Intra- and intergeneric mating behaviour of ascosporogenous yeasts I. Quantitative analysis of sexual agglutination

When respective opposite mating types of the heterothallic yeastsare mixed, remarkable sexual agglutination occurs. This is consideredto be indispensable for the subsequent cell fusion and karyogamy.Based on the Duysens's findings (1956) that the heterogeneousdistribution or localization of pigment in particles causedto flatten their absorption spectrum, we developed the followingequation to express the intensity of agglutination: I/flattening coefficient (designated agglutination index, A.I.) expresses mean value of aggregateradii as a parameter to express agglutination intensity. TheA.I. is easily measurable with a spectrophotometer. The bestfit of k with the experimental values was calculated with acomputer. The other parameter to express the intensity of agglutination,mean cell number per aggregate (N?), was roughly estimated bythe equation, The analysis of this parameter supported the above relationship between A.I.and . The approximations of the relationship between A.I. and are also presented and their validity is discussed. ¹ A part of this work was reported in Japanese in Ref. (24). (Received June 9, 1978; )     

Mating reaction inSaccharomyces cerevisiae VIII. Mating-type-specific substances responsible for sexual cell agglutination

The agglutination factors ofa and α mating types ofSaccharomyces cerevisiae were solubilized from isolated cell-wall fractions by treatment with snail enzyme (Glusulase) and shown to be adsorbed specifically by cells of the opposite mating type, resulting in the loss of agglutinability of these cells. The agglutination factors ofa and α types adsorbed by cells of the opposite mating type at pH 5.5 were eluted at pH 9.0. These factors were further purified on Sepharose 4B. From the elution pattern on Sepharose 4B, the molecular weights of the solubilized agglutination factors are estimated to be about one million. Thus purified agglutination factors contained carbohydrate and protein and were considerably resistant to heat treatment. Neutral protease ofBacillus subtilis inactivated botha and α type agglutination factors. Trypsin inactivated the α type agglutination factor only.     

Structural basis of cell-cell interactions in the immune system

During the past year, advances in our understanding of receptor-ligand interactions between opposing cell surfaces have occurred at a structural level. These include adhesion involving CD2-CD58, antigen-specific T-cell receptor interactions with peptides bound to major histocompatibility complex molecules (both pMHCI and pMHCII), the CD8alphaalpha co-receptor-pMHCI interaction and the binding of two distinct classes of natural killer receptors to self-MHC ligands.     

The release of sex-specific substances responsible for sexual agglutination from haploid cells of Saccharomyces cerevisiae

Cell surface substances responsible for sexual cell agglutination were successfully released in a large quantity from heterothallic haploid cells of Saccharomyces cerevisiae by a newly established autoclaving method. The conditions for this releasing phenomenon were examined. The sexual agglutination substances were solubilized most efficiently when the cells, suspended in a 30 mM Tris-HCl, pH 7.0, 5 mM EDTA solution, were autoclaved at a pressure of 1 kg/cm² at 120 °C for 3 min. The substances were specifically adsorbed by the cell surface of the opposite mating type, resulting in the masking of agglutinability of the cells of the opposite mating type. The substances were not released from the surface of cells which lacked sexual cell agglutination. The evidence suggesting the formation of a molecular complex between a- and α-agglutination substances in vitro is also presented. The above procedure is applicable to the solubilization of surfage agglutination substances from various strains of S. cerevisiae.     

Regulation of the production of the agglutination substances responsible for sexual agglutination in Saccharomyces cerevisiae: Changes associated with conjugation and temperature shift

Summary Isolated zygotes showed self-agglutination caused by the sex-specific glycoproteins, the agglutination substances responsible for sexual agglutination. The agglutination substances of both a and mating types were detected in the extracts obtained by the autoclave method from zygotes. Although the first diploid daughter cells from zygotes showed self-agglutinability, the self-agglutinability decreased gradually in the successive diploid daughter cells. The self-agglutination in diploid cells was also brought about by the complementary binding of the sex-specific agglutination substances of opposite mating types.The constitutive sexual agglutinability in a and cells was lost with concomitant loss of the agglutination substances in both cell wall and cytoplasmic fractions when cultured at a temperature higher than 35°C.The repression of the production of the agglutination substances was reversed by the opposite mating type pheromones even at the repressive temperature, 36°C, associated with the appearance of sexual agglutinability. The sex pheromones, a substance-I and substance-I, and the binding substance for substance-I were produced even at 36°C, repressive for the production of the agglutination substances.     

