MG160, A MEMBRANE-PROTEIN OF THE GOLGI-APPARATUS WHICH IS HOMOLOGOUS TO A FIBROBLAST GROWTH-FACTOR RECEPTOR AND TO A LIGAND FOR E-SELECTIN,IS FOUND ONLY IN THE GOLGI-APPARATUS AND APPEARS EARLY IN CHICKEN-EMBRYO DEVELOPMENT

While over 20 intrinsic proteins of the Golgi apparatus have been iden tified and sequenced, there is no information on their developmental h istory, i.e., whether all Golgi proteins are expressed simultaneously or whether there is a hierarchical or stage-specific order of their ex pression during embryonic development. In this study we have examined the emergence and distribution of MG160 during the development of chic ken embryos. MG160 is a conserved membrane sialoglycoprotein of the Go lgi apparatus of most cells displaying over 90% amino acid sequence id entities with two apparently unrelated molecules, namely CFR, a chicke n fibroblast growth factor receptor, and ESL-1, a ligand for E-selecti n (Gonatas et al., J. Biol. Chem. 1989, 264, 646-653; Burrus and Olwin , J. Biol. Chem. 1989, 264, 18647-18653; Burrus et al., Mol. Cell Biol . 1992, 12, 5600-5609; Gonatas et al., J. Cell Sci. 108, 457-467; Stee gmaier et al., Nature 1995, 373, 615-620). This study was carried out by in situ hybridization, using a 56-mer antisense probe for the chick en homologue of MG160 which differs only by four bases from the corres ponding segment of the rat cDNA and by immunocytochemistry and Western blotting using a polyclonal antiserum against MG160. The protein was ubiquitously and exclusively localized in the Golgi apparatus and appe ared early in development within the ectoblast and primitive endoblast prior to the formation of the primitive streak. At 2 to 3 days, MG160 was particularly prominent in the notochord, neural tube, somites, an d cartilage cells. In organs with central lumens, such as the neural t ube, the Gels apparatus, visualized by immunostaining for MG160, was e longated and it was located at the apical pole of cells. In 6-day-old embryos, the ongoing physiologic degeneration of the notochord was acc ompanied by fragmentation of the immunostained Gels apparatus and decr eased labeling of the mRNA for MG160. In order to gain information on possible interactions between MG160 and basic fibroblast growth factor (bFGF), the localization of both molecules was studied by immunocytoc hemistry in 3-day-old chicken embryos. While MG160 was ubiquitous in t he Golgi apparatus of all cells and tissues, endogenous bFGF was not d etected, while exogenous bFGF bound only to basement membranes. These results indicate that MG160 is a primordial protein of the Golgi appar atus and are consistent with the hypothesis that the binding of MG160 to fibroblast growth factors and E-selectin is not related to the stil l unknown principal function of MG160 in the Golgi apparatus. (C) 1995 Academic Press Inc.