GSG1, a yeast gene required for sporulation

A Single-Cell Landscape of Spermioteleosis in Mice and Pigs

(1) Background: Spermatozoa acquired motility and matured in epididymis after production in the testis. However, there is still limited understanding of the specific characteristics of sperm development across different species. In this study, we employed a comprehensive approach to analyze cell compositions in both testicular and epididymal tissues, providing valuable insights into the changes occurring during meiosis and spermiogenesis in mouse and pig models. Additionally, we identified distinct gene expression signatures associated with various spermatogenic cell types. (2) Methods: To investigate the differences in spermatogenesis between mice and pigs, we constructed a single-cell RNA dataset. (3) Results: Our findings revealed notable differences in testicular cell clusters between these two species. Furthermore, distinct gene expression patterns were observed among epithelial cells from different regions of the epididymis. Interestingly, regional gene expression patterns were also identified within principal cell clusters of the mouse epididymis. Moreover, through analysing differentially expressed genes related to the epididymis in both mouse and pig models, we successfully identified potential marker genes associated with sperm development and maturation for each species studied. (4) Conclusions: This research presented a comprehensive single-cell landscape analysis of both testicular and epididymal tissues, shedding light on the intricate processes involved in spermatogenesis and sperm maturation, specifically within mouse and pig models.

Mutational analysis of the yeast TRAPP subunit Trs20p identifies roles in endocytic recycling and sporulation

Trs20p is a subunit of the evolutionarily conserved TRAPP (TRAnsport Protein Particle) complex that mediates various aspects of membrane trafficking. Three TRAPP complexes have been identified in yeast with roles in ER-to-Golgi trafficking, post-Golgi and endosomal-to-Golgi transport and in autophagy. The role of Trs20p, which is essential for viability and a component of all three complexes, and how it might function within each TRAPP complex, has not been clarified to date. To begin to address the role of Trs20p we generated different mutants by random mutagenesis but, surprisingly, no defects were observed in diverse anterograde transport pathways or general secretion in Trs20 temperature-sensitive mutants. Instead, mutation of Trs20 led to defects in endocytic recycling and a block in sporulation/meiosis. The phenotypes of different mutants appear to be separable suggesting that the mutations affect the function of Trs20 in different TRAPP complexes.

Vacuolar (H+)-ATPases in Caenorhabditis elegans: what can we learn about giant H+ pumps from tiny worms?

Vacuolar (H(+))-ATPases, also called V-ATPases, are ATP-driven proton pumps that are highly phylogenetically conserved. Early biochemical and cell biological studies have revealed many details of the molecular mechanism of proton pumping and of the structure of the multi-subunit membrane complex, including the stoichiometry of subunit composition. In addition, yeast and mouse genetics have broadened our understanding of the physiological consequences of defective vacuolar acidification and its related disease etiologies. Recently, phenotypic investigation of V-ATPase mutants in Caenorhabditis elegans has revealed unexpected new roles of V-ATPases in both cellular function and early development. In this review, we discuss the functions of the V-ATPases discovered in C. elegans.

The protein kinase Hal5p is the high-copy suppressor of lithium-sensitive mutations of genes involved in the sporulation and meiosis as well as the ergosterol biosynthesis in Saccharomyces cerevisiae

From a genome-scale genetic screen, we have identified 114 lithium-sensitive and 6 lithium-tolerant gene mutations in Saccharomyces cerevisiae. Twenty-five of these identified lithium-sensitive mutations are of genes previously reported to be involved in sporulation and meiosis, whereas thirty-six of them are of genes involved in the vacuolar protein sorting (VPS) pathway, mainly functioning in the membrane docking and fusion. Accordingly, the lithium-sensitive phenotypes for one third of identified VPS mutants well correlate to their intracellular lithium contents in response to lithium stress. This indicates the integrity of the VPS pathway is critic for the ion homeostasis in yeast cells. The halotolerant protein kinase Hal5p, a regulator of the potassium transporter Trk1p, is shown to be the high-copy suppressor of nearly one third of identified lithium-sensitive mutations of genes involved in the sporulation and meiosis as well as in the biosynthesis of ergosterol. These results suggest that Hal5p-mediated ion homeostasis is important for these two biological processes.

