Student Journal of Cell and Molecular Biology

A Review of ADP-Ribosylation Factor-Like 1’s Role in Vesicular Trafficking and Autophagy in Saccharomyces cerevisiae

2024-06-18T09:52:58-07:00

DP-ribosylation factor-like protein 1 (Arl1p) is a GTPase that functions in organelle recycling and membrane trafficking pathways within Saccharomyces cerevisiae (S. cerevisiae). By disturbing Arl1p’s protein interactions and creating arl1Δ mutants, researchers observed a loss of trans-Golgi network (TGN) structure, the unregulated production of endosomes, and an inability to move proteins to the cell membrane and recruit tethering proteins to the TGN for vesicle tethering and formation. Specifically, Arl1p was found to be necessary in the stress induced tethering of retrograde vesicles originating from early endosomes. This function in stress reduction is further seen through the role of Arl1p in macroautophagy. The GTPase has been found to work as a facilitator and as an independent pathway to Ypt6p, a GTPase protein with an independent pathway facilitating phagophore synthesis and vesicle fusion with Arl1p; with evidence suggesting Arl1p functions to promote central vacuole synthesis. These studies place Arl1p as a component of trans-Golgi structure, vesicle trafficking and autophagy pathways in S. cerevisiae.

Inability to Regulate Cell Wall Integrity and Cell Cycle Progression in Smi1-∆ Mutant Cells in Saccharomyces cerevisiae

2024-06-18T09:58:54-07:00

Saccharomyces cerevisiae is a yeast species often used as a model for eukaryotic organisms. In S. cerevisiae, the SMI1 gene and resulting protein, Smi1p, have been found to have an important role in controlling cell wall integrity by regulating cell cycle progression. Smi1p is a key coordinator between the cell wall integrity pathway and the cell cycle progression pathway. Here, we review the effects of a SMI1 gene knockout, cells with the smi1-∆ allele, to further learn about the function of the SMI1 gene in yeast cells. Mutant smi1-∆ cells experience challenges mediating cell cycle progression and regulating cell wall integrity leading to decreased cell reproduction and cell wall defects. The smi1-∆ cells have reduced (1,3)-beta-glucan synthesis causing higher sensitivity to cell wall damaging agents. This review synthesizes research from eight studies to describe what is already known about the SMI1 gene, the role of Smi1p in biochemical cell pathways, and smi1-∆ mutant cells. As well, the review offers direction for further research on smi1-∆ cells that could lead to a better understanding of the SMI1 gene function in S. cerevisiae.

Ltv1 and Its Role in Protein Trafficking and Ribosomal Assembly in Saccharomyces cerevisiae

2024-06-17T14:43:40-07:00

In Saccharomyces cerevisiae, ltv1 is involved in assembling and trafficking the 40S subunit in ribosomes, as well as trafficking other proteins such as GAP1p. LTV1p helps facilitate 40S subunit assembly by binding ENP1p and recruiting other proteins. After, nuclear export of the 40S subunit occurs via the leucine-rich nuclear export signal (NES). The formation of ribosomes is essential for protein synthesis, therefore, mutating ltv1 has many physiological consequences. Several studies have reported that the deletion mutant, ltv1-Δ affects growth, sensitivity to stressors and ribosomal assembly and production in S. cerevisiae. This review summarizes current findings on the ltv1 gene, LTV1p protein structure and function, as well as the consequences of ltv1 knockout mutation. Although ltv1 is involved in several molecular pathways, the involvement of ltv1 in plasma membrane recycling and 40S subunit assembly is not fully understood. It is also unknown how ltv1-Δ mutants respond to stressors such as changes in pH and increased temperature. Therefore, this review proposes a mechanism for how ltv1 is involved in pre-40S subunit assembly and suggests what type of research can be done to broaden our understanding of the ltv1 gene.

Downstream Effects of the Atp4Δ Mutation in Saccharomyces cerevisiae

2024-06-18T10:05:56-07:00

Expression of atp4 in yeast cells produces subunit 4, a structural component of ATP synthase in the mitochondria embedded in the membrane and making up the peripheral stalk. The gene is thought to have a role in the oligomerization of ATP synthase, which contributes to the curvature of the mitochondrial membrane, cristae formation, and membrane stability. Studies have shown that in the absence of this gene, yeast cells display abnormal mitochondrial structures and membrane instability, supporting this idea. Mutant strains had an overall smaller life span in comparison to the wildtype and displayed deficiencies in its growth and respiration, specifically its oxygen consumption rate and ATP levels. These results have suggested the role of subunit 4 in the assembly of the proper ATP synthase structure that drives these attributes. In addition to mitochondrial membrane stability and cell respiration, the protein may also have a role in mitochondrial genome maintenance. The gene’s potential involvement in mitochondrial DNA (mtDNA) replication has been proposed due to rapid losses of mtDNA in the mutant strain. Future studies addressing the gap in the literature surrounding the mechanisms driving these observations have been encouraged.

