Observations ultrastructurales sur la parathyroïde de souris

Résumé La parathyroïde de souris ne diffère pas essentiellement par sa structure générale de celles des autres espéces étudiées. Les cellules glandulaires se caractérisent cependant par une plus grande richesse en matériel sécrétoire figuré. La présence de ce matériel figuré dans les cavités golgiennes permet de suivre l'élaboration de granules sécrétoires typiques d'un diamètre de 160 à 200 m qui sont spécialement abondants chez la souris. Ces granules ne sont pas excrétés au pôle vasculaire des cellules; ils migrent vers les parois cellulaires apicales et latérales, fusionnent avec la membrane plasmique et semblent être excrétés sous forme soluble dans les espaces intercellulaires. Il n'existe dans la parathyroïde de souris, comme dans celle du hamster et du rat, qu'un seul type cellulaire fondamental. Les éléments clairs et sombres ne diffèrent que par leur densité hyaloplasmique; cette différence s'accuse plus ou moins selon la qualité du prélèvement.

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Summary The structure of the mouse parathyroid does not differ essentially from other species studied. However, the glandular cells are characterized through an abundance in visible secretory material. The presence of this material in the cavities of the Golgi apparatus makes it possible to observe the formation of the typical secretory granules (160–200 m in diameter) which are particularly abundant in the mouse parathyroid. These granules are not secreted directly at the vascular pole; they migrate to the apical and lateral walls, fuse with the plasma membrane, and seen to pass into the cellular space in a soluble form. In the mouse parathyroid, as in the hamster and rat, there is only one fundamental cell type. The difference between dark and clear cells lies in the density of their hyaloplasm, which, however, is a consequence of the pretreatment of the material (fixation).

     

Hypomethylation of the aquatic invasive plant,Ludwigia grandiflora subsp. hexapetala mimics the adaptive transition into the terrestrial morphotype

Ongoing global changes affect ecosystems and open up new opportunities for biological invasion. The ability of invasive species to rapidly adapt to new environments represents a relevant model for studying short-term adaptation mechanisms. The aquatic invasive plant, Ludwigia grandiflora subsp. hexapetala, is classified as harmful in European rivers. In French wet meadows, this species has shown a rapid transition from aquatic to terrestrial environments with emergence of two distinct morphotypes in 5 years. To understand the heritable mechanisms involved in adjustment to such a new environment, we investigate both genetic and epigenetic as possible sources of flexibility involved in this fast terrestrial transition. We found a low overall genetic differentiation between the two morphotypes arguing against the possibility that terrestrial morphotype emerged from a new adaptive genetic capacity. Artificial hypomethylation was induced on both morphotypes to assess the epigenetic hypothesis. We analyzed global DNA methylation, morphological changes, phytohormones and metabolite profiles of both morphotype responses in both aquatic and terrestrial conditions in shoot and root tissues. Hypomethylation significantly affected morphological variables, phytohormone levels and the amount of some metabolites. The effects of hypomethylation depended on morphotypes, conditions and plant tissues, which highlighted differences among the morphotypes and their plasticity. Using a correlative integrative approach, we showed that hypomethylation of the aquatic morphotype mimicked the characteristics of the terrestrial morphotype. Our data suggest that DNA methylation rather than a new adaptive genetic capacity is playing a key role in L. grandiflora subsp. hexapetala plasticity during its rapid aquatic to terrestrial transition.     

Habitat mediates the outcome of a cleaning symbiosis for a facultatively burrowing crayfish

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