Zhi-Chun Lai Professor of Biology and Biochemistry & Molecular Biology 201 Life Sciences Building, University Park, PA 16802 Phone: (814) 863-0479; Lab: 863-3546 Fax: (814) 865-9131 Email: zcl1@psu.edu B.S. in biology, Peking University Ph.D. in molecular genetics, Albert Einstein College of Medicine Lai Lab Web Site

Growth Control and Cancer Genetics

Using fruit fly, zebrafish and mammalian cells as our experimental models, our main research goal is to understand how tissue growth and organ size are normally regulated during animal development and how disruption of such regulation can lead to cancer development.

In recent years, a growth inhibitory pathway mediated by tumor suppressors such as Hippo and Warts (Wts)/Lats protein kinases has been found to be critical for tissue growth and organ size control.  In 2005, my laboratory discovered a novel component of this pathway, Mob as tumor suppressor (Mats) (Lai et al., Cell 2005).  Mats functions as a coactivator of Wts kinase, and Mats function is conserved in evolution. Moreover, we found that Mats is a target of Hippo kinase.  Mats phosphorylation by Hippo increases its affinity with Wts/Lats and ability to increase Wts catalytic activity to target a key downstream oncogeneic protein Yorkie (Yki).  Importantly, the mechanism by which Mats is activated by Hippo via phosphorylation is conserved from flies to human (Wei et al., EMBOJ 2007).  Our discovery of the mats gene family has led us into studies using zebrafish, mice and human cells.  Some ongoing research projects are described below.

(1). Most of our current knowledge about Hippo signaling has come from studies in Drosophila.  It is not clear how Hippo pathway components in mammals such as human might function to regulate tissues growth.  In collaboration with Dr. K.-L. Guan’s laboratory at UC San Diego, a human oncoprotein YAP (a human homolog of fly Yki) has been investigated.  It turned out that Lats/Mats-mediated phosphorylation and cytoplamic localization is critical for YAP inhibition in controlling tissue growth and cell contact inhibition.  This is the first time that Hippo signaling is shown to mediate growth inhibition by targeting YAP oncoprotein in mammals (Zhao et al., Genes & Dev. 2007).  Moreover, transcription coactivator Yki was found to function as a binding partner with a DNA-binding transcription factor Scalloped (Sd) to control cell number and tissue growth.  Similarly, human YAP works with TEAD family of transcription factors (human Sd proteins) to regulate target gene expression to induce cell growth and epithelial-mesenchymal transition (Zhao et al., Genes & Dev. 2008).  Thus, as newly identified components in the Hippo pathway, Sd/TEAD and Yki/YAP proteins function together to promote tissue growth by regulating target gene transcription.  These studies support a model that defective Hippo signaling leads to human cancer development.

(2). We have used zebrafish as a model to test a hypothesis that the function of mats as a growth regulator is evolutionarily conserved in vertebrate animals.  Through a morpholino-based knockdown approach, we found that mats1 plays a critical role during zebrafish early development as mats1 morphant embryos exhibited severe developmental delay similar to that of Drosophila homozygous mats mutants.  This abnormal phenotype was mainly caused by defective cell proliferation and apoptosis.  Interestingly, mats1 morphant cells proliferate faster than normal cells in chimeric embryos similar to what was observed in Drosophila mats mosaic individuals.  These results support the idea that the growth regulatory function of mats genes is conserved during evolution.

Photoreceptor Cell Fate Determination

Signaling pathways that involve two receptor tyrosine kinases (Drosophila homolg of EGF receptor and Sevenless) are responsible for transmitting developmental signals to determine cell fates in the eye. However, inhibitory regulation that is required to control cellular competence to respond to inductive signals is less understood. Our research is focused on two nuclear proteins encoded by the yan and tramtrack (ttk) genes. Loss of the yan or ttk function results in the differentiation of ectopic photoreceptors. yan encodes an ETS DNA-binding protein and ttk encodes two zinc-finger proteins. In the presumptive R7 photoreceptor cells, both yan and ttk appear to act antagonistically to the proneural signal mediated by sevenless and Ras1. Moreover, yan and ttk synergistically interact to inhibit the formation of R7 cells. Thus, yan and ttk constitute of a negative nuclear regulatory system that maintains precursor cells in an undifferentiated state until they receive positive signaling, for example, the sevenless-mediated signaling for the development of R7 neuron. An unsolved question is how such inhibitory system is established in precursor cells. To investigate this issue, we are examining yan expression in some mutant background. It is possible that Notch signaling is responsible for the induction of yan expression. We are also currently trying to identify regulatory sequences that can specify yan expression in the developing eye by using a transgenic approach.

