrique (Southern Aveyron). They come from near Calmels. They are the first fossil woods collected and described in this basin.The secondary wood refers to the form genus Dadoxylon and more exactly to the speciesDadoxylon schrollianum (Goeppert, 1864–65) Frentzen, 1931, Frentzen, 1931. The pith is certainly related with the pith structure of Walchiapremnon valdajolenseFlorin, 1940.The association of a Dadoxylon secondary wood with an irregularly septate pith containinggroups of probably sclerotic cells can be found in Cedroxylon varollenseRenault, 1893–1896, Renault and Roche, 1894 from the Basin of Autun. It is not possible to conserve the species varollense in the genus Cedroxylon and we propose the form genus Scleromedulloxylon for the petrified structure from Autun and for the fossil woods of St-Affrique.Furthermore, a comparative anatomical study of the different Permo-Carboniferous structuresfrom the Euramerican province let us, when it is possible, distinguish structure-types related to Cordaitophyts or to Coniferophyts. In the present case, Scleromedulloxylo should rather correspond to the fossil wood of an Autunian Coniferophyt, that is to Walchia structure.     

La médicalisation de la sexualité: Aspects sociologiques et historiques

The paper gives an introduction to a discussion about the process of medicalization of sexuality. This process is defined as: a social construction of knowledge on sexuality based on a biological conception of the body and health; clinical practice based on diagnosis and medical technologies; a strong relation between medecine and sexual morality. The paper is based on a study of the medical treatment of masturbation, sterilization and homosexuality in a historical perspective. Then the paper, shows how, currently, the process of medicalization of sexuality is twofold: on one hand stimulation of «normal» sexual activity (pharmacological treatment of sexual dysfunction) and inhibition of deviant sexual behavior (sexual abusers). At last, the paper, gives a short view on the potential transformations of the patient-doctor interaction.