The presence and subcellular distribution of sterol carrier protein 2 in embryonic-chick tissues.

Transport of lipids from the yolk to the tissues of the chick embryo is slow during the first 2 weeks of development, but increases abruptly during the last week. Evidence suggests that the lipid traverses the cytoplasm of the yolk-sac membrane before secretion as lipoprotein into the fetal circulation. Little is known about the cytoplasmic transport of lipid in avian systems, but recently the presence of sterol carrier protein 2 (SCP2) was reported in chicken liver. Here we examine the cells of yolk-sac membrane, liver and small intestine for the presence of this protein as a function of the time of embryonic development. The quantity of SCP2 present in the embryonic cells did not appear to correlate with the rate of lipid flux in these tissues. The abrupt appearance of a high-molecular-mass form of SCP2 was detected in small intestine shortly before hatching, but the significance of this protein is not clear. The presence of SCP2 in these tissues was also confirmed by immunocytochemical techniques. Similarly to SCP2 of mammalian cells, avian SCP2 is localized in both peroxisome-like structures and mitochondria. To a lesser extent it is associated with the endoplasmic reticulum.