Expression and alternative splicing of PLXNB3 in adult human tissues. (A), expression analysis of PLXNB3 in adult human tissues by poly(A)+ mRNA northern blot. (B), the blot was stripped and reprobed with β-actin probe. Molecular weight in kb is indicated at the left side. (C-E), tissue distribution of three isoforms of PLXNB3 due to alternative splicing of the 3'- part of exon 27. Fragments were amplified by RT-PCR using a common forward primer and isoform-specific reverse primers. Fragment sizes (bp) are given on the right. ΦX174 DNA cleaved by HaeIII was used as size standard. (C), 698 bp fragment containing full length exon 27. (D), 536 bp fragment lacking the 3'-terminal part of exon 27 and coding for a C-terminally truncated B3. (E), 356 bp fragment lacking (in-frame) 246 bp of exon 27. (F-H), possible protein structures of B3 predicted by mRNA isoforms generated through alternative splicing of exon 27. (F), full length isoform; (G), C-terminally truncated B3 predicted by the isoform shown in D; (H), structure of the B3 isoform lacking 246 bp of exon 27 (missing 83 amino acids marked by arrow) as shown in E. SP, signal peptide; Sema, semaphorin domain; MRS, Met-related sequences; IPT, immunoglobulin-like fold shared by plexins and transcription factors; TM, transmembrane domain; SP1/SP2, two different parts of the sex plexin domain.