Cloning and expression of retinoblastoma-binding protein 4 gene in embryo diapause termination and in response to salinity stress from brine shrimp Artemia sinica.

Retinoblastoma binding protein 4 (RBBP4) is a nuclear protein with four WD-repeat sequences and thus belongs to a highly conserved subfamily of proteins with such domains. This retinoblastoma-binding protein plays an important role in nucleosome assembly and histone modification, which influences gene transcription and regulates cell cycle and proliferation. Artemia sinica (brine shrimp) undergoes an unusual diapause process under stress conditions of high salinity and low temperature. However, the role of RBBP4 in diapause termination of embryo development in A. sinica remains unknown. Here, the full-length cDNA of the As-rbbp4 gene was obtained from A. sinica and found to contain 1411 nucleotides, including a 1281 bp open reading frame (ORF), 63 bp 5'-untranslated region (UTR) and a 67-bp 3'-UTR, which encodes a 427 amino acid (48 kDa) protein. Bioinformatic analysis indicated As-RBBP4 to be mainly located in the nucleus, with a theoretical isoelectric point of 4.79. Protein sequence domain analysis showed that As-RBBP4 is a conserved protein, especially in the WD40 domain. No specificity in expression of this gene was observed in tissues or organs by in situ hybridization. Real-time quantitative PCR and Western blot analyses of As-RBBP4 gene and protein expression, respectively, showed notably high levels at 10 h and a subsequent downward trend. Obvious trends in upregulation of As-RBBP4 were observed under conditions of low temperature and high salinity stress. As-E2F1 and As-CyclinE also presented similar trends as that of As-RBBP4 in Western blots. Analysis of the RBBP4 expression in early embryonic development of A. sinica indicated that this protein plays an important role in diapause termination and cell cycle regulation.