Novel expression of importin α homologue in marine teleost, Pagrus major

Importin α proteins are critical modulators of the classical nuclear protein import pathway. Although the physiological roles of importin α have been extensively studied in invertebrates and mammals, very little is known about their counterparts in lower vertebrates. In this study, to elucidate the roles of importin α in a teleost species, we isolated and characterized red seabream (Pagrus major) importin α cDNA derived from ovary and found changes in the mRNA levels of importin α in male and female red seabream during sexual maturation. The 1846-bp cDNA encodes a 520 amino acid protein that includes the importin β-binding domain, a short acidic domain, and an armadillo (arm) repeat domain. Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) showed transcription of red seabream importin α in testis and ovary but not in the other tissues. The importin α mRNA levels in males increase in association with testicular development, whereas those in females remain high throughout sexual maturation. These findings suggest that red seabream ovary-derived importin α may be controlled in a tissue-specific manner and may perform unique functions in the gonad in addition to its involvement in nuclear transport.