A portion of of exon 3 and all of exons 4 through 6 were replaced by homologous recombination with a neo cassette in the opposite orientation of the endogenous gene. These exons encode the last 126 amino acids of the 201 amino acid long extracellular domain. RT-PCR of spleen and bone marrow indicated no transcript was present in mutant mice; in contrast, mRNA expression of Tnfsf12 and Senp3 (which flank within ~1 kb) in spleen was normal. (J:88910)