The fine structure of newborn and fetal mouse liver and of newborn kidney cells homozygous for any of three albino alleles known to have multiple biochemical effects was investigated. Electron microscope studies of mutant cells revealed dilation and vesiculation of the rough endoplasmic reticulum in parenchymal liver cells, as well as dilation and other anomalies of the Golgi apparatus. These abnormalities were observed in all newborn mutants but never in littermate controls. Although they were most pronounced in liver parenchymal cells, they were found also to a lesser degree in kidney cells, but they were absent altogether in other cell types of the mutant newborn. Homozygous fetuses showed similar anomalies in the liver at 19 days of gestational age. In one of the alleles studied, mutant liver parenchymal cells were found to be abnormal as early as the 18th day of gestation. There appears to be a striking parallelism between the biochemical defects and those of the cellular membranes in homozygous mutant newborn and fetuses. Although the specific nature of the mutational effect on membrane structure remains unknown, the results are compatible with the assumption that a mutationally caused defect in a membrane component interferes with a mechanism vital in the integration of morphological and biochemical differentiation.

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