Figure 3.

Expression of an insert at splice site 4 in neurexin-1 islet transcripts. A, Schematic representation of splice insertions in neurexin gene family members. A total of five alternative exons have been described in the neurexin-1 gene. An insert at splice site 4 is known to promote the formation of inhibitory synapses. The laminin-neurexin-SHBG (LNS) domains are extracellular. B, Τo determine whether neurexin transcripts in human islets (Isl) and rat-derived INS-1 (Ins) β-cells contain an insert in splice site 4, primers were designed to either flank or sit on this insert. PCR was performed using cDNA from either human islets or INS-1 cells and either rat or human brain (Br). Transcripts with an insert at splice site 4, but not ones lacking, were detected in both human islets and INS-1 cells. As expected, neurexin-1 transcripts both with and without an insert at site 4 were detected in rat brain. In contrast, in human brain, human islets and INS-1 β-cells, only transcripts containing an insert at splice site 4 were detected. −, Absence of insert; EGF, epidermal growth factor domain; Nt, no template; +, presence of insert.