Elucidating the Effects of Restrictive Temperatures on the Function of Arl1p in Ion Homeostasis in Saccharomyces cerevisiae

2024-06-18T10:51:44-07:00

Strict regulation of ion homeostasis is necessary for cell function and survival. Arl1p, a member of the ADPribosylation factor-like protein family, is known to function in ion homeostasis by mediating lithium (Li⁺) tolerance and regulating potassium ion (K+) influx in Saccharomyces cerevisiae. Given that arl1Δ mutants show temperature sensitivity, this study investigates the effects of restrictive temperatures on the function of Arl1p in regulating Li⁺ tolerance and the role of K+ in enhancing Li⁺ tolerance. We have characterized cell growth rates of arl1Δ mutant and wild-type cells in the presence of Li⁺ and K⁺ at optimal (30℃) and restrictive (37℃) temperatures using haemocytometry. We report that Li⁺ sensitivity was exacerbated at restrictive temperatures in the wild-type cells, but not in arl1Δ mutants, suggesting the potential temperature sensitivity of Arl1p. Further, we report that K⁺ was sufficient to suppress Li⁺-induced decreases in cell growth in wildtype and arl1Δ mutant cells at optimal and restrictive temperatures, suggesting that K⁺ functions as a growth factor in S. cerevisiae. Future studies may aim to further elucidate the relationship between temperature and ion homeostasis.

An Investigation of Potential Acetic Acid Sensitivity in Ltv1-Δ S. cerevisiae

2024-06-18T10:14:30-07:00

This study investigated the effects of acetic acid on wild-type (WT-a) and ltv1-Δ Saccharomyces cerevisiae. We hypothesized that the ltv1-Δ strain, with defects in ribosomal biosynthesis and increased translational errors, would be more sensitive to acetic acid compared to WT-a. Both strains were exposed to different concentrations of acetic acid (0.3, 0.6, and 1.2 g/L), and cell density and the nuclear to the cytoplasmic (NC) ratio were measured with fluorescence microscopy. Results revealed that ltv1-Δ exhibited increased resistance to acetic acid, as evidenced by decreased fluctuations in cell counts in different acetic acid treatments compared to WT-a. However, ltv1-Δ cells were found to be more prone to apoptosis and have a higher NC ratio than WT-a cells when exposed to certain concentrations of acetic acid. These results suggest that the induction of apoptosis by acetic acid is not dose-dependent but more efficient in the ltv1-Δ strain. This implies that ltv1-Δ cells may have increased resistance to acetic acid due to the mistranslation of proteins required for acetic acid stress sensitivity. This study has implications for the biotechnology industry and may aid in the development of new strategies to enhance yeast fermentation processes.

Chitin Levels and Cell Death in Saccharomyces cerevisiae Smi1-∆ Cells Exposed to Antifungal Treatment

2024-06-18T10:58:48-07:00

The SMI1 gene plays an integral role in the coordination of a cell wall integrity (CWI) pathway in Saccharomyces cerevisiae. Thus, smi1-∆ mutant cells present cell wall defects due to their reduced capacity to synthesize cell wall components. Responding to weakened cell walls, yeast cells produce increased amounts of chitin as a compensatory mechanism. It was hypothesized that smi1-∆ cells will present lower cell death rates, increased chitin levels, and therefore present an increased tolerance to antifungals. Wildtype-a (WTa) cells, and smi1-∆ cells were treated with imidazole to study antifungal effects on cell viability and chitin production in smi1-∆ S. cerevisiae cells. To examine the effects of an antifungal stressor, cell death was quantified using hemocytometry and chitin levels were visualized using fluorescence microscopy. Imidazole-exposed smi1-∆ cells exhibit significantly lower cell death percentages. smi1-∆ cells have significantly higher cell wall chitin levels than WT-a cells and display further increases with antifungal treatment. These findings indicate that CWI pathway disruption in smi1-∆ cells may lead to an increased antifungal-tolerance. Examining interrupted CWI pathway compensatory mechanisms in mutant S. cerevisiae cells allows for a greater understanding of yeast tolerance to drugs, and aids in the development of more potent fungal infection medications.

Autophagy in Saccharomyces cerevisiae: A Study of Arl1p's Role in Heat and Starvation-Induced Cell Stress

2024-06-18T10:45:08-07:00

ADP-ribosylation factor-like protein (Arl1p) is a component of autophagy pathways within Saccharomyces cerevisiae (S. cerevisiae), a model organism used in studying human autophagy pathways and related diseases. In the non-specialized macroautophagy and specialized Cytoplasm-to-vacuole (Cvt) trafficking pathways, Arl1p facilitates three main processes: synthesis of acidic phagophores facilitation of the docking and tethering of Atg9p mediated autophagosomes, and fusion of autophagosomes with the vacuole. The current understanding of autophagy emphasizes the importance of cellular recycling for cellular maintenance during growth. We used fluorescence microscopy to visualize acridine orange (AO) stained acidic compartments and DAPI stained nuclei, and analyzed AO/DAPI quantity in cells incubated in conditions of both nitrogen starvation and non-permissive temperatures. We found significant increases in autophagosomes within the cytoplasm of arl1Δ mutants after incubation in nitrogen starvation conditions, thus deter mining that arl1Δ mutants are unable to fuse autophagosome content. We conducted western blots by antibody tagging aminopeptidase 1 (Ape1) to determine Arl1p’s role in the Cvt pathway. We found starvation conditions resulted in significantly more Ape1 translocation, and no significant difference between arl1Δ mutant and wildtype cells. Thus, Arl1p maintains a supporting role in autophagy.