Killer toxins are antifungal proteins produced by many species of “killer” yeasts, including the brewer's and baker's yeast Saccharomyces cerevisiae. Screening 1270 strains of S. cerevisiae for killer toxin production found that 50% are killer yeasts, with a higher prevalence of yeasts isolated from human clinical samples and winemaking processes. Since many killer toxins are encoded by satellite double-stranded RNAs (dsRNAs) associated with mycoviruses, S. cerevisiae strains were also assayed for the presence of dsRNAs. This screen identified that 51% of strains contained dsRNAs from the mycovirus families Totiviridae and Partitiviridae, as well as satellite dsRNAs. Killer toxin production was correlated with the presence of satellite dsRNAs but not mycoviruses. However, in most killer yeasts, whole genome analysis identified the killer toxin gene KHS1 as significantly associated with killer toxin production. Most killer yeasts had unique spectrums of antifungal activities compared to canonical killer toxins, and sequence analysis identified mutations that altered their antifungal activities. The prevalence of mycoviruses and killer toxins in S. cerevisiae is important because of their known impact on yeast fitness, with implications for academic research and industrial application of this yeast species.

Mycoviruses are widely distributed across fungi, including the yeasts of the Saccharomycotina subphylum. This manuscript reports the first double-stranded RNA (dsRNA) virus isolated from Pichia membranifaciens. This novel virus has been named Pichia membranifaciens virus L-A (PmV-L-A) and is a member of the Totiviridae. PmV-L-A is 4579 bp in length, with RNA secondary structures similar to the packaging, replication, and frameshift signals of totiviruses that infect Saccharomycotina yeasts. PmV-L-A was found to be part of a monophyletic group within the I-A totiviruses, implying a shared ancestry between mycoviruses isolated from the Pichiaceae and Saccharomycetaceae yeasts. Energy-minimized AlphaFold2 molecular models of the PmV-L-A Gag protein revealed structural conservation with the Gag protein of Saccharomyces cerevisiae virus L-A (ScV-L-A). The predicted tertiary structure of the PmV-L-A Pol and other homologs provided a possible mechanism for totivirus RNA replication due to structural similarities with the RNA-dependent RNA polymerases of mammalian dsRNA viruses. Insights into the structure, function, and evolution of totiviruses gained from yeasts are essential because of their emerging role in animal disease and their parallels with mammalian viruses.

Compared to other species of Candida yeasts, the growth of Candida glabrata was inhibited by many different strains of Saccharomyces killer yeasts. The ionophoric K1 and K2 killer toxins were broadly inhibitory to all clinical isolates of C. glabrata from patients with recurrent vulvovaginal candidiasis despite high levels of resistance to clinically relevant antifungal therapeutics.

Functional adipose tissue is essential for maintaining systemic metabolic homeostasis. Dysfunctional adipose tissue, characterized by increased fibrosis, hypoxia and chronic inflammation, is often associated with obesity and promotes the onset of metabolic disease, such as type 2 diabetes. During nutrient excess, adipose tissue function can be preserved by the generation of new adipocytes from adipocyte stem cells, illustrating the importance of identifying the physiological regulators of adipogenesis. Here, we discover a cilia-localized signaling pathway through which the pro-inflammatory lipid metabolite prostaglandin E2 (PGE2) suppresses adipogenesis. We demonstrate that PGE2 specifically signals through the E-type prostaglandin receptor 4 (EP4) localized to the primary cilium of adipocyte stem cells. Activation of ciliary EP4 initiates a cAMP-independent signaling cascade that activates Rho-associated protein kinase 2 (ROCK2), resulting in the retention of actin stress fibers that prevent adipogenesis. These findings uncover a compartmentalized regulatory mechanism of adipogenesis by which primary cilia alter whole-cell physiology, cell fate, and ultimately adipose tissue expansion in response to an inflammatory hormone, offering insight into how chronic inflammation may contribute to adipose tissue dysfunction and metabolic disease progression.

Obesity increases breast cancer risk and tumor aggressiveness, yet the mechanisms underlying this association remain unclear. In this work, we identify a tumor-suppressive lipid signaling pathway in which mammary adipocytes secrete the oxylipin 9S-hydroxyoctadecadienoic acid (9S-HODE). 9S-HODE induces ferroptosis in breast cancer cells by disrupting iron homeostasis. Adipocytes in obese mammary tissue produce less 9S-HODE, and tumors in obese mice exhibit reduced ferroptosis. Accordingly, ferroptosis inhibition accelerates tumor growth in lean mice, and restoring 9S-HODE suppresses tumor growth in obese mice. In humans, mammary 9S-HODE content is inversely correlated with body mass index, and 9S-HODE inhibits patient-derived breast cancer organoid growth. These findings identify the loss of adipocyte-derived 9S-HODE as a mechanism by which obesity promotes breast cancer and suggest that the restoration of ferroptosis-inducing lipid signaling may be a therapeutic strategy.

Metabolic diseases such as type 2 diabetes are often associated with adipose tissue dysfunction and obesity. Disorders of the primary cilium, or ciliopathies, can lead to obesity and the development of metabolic disease, as these signaling organelles regulate both the satiety pathway and adipose tissue expansion. Alström syndrome, a ciliopathy caused by loss of function of the ALMS1 gene, is linked to hyperphagia, obesity, and early-onset type 2 diabetes, though how ALMS1 functions throughout the body to maintain energy homeostasis and metabolic health remains unclear. Here we demonstrate that ALMS1 loss in cultured preadipocytes and primary adipocyte progenitor cells from visceral, but not subcutaneous, mouse white adipose tissue depots inhibits their ability to undergo adipogenesis. Isolated primary adipocyte progenitor cells and cultured preadipocytes exhibit reduced ciliation and decreased centriole cohesion in the absence of ALMS1. Further, ALMS1 knockout preadipocytes retain the ciliary localization of G protein-coupled receptors known to influence adipogenesis, yet fail to undergo the changes in adipogenesis expected with their activation, consistent with a defect in ciliary transduction downstream of receptor localization. These findings demonstrate a new role for the ciliopathy gene Alms1 in directly regulating adipose tissue expansion through the regulation of ciliary signals required for adipogenesis.