The TRAPP complex: insights into its architecture and function

Vesicle‐mediated transport is a process carried out by virtually every cell and is required for the proper targeting and secretion of proteins. As such, there are numerous players involved to ensure that the proteins are properly localized. Overall, transport requires vesicle budding, recognition of the vesicle by the target membrane and fusion of the vesicle with the target membrane resulting in delivery of its contents. The initial interaction between the vesicle and the target membrane has been referred to as tethering. Because this is the first contact between the two membranes, tethering is critical to ensuring that specificity is achieved. It is therefore not surprising that there are numerous ‘tethering factors’ involved ranging from multisubunit complexes, coiled‐coil proteins and Rab guanosine triphosphatases. Of the multisubunit tethering complexes, one of the best studied at the molecular level is the evolutionarily conserved TRAPP complex. There are two forms of this complex: TRAPP I and TRAPP II. In yeast, these complexes function in a number of processes including endoplasmic reticulum‐to‐Golgi transport (TRAPP I) and an ill‐defined step at the trans Golgi (TRAPP II). Because the complex was first reported in 1998 (1), there has been a decade of studies that have clarified some aspects of its function but have also raised further questions. In this review, we will discuss recent advances in our understanding of yeast and mammalian TRAPP at the structural and functional levels and its role in disease while trying to resolve some apparent discrepancies and highlighting areas for future study.

Biochemical and crystallographic studies reveal a specific interaction between TRAPP subunits Trs33p and Bet3p

Transport protein particle (TRAPP) comprises a family of two highly related multiprotein complexes, with seven common subunits, that serve to target different classes of transport vesicles to their appropriate compartments. Defining the architecture of the complexes will advance our understanding of the functional differences between these highly related molecular machines. Genetic analyses in yeast suggested a specific interaction between the TRAPP subunits Bet3p and Trs33p. A mammalian bet3-trs33 complex was crystallized, and the structure was solved to 2.2 angstroms resolution. Intriguingly, the overall fold of the bet3 and trs33 monomers was similar, although the proteins had little overall sequence identity. In vitro experiments using yeast TRAPP subunits indicated that Bet3p binding to Trs33p facilitates the interaction between Bet3p and another TRAPP subunit, Bet5p. Mutational analysis suggests that yeast Trs33p facilitates other Bet3p protein-protein interactions. Furthermore, we show that Trs33p can increase the Golgi-localized pool of a mutated Bet3 protein normally found in the cytosol. We propose that one of the roles of Trs33p is to facilitate the incorporation of the Bet3p subunit into assembling TRAPP complexes.

Trs85 (Gsg1), a Component of the TRAPP Complexes, Is Required for the Organization of the Preautophagosomal Structure during Selective Autophagy via the Cvt Pathway

Autophagosomes and Cvt vesicles are limited by two membrane layers. The biogenesis of these unconventional vesicles and the origin of their membranes are hardly understood. Here we identify in Saccharomyces cerevisiae Trs85, a nonessential component of the TRAPP complexes, to be required for the biogenesis of Cvt vesicles. The TRAPP complexes function in endoplasmic reticulum-to-Golgi and Golgi trafficking. Growing trs85delta cells show a defect in the organization of the preautophagosomal structure. Although proaminopeptidase I is normally recruited to the preautophagosomal structure, the recruitment of green fluorescent protein-Atg8 depends on Trs85. Autophagy proceeds in the absence of Trs85, albeit at a reduced rate. Our electron microscopic analysis demonstrated that the reduced autophagic rate of trs85delta cells does not result from a reduced size of the autophagosomes. Growing and starved cells lacking Trs85 did not show defects in vacuolar biogenesis; mature vacuolar proteinase B and carboxypeptidase Y were present. Also vacuolar acidification was normal in these cells. It is known that mutations impairing the integrity of the ER or Golgi block both autophagy and the Cvt pathway. But the phenotypes of trs85delta cells show striking differences to those seen in mutants with defects in the early secretory pathway. This suggests that Trs85 might play a direct role in the Cvt pathway and autophagy.

Trs85 is required for macroautophagy, pexophagy and cytoplasm to vacuole targeting in Yarrowia lipolytica and Saccharomyces cerevisiae

Yarrowia lipolytica was recently introduced as a new model organism to study peroxisome degradation in yeasts. Transfer of Y. lipolytica cells from oleate/ethylamine to glucose/ammonium chloride medium leads to selective macroautophagy of peroxisomes. To decipher the molecular mechanisms of macropexophagy we isolated mutants of Y. lipolytica defective in the inactivation of peroxisomal enzymes under pexophagy conditions. Through this analysis we identified the gene YlTRS85, the ortholog of Saccharomyces cerevisiae TRS85 that encodes the 85 kDa subunit of transport protein particle (TRAPP). A parallel genetic screen in S. cerevisiae also identified the trs85 mutant. Here, we report that Trs85 is required for nonspecific autophagy, pexophagy and the cytoplasm to vacuole targeting pathway in both yeasts.

