Bir1 deletion causes malfunction of the spindle assembly checkpoint and apoptosis in yeast

Bone morphogenetic protein 15 gene disruption affects the in vitro maturation of porcine oocytes by impairing spindle assembly and organelle function

Bone morphogenetic protein 15 (BMP15) plays a crucial role in the porcine follicular development. However, its exact functions in the in vitro maturation (IVM) of porcine oocytes remain largely unknown. Here, through cytoplasmic injection of a preassembled crRNA-tracrRNA-Cas9 ribonucleoprotein complex, we achieved BMP15 disruption in approximately 54 % of the cultured porcine oocytes. Editing BMP15 impaired the IVM of porcine oocytes, as indicated by the significantly increased abnormal spindle assembly and reduced first polar body (PB1) extrusion. The editing also impaired cytoplasmic maturation of porcine oocytes, as reflected by reduced abundant of Golgi apparatus and impaired functions of mitochondria. The impaired IVM of porcine oocytes by editing BMP15 possibly was associated with the attenuated SMAD1/5 and EGFR-ERK1/2 signaling in the cumulus granulosa cells (CGCs) and the inhibited MOS/ERK1/2 signaling in oocytes. The attenuated MOS/ERK1/2 signaling may contribute to the inactivation of maturation promoting factor (MPF) and the increased abnormal spindle assembly, leading to reduced PB1 extrusion. It also may contribute to reduced Golgi apparatus formation, and impaired functions of mitochondria. These findings expand our understanding of the regulatory role of BMP15 in the IVM of porcine oocytes and provide a basis for manipulation of porcine reproductive performance.

Quercetin protects porcine oocytes from in vitro aging by reducing oxidative stress and maintaining the mitochondrial functions

Quercetin (QUE) is a component of the flavonoid family that shows various therapeutic properties, such as antioxidant effects. However, whether QUE affects porcine oocyte in vitro aging has not yet been investigated. Therefore, in this study, we applied various doses of QUE to freshly isolated porcine oocytes and found that 10 µM QUE improved the oocyte maturation rate in vitro, as reflected by the increased degree of cumulus cell expansion and first polar body extrusion. More importantly, we found that QUE reduced in vitro aging and improved the maturity level of porcine oocytes after another 24 h of culturing, accompanied by the upregulated expression levels of bone morphogenetic protein 15, growth differentiation factor 9, Moloney sarcoma oncogene, and cyclin-dependent kinase 2. In addition, we found that QUE treatment significantly reduced the intracellular reactive oxygen species levels, apoptosis, and autophagy and upregulated the expression levels of superoxide dismutase 2 and catalase in aged porcine oocytes. In addition, QUE restored impaired mitochondrial membrane potential and spindle assembly in aged porcine oocytes. Our findings demonstrate that QUE can protect porcine oocytes from in vitro aging by reducing oxidative stress and maintaining mitochondrial function.

In vitro interactions between IAP antagonist AT406 and azoles against planktonic cells and biofilms of pathogenic fungi Candida albicans and Exophiala dermatitidis

In vitro interactions of AT406, a novel IAP antagonist, and azoles including itraconazole, voriconazole, and fluconazole against planktonic cells and biofilms of Candida albicans and Exophiala dermatitidis were assessed via broth microdilution checkerboard technique. AT406 alone exhibited limited antifungal activity. However, synergistic effect between AT406 and fluconazole was observed against both planktonic cells and biofilms of C. albicans, including one fluconazole-resistant strain. Moreover, synergism was also demonstrated between AT406 and itraconazole against both planktonic cells and biofilms of E. dermatitidis. No interaction was observed between AT406 and voriconazole. No antagonism was observed in all combinations.

