关键词: 梅花鹿, 激活素A, 颗粒细胞, 真核表达, 蛋白纯化

Abstract:

【Objective】The objective of this study was to investigate the eukaryotic expression and biological activity of recombinant Cervus Nippon Activin A protein, which would provide an experimental basis for further clarification on the physiological function of Activin A in the maturation of the oocytes of Cervus Nippon. 【Method】 The full length cDNA of Activin βA (ACTBA) gene was acquired by RT-PCR (Reverse Transcription-Polymerase Chain Reaction) technology. Bioinformatics tools were used to determine the characteristics of Activin βA sequence. The homologous sequences of Activin βA from other species were downloaded from NCBI, the deduced amino acid sequence of Activin βA was aligned by using the Clustal X (1.83) software, and the phylogenetic tree was constructed by using MEGA 4. Recombinant plasmids of pcDNA4/ACTBA were constructed, and then transfected into CHO cells to express target proteins in vitro. Target proteins were detected by Immunofluorescence technology and Western blot technology, and then purified by Ni-NTA affinity chromatography column. The effects of the treatment of purified Cervus Nippon Activin A on the phosphorylation of SMAD2 and SMAD3 proteins in porcine granulosa cells were investigated through Western blot, as well as the expression levels of steroid hormone-related enzymes in porcine granulosa cells treated with recombinant Cervus Nippon Activin A were detected by real-time PCR and Western blot. 【Result】 The Cervus Nippon Activin A was cloned, which contained 1 278 bp, encoding 426 amino acids. The homology comparison showed that the sequence of ACTBA gene in Cervus Nippon had the highest 98.4% identity with that in cattle. Phylogenetic analysis showed that it had the closest relationship with that in Bos taurus and Capra hircus. The data through endonuclease digestion, PCR and DNA sequencing showed the eukaryotic expression plasmid was constructed successfully. Immunofluorescent results showed that this plasmid expressed in CHO cells successfully, and Activin A protein mainly presented in the cytoplasm of CHO cells. Western blot data showed that the protein molecular weight of precursor Activin A was about 58 kD. Treatment with the purified recombinant mature Activin A through nickel affinity chromatography triggered the phosphorylation of SMAD2 and SMAD3 proteins in porcine granulosa cells, indicating that the functional Activin A could activate the SMAD signaling pathway. Treatment of primary porcine granulosa cells with mature Activin A increased the mRNA and protein levels of P450 aromatase and decreased the mRNA and protein levels of steroidogenic acute regulatory protein (StAR). Meanwhile, the treatment of mature Activin A also enhanced FSHR mRNA levels and decreased LHR mRNA levels in primary pig granulosa cells. Whereas it did not alter the mRNA levels of P450 side chain cleavage enzyme and 3β-hydroxysteroid dehydrogenase in porcine granulosa cells. Thus, the recombinant protein of Cervus Nippon Activin A could enhance the biological effects of FSH in granulosa cells, and attenuate biofunctions of LH in granulosa cells. 【Conclusion】 The eukaryotic expression vector of Activin A protein was successfully constructed in our study. The recombinant Activin A protein had high purity and bioactivity, which provided a foundation for further study of the biological functions and physiological mechanisms of Activin A．

Key words: Cervus nippon, Activin A, granulosa cells, eukaryotic expression, protein purification