Identification and characterization of five new subunits of TRAPP

TRAPP (transport protein particle), a multiprotein complex containing ten subunits, plays a key role in the late stages of endoplasmic reticulum to Golgi traffic in the yeast Saccharomyces cerevisiae. We previously described the identification of five TRAPP subunits (Bet5p, Trs20p, Bet3p, Trs23p and Trs33p). Now we report the identification of the remaining five subunits (Trs31p, Trs65p, Trs85p, Trs120p and Trs130p) as well as an initial characterization of the yeast complex and its human homologue. We find that three of the subunits are dispensable for growth and a novel sequence motif is found in Bet3p, Trs31p and Trs33p. Furthermore, biochemical characterization of both yeast and human TRAPP suggests that this complex is anchored to a Triton X-100 resistant fraction of the Golgi. Differences between yeast and human TRAPP as well as the relationship of TRAPP subunits to other docking/tethering factors are discussed.

Disruption of six novel yeast genes located on chromosome II reveals one gene essential for vegetative growth and two required for sporulation and conferring hypersensitivity to various chemicals

A PCR-based method for targeted gene deletion by kanMX4 module was used to construct complete deletion mutants of six individual open reading frames from chromosome II: YBR128c, YBR131w, YBR133c, YBR137w, YBR138c and YBR142w. The ORFs were deleted in two diploid strains, FY1679 and W303. Sporulation and tetrad analysis revealed that only one ORF, YBR142w, encoding a putative DEAD-box RNA helicase, is an essential gene. A systematic phenotypic analysis of the deleted mutants was carried out. Homozygous diploids ybr128cDelta/ybr128cDelta and ybr131wDelta/ybr131wDelta did not sporulate. The ybr131cDelta mutant whether haploid or homozygous diploid, in addition displayed an increased sensitivity to Caffeine, Calcium and Zinc, and to emphasize this phenotype we named the gene CCZ1. ORF YBR133c was independently reported by others as Histone Synthetic Lethal (HSL7) (Ma et al., 1996). We found that the aberrant morphology characteristic for ybr133cDelta (hsl7Delta) cells was observed in W303 but not in FY1679 genetic background. Furthermore, we observed that deletion of YBR133c had a pleiotropic effect under a wide range of conditions, including increased sensitivity to calcium, caffeine, calcofluor white, vanadate and verapamil. The effects of the deletion were reinforced in W303 background. We found no phenotypic effects of the two remaining deletions, ybr137wDelta and ybr138cDelta.

Yeast meiotic mutants proficient for the induction of ectopic recombination

A screen was designed to identify Saccharomyces cerevisiae mutants that were defective in meiosis yet proficient for meiotic ectopic recombination in the return-to-growth protocol. Seven mutants alleles were isolated; two are important for chromosome synapsis (RED1, MEK1) and five function independently of recombination (SPO14, GSG1, SPOT8/MUM2, 3, 4). Similar to the spoT8-1 mutant, mum2 deletion strains do not undergo premeiotic DNA synthesis, arrest prior to the first meiotic division and fail to sporulate. Surprisingly, although DNA replication does not occur, mum2 mutants are induced for high levels of ectopic recombination. gsg1 diploids are reduced in their ability to complete premeiotic DNA synthesis and the meiotic divisions, and a small percentage of cells produce spores. mum3 mutants sporulate poorly and the spores produced are inviable. Finally, mum4-1 mutants produce inviable spores. The meiotic/sporulation defects of gsg1, mum2, and mum3 are not relieved by spo11 or spo13 mutations, indicating that the mutant defects are not dependent on the initiation of recombination or completion of both meiotic divisions. In contrast, the spore inviability of the mum4-1 mutant is rescued by the spo13 mutation. The mum4-1 spo13 mutant undergoes a single, predominantly equational division, suggesting that MUM4 functions at or prior to the first meiotic division. Although recombination is variably affected in the gsg1 and mum mutants, we hypothesize that these mutants define genes important for aspects of meiosis not directly related to recombination.