Transport of serum transthyretin into chicken oocytes. A receptor-mediated mechanism.
Transthyretin (TTR) is involved in the transport of thyroid hormones and, due to its interaction with serum retinol-binding protein, also of vitamin A. The importance of both ligands in vertebrate embryonic development has prompted us to investigate the molecular details of TTR transport function in a powerful germ cell system, the rapidly growing chicken oocytes. Yolk TTR is derived from the circulatory system, since biotinylated TTR was recovered by immunoaffinity chromatography of yolk obtained from a hen previously infused with in vitro biotinylated chicken serum proteins. In concordance with the intraoocytic localization in an endosomal compartment, ligand blotting and chemical cross-linking experiments revealed the presence of a approximately 115-kDa TTR-binding oocyte membrane protein. This putative TTR receptor was not detected in chicken ovarian granulosa cells or embryonic fibroblasts and was different from the previously described oocyte-specific receptor for two estrogen-induced chicken serum lipoproteins, vitellogenin and very low density lipoprotein (Barber, D. L., Sanders, E. J., Aebersold, R., and Schneider, W. J. (1991) J. Biol. Chem. 266, 18761-18770). Furthermore, in contrast to the serum levels of the yolk precursor lipoproteins, those of TTR were not significantly changed by estrogen; thus, TTR represents a newly defined, estrogen-independent class of yolk precursor proteins. These data strongly suggest that oocytic TTR is derived from the circulation, where it is a constitutive component, and deposited into yolk as a result of endocytosis mediated by a specific receptor.
Department of Molecular Genetics, University and Biocenter, Vienna, Austria.
A V
AV
Vieira
E J
EJ
Sanders
W J
WJ
Schneider
D000818:Animals; D001692:Biological Transport; D001710:Biotin; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D002846:Chromatography, Affinity; D004530:Egg Yolk; D004591:Electrophoresis, Polyacrylamide Gel; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006107:Granulosa Cells / Q000378:metabolism; D008297:Male; D009865:Oocytes / Q000378:metabolism*; D009928:Organ Specificity; D010058:Oviposition; D011228:Prealbumin / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D017457:Receptors, Albumin / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*
D011228:Prealbumin; D017457:Receptors, Albumin; C091986:transthyretin receptor; D004958:Estradiol; D001710:Biotin