Members of the tumor necrosis factor receptor TNFR) superfamily are type I membrane proteins which share homology in their extracellular domain ECD), containing three to six cysteine-rich repeats CRRs) of approximately six cysteines each Ware et al. 1996). They trigger a pleiotropic range of responses, from apoptosis and differentiation to proliferation. Generally, they are not related in their cytoplasmic regions, but WSL DR3, Apo3, TRAMP, LARD, TR3, TNFRSF12) is one of six TNFR family members TNFR1, CD95/FAS, DR4, DR5, and DR6) with additional homology in the cytoplasmic ªdeath domain, º through which these receptors trigger apoptosis Itoh et al. 1991; Tartaglia et al. 1993). WSL, like TNFR, recruits TNFR1-associated death domain protein TRADD) and Fas-associated death domain-containing protein Bodmer et al. 1997; Chinnaiyan et al. 1996; Kitson et al. 1996) as downstream effectors of apoptosis. WSL also recruits TRAF2 via TRADD

Kitson et al. 1996; Marsters et al. 1996), and thus activates NF-кB, which induces the transcription of a number of immune genes Hunter and Karin 1992). Definition of WSL function is likely to be complicated by the presence of at least 13 splice variants Kitson et al. 1996; Screaton et al. 1997; Warzocha et al. 1998). We report here the isolation of the mouse homologue of human WSL, defining and comparing the genomic structure, chromosome location, tissue expression, and splice variants of human and mouse WSL. A full-length hWSL-1 cDNA was used to screen a 129Sv mouse genomic library in the EMBL3A vector Frischauf et al. 1983). The probe was labelled with 32P-dCTP; screening and purification were performed by standard methods Sambrook et al. 1989). A single clone, identified from 8 105 plaques, was mapped and fragments subcloned into pBluescriptII KS+/±). A lack of signals from 59 hWSL probes precluded detailed mapping of the 59 end of the mouse gene. As an alternative approach, sequencing of cloned RTPCR products from thymic cDNA was used to identify exon: intron boundaries by known splice junctions Table 1). The coding part of the gene spanned 5 kb with ten exons Fig. 1A). Rapid amplification of cDNA ends-PCR and sequencing were used to define the less homologous leader and 59 region of the gene data not shown).