Identification of Xenopus Cortactin: Two Isoforms of the Transcript and Multiple Forms of the Protein

Cortactin was initially identified as a substrate for Src tyrosine kinase. It interacts with the filamentous actin in the cell cortex through the tandem repeats of 37-amino acid. In this report, we describe the identification of a Xenopus homolog of cortactin. The deduced amino acid sequence shares over 70% identity with human, mouse, and chicken cortactin. Northern and Western blot analyses revealed that Xenopus cortactin is widely expressed in Xenopus tissues. Analysis of the transcripts using polymerase chain reaction revealed two isoforms being different in the number of the tandem repeats. The major isoform has 6.5 tandem repeats but the minor one has 5.5 tandem repeats. As the sixth repeat, which is missed in the minor isoform, is encoded by a single exon flanked by introns on both sides, these two isoforms are likely to be generated by alternative splicing. We propose that cortactin regulates the construction of actin cytoskeleton by altering the number of its tandem repeats.