Cloning and chromosomal mapping of a gene isolated from thymic stromal cells encoding a new mouse type II membrane serine protease, epithin, containing four LDL receptor modules and two CUB domains

We cloned and sequenced a mouse gene encoding a new type of membrane bound serine protease (epithin) containing a multidomain structure. The initial c DNA clone was found previously in a polymerase chain reaction (PCR)-based s ubtractive library generated from fetal thymic stromal cells. and the messa ge was shown to be highly expressed in a thymic epithelial nurse cell line. A clone isolated from a severe combined immunodeficiency (SCID) thymus lib rary and extended to its full length at the 5' end with the RACE technique contains an open reading frame of 902 amino acids. Based on the sequence of this clone, the predicted protein structure is a type II membrane protein with a C-terminal serine protease domain linked to the membrane by four low density Lipoprotein receptor modules and two CUB domains. High message exp ression by northern blotting was detected in intestine, kidney, lung, SCID, and Rag-2(-/-) thymus, and 2-deoxyguanosine-treated fetal thymic rudiment, but not in skeletal muscle, liver, heart, testis, and brain. Sorted MHC cl ass II+ and II- fetal thymic stromal cells were positive for expression by reverse transcriptase-PCR, whereas CD45(+) thymocytes were not. Tnt: gene w as found in chicken and multiple mammalian species under low stringency Sou thern hybridization conditions. Under high stringency conditions, only a si ngle gene per haploid genome was identified in the mouse. This gene, Prss14 (protease, serine, 14), was mapped to mouse chromosome 9 and is closely li nked to the Fli1 (Friend leukemia integration 1) gene.