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The presence and subcellular distribution of sterol carrier protein 2 in embryonic-chick tissues
M P Reinhart1, S J Avart, T O Dobson
1USDA-ARS-ERRC, Philadelphia, PA 19118.
Insights
Sterol carrier protein 2 (SCP2) quantity in chick embryo cells doesn't correlate with lipid transport rates. A new high-molecular-mass SCP2 form appears in the small intestine before hatching.
Area of Science:
- Embryology
- Biochemistry
- Cell Biology
Background:
- Lipid transport from yolk to chick embryo tissues accelerates in the final embryonic week.
- Cytoplasmic lipid transport mechanisms in avian systems are poorly understood.
- Sterol carrier protein 2 (SCP2) has been identified in chicken liver.
Purpose of the Study:
- To investigate the presence of sterol carrier protein 2 (SCP2) in chick embryo yolk-sac membrane, liver, and small intestine cells.
- To examine the relationship between SCP2 levels and lipid flux during embryonic development.
- To determine the subcellular localization of avian SCP2.
Main Methods:
- Quantitative analysis of SCP2 in embryonic tissues.
- Immunocytochemical techniques to confirm SCP2 presence and localization.
- Developmental stage analysis of SCP2 expression.
Main Results:
- SCP2 quantity in embryonic cells did not correlate with lipid flux rates.
- A high-molecular-mass form of SCP2 appeared in the small intestine shortly before hatching.
- Avian SCP2 was localized in peroxisome-like structures, mitochondria, and to a lesser extent, the endoplasmic reticulum.
Conclusions:
- SCP2 levels do not appear to directly regulate the rate of lipid transport in developing chick embryos.
- The function of the high-molecular-mass SCP2 form in the small intestine remains unclear.
- Avian SCP2 shares subcellular localization patterns with its mammalian counterpart.
Abstract:
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.