Neural Morphogenesis

Construction of a functional organ such as eye requires not only specification of many different cell types, but also proper assembly of these cells in a highly ordered manner. Our preliminary work demonstrated that the delayed furrow (defu) gene can be a critical regulator of eye morphogenesis. Removal of the defu gene activity results in failure of proper spacing between developing unit eyes and coordinated sequences of unit eye assembly. Our ongoing research is aimed at molecular genetic characterization of the defu gene. Future directions of this project include biochemical and evolutionary studies of the defu gene.

Representative Publications:

• Yuan Y., Lin, S., Zhu, Z., Zhang, W., and Lai, Z.-C. (2008). Mob as tumor suppressor gene mats1 is required for growth control in developing zebrafish embryos. The International Journal of Developmental Biology, in press.

• Zhao, B., Ye, X., Yu, J., Li, L., Li, W., Li, S., Yu, J., Lin, J. D., Chinnaiyan, A. M., Lai, Z.-C. and Guan, K.-L. (2008). TEAD mediates YAP dependent gene induction and growth control. Genes & Development 22: 1962-1971.

• Yang, Y., Gupta, V., Ho, L.-L., Zhou, B., Fan, Q., Zhu, Z., Zhang, W., and Lai, Z.-C. (2008). Both upstream and downstream intergenic regions are critical for the mob as tumor suppressor gene activity in Drosophila. FEBS Letters 582: 1766-1770.

• Shimizu, T., Ho, L.-L. and Lai, Z.-C. (2008). The mob as tumor suppressor gene is essential for early development and regulates tissue growth in Drosophila. Genetics 178: 957-965.

• Zhao, B., Wei, X. Li, W., Udan, R. S., Yang, Q., Kim, J., Xie, J., Ikenoue, T., Yu, J., Li, L., Zheng, P., Ye, K., Chinnaiyan, A., Halder, G., Lai, Z.-C. and Guan, K.-L. (2007). Inactivation of YAP oncoprotein by the Hippo pathway is involved in cell contact inhibition and tissue growth control. Genes & Development 21: 2747-2761. (This paper was selected by Faculty of 1000).

• Wei, X., Shimizu, T., and Lai, Z.-C. (2007). Mob as tumor suppressor is activated by Hippo kinase in growth inhibition in Drosophila. The EMBO Journal 26: 1772-1781.

• Yuan, Y., Zhu, Z.-Y., Lai, Z.-C. and Zhang, W.-X. (2006). Progress on Breast Cancer Metastasis Suppressor 1 (BRMS1). Hereditas 28: 1-8.

• Lai, Z.-C. Wei, X., Shimizu, T., Ramos, E., Rohrbaugh, M., Nikolaidis, N., Ho, L.-L., and Li, Y. (2005). Control of cell proliferation and apoptosis by Mob as tumor suppressor, Mats. Cell 120: 675-685. (This paper was selected by Faculty of 1000)

• Li, Y., Fetchko, M., Lai, Z.-C. and Baker, N. E. (2003). Scabrous and Gp150 are endosomal proteins that regulate Notch activity. Development 130: 2819-2827.

• Ramos, E., Price, M., Rohrbaugh, M. and Lai Z.-C.  (2003). Complex expression of the yan gene in Drosophila melanogaster is controlled by distinct cis-acting regulatory elements. Development Genes & Evolution 213: 83-89.

• Rohrbaugh, M., Ramos, E., Nguyen, D., Price, M., Wen, Y. and Lai Z.-C. (2002). Notch activation of yan expression is antagonized by RTK/Pointed signaling in the Drosophila eye. Current Biology 12: 576-581. (This paper was selected by Faculty of 1000)

• Fetchko, M., Huang, W., Li, Y. and Lai, Z.-C. (2002). Drosophila Gp150 is required for early ommatidial development through modulation of Notch signaling. The EMBO Journal 21: 1074-1083.

