Identification and tissue-specific expression of a novel isoform of Semaphorin 3D.

Background: Semaphorins are a family of secreted and membrane-associated proteins involved in axon guidance in the developing brain as well as morphogenesis in various organs. There has been no report on the expression of different transcripts of the genes encoding Class 3 Semaphorins with different protein structures.

Methods: Molecular cloning of rat Semaphorin 3D gene and the expression analysis at gene and protein levels were performed.

Results: We have isolated two cDNAs encoding rat Sema 3D, a Class 3 Semaphorin. One clone is predicted to encode a protein with a structure common to Class 3 Semaphorins. The other clone encodes a novel isoform of Sema 3D lacking half of the C2-type Ig domain and the entire basic region; this isoform is predicted to have a different structure from Class 3 Semaphorins. Analysis of protein expression using a cell culture system revealed that this splice variant isoform is not secreted into the media, whereas the classical Class 3 isoform is a secreted protein. The expression of each isoform shows tissue-specificity.

General Significance: Our present findings suggest that gene regulation, via an alternative splicing mechanism, affects not only the tissue-specificity of Sema 3D expression, but also the distance over which it can act.