THE PRESENCE AND SUBCELLULAR-DISTRIBUTION OF STEROL CARRIER PROTEIN-2IN EMBRYONIC-CHICK TISSUES

Transport of lipids from the yolk to the tissues of the chick embryo i s 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 int o the fetal circulation. Little is known about the cytoplasmic transpo rt of lipid in avian systems, but recently the presence of sterol carr ier protein 2 (SCP2) was reported in chicken liver. Here we examine th e cells of yolk-sac membrane, liver and small intestine for the presen ce 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 ap pearance of a high-molecular-mass form of SCP2 was detected in small i ntestine shortly before hatching, but the significance of this protein is not clear. The presence of SCP2 in these tissues was also confirme d by immunocytochemical techniques. Similarly to SCP2 of mammalian cel ls, avian SCP2 is localized in both peroxisome-like structures and mit ochondria. To a lesser extent it is associated with the endoplasmic re ticulum.