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Absence of apolipoprotein B-48 in the chick, Gallus domesticus
P Tarugi1, L Albertazzi, S Nicolini
1Istituto di Patologia Generale, Università di Modena, Italy.
Insights
Chick plasma contains only apolipoprotein B-100 (apoB-100), not apoB-48. Chick intestine produces apoB-100 and apoB-95, but lacks apoB-48 synthesis, explaining its absence in plasma.
Area of Science:
- Biochemistry
- Molecular Biology
- Lipid Metabolism
Background:
- Apolipoprotein B (apoB) is a key structural protein in plasma lipoproteins.
- Different apoB forms (apoB-100, apoB-48) exist in various species, with distinct roles in lipid transport.
- The presence and synthesis of apoB forms in avian species, particularly chicks, are not well-characterized.
Purpose of the Study:
- To determine if multiple apoB forms are present in chick plasma.
- To identify which apoB forms are synthesized in vitro by chick liver and intestine during development.
Main Methods:
- Isolation and analysis of plasma lipoproteins (d < 1.019 g/ml) from chicks.
- SDS-PAGE and immunoblotting to detect apoB forms.
- In vitro synthesis studies using [35S]methionine labeling of liver and intestinal slices from chick embryos and post-hatch chicks.
Main Results:
- Chick plasma exclusively contained apoB-100; apoB-48 was undetectable.
- Portomicrons, chick equivalents of chylomicrons, also contained only apoB-100.
- Chick liver synthesized apoB-100, while the intestine produced apoB-100 and a smaller form (similar to apoB-95), but no apoB-48.
Conclusions:
- The absence of apoB-48 in chick plasma is due to its lack of synthesis in the intestine.
- Chick intestine may lack the necessary molecular machinery for apoB mRNA editing to produce apoB-48.
- This study elucidates the specific apoB forms in chick lipoproteins and their tissue-specific synthesis.
Abstract:
This study was designed to investigate: a) whether multiple forms of apoB are present in chick plasma lipoproteins; and b) which forms of apoB are produced in vitro by liver and intestine at various stages of pre- and post-natal development. Plasma lipoproteins of d less than 1.019 g/ml, isolated from fasted and nonfasted chicks, contained exclusively the high molecular weight apoB form (apoB-100) that comigrated with human and rat apoB-100 on SDS-PAGE gel. No apoB-48 was detected either in overloaded Coomassie blue-stained gels or after immunoblotting. ApoB-100 but no apoB-48 was found in portomicrons, the triglyceride-rich lipoproteins equivalent to chylomicrons, that in the chick are transported via the porto-mesenteric venous system. To ascertain whether a minute amount of apoB-48 was present in chick plasma, [35S]methionine was injected intraduodenally and the 35S-labeled d less than 1.019 g/ml plasma lipoproteins were isolated 45 min later from the systemic and the porto-mesenteric circulation. Only apoB-100 was found to be labeled in these lipoproteins. Cholesterol feeding did not induce the appearance of apoB-48 in plasma despite a marked accumulation of cholesterol-rich d less than 1.040 g/ml lipoproteins in the plasma. In vitro synthesis of apoB forms was studied in liver and intestinal slices isolated from chick embryos (8 and 5 days before hatching), newly hatched chicks (2 and 7 days after hatching), and young chicks (21 days old) that were incubated in the presence of [35S]methionine. At each stage of development, liver slices secreted predominantly apoB-100. Intestinal slices of newly hatched and young chicks secreted two forms of apoB: apoB-100 and an additional form with an electrophoretic mobility similar to rat plasma apoB-95. No apoB-48 was synthesized or secreted by the intestine. Our results indicate that the absence of apoB-48 in chick plasma reflects the lack of synthesis of this peptide in the intestine. It is conceivable that in chick intestine the recently described molecular mechanism responsible for the co/posttranscriptional modification of apoB mRNA leading to the formation of apoB-48 is lacking or defective.