A colour reaction for the differentiation of ascomycetous and hemibasidiomycetous yeasts

Seventy yeast strains, representative of twenty-six ascogenous genera, four saprobic hemibasidiomycetous genera and thirteen genera of the Cryptococcales were tested for their reaction with the stabilized aromatic diazonium compound, Diazonium Blue B salt. An aqueous, buffered solution of this compound gave a characteristic red colouration with the colonies of the hemibasidiomycetous species and those Cryptococcales characterized by the hemibasidiomycetous cell-wall type. The characteristic colour reaction was not observed with colonies of either the ascomycetous yeasts or those Cryptococcales characterized by the ascomycetous cell-wall type.The possible taxonomic use of the colour reaction with Diazonium Blue B salt as an affinitive characteristic is discussed.     

Developmental plasticity in neural circuits controlling birdsong: sexual differentiation and the neural basis of learning.

In many species of passerine songbirds, males learn their song during defined periods of life. Female song is often reduced or absent, as are the brain regions controlling song. Sexual differences in the brain arise because of the action of sex steroids, which trigger the formation of some neural pathways (especially the pathway from the higher vocal center to the robust nucleus) and prevent the atrophy of others in males. These neural changes occur during periods of developmental song learning and can recur during periods of learning in adult birds. The process of learning is correlated with major increases or decreases in the numbers of neurons in specific neuronal populations, suggesting that the formation or loss of specific neural pathways regulates the ability to learn. Species differences in sexual differentiation and learning allow informative cross-species comparisons of neural structure and behavior.     

Genetic differentiation of the sherry yeasts Saccharomyces cerevisiae

Molecular genetic study of the yeast Saccharomyces cerevisiae isolated at various stages of sherry making (young wine, solera, and criadera) in various winemaking regions of Spain demonstrated that sherry yeasts diverged from the primary winemaking yeasts according to several physiological and molecular markers. All sherry strains independently of the place and time of their isolation carry a 24-bp deletion in the ITS 1 region of ribosomal DNA, whereas the yeasts of the primary winemaking lack this deletion. Molecular karyotypes of the sherry yeast from different populations were found very similar.     

Vesicle interactions as a model for the retinal cell-cell recognition mediated by R-cognin

The action of R-cognin, a chick neural retina cell recognition glycoprotein, was investigated in vesicles of retina cell membranes. It was found that the aggregation of the vesicles was dependent on membrane proteins, and specifically R-cognin, as vesicle aggregation was inhibited by R-cognin antibody (Fab'). The R-cognin content of the vesicles, and their ability to aggregate, decreased with increasing embryonic age of the tissue. R-cognin mediated aggregation of the vesicles was not dependent on exogenous calcium. Thus, R-cognin was calcium-independent in its membrane linking activity.     

Physical mapping and RFLP analysis of mtDNAs from the ascosporogenous yeasts: Saccharomyces exiguus, S. kluyveri and Hansenula wingei.

Mitochondrial DNAs from the ascosporogenous yeasts S. exiguus, S. kluyveri and H. wingei were prepared by a new rapid method without CsCl isopycnic centrifugation. The mtDNA RFLPs were identified and clearly distinguished each species from the other. The physical maps were constructed by single and double digestion with nine restriction endonucleases. The location of rRNA genes was assigned to the maps by Southern hybridization with synthetic consensus probes. The genome sizes of these mtDNAs were estimated to be 45 kb for S. exiguus, 54 kb for S. kluyveri and 27 kb for H. wingei. The mtDNA RFLP analysis indicates a phylogenetic relationship among these yeasts. This indicates that S. cerevisiae is closer to H. wingei than S. kluyveri. However, the derived phylogenetic tree is completely consistent with that which was previously constructed on amino acid replacement in mating pheromones and electrophoretic karyotypes (Yoshida et al., 1989).