Les premiers vertébrés et les premières étapes de l’évolution du crâne

The earliest vertebrates and the first steps of the evolution of the skull. Vertebrates are one of the few metazoan taxa, which display a well-corroborated phylogenetic pattern, a good and anatomically informative fossil record, and a relatively slow ontogenetic development. They are thus a favourite taxon for illustrating evolution as a historical process, although the stem of the vertebrate tree remains poorly documented by fossils, except for some Early Cambrian forms. Therefore, the characterization of the vertebrates now rests essentially on a small number of developmental characters, mostly involved in the rise of the skull, and whose precursors may occur in other chordates. The tree of the crown-group vertebrates also shows some major morphological gaps due to early extinctions, but a number of Palaeozoic stem gnathostome taxa helps in documenting the agnathan-gnathostome evolutionary transition. However, stem cyclostomes remain elusive.     

Proposition de reconstitution du deuxième crâne d’Homo erectus de Yunxian (Chine)

A proposal of reconstruction of the second Homo erectus skull from Yunxian (China). In 1989 and 1990, two Homo erectus crania were recovered from Yunxian (Hubei province) in archaeological levels dated to more than 780 000 years. Considered along with Lantian, these skulls represent the oldest human remains discovered in China to date, constituting important palaeontological finds. Nevertheless, the crania were badly deformed during the course of fossilization, necessitating extensive cranial reconstruction. Of the two crania, only Yunxian II was in sufficient condition to carry out this reconstruction. Using sophisticated techniques only recently applied in human palaeontology, including computed tomography and rapid prototyping, and incorporating taphonomic and morphometrically-based hypotheses, we were able to correct virtually the deformation and to produce a 3D prototype of Yunxian II. To cite this article: A. Vialet et al., C. R. Palevol 4 (2005).     

Fertilité de l’homme en fonction de l’âge

The aim of this work was to analyse the evolution of sperm characteristics according to age. To this end we analysed the spermogram of 2,126 men aged 20 to 64 who came for consultation for feminine indications for in vitro fertilization at the Clermont-Ferrand Human Reproduction Unit during the period 1980 to 1994. A search for a link between the age of the patient at the time of the spermogram and 10 sperm parameters, by studying a linear regression, did not reveal any evidence of a significant correlation between the age and the parameters studied. The mean values for volume, concentration of spermatozoa, percentage of mobile forms (normal, diminished), percentage of typical and mobile forms and percentage of abnormal forms were compared for age classes covering 5 years. These values showed no significant difference according to the age classes. Between 20 and 60 years the essential parameters of the spermogram seem generally to be independent of age, from which it can be deduced that ejaculate quality remains the same until 50 years of age. However a bias in the recruitment of the population studied and a very wide spread for the values for a given age mean that we may not have detected fluctuations in sperm characteristics linked with age.     

Cellules riches en glycogène dans l'épendyme du ventricule latéral du cerveau de rat

Summary The ependyma of the lateral ventricle of the rat brain was investigated at different ages from 20 days to adulthood.A particular cell type occurs in the external wall of the ventricle, where the proliferative subependymal layer is present. These cells found at all ages studied, are characterized by a high content of glycogen, and a structure different of typical ependymal cells.A large number of nerve endings is situated in close vicinity of these cells, either free in the ventricle lumen, or sometimes ensheathed in the cells. No synapse was found between these endings an the glycogen-rich cells.These glycogen-rich cells undergo several modifications with age: their glycogen content is reduced in the adult, and they acquire a few cilia and gliofilaments. It is suggested that they represent a transitory differentiation of the ependyma, functionally linked with the proliferative subependymal layer.

     

La gouttelette cytoplasmique résiduelle du spermatozoïde

The cytoplasmic droplet of spermatozoa is a small outpouching of cytoplasm observed in man and many mammalian species. This cytoplasmic persistance on spermatozoa is of unknown significance. It is associated with infertility and is due to a spermiation or epididymal maturation abnormality. Several etiological mechanisms have been suggested. Seminal fructose and testosterone concentrations have been correlated with the presence of cytoplasmic droples. Creatine kinase, glucose 6-phosphate dehydrogenase enzymes in the droplet and products of lipid peroxidation could be used as biochemical markers of this cytological abnormality. There is a significant increase in cytoplasmic droplets in HIV seropositive and in khat addicted subjects. Deleterious effects on fertility could be due to membrane modifications of the spermatozoa and/or reactive oxygen species generation via enzymatic activities in the residual cytoplasm.     

Prostasomes, dérivés actifs de l’oxygène et sperme humain

Prostasomes are particular lipid vesicles secreted by the human prostate and found in the semen. No specific action has yet been attributed to prostasomes, but they appear to act at various levels. For example, prostasomes enhance sperm motility in vitro and participate in the immunomodulation properties of seminal plasma. Excessive production of reactive oxygen species (ROS) in human semen has a negative influence on the functional capacities of spermatozoa. The presence of leukocytes in semen is associated with increased production of ROS that can be harmful to sperm cells, under certain conditions. Previous results tend to suggest a possible role of prostasomes on ROS production in human semen. After reviewing the literature concerning the structural and functional characteristics of prostasomes and the role of ROS in human semen, we report our results concerning the influence of prostasomes on ROS production and the consequences on semen. We have demonstrated that prostasomes exert an antioxidant function in human semen. This function is effective both on polymorphonuclear neutrophils and on sperm cells. The mechanism of action of prostasomes is unusual, as they act on ROS production mainly on the plasma membranes of neutrophils. They induce a decrease of NADPH-oxidase activity associated with rigidification of the plasma membrane. Prostasomes protect the functional capacities of spermatozoa during an oxidative stress created by the presence of NADPH in the incubation medium.     

Révision de la faune de mammifères du Miocène supérieurde Menacer (ex-Marceau), Algérie: Discussion sur l'âge du gisement

The revision of the fauna from Menacer (formerly Marceau), Algeria, has resulted in important modifications in the faunal list initially established by Arambourg (1959). Thirteen taxa are thereby counted. The Menacer locality has been classically paralleled with the Vallesian site of Bou Hanifia. Now the new faunal indications and the geologic data concerning the age of Menacer suggest, rather, a Turolian age.     

L’analyse automatisée de la morphologie du spermatozoïde

Examination of sperm morphology is one factor of evaluation of sperm function, but it can also be considered as a biomarker of testicular function. All publications showed a high variability in observed results, in relation with different methods of staining slides and classifying sperm morphology, and a large subjectivity in the visual assessment. Automated sperm morphology analysis (ASMA) have the potential to provide more objective, accurate, and precise morphometric measurements of spermatozoa. Standardisation of the methods of slides preparation is first essential. Analysis of the sperm head morphometry appears the more accessible for the ASMA and could give selective parameters in the evaluation of fertility, in complement with motion sperm analysis. In the other hand automated analysis of all sperm abnormalities appears illusory with actual instruments, because the midpiece or the flagellum is a little structure weakly stained, and thus difficult to be identified by the computer. Until more rigorous and consistent definitions of sperm features can be developped, in relation with testicular function, the pronostic value of existing sperm abnormalities classifications is limited.