Article révisé par les pairs
| Résumé : | 1. Morphological aspects of the development of the hepatobilio-pancreatic complex were studied in serial sections of 9-, 10- and 11-day mouse embryos. Histochemical techniques were also used to identify nucleic acid, glycogen, neutral mucopolysaccharides as well as for localization of alkaline phosphatase, 5'nucleotidase (AMP-PH) and non specific ATP-PH enzymatic activities. 2. Migration and proliferation of the hepatic cords leading to the formation of parenchymal tissue start in the youngest 9-day embryos (19 to 20 metameres). The migrating cells are characterized by a high RNA content, in contrast to the low RNA content of the septum transversum. At the same stage, the juxta-sinusal part of this septum, which probably contributes to the induction of the endoblastic primordium of the liver, shows a large storage of glycogen. The growth and positioning of the hepatogenic cells are still taking place actively at day 10, resulting in an already large and trilobed liver at day 11. At this point, several different cellular types are distinguishable in the cell mass, thanks to various histochemical modifications. 3. At day 10 and even better at day 11, the hepatoblasts themselves are distinguishable by a newly acquired and very intense AMP-PH activity. At day 11, scattered cellular islets probably of hematoblastic nature display no such activity; on the other hand, the latter cells show some structural characteristics different from those of the future hepatocytes. A strong ATP-PH reaction selectively characterizes all vascular endothelial cells; this clearly demonstrates the early organization of a capillary plexus tapped by the vitelline veins in the septum transversum. It indicates, therefore, that the beginning of angiogenesis preceeds the positioning of the hepatic cords. At day 11, a selective alkaline phosphatase reaction simultaneously appears in extra-hepatic parts of the septum transversum and in many isolated cells of the parenchymal primordium; they probably represent presumptive Kupffer cells. 4. The present study gives no direct information on the problem of the origin and the development of the intrahepatic bile canaliculi. The extra-hepatic bile ducts result from the growth of the epithelial hepatic diverticulum. Their primordium is characterized early by a very low RNA content. Among the accessory biliary ducts, only the gall bladder shows a very high alkaline phosphatase activity. 5. While establishing the chronology and topography of the developing dorsal and ventral pancreatic buds, this study revealed an intense and selective ATP-PH activity among groups of peripheral cells responsible for the growth of the dorsal pancreas. 6. The results are compared with descriptive data obtained in human embryos as well as with histochemical and experimental information pertaining to mice and other mammals. |
