Biology subjects

Igarashi, M. G.

Publications and source records attributed to Igarashi, M. G..

3 recordsLinked to original sources

bioRxiv2026

Physiological architecture and evolutionary origins of cellular adaptability

The capacity to adapt to complex environments ( adaptability) is a defining property of cells. Yet, its relationship across single-cell physiology, population-level responses, and evolutionary timescales remains unclear. We performed single-cell transcriptional profiling of budding yeast across 20 complex environments before and after long-term selection for increased osmotolerance. In ancestral populations, transcriptional responses organized into a reproducible hierarchy where adaptation to certain cues took precedence over others. This hierarchy mechanistically originated within individual cells through contingent regulation of translation initiation. Evolution for >3,000 generations under osmotic stress increased osmotolerance while reordering this hierarchy, selectively deprioritizing osmotic stress as an organizing axis of adaptation. The derived strain exhibited impaired integration of stress responses, defective translational coordination, and reduced fitness outside the selected condition. Together, these findings illustrate that cellular adaptability is an evolved architecture whose form is set by the history of selection. One Sentence SummaryCells adapt to complex environments via a prioritization hierarchy; this hierarchy is shaped by the frequency and magnitude of environmental fluctuations in their evolutionary history.

cell biology↗

bioRxiv2025

Solid-State NMR Analysis of Schizosaccharomyces pombe Reveals Role of α-Amylase Family Enzymes in Cell Wall Structure and Function

The fission yeast Schizosaccharomyces pombe is a widely employed model organism for studying the eukaryotic cell cycle. Like plants and bacteria, S. pombe must build a cell wall in concert with its cell cycle, but how cell wall-synthesizing and remodeling enzymes mediate this process remains unclear. Here we characterize the functions of Aah1 and Aah3, two related S. pombe -amylases that are putative members of this evolutionarily conserved family of cell wall-modifying proteins. We found that unlike rod-shaped wildtype S. pombe cells, aah1{Delta} aah3{Delta} cells are nearly spherical, grow slowly, have thickened cell walls, and have severe defects in cell separation following cytokinesis. Solid-state NMR spectroscopy analyses of intact wildtype and aah1{Delta} aah3{Delta} cells revealed that aah1{Delta} aah3{Delta} cell walls are rigidified with a significant reduction in the -glucan matrix, characterized by reduced amounts of the major -1,3-glucan and the minor -1,4-glucan within the rigid and mobile phases; this reduction was compensated for by a two-fold increase in {beta}-glucan content. Indeed, viability of aah1{Delta} aah3{Delta} cells depended on {beta}-glucan upregulation and the cell wall integrity pathway that mediates it. While aah1{Delta} aah3{Delta} cells resemble cells with impaired function of the transglycosylation domain of -glucan synthase 1 (Ags1), increased expression of Aah3 does not compensate for impaired Ags1 function or vice-versa. Overall, our data suggest that Aah1 and Aah3 are required in addition to Ags1, likely downstream, for the transglycosylation of -glucan chains to generate fibers of appropriate dimensions to support proper cell morphology, growth, and division. Significance StatementThis study utilized a range of imaging techniques and high-resolution solid-state NMR spectroscopy of intact S. pombe cells to refine our understanding of S. pombe cell wall composition. This study also determined that two related GPI-anchored -amylase family proteins, Aah1 and Aah3, likely act as transglycosylases non-redundantly with an -glucan synthase in the synthesis of -glucan chains of appropriate content and size to support polarized growth and cell division. Our results also highlight the anti-fungal therapeutic potential of GPI-anchored enzymes acting in concert with glucan synthases.

microbiology↗

bioRxiv2022

Multiple polarity kinases inhibit phase separation of F-BAR protein Cdc15 and antagonize cytokinetic ring assembly in fission yeast

The F-BAR protein Cdc15 is essential for cytokinesis in Schizosaccharomyces pombe and it plays a key role in attaching the cytokinetic ring (CR) to the plasma membrane. Cdc15s abilities to bind to the membrane and oligomerize via its F-BAR domain are inhibited by phosphorylation of its intrinsically disordered region (IDR). Multiple cell polarity kinases regulate Cdc15 IDR phosphostate, and of these the DYRK kinase Pom1 phosphorylation sites on Cdc15 have been shown in vivo to prevent CR formation at cell tips. Here, we compared the ability of Pom1 to control of Cdc15 phosphostate and cortical localization to that of other Cdc15 kinases: Kin1, Pck1, and Shk1. We identified distinct but overlapping cohorts of Cdc15 phosphorylation sites targeted by each kinase, and the number of sites correlated with each kinases abilities to influence Cdc15 PM localization. Coarse-grained simulations predicted that cumulative IDR phosphorylation moves the IDRs of a dimer apart and toward the F-BAR tips. Further, simulations indicated that the overall negative charge of phosphorylation masks positively charged amino acids necessary for F-BAR oligomerization and membrane interaction. Finally, simulations suggested that dephosphorylated Cdc15 undergoes phase separation driven by IDR interactions. Indeed, dephosphorylated but not phosphorylated Cdc15 undergoes liquid-liquid phase separation to form droplets in vitro that recruit Cdc15 binding partners. In cells, Cdc15 phosphomutants also formed PM-bound condensates that recruit other CR components. Together, we propose that a threshold of Cdc15 phosphorylation by assorted kinases prevents Cdc15 condensation on the PM and antagonizes CR assembly.

cell biology↗