Molecular Cloning and Developmental Expression Patterns of the Striatin Gene Encoding A Member of the Regulatory Subunits for the Protein Serine/ Threonine Phosphatase-2A in Fish.

Purpose: The protein phosphatase-2A (PP-2A) is one of the most important serine/threonine phosphatases in eukaryotes. The holoenzyme of PP-2A consists of three subunits: a scaffold A subunit, a catalytic C subunit and a regulatory B subunit. While both A and C subunits are coded by two different genes, the B subunits exist in 26 or more isoforms which are encoded by at least 15 different genes. Previous studies have shown that besides regulating specific PP-2A activity, various B subunits may have other functions. To explore the possible roles of the regulatory subunits of PP-2A in vertebrate development, we have cloned the gene encoding goldfish striatin, a member of the B’” family regulatory subunits for PP-2A, and determined their tissue-specific and temporal expression patterns. Methods: The cDNA cloning was conducted with RT-PCR-based RACE. The mRNA expression levels for the goldfish striatin were analyzed with RT-PCR. The expression levels of the striatin protein from goldfish were determined with Western blot analysis. The semi-quantitation of the mRNA and protein expression levels was conducted with the software of U-scanning. Results: Our study revealed that the full length cDNA for striatin consists of 2965 bp coding for a deduced protein of 769 amino acids, which bears a very high level of amino acid sequence identity with the homolog protein from other species. The striatin mRNA is highly expressed in the kidney, to a less degree in brain, fin, muscle, liver, ovary and gill, and the lowest in testis and heart. Similar pattern of protein expression is detected in the above 9 tissues. During the development of goldfish, the striatin mRNA maintains a relatively high level at the 2-cell, multiple cell and blastula stages. Then, it drops down substantially at gastrula stage and fluctuates around this level in the next 8 different stages. At the protein level, the striatin maintained higher level from 2-cell to gastrula stages, then decreased at neurula and optic vesicle stages, and gradually increased again to peak at eye pigmentation stage, then slightly decreased in the next few stages of development. Conclusions: Our results suggest that the striatin may play an important role in regulating goldfish development and adult tissue homeostasis. While the former function may or may not occur through PP- 2A functions, the later function appears to occur via PP-2A activity.