Ross Buchan

Ross Buchan

Associate Professor, Molecular and Cellular Biology
Associate Professor, BIO5 Institute
Primary Department
Contact
(520) 626-1881

Work Summary

Work Summary

The Buchan lab studies how cells regulate gene expression at the level of cytoplasmic messenger RNA (mRNA), the templates of protein synthesis. Areas of particular interest include mRNA-protein bodies called stress granules and P-bodies, which regulate mRNA function, cell signaling, and are implicated in the pathology of viral replication, various cancers and neurodegenerative diseases such as ALS.

Research Interest

Research Interest

The control of gene expression is critical to nearly all aspects of cellular biology, from maintaining basic cell function and identity, to the ability of cells to respond to numerous signals that arise during processes such as development, exposure to pathogens or changes in the cellular environment. A key means by which all cells enact appropriate gene expression responses is to alter the function of messenger RNAs (mRNAs). mRNAs exist in different functional states, dependent upon the proteins bound to them. These states include translation (protein synthesis), repression (off state) and decay. The localization of an mRNAs can also affect its function, thus cells are offered an array of spatial and temporal mechanisms for gene expression control at the mRNA level. mRNAs can also cycle between these different functional states. For example, mRNAs exiting translation often accumulate in distinct mRNA-protein (mRNP) assemblies known as P-bodies and stress granules, from which they may ultimately return to translation again or possibly undergo mRNA decay. Dr Buchan (Ph.D, B.S.) and his lab are particularly interested in the study of P-bodies and stress granules. These conserved, mRNA-protein (mRNP) bodies contain important protein regulators of mRNA decay and translation, as well as signaling proteins, and thus affect gene expression control and cell signaling pathways. In addition, they strongly resemble other important mRNP granules that function in embryogenesis (maternal granules) and memory formation (neuronal transport granules). Finally, stress granules and P-bodies have numerous connections to disease, such as an involvement in RNA viral replication, elevated levels in certain cancer types, as well as the formation of aberrant stress granules in neurodegenerative diseases such as Amyotrophic Lateral Sclerosis (ALS). The Buchan lab uses yeast and cell line models to study the assembly, disassembly and function of stress granules and P-bodies, and how aspects of stress granule and P-bodies contribute to ALS and forms of cancer

Publications

Buchan, J. R., Yoon, J., & Parker, R. (2011). Stress-specific composition, assembly and kinetics of stress granules in Saccharomyces cerevisiae. Journal of cell science, 124(Pt 2), 228-39.

Eukaryotic cells respond to cellular stresses by the inhibition of translation and the accumulation of mRNAs in cytoplasmic RNA-protein (ribonucleoprotein) granules termed stress granules and P-bodies. An unresolved issue is how different stresses affect formation of messenger RNP (mRNP) granules. In the present study, we examine how sodium azide (NaN(3)), which inhibits mitochondrial respiration, affects formation of mRNP granules as compared with glucose deprivation in budding yeast. We observed that NaN(3) treatment inhibits translation and triggers formation of P-bodies and stress granules. The composition of stress granules induced by NaN(3) differs from that of glucose-deprived cells by containing eukaryotic initiation factor (eIF)3, eIF4A/B, eIF5B and eIF1A proteins, and by lacking the heterogeneous nuclear RNP (hnRNP) protein Hrp1. Moreover, in contrast with glucose-deprived stress granules, NaN(3)-triggered stress granules show different assembly rules, form faster and independently from P-bodies and dock or merge with P-bodies over time. Strikingly, addition of NaN(3) and glucose deprivation in combination, regardless of the order, always results in stress granules of a glucose deprivation nature, suggesting that both granules share an mRNP remodeling pathway. These results indicate that stress granule assembly, kinetics and composition in yeast can vary in a stress-specific manner, which we suggest reflects different rate-limiting steps in a common mRNP remodeling pathway.

Buchan, J. R., Capaldi, A. P., & Parker, R. (2012). TOR-tured yeast find a new way to stand the heat. Molecular cell, 47(2), 155-7.
BIO5 Collaborators
Ross Buchan, Andrew P Capaldi

In this issue, Takahara and Maeda (2012) discover that together, Pbp1 and sequestration of the TORC1 complex in cytoplasmic mRNP stress granules provides a negative regulatory mechanism for TORC1 signaling during stress.

Buchan, J. R., Nissan, T., & Parker, R. (2010). Analyzing P-bodies and stress granules in Saccharomyces cerevisiae. Methods in enzymology, 470, 619-40.

Eukaryotic cells contain at least two types of cytoplasmic RNA-protein (RNP) granules that contain nontranslating mRNAs. One such RNP granule is a P-body, which contains translationally inactive mRNAs and proteins involved in mRNA degradation and translation repression. A second such RNP granule is a stress granule which also contains mRNAs, some RNA binding proteins and several translation initiation factors, suggesting these granules contain mRNAs stalled in translation initiation. In this chapter, we describe methods to analyze P-bodies and stress granules in Saccharomyces cerevisiae, including procedures to determine if a protein or mRNA can accumulate in either granule, if an environmental perturbation or mutation affects granule size and number, and granule quantification methods.

Buchan, J. R., & Parker, R. (2007). Molecular biology. The two faces of miRNA. Science (New York, N.Y.), 318(5858), 1877-8.
Buchan, J. R., Muhlrad, D., & Parker, R. (2008). P bodies promote stress granule assembly in Saccharomyces cerevisiae. The Journal of cell biology, 183(3), 441-55.

Recent results indicate that nontranslating mRNAs in eukaryotic cells exist in distinct biochemical states that accumulate in P bodies and stress granules, although the nature of interactions between these particles is unknown. We demonstrate in Saccharomyces cerevisiae that RNA granules with similar protein composition and assembly mechanisms as mammalian stress granules form during glucose deprivation. Stress granule assembly is dependent on P-body formation, whereas P-body assembly is independent of stress granule formation. This suggests that stress granules primarily form from mRNPs in preexisting P bodies, which is also supported by the kinetics of P-body and stress granule formation both in yeast and mammalian cells. These observations argue that P bodies are important sites for decisions of mRNA fate and that stress granules, at least in yeast, primarily represent pools of mRNAs stalled in the process of reentry into translation from P bodies.