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First published online June 26, 2009
Journal of Experimental Biology 212, 2176-2182 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.031377
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Rapid clearance of circulating protein by early chicken embryo blood cells

Guojin Wu and Zandong Li*

Department of Biochemistry and Molecular Biology, College of Biology Science and State Key Laboratory for Agrobiotechnology, China Agricultural University, No. 2, Yuanmingyuan West Road, Beijing 100193, China

* Author for correspondence (e-mail: lzdws{at}cau.edu.cn)

Accepted 16 April 2009

It has been speculated that free amino acids digested from proteins in bird eggs are transported to the circulation for the nourishment of the embryo. In the present study, we found that early chicken embryo protein in the serum might be utilized efficiently as a nutrient. Proteins injected into the blood of embryonic day 3 (E3) embryos were partially degraded and rapidly cleared. The rapid clearance of the injected proteins might be the result of efficient pinocytosis by blood cells, which then efficiently digested the intracellular proteins. An evaluation of the fluorescence intensity of injected fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) indicated that about half was taken up by the blood cells 80 min after injection. About 4 h after injection, most of the FITC-BSA was digested and the products were released into the serum, which implies that circulating blood cells may serve as a digestive system in early chick embryos. However, the endocytic activity of blood cells decreased after E5, and BSA may reside in the circulation with a longer half-life after E5. These results imply that blood cells would serve as a digestive system only in early embryos. In summary, the mechanism revealed here gives the early embryo the ability to make use of protein as a nutrient without prior digestion outside the embryo.

Key words: chicken embryo, amino acids, protein, blood cells, pinocytosis, digestion


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© The Company of Biologists Ltd 2009