Structure and function of SMOC-1 and SMOC-2, two novel calcium-binding proteins associated with basement membranes

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We have isolated two novel genes encoding secreted modular proteins containing a calcium-binding domain that are structurally related to the BM-40 protein family and were termed SMOC-1 and SMOC-2. Recombinant expression in eucaryotic cells showed that both proteins are glycoproteins with a calcium-dependent conformation. Results from northern blots, RT-PCR and immunoblots demonstrated a widespread expression in many tissues. Immunofluorescence studies and immunogold electron microscopy with an antiserum directed against SMOC-1 revealed, that the protein is an integral component of basement membranes although it is not a constitutive basement membrane protein. In the ovary, basement membranes around follicles are devoid of SMOC-1, here the protein is located in the zona pellucida surrounding the oocyte. We will analyse the expression pattern of SMOC-2 in similar detail as done for SMOC-1. In addition, we will investigate the spatio-temporal expression of both proteins during embryonal development and identify their cellular origin. Recombinant proteins will be used to identify binding partners in interaction studies. The relevance of in vitro interactions will be verified by colocalization studies. Involvement of SMOC-1 and SMOC-2 in cellular processes will be addressed by different in vitro assays concerning fertilization, cell adhesion and cell migration. At a later stage of the project, the domains responsible for interactions or cellular functions will be mapped by the use of recombinant fragments. Mice deficient in either SMOC-1 or SMOC-2 will be generated and analyzed.