Graydon B. Gonsalvez, Ph.D.
Department of Cellular Biology and Anatomy
Office: R&E Building, CB2915D
R&E Building, CB2905 and 2906
94-98 BA Carthage College, Kenosha, WI
98-04 Ph.D. Medical College of Wisconsin, Milwaukee, WI
Post Doctoral Training
04-07 Case Western Reserve University, Cleveland, OH
07-09 University of North Carolina, Chapel Hill, NC
Molecular mechanisms underlying the establishment of cell polarity
One of the earliest events in the life cycle of a multi-cellular organism is establishment of polarity. In order for an embryo to develop into an adult, thousands of cell fate specification events must occur. Underlying each of these events is a polarized precursor cell that divides to produce daughter cells with different developmental fates. Once established during embryogenesis, polarity is maintained in the adult and is an essential for the proper functioning of numerous cell types. Neurons, fibroblasts, epithelia, and the migratory cells of the immune systems are just a few examples of highly polarized cells present in our bodies. Major defects in cell polarity are often incompatible with life, whereas subtle defects results in a wide spectrum of diseases including cancer, kidney diseases, platelet diseases, multiple sclerosis, and fragile X syndrome.
The main question addressed by our lab relates to the molecular mechanisms used by cells to establish and maintain polarity. The model organism we currently use is Drosophila melanogaster. The Drosophila oocyte, in particular, serves as an excellent paradigm for understanding cell polarity. The polarity of the oocyte is established by the specific localization of three distinct mRNAs. One of these messages, oskar, is localized to the posterior pole of the oocyte (Fig.1, top panel, arrow). Consequently, Oskar protein is restricted to this region of the egg where it functions to establish germ cell fate and posterior patterning in the future embryo. We recently discovered that a subset of corespliceosomal proteins called Sm proteins have a novel, non-splicing function in oskar mRNA localization. Strains that are mutantsn for these Sm proteins contain oocytes in which oskar mRNA is delocalized (Fig. 1, bottom panel).
Fig. 1: Localization of oskar mRNA in wild-type and sm mutant oocytes. In wild-type oocytes oskar mRNA is localized to the posterior pole. In the mutant, oskar mRNA is delocalized.
Since oskar mRNA is delocalized in the sm mutants, the oocytes lacks polarity. Consequently, embryos derived from these eggs do not form germ cells, are improperly patterned, and die during development (Fig. 2).
Fig. 2: Germ cells are shown in green and a marker for patterning is shown in red. Wild-type embryos contain germ cells and are properly patterned. As a consequence of oskar mRNA delocalization, mutant sm females produce embryos that lack germ cells and are improperly patterned.
Our current focus is on understanding the molecular pathways underlying these defects. Put simply, how do Sm proteins function during oogenesis to specify polarity? Eukaryotic Sm proteins are best known for their function in splicing. However, these proteins existed almost two billion years before the first splicing event. Clear orthologs of Sm proteins can be found in all three domains of life – bacteria, archaea and eukaryotes. Thus they all share a common origin. The ancestral functions of the Sm-orthologs suggest that their role in pre-mRNA splicing might be more recently evolved. The common feature shared by all Sm proteins is their ability to bind and regulate RNA. We therefore hypothesize that the Sm proteins function during oogenesis by binding oskar mRNA (and possibly other RNAs) and enabling its proper localization within the oocyte.
Long term goals: Work from our lab as well as others have shown that Sm proteins have functions in addition to splicing. Our goal is to fully examine the diverse biological roles of these fascinating ancient proteins. Initial studies will take advantage of the powerful genetic and cell biological tools available with the Drosophila model system. The ultimate goal of our research is to translate what we have discovered in Drosophila to a mammalian model system.
Approaches: We use a variety of tools such as genetics, cell biology and biochemistry to test our hypotheses. Numerous molecular techniques such as RT-PCR, western blotting, immunoprecipitation and in situ hybridization are routinely used.
Graydon B. Gonsalvez, T.K. Rajendra, Ying Wen and A. Gregory Matera. Sm proteins specify germ cell fate by regulating the localization of cytoplasmic oskar mRNA. Development, July 2010 137: 2341-2351
Graydon B. Gonsalvez and A. Gregory Matera. Post-translational modification of Sm proteins: Diverse roles in snRNP assembly and germline specification, Post-Transcriptional RNA processing in Eukaryotes, J.Y. Wu (editor), Wiley-Blackwell Press, Weinheim, Germany (invited book chapter, in press).
Graydon B. Gonsalvez, Kavita Praveen, Amanda Hicks, Liping Tian, and A. Gregory Matera. Sm protein methylation is dispensable for snRNP assembly in Drosophila melanogaster. RNA. 2008, May 14:878–887.
Graydon B. Gonsalvez, Liping Tian, Jason K. Ospina, François-Michel Boisvert, Angus I. Lamond, and A. Gregory Matera. Two distinct arginine methyltransferases are required for biogenesis of Sm-class ribonucleoproteins. Journal of Cell Biology. 2007 Aug 27;178(5):733-40.
T.K. Rajendra, Graydon B. Gonsalvez, Karl B. Schpargel, Helen K. Salz, and A. Gregory Matera. A Drosophila model for Spinal Muscular Atrophy reveals a sarcomeric function for SMN in striated muscle. Journal of Cell Biology. 2007 Mar 12;176(6):831-41.
Carl R. Urbinati, Graydon B. Gonsalvez, John P. Aris, and Roy M. Long. Loc1p is required for efficient assembly and nuclear export of the 60S ribosomal subunit. Mol Genet. Genomics. 2006 Oct;276(4):369-77.
Graydon B. Gonsalvez, T.K. Rajendra, Liping Tian, and A. Gregory Matera.
The Sm-protein methyltransferase, dart5, is essential for germ-cell specification and maintenance. Current Biology. 2006 Jun 6; 16(11): 1077-1089
Jason K. Ospina, Graydon B. Gonsalvez, Janna Bednenko, Edward Darzynkiewicz , Larry Gerace, and A. Gregory Matera. Crosstalk between Snurportin1 Subdomains. M ol Biol Cell . 2005 Oct;16(10):4660-71.
Gonsalvez, Carl Urbinati, and Roy M. Long (2005). RNA
Localization in Yeast – Moving Towards a Mechanism.
Biology of The Cell. Jan; 97(1):75-86
Graydon B. Gonsalvez, Jamie L. Little and Roy M. Long (2004). ASH1 mRNA Anchoring Requires Reorganization of the Myo4p/She3p/She2p Transport Complex. Journal of Biological Chemistry. Oct 29; 279(44):46286-94
Graydon B. Gonsalvez, Katrina A. Lehmann, Derek K. Ho, Eleni Stanitsa , James R.Williamson, and Roy M. Long (2003) . She2p mRNA-Binding Activity is Required for Proper Asymmetric Sorting of the Myo4p-She3p Complex to daughter cells. RNA , Nov;9(11):1383-99.
Roy M. Long, Wei Gu, Xiuhua Meng, Graydon Gonsalvez, Robert H. Singer, and Pascal Chartrand. (2001). An Exclusively Nuclear RNA-binding Protein Affects Asymmetric Localization of ASH1 mRNA and Ash1p in Yeast. Journal of Cell Biology , 153 : 307-318.
Revised Jan 2011