Figure 2.

Genomic organization of neurexin genes. (a) Gene organization of mouse neurexins (nrxn) with exons (vertical lines) segregating introns (horizontal lines). The nrxn2 gene is 10 times smaller than nrxn1 or nrxn3 due to shorter introns but the relative positions of transcription starts for α-variants and β-variants (kinked arrows) are similar in all cases. Red numbers indicate alternatively spliced exons, while β-specific exons are in black. The first splice site (SS#1) accepts different inserts derived from combinations of two to four mini exons, whereas others such as SS#2 can also use parts of an insert sequence from one exon. (b) Vertebrate nrxn genes are up to 100 times longer than the single nrxn from invertebrates. The length ratio of Drosophila (dm nrxn) to mouse neurexins (ms nrxn) 2 and 3 is 1:10:100, respectively.