Hung Tseng, Ph.D. -- Dermatology Faculty

Education
1979 B.A. Peking University
1986 Ph.D. Johns Hopkins University

Research Area of Interest
Regulation of keratinocyte proliferation and tumorigenesis. Regulation of rRNA synthesis in keratinocytes, ocular epithelial cells and the germ cells of testis and ovary. Signal transduction pathways that influence rRNA transcription (e.g. Sonic Hedgehog).

Research Summary
My research interest is to understand the tissue/cell-type-specific regulation of rRNA synthesis. This interest arose from our finding that basonuclin, a zinc-finger protein I discovered 10 years ago while a postdoc in Prof. Howard Green's lab (Tseng and Green, 1992, 1994), is likely to be a cell-type specific transcription factor for the ribosomal rRNA genes (rDNAs). We found that basonuclin is associated with the rDNA loci on mitotic chromosomes, typical of transcription factors for the rDNA (Tseng et al., 1999); that the zinc fingers of basonuclin bind to the promoter of rDNA at three evolutionarily highly conserved sites (Iushi and Green, 1999; Tseng et al., 1999; Tian et al., 2001) and that basonuclin can stimulate transcription from an rDNA promoter in a co-transfection assay (Tian et al., 2001). These studies have led us to propose that one of the biological functions of basonuclin is to enhance rRNA transcription from a basal level. All cells require rRNA transcription, but its enhancement is particularly necessary when the rate of protein synthesis increases in proliferation and protein accumulation. One of the novel aspects of the action of basonuclin is that it is cell-type-specific. Basonuclin is only present in abundance in the basal keratinocytes of the stratified epithelia and the germ cells of the testis and ovary. This makes it different from all previously described Pol I transcription factors, which are thought to be ubiquitous. Basonuclin therefore provides a first opportunity to study the cell-type specific mechanism of enhancing rRNA transcription. Its existence also raises a number of interesting questions. For example:

Why individual cell types need such a factor? How many such factors are there, and which cell types have them? How does such a factor work, how does it interact with other known, ubiquitous factors? How effective is it in stimulating/inhibiting rRNA transcription? How is the expression of such a factor regulated during normal development and diseases?

Our study of basonuclin focuses on two aspects of the action of the protein: i) its requirements in the cells that contain the protein; ii) the molecular mechanism by which it modifies the transcription of rDNA. The requirement of basonuclin in the basal keratinocytes and the germ cells of testis and ovary are being investigated by transgenic mouse models, in which the content of basonuclin in these cells is reduced or eliminated by RNA interference (RNAi) and the Cre-lox methods, respectively, or the function of basonuclin is interfered by dominant-negative mutations. By examining the phenotypic changes caused by reduced basonuclin content or function, we will be able to assess the role of basonuclin in these cells. We are taking a biochemical approach to investigate how basonuclin increases transcription from the rDNA promoter. We focus on the transcription initiation step where most likely basonuclin exerts its action. The interaction of basonuclin and the basic components of the Pol I transcription initiation complex will be examined by EMSA, immunoprecipitation and Western blot. The effect of basonuclin on the transcription initiation will be tested by an in vitro transcription system. These studies will allow us to understand the transcription initiation events in which basonuclin plays a part.

The existence of basonuclin raises a larger question, which has been largely ignored in the past, namely, how do individual cell types regulate rRNA synthesis in development. A difficulty in investigating this question is the lack of a method to measure the rate of rRNA transcription of each cell types in vivo. We are developing methods which will let us assess the rate of rRNA transcription in tissue sections of complex cellular composition.

Significance: The importance of ribosome synthesis to cellular function cannot be overstated. It is not difficult to imagine the immediate and devastating effect of a complete shut down of ribosome synthesis to a dividing cell. Transcription of rRNA is the rate-limiting step in ribosome biogenesis and therefore it is a key point of regulation by intra- and extra-cellular signals. Ribosomal RNA transcription is one of the first and the best studied gene regulatory mechanisms. Most of the molecular and biochemical dissections of the Pol I transcription apparatus rely on materials obtained from cultured cells (e.g. Hela cells for the human Pol I and Erhlich ascites for that of the mouse). Although this approach provides a convenient and economical source of Pol I complex and has yielded a wealth of information regarding the molecular composition of Pol I-transcription apparatus and regulation, it does overlook the issue of cell-type-specific regulation of rRNA transcription. The serendipitous discovery of basonuclin as a cell-type-specific regulator of rRNA transcription presents a first opportunity to investigate this aspect of the regulation of this important gene.

Dr. Tseng's Lab Personnel:
Chunhua Cui, M.D., Post Doctoral Researcher
xiaohong Zhang, Ph.D., Post Doctoral Researcher
Shengliang Zhang, Ph.D., Post Doctoral Researcher
Jiangchao Qian, Ph.D., Post Doctoral Researcher
David Tseng, Student

Selected Publications

Tseng, Hung, and Howard Green, . 1988. Remodeling of the involucrin gene during primate evolution Cell 54:491-496

Tseng, Hung, and Howard Green 1992. Basonuclin: A keratinocyte protein with multiple pairs of zinc fingers. Proc. Nat. Acad. Sci. 89: 10311-10315.

Tseng, Hung, and Howard Green 1994. Association of keratinocyte basonuclin with colony-forming ability and absence of terminal differentiation. J Cell Biol 126(2):495-506.

Tseng, Hung, 1997. Complementary oligonucleotides and the origin of the mammalian involucrin gene. Gene 194:87-95

Mahoney, My — G.,Wei Tang, MingMing Xiang,George Gerton, Steward Moss, John Stanley and Tseng, Hung, 1998 Translocation of zinc finger protein basonuclin from the mouse germ cell nucleus to the midpiece of the spermatozoon during spermiogenesis. Biology of Reproduction 59, 388-394

Tseng, Hung, Jaclyn A. Biegel and Ray Brown 1999 Basonuclin is associated with ribosomal RNA genes on human keratinocyte mitotic chromosomes. J Cell Sci 129(18):3039-3047

Tseng, Hung 1999 DNA cloning without restriction enzyme and ligase. BioTechniques 27:1240-1244
Tian, Qinjie, Gregory S. Kopf, Raymond S. Brown and Hung Tseng 2001. Function of basonuclin in increasing transcription of the ribosomal RNA genes during mouse oogenesis. Development, 128:407-416
Cui, Chunhua and Hung Tseng, 2004. Estimation of ribosomal RNA transcription rate in situ. Biotechniques, 36: 134
Cui, Chunhua, Thomas Elsam, Qinjie Tian, John T. Seykora, Marina Grachtchouk, Andrzej Dlugosz, and Hung Tseng, 2004. Gli proteins up-regulate the expression of basonuclin in basal cell carcinoma. Cancer Research, 64, 5651-5658
Howard Green and Hung Tseng, 2004. Basonuclin: A Zinc Finger Protein of epithelial cells and reproductive germ cells. In Zinc Finger Proteins: from Atomic Contact to Cellular Function. Ed. S. Iuchi and N. Kuldell, Landes Bioscience.
Ma, Jun, Richard M. Schultz and Hung Tseng, 2005. Basonuclin: A novel mammalian maternal effect gene. Submitted
Qian, Jiangchao and Hung Tseng, 2005. Mapping rRNA transcription activity in mouse eye. In preparation