Analysis The Function Of Cyc17 Cyclins In Meiosis Of Tetrahymena Thermophila

Cyclins can activate the cyclin-dependent kinase(Cdks) and form a Cyclin-Cdk complex which can control the cell cycle. There are 8 Cyclin family proteins(from A to H) in higher eukaryotes. Each Cyclin family includes several cyclins and different Cyclins play different roles in cell cycle progression. They have different amino acids composition but share a conserved 100 amino acids region which called Cyclin box. Of which Cyclin A Can form a complex with Cdk2 or Cdc2(Cdk1), respectively. And promote the cell cycle into the S phase and M phase.Cyclin A1 is included in the Cycling A family. It is a highly expressed protein in the mammalian testis. Reserchers knocked out the Ccna1 in mouse,it made the male mouse become sterility. And they found Cyclin A1 was only expressed in mouse meiotic testis. This indicated that Cyclin A1 has a key role in meiosis.The ciliated protozoan Tetrahymena thermophila is a unicellular eukaryote. It has a well-regulated cell cycle progression and very complex nuclear development process in its sexual reproduction. So it is an ideal model organism to study the function of cyclins in cell cycle progression. Under nutritional conditions, Tetrahymena thermophila cells undergo asexual reproduction, but the starvation treatment will induce the conjugation(sexual reproduction of ciliate) betweent two Tetrahymena thermophila cells that have different mating types. The sexual reproduction of Tetrahymena thermophila includes meiosis and mitosis, and what's the Cyclins function in the meiosis? We don't know clearly. In this study, we investigated the functions of one of the conjugation-specific expressed Cyclins(Cyc17) in Tetrahymena thermophila meiosis. We obtained the flowing results: 1. Bioinformatics analysis of Tetrahymena thermophila Cyc17 geneWe investigated the Cyc17 gene from the Tetrahymena Genome Database(TGD, http://ciliate.org/).It is 1820 bp in full length, wherein the coding sequence has 1558 bp long and encodes 519 amino acids with the predicated molecular weight of 61.2KD. By BLAST search, we found that Tetrahymena thermophila Cyc17 has high sequence similarity with Cyclin A1 in other species and contains a conserved N-terminal and C-terminal domain. So the Cyc17 gene is be homologue with Cyclin A1. By searching the mRNA expression profile of Cyc17 in TetraFGD(http://tfgd.ihb.ac.cn/),we found that Cyc17 has no expression vegetative growth and starvation, but it is highly expressed in conjugation, especially 6hrs after mixing.So we speculated that Cyc17 gene has a pivotal function in meiosis of Tetrahymena thermophila. 2. Konck-out the Cyc17 gene in Tetrahymena thermophilaTetrahymena thermophila strains CU427 and CU428 serve as wild type strains for knocking-out. After we get the ?Cyc17 strains with different mating types,we starved them and mixed them equally, then observed their nuclear development during meiosis. The wild type strains serve as a control. By using DAPI staining,we found that the ?Cyc17 cell strains unable to finish the meiosis process. However, the fluorescence in situ hybridization experiment indicated that the meiotic homologous recombination was accomplished in ?Cyc17 cell strains.By Gimesa staining, we found that the MIC nuclear development arrested in the Diakinesis-Metephase I.At last, we found there is no viable cells in sexual progeny of ?Cyc17 cells.In this study, we fist knocked out the Cyc17 gene and preliminarily revealed the function of this cyclin inTetrahymena thermophila meiosis. This will serve as an important resources for the subsequent research.