Mutant power: using mutant allele collections for yeast functional genomics

The budding yeast has long served as a model eukaryote for the functional genomic analysis of highly conserved signaling pathways, cellular processes and mechanisms underlying human disease. The collection of reagents available for genomics in yeast is extensive, encompassing a growing diversity of mutant collections beyond gene deletion sets in the standard wild-type S288C genetic background. We review here three main types of mutant allele collections: transposon mutagen collections, essential gene collections and overexpression libraries. Each collection provides unique and identifiable alleles that can be utilized in genome-wide, high-throughput studies. These genomic reagents are particularly informative in identifying synthetic phenotypes and functions associated with essential genes, including those modeled most effectively in complex genetic backgrounds. Several examples of genomic studies in filamentous/pseudohyphal backgrounds are provided here to illustrate this point. Additionally, the limitations of each approach are examined. Collectively, these mutant allele collections in Saccharomyces cerevisiae and the related pathogenic yeast Candida albicans promise insights toward an advanced understanding of eukaryotic molecular and cellular biology.

Why are essential genes essential? - The essentiality of Saccharomyces genes

Essential genes are defined as required for the survival of an organism or a cell. They are of particular interests, not only for their essential biological functions, but also in practical applications, such as identifying effective drug targets to pathogenic bacteria and fungi. The budding yeast Saccharomyces cerevisiae has approximately 6,000 open reading frames, 15 to 20% of which are deemed as essential. Some of the essential genes, however, appear to perform non-essential functions, such as aging and cell death, while many of the non-essential genes play critical roles in cell survival. In this paper, we reviewed and analyzed the levels of essentiality of the Saccharomyces cerevisiae genes and have grouped the genes into four categories: (1) Conditional essential: essential only under certain circumstances or growth conditions; (2) Essential: required for survival under optimal growth conditions; (3) Redundant essential: synthetic lethal due to redundant pathways or gene duplication; and (4) Absolute essential: the minimal genes required for maintaining a cellular life under a stress-free environment. The essential and non-essential functions of the essential genes were further analyzed.

Sro7 and Sro77, the yeast homologues of the Drosophila lethal giant larvae (Lgl), regulate cell proliferation via the Rho1-Tor1 pathway

Saccharomyces cerevisiae Sro7 and Sro77 are homologues of the Drosophila tumour suppressor lethal giant larvae (Lgl), which regulates cell polarity in Drosophila epithelial cells. Here, we showed that double mutation of SRO7/SRO77 was defective in colony growth. The colony of the SRO7/SRO77 double deletion was much smaller than the WT and appeared to be round with a smooth surface, compared with the WT. Analysis using transmission electron microscopy revealed multiple defects of the colony cells, including multiple budding, multiple nuclei, cell lysis and dead cells, suggesting that the double deletion caused defects in cell polarity and cell wall integrity (CWI). Overexpression of RHO1, one of the central regulators of cell polarity and CWI, fully recovered the sro7Δ/sro77Δ phenotype. We further demonstrated that sro7Δ/sro77Δ caused a decrease of the GTP-bound, active Rho1, which in turn caused an upregulation of TOR1. Deletion of TOR1 in sro7Δ/sro77Δ (sro7Δ/sro77Δ/tor1Δ) recovered the cell growth and colony morphology, similar to WT. Our results suggested that the tumour suppressor homologue SRO7/SRO77 regulated cell proliferation and yeast colony development via the Rho1-Tor1 pathway.

Stressing mitosis to death

The final stage of cell division (mitosis), involves the compaction of the duplicated genome into chromatid pairs. Each pair is captured by microtubules emanating from opposite spindle poles, aligned at the metaphase plate, and then faithfully segregated to form two identical daughter cells. Chromatids that are not correctly attached to the spindle are detected by the constitutively active spindle assembly checkpoint (SAC). Any stress that prevents correct bipolar spindle attachment, blocks the satisfaction of the SAC, and induces a prolonged mitotic arrest, providing the cell time to obtain attachment and complete segregation correctly. Unfortunately, during mitosis repairing damage is not generally possible due to the compaction of DNA into chromosomes, and subsequent suppression of gene transcription and translation. Therefore, in the presence of significant damage cell death is instigated to ensure that genomic stability is maintained. While most stresses lead to an arrest in mitosis, some promote premature mitotic exit, allowing cells to bypass mitotic cell death. This mini-review will focus on the effects and outcomes that common stresses have on mitosis, and how this impacts on the efficacy of mitotic chemotherapies.