Michael D. Sheets

RNA regulation of cell fate and function

Research in the Sheets lab lies at the interface of RNA-protein biochemistry and developmental biology. We focus on the translational repression of mRNAs, a prevalent mechanism used by eukaryotic cells to regulate gene expression. Temporally and spatially controlled translational repression of specific target mRNAs is particularly important during animal development when changes in protein levels must be precisely controlled to guide cell-fate specification. We breakdown our studies to define translational repression mechanisms into three steps. First, we define the RNA binding proteins that are essential for repression of developmentally important target mRNAs  and determine the RNA sequence(s) and/or RNA structures that these proteins recognize. Second, we engineer defined mutations in the target mRNAs and proteins and examine how they alter translational repression and animal development in a model vertebrate organism, developing embryos of the African clawed frog, Xenopus laevis. Third, we seek to examine and define the biological and biochemical roles of the proteins encoded by the target mRNAs to understand how their temporal and spatial regulation at the level of translation guides specific cell-fate decisions required for normal development.

We have applied this three-step approach to the highly conserved Bicaudal-C (Bicc1) RNA binding protein to determine how it functions to select and repress specific target mRNAs. We have recently shown that the ability of Bicc1 to bind to target mRNAs is essential for the earliest developmental transitions in vertebrates, and have successfully defined many important Bicc1 target mRNAs. Our studies exploit the many advantages of Xenopus laevis embryos for studying RNA regulatory processes and development. For example, we established quantitative translational reporter assays that have provided new mechanistic insights into Bicc1-RNA binding and translational repression. Importantly, a molecular understanding of Bicc1 is critical to advancing several biomedically relevant research areas, including our knowledge of complex human disorders, such as polycystic kidney disease and major depressive disorder (MDD). Most recently, we have started to use genetically altered human induced pluripotent stem cells (IPSCs) to model specific disease states that arise as a result of Bicc1 defects and define the normal and abnormal functions of Bicc1 in these contexts.

Selected Publications:

A single KH domain in Bicaudal-C links mRNA binding and translational repression functions to maternal development. Dowdle ME, Park S, Blaser Imboden S, Fox CA, Houston DW, Sheets MD. Development. 2019 May 15;146(10).

Assaying NanoLuc Luciferase Activity from mRNA-Injected Xenopus Embryos. Sheets MD. Methods Mol Biol. 2019;1920:33-39. doi: 10.1007/978-1-4939-9009-2_3.

Coordinated d-cyclin/Foxd1 activation drives mitogenic activity of the Sonic Hedgehog signaling pathway. Fink DM, Sun MR, Heyne GW, Everson JL, Chung HM, Park S, Sheets MD, Lipinski RJ. Cell Signal. 2018 Apr;44:1-9.

Pathogenic TFG Mutations Underlying Hereditary Spastic Paraplegia Impair Secretory Protein Trafficking and Axon Fasciculation. Slosarek EL, Schuh AL, Pustova I, Johnson A, Bird J, Johnson M, Frankel EB, Bhattacharya N, Hanna MG, Burke JE, Ruhl DA, Quinney K, Block S, Peotter JL, Chapman ER, Sheets MD, Butcher SE, Stagg SM, Audhya A. Cell Rep. 2018 Aug 28;24(9):2248-2260.

Horizontal Gel Electrophoresis for Enhanced Detection of Protein-RNA Complexes. Dowdle ME, Imboden SB, Park S, Ryder SP, Sheets MD. J Vis Exp. 2017 Jul 28;(125).

Controlling the Messenger: Regulated Translation of Maternal mRNAs in Xenopus laevis Development. Sheets MD, Fox CA, Dowdle ME, Blaser SI, Chung A, Park S. Adv Exp Med Biol. 2017;953:49-82. Review.

A gradient of maternal Bicaudal-C controls vertebrate embryogenesis via translational repression of mRNAs encoding cell fate regulators. Park S, Blaser S, Marchal MA, Houston DW, Sheets MD. Development. 2016 Mar 1;143(5):864-71.