Abstract
The human CD44 cell surface glycoprotein family which has been implicated in lymphocyte homing, tumor metastasis, and extracellular matrix attachment consists of a large number of related isoforms that derive from the differential splicing of a single CD44 gene transcript. Recent mapping of the CD44 locus in man indicated the presence of at least nine alternative exons within the region of the gene encoding the variable membrane proximal extracellular domain. Here we report the identification of a 10th alternative exon (termed V1) in the mouse, human, and rat CD44 genes. We demonstrate tissue-specific patterns of expression for transcripts containing exons V1-V10 in the mouse and a highly restricted usage of exon V1 in transcripts from mouse gastric tissue. Close sequence homology between exons V1-V10 from mouse rat and human points to a specific functional role rather than a purely structural role for the membrane proximal extracellular domain of the CD44 molecule.
Highlights
Pgp-1 (CD44) Homing Receptor not yet clear hothwe apparent affinityof CD44 for these matrix components relates to lymphocyte trafficking
The human CD44 cell surface glycoprotein family which has been implicated in lymphocyte homing, tumor metastasis, and extracellular matrix attachment consists of a large numberof related isoforms that derive from the differential splicing of a single CD44 gene transcript
For Southern blotting, mouse PCR products were transferred to ni-. trocellulose (HybondC Extra, Amershamplc., United Kingdom)and the filters were hybridizedwith the 32P-end-labeledalternative exon probes Fvl-FvlO or with the "universal" probe FvOb located immediately upstream of the mouse CD44 insert site(see Fig. 1).Blots were washed a t 5 "C below the calculated thermal melting point (6 X SSC) for 15 min prior to autoradiography
Summary
Each exon is named according to the variable exon location and the forward (F)or reverse (R) orientation. In all cases the primers refer to mouse sequences except where indicated otherwise. Following digestiown ith the relevant restriction enzymes, the amplified products were cloned into pUC18 and recombinant clones identified by PCR of single bacterial colonies. Part of the human exonV1wassequencedfrom a PCR product generated from the genomicclonep44.19 [18] using the conserved mouse V1 primer Fvl and the human V2 primer Rv2human. For Southern blotting, mouse PCR products were transferred to ni-. Trocellulose (HybondC Extra, Amershamplc., United Kingdom)and the filters were hybridizedwith the 32P-end-labeledalternative exon probes Fvl-FvlO or with the "universal" probe FvOb located immediately upstream of the mouse CD44 insert site(see Fig. 1).Blots were washed a t 5 "C below the calculated thermal melting point (6 X SSC) for 15 min prior to autoradiography For Southern blotting, mouse PCR products were transferred to ni-. trocellulose (HybondC Extra, Amershamplc., United Kingdom)and the filters were hybridizedwith the 32P-end-labeledalternative exon probes Fvl-FvlO or with the "universal" probe FvOb located immediately upstream of the mouse CD44 insert site(see Fig. 1).Blots were washed a t 5 "C below the calculated thermal melting point (6 X SSC) for 15 min prior to autoradiography
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