Cell communication, cell union, and initiation of meiosis in ciliate conjugation

Sexual cell cycle initiation is regulated by CDK19 and CYC9 in Tetrahymena thermophila

To investigate the mechanisms underlying initiation of the sexual cell cycle in eukaryotes, we have focused on cyclins and cyclin-dependent kinases (CDKs) in the well-studied model ciliate, Tetrahymena thermophila We identified two genes, CDK19 and CYC9, which are highly co-expressed with the mating-associated factors MTA, MTB and HAP2. Both CDK19 and CYC9 were found to be essential for mating in T. thermophila Subcellular localization experiments suggested that these proteins are located at the oral area, including the conjugation junction area, and that CDK19 or CYC9 knockout prevents mating. We found that CDK19 and CYC9 form a complex, and also identified several additional subunits, which may have regulatory or constitutive functions. RNA sequencing analyses and cytological experiments showed that mating is abnormal in both ΔCDK19 and ΔCYC9, mainly at the entry to the co-stimulation stage. These results indicate that the CDK19-CYC9 complex initiates the sexual cell cycle in T. thermophila.

Identification, characterization, and complete amino acid sequence of the conjugation-inducing glycoprotein (blepharmone) in the ciliate Blepharisma japonicum

Conjugation in Blepharisma japonicum is induced by interaction between complementary mating-types I and II, which excrete blepharmone (gamone 1) and blepharismone (gamone 2), respectively. Gamone 1 transforms type II cells such that they can unite, and gamone 2 similarly transforms type I cells. Moreover, each gamone promotes the production of the other gamone. Gamone 2 has been identified as calcium-3-(2'-formylamino-5'-hydroxy-benzoyl) lactate and has been synthesized chemically. Gamone 1 was isolated and characterized as a glycoprotein of 20-30 kDa containing 175 amino acids and 6 sugars. However, the amino acid sequence and arrangement of sugars in this gamone are still unknown. To determine partial amino acid sequences of gamone 1, we established a method of isolation based on the finding that this glycoprotein can be concentrated by a Con A affinity column. Gamone 1 is extremely unstable and loses its biological activity once adsorbed to any of the columns that we tested. By using a Con A affinity column and native PAGE, we detected a 30-kDa protein corresponding to gamone 1 activity and determined the partial amino acid sequences of the four peptides. To isolate gamone 1 cDNA, we isolated mRNA from mating-type I cells stimulated by synthetic gamone 2 and then performed rapid amplification of cDNA ends procedures by using gene-specific primers and cloned cDNA of gamone 1. The cDNA sequence contains an ORF of 305 amino acids and codes a possibly novel protein. We also estimated the arrangement of sugars by comparing the affinity to various lectin columns.

Polypeptides during early conjugation in Tetrahymena thermophila

As Tetrahymena thermophila cells differentiate from their vegetative life cycle to sexual reproduction, their polypeptide pattern undergoes a series of changes. These changes have been traced in extracellular, cellular, and subcellular compartments. The first alteration is induced by the nutritional shift-down and results in stimulation of at least one ciliary polypeptide and affects a series of polypeptides from other compartments. The second alteration is induced by mixing starved cells of complementary mating types and this stimulates the synthesis of nine ciliary polypeptides before pairs have formed and eight afterwards. At least five of these early and one of the late conjugation-related ciliary polypeptides are removed by low concentrations of EDTA, indicating that they are located on the external side of the plasma membrane. No differences were observed between polypeptides excreted during starvation and after mixing of complementary mating types. At Tris concentrations restrictive for conjugation, cilia lack the conjugation-related polypeptides. Some of these are instead found among the excreted polypeptides. Using O'Farrell gels and silver staining on isogenic cells of all possible mating types, we have been unable to correlate changes in polypeptide patterns to specific mating types.

Stage-specific changes in protein synthesis during conjugation in Tetrahymena thermophila

Conjugation in the free-living ciliate Tetrahymena thermophila is an inducible developmental system which results in a synchronized reorganization of the genetic material in both mates of a pair. The cytological events were followed by Feulgen stainings of simultaneously mating cells and protein synthesis was revealed using [35S]methionine pulse labelling and two-dimensional gel electrophoresis. At least 33 proteins, including 24 conjugation-specific proteins, with apparent molecular weights (Mr) between 61 and 200 X 10(3) are stimulated during conjugation. Two slightly acidic proteins (Mr 89 and 73 X 10(3), respectively) are stimulated shortly after mixing of mating-competent cells and mainly before tight pairs are formed. Ten proteins are stimulated during meiosis, and two of these (Mr 90 and 78 X 10(3), respectively) are particularly interesting, since they are highly stimulated and more basic (pI values around 8.5) than most other proteins detected. Twelve proteins are stimulated essentially between pairing and early macronuclear development, three are stimulated from shortly before zygote formation and during the post-zygotic divisions, and six are stimulated during late conjugation, at various parts of macronuclear development. The functions of the conjugation-stimulated proteins are discussed.