Identification and characterization of a novel family of mammalian ependymin-related proteins (MERPs) in hematopoietic, nonhematopoietic, and malignant tissues

Evidence is presented for a family of mammalian homologs of ependymin, whic h we have termed the mammalian ependymin-related proteins (MERPs). Ependymi ns are secreted glycoproteins. that form the major component of the cerebro spinal fluid in many teleost fish. We have cloned the entire coding region of human MERP-1 and mapped the gene to chromosome 7p14.1 by fluorescence in situ hybridization. In addition, three human MERP pseudogenes were identif ied on chromosomes 8, 16, and X. We have also cloned the mouse MERP-1 homol og and an additional family member, mouse MERP-2. Then, using bioinformatic s, the mouse MERP-2 gene was localized to chromosome 13, and we identified the monkey MERP-1 homolog and frog ependymin-related protein (ERP). Despite relatively low amino acid sequence conservation between piscine ependymins , toad ERP, and MERPs, several amino acids (including four key cysteine res idues) are strictly conserved, and the hydropathy profiles are remarkably a like, suggesting the possibilities of similar protein conformation and func tion. As with fish ependymins, frog ERP and MERPs contain a signal peptide typical of secreted proteins. The MERPs were found to be expressed at high levels in several hematopoietic cell lines and in nonhematopoietic tissues such as brain, heart, and skeletal muscle, as well as several malignant tis sues and malignant cell lines. These findings suggest that MERPs have sever al potential roles in a range of cells and tissues.