t-complex-associated embryonic surface antigen homologous to mLAMP-1. II. Expression and distribution analyses.

We have previously demonstrated that a mouse t-complex-associated antigen (ESGp) is present on the cell surface, specifically at areas of cell-cell contact, of cleavage stage embryos and embryonal carcinoma cell lines. In the accompanying paper, we document isolation, purification, and partial sequencing of this molecule. Amino-terminal and internal peptide fragments are highly homologous to the mouse lysosomal-associated membrane protein-1 (mLAMP-1). We also demonstrate considerable similarity, though not necessarily identity, between these two antigens through both biochemical and molecular analyses. In this report we use immunological techniques to compare the expression and distribution of these antigens in various cell lines as well as mouse tissues and preimplantation stage embryos. The data presented indicate that there are: (1) different antigenic forms of the ESGp/ mLAMP-1 homologues and (2) changes in the molecular composition and expression of these forms during embryogenesis and differentiation. It is obvious from these studies that mLAMP-1 is not strictly a static molecule whose sole function is to protect the lumenal side of the lysosomal membrane but rather is a dynamic molecule of potential import in many other cellular and organismal functions.