Molecular cloning and expression of cDNA coding for four spliced isoforms of casein kinase Iα in goldfish oocytes

Casein kinase I (CKI) is a member of the serine/threonine protein kinases and located in a separate group within the superfamily of eukaryotic protein kinases. CKI isoforms regulate several checkpoints of the cell cycle and meiosis. In higher eukaryotes, CKIα has four isoforms produced through the alternative splicing of two short inserts. Here, we report the cloning, sequencing and expression of four alternatively spliced isoforms of CKIα from goldfish ovary. The cloned cDNAs were 2099-3002-bp long and classified as CKIα, CKIαS, CKIαL and CKIαLS. It was revealed that two major (3.0 and 2.0 kb) messages were strongly expressed in the ovary. Four isoforms are expressed in previtellogenic to vitellogenic oocytes. In the huge nucleus of the oocyte, referred to as the germinal vesicle, CKIαS is dominant and CKIαL is expressed at a detectable level. Immunoblot analysis revealed that CKIα and CKIαS are major products in both immature and mature oocytes. These two isoforms were expressed in a tissue-dependent manner.