par Milaire, Jean 
Référence Birth defects original article series, 13, 1, page (37-67)
Publication Publié, 1977
Référence Birth defects original article series, 13, 1, page (37-67)
Publication Publié, 1977
Article révisé par les pairs
| Résumé : | The purpose of the present survey is to group together a number of histochemical observations which are suggestive of the occurrence of morphogenetic gradients during the development of a limb. Three groups of histochemical changes can be distinguished. The first one concerns changes observed at the very early stages and therefore can be related to the basic morphogenetic mechanisms responsible for the onset, of the limb bud outgrowth and for the primary modelling of the undifferentiated rudiment. During the same period, a second category of histochemical observations can be helpful in the detection of morphogenetic gradient; they concern some rare instances in which different groups of apparently similar cells mingle together while retaining selective histochemical properties according to their origin. The predominance of the one or the other cell population in different areas of the early limb bud can be interpreted in terms of asymmetric morphogenetic patterns. At older stages, the histochemical techniques permit an early detection of various metabolic changes related to the onset of tissular differentiation. These changes often occur before the related structural modifications take place; they provide thus a third group of significant information about the topographic distribution of the previous morphogenetic events involved in the establishment of a regional pattern of histodifferentiation. When such modifications are carefully followed from stage to stage and compared in different presumptive segmental areas, many of them can be interpreted as the late expression of earlier morphogenetic gradients. |
