Electron Microscopy on the Pre- and Post-natal Development of the Pancreatic Acinar Cell of the Mouse

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Abstract
The secretory granule seems to be formed within the cavity of the rough-surfaced endoplasmic reticulum in the early stages of prenatal differentiation, days 15 to 16 of gestation, in which the organellae of the acinar cell are not sufficiently developed. However, when the cellular differentiation is advanced, 3 to 4 days after birth, a transition of the Golgi vacuole to granule and changes of density of the granular contents are observed. This fact may suggest that the site of synthesis of secretory products is in the endoplasmic reticulum and the site of their accumulation is within the Golgi complex. No evidence suggesting direct transformation of mitochondria into granule was obtained. Some differences of properties and formation mechanisms of the secretory granule in various stages were observed. That is, the secretory granules seen in the end of gestation are larger than those in the postnatal stages and showed the figure of "central condensation" in their maturing process. On the contrary, the secretory granules in the postnatal stages are the same size as those of the adult and matured by diffuse condensation of their contents. From this fact it is presumed that there are some differences in enzymatic activities and chemical characters between both granules.
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