• Nguyen, D., Rohrbaugh, M., and Lai, Z.-C.  (2000). The Drosophila homolog of Onecut homeodomain proteins is a neural-specific transcription activator with a potential role in regulating neural differentiation. Mechanisms of Development 97: 55-70.

• Wen, Y., Nguyen, D., Li, Y. and Lai, Z.-C. (2000). The N-terminal BTB/POZ domain and C-terminal sequences are essential for Tramtrack69 to specify cell fate in the developing Drosophila eye. Genetics 156: 195-203.

• Dhulkotia, D., Nguyen, D. and Lai, Z.-C. (2000). Evolutionary conservation of a Leucine-Rich Repeat transmembrane protein Gp150 in Drosophila and Bombyx. Development Genes & Evolution 210: 145-150.

• Lai, Z.-C. and Li, Y.  (1999). Tramtrack69 is positively and autonomously required for Drosophila photoreceptor development. Genetics 152: 299-305.

• Price, M. and Lai, Z.-C. (1999). The yan gene is highly conserved in Drosophila and its expression suggests a complex role throughout development. Development Genes & Evolution 209: 207-217.

• van Huizen, R., Miller, K., Chen, D.-M., Li, Y., Lai, Z.-C., Raab, R.W., Stark, W.S., Shortridge, R.D. and Li, M.  (1998). Two distantly positioned PDZ domains mediate multivalent INAD-Phospholipase C interactions essential for G protein-coupled signaling. The EMBO Journal 17: 2285-2297.

• Lai, Z.-C., Fetchko, M. and Li, Y. (1997). Repression of Drosophila photoreceptor cell fate through cooperative action of two transcriptional repressors Yan and Tramtrack. Genetics 147: 1131-1137.

• Li, S., Li, Y., Carthew, R. W. and Lai, Z.-C. (1997). Photoreceptor cell differentiation requires regulated proteolysis of the transcriptional repressor Tramtrack. Cell 90: 469-478.

  Balczarek, K.A., Lai, Z.-C. and Kumar, S. (1997). Evolution and functional diversification of the Paired box (Pax)DNA-binding domains. Molecular Biology & Evolution 14: 829-842.

• Kumar, S., Balczarek, K.A. and Lai, Z.-C. (1996). Evolution of the hedgehog gene family.  Genetics 142: 965-972.

• Lai, Z.-C., Harrison, S., Karim, F., Li, Y. and Rubin, G. M. (1996). Loss of tramtrack gene activity results in ectopic R7 cell formation, even in a sina mutant background. Proc. Natl. Acad. Sci. USA 93: 5025-5030.

• Treisman, J. E., Lai, Z.-C. and Rubin, G. M. (1995). shortsighted acts in the decapentaplegic pathway in Drosophila eye development and has homology to a mouse TGF-b responsive gene. Development 121: 2835-2845.

• Lai, Z.-C., Rushton, E., Bate, M. and Rubin, G. M. (1993). Loss-of-function of the Drosophila zfh-1 gene results in abnormal development of mesodermally derived tissues. Proc. Natl. Acad. Sci. USA 90: 4122-4126.

• Lai, Z.-C. and Rubin, G. M. (1992). Negative control of photoreceptor development in Drosophila by the product of the yan gene, an ETS domain protein. Cell 70: 609-620.

• Fortini, M. E., Lai, Z.-C. and Rubin, G. M. (1991). The Drosophila zfh-1 and zfh-2 genes encode novel proteins containing both zinc-finger and homeodomain motifs. Mechanisms of Development 34: 113-122.

• Lai, Z.-C., Fortini, M. E. and Rubin, G. M. (1991). The embryonic expression patterns of zfh-1 and zfh-2, two Drosophila genes encoding novel zinc-finger homeodomain proteins. Mechanisms of Development 34: 123-134.

Search the MEDLINE database at PubMed for articles by Z.-C. Lai