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RESEARCH:
      Control of alternative pre-mRNA splicing in relation to neuronal memory and 
      hormone secretion

We study the molecular basis of control of alternative pre-messenger RNA splicing in relation to cell functions and diseases.

Alternative splicing is a common way of gene expression regulation that can generate multiple mRNA and often protein isoforms from a single gene. Almost all human gene transcripts are alternatively spliced and some are known to generate extremely diverse protein isoforms. This likely contributes to the proteomic complexity, particularly in neurons and endocrine cells.  In experimental animals, genetic deficiencies in alternative splicing factors result in developmental defects or embryonic-lethal phenotypes. In humans, aberrant splicing leads to genetic diseases such as neurodegeneration. However, it remains largely unclear how alternative splicing is controlled, particularly by cellular signals. With complex splicing patterns, widespread presence but unclear regulatory mechanisms, alternative splicing and its regulation pose a tremendous challenge in the post-genome era.

For example, in electrically excitable cells such as neurons, endocrine and muscle cells, ion channels conduct ions in/out of the cells to generate electrical firings that are important for cell functions including neuronal memory, hormone secretion and muscle contraction. These processes are believed to be critical for higher order phenotypes such as learning, behavior, metabolism and heart beating. How these processes are finely tuned during development and in adult life is still a mystery to researchers. Alternative splicing provides a unique way to diversify proteins in these processes and may play a critical role here. Interestingly, alternative splicing of some ion channel genes has been found to be regulated by membrane depolarization, the first part of an action potential, implying a gene expression change related to  the electrophysiological memory observed in neurons or adaptive changes in hormone secretion. However, the molecular basis of splicing regulation by membrane depolarization remains unclear.

We have used the STREX (stress axis-regulated exon) variant of the Slo BK potassium channel gene as a model to study how cell signals regulate the choice of alternative splice sites in pre-mRNAs. Inclusion of the STREX exon enhances the calcium sensitivity of BK channels and likely modulates cellular electrical properties related to hearing frequency tuning or adaptive changes in learning and memory. Its regulation by stress hormones and the calcium/calmodulin-dependent protein kinase IV (CaMK IV) makes it an interesting target for dissecting the components regulating alternative splicing as well as understanding the impact of splicing regulation on neuronal electrical properties. A first step toward this goal was made by coupling CaMK IV with a pre-mRNA element (CaRRE1) sufficient to confer CaMK IV response to an otherwise non-responsive exon. We have recently identified the splicing factor hnRNP L as an essential component of the CaMKIV-regulated splicing.  We are currently  characterizing  the regulation of hnRNP L and its homologue LL by CaMKIV.

Others being studied include exons involved in neuronal synaptic function or cell growth/apoptosis.

We hope these studies will provide molecular details of signal-regulated splicing and knowledge to help us reverse aberrant splicing in genetic diseases.

Keywords: molecular biology, RNA, processing, splicing, gene regulation, gene expression, proteomic diversity, complexity, splicing factors, protein kinases, cell signaling, neurons, endocrine cells, genetic diseases, cancer.

PUBLICATIONS:                                                                                               mapleafr

1.      Cao WG, Sohail, M., Liu, G., Koumbadinga, G.A., Lobo, V.G., Xie, J. Differential effects of PKA-controlled CaMKK2 variants on neuronal differentiation. RNA Biology, 2011, 8(6):1061-1072.|PDF|

2.      Li, H.Z., Liu, G.D., Yu, J.K., Cao, W.G., Lobo, V.G., Xie, J. In vivo selection of kinase-responsive RNA elements controlling alternative splicing. J. Biol. Chem. 2009, 284:16191-16201. |PDF|

3.      Yu JK, Hai, Y., Liu, G.D., Fang, T.L., Kung, S.K.P., Xie, J. The heterogeneous nuclear ribonucleoprotein L is an essential component in the Ca++/calmodulin-dependent protein kinase IV-regulated alternative splicing through cytidine-adenosine repeats. J. Biol. Chem. 2009, 284:1505-1513. |PDF|

4.      Hai, Y., Cao, W.G., Liu, G.D., Hong, S., Abou Elela, S., Klinck, R., Chu, J.Y., Xie, J.. A G-tract element in apoptotic agents-induced alternative splicing. Nucleic Acids Res, 2008, 36(10):3320-3331. |PDF|

5.      Xie, J. Control of alternative pre-mRNA splicing by calcium signals. BBA-Gene Regulatory Mechanisms, 2008, 1779(8):438-452. |PDF|

6.      Xie Y, Yang H, Miller JH, Shih DM, Hicks GG, Xie J, Shiu RP: Cells deficient in oxidative DNA damage repair genes Myh and Ogg1 are sensitive to oxidants with increased G2/M arrest and multinucleation. Carcinogenesis 2008, 29:722-728.

7.      Ma, S., Liu, G., Sun, Y. & Xie, J. Relocalization of the polypyrimidine tract binding protein during PKA-induced neurite growth. BBA-Molecular Cell Research, 2007 June 1773(6):912-923. |PDF|

8.      Edirimanne VE, Woo CW, Siow YL, Pierce GN, Xie JY, O K: Homocysteine stimulates NADPH oxidase-mediated superoxide production leading to endothelial dysfunction in rats. Can J Physiol Pharmacol 2007, 85:1236-1247.

9.      Lee JA, Xing Y, Nguyen D, Xie J, Lee CJ, Black DL: Depolarization and CaM kinase IV modulate NMDA receptor splicing through two essential RNA elements. PLoS Biol 2007, 5:e40.

10.   Coutinho G, Xie JY, Du LT, Brusco A, Krainer AR, Gatti RA: Functional significance of deep intronic mutation in the ATM gene and evidence for an alternative Exon 28a. Human Mutation 2005, 25:118-124.

11.   Xie J, Jan C, Stoilov P, Park J, Black DL. A consensus CaMK IV-responsive RNA sequence mediates regulation of alternative exons in neurons. RNA, 2005 Dec 11(12):1825-1834.

12.   Li CY, Chu JY, Yu JK, Huang XQ, Liu XJ, Shi L, Che YC, Xie J: Regulation of alternative splicing of Bcl-x by IL-6, GM-CSF and TPA. Cell Research 2004, 14:473-479.

13.   Xie J, Lee JA, Kress TL, Mowry KL, Black DL. Protein Kinase A Phosphorylation Modulates Transport of the Polypyrimidine Tract-Binding Protein. PNAS, 2003 July 22;100(15):8776-8781

14.   Xie J & Black DL. A CaMK IV responsive RNA element mediates depolarization-induced alternative splicing of ion channels. Nature(London). 2001 Apr 19;410(6831):936-939. 

15.   Xie J & McCobb DP. Control of alternative splicing of potassium channels by stress hormones. Science(WashingtonDC). 1998 Apr 17;280(5362):443-6.

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Research in this lab has been supported by CIHR , NCIC, CBCF, NSERC, MMSF, MHRC and CFI. HOME
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CONTACT:

Jiuyong Xie

University of Manitoba
Department of Physiology
439 Basic Medical Sciences Bldg
745 Bannatyne Avenue
Winnipeg, MB  CANADA
R3E 0J9

Tel    204 975 7774 (O)
         204 977 5668 (Lab)
Fax   204 789 3934


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