Researcher’s Profile

Debra J. Wolgemuth, PhD

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We have identified a novel mammalian A-type cyclin, cyclin Al, which we have shown to be expressed at highest levels if not exclusively in the testis in mice and humans. Targeted mutagenesis of the gene for cyclin A1 results in viable progeny but male sterility, while females are fully fertile. Cyclin A1-deficient male germ cells arrest at the G2/M transition of meiotic prophase I. The cells do not form haploid spermatids and rather, exhibit properties suggestive of a rapid entry into an apoptotic cell death. Our hypothesis is that there is a primary cell death response that is specifically activated in response to cell cycle arrest. We wish to understand the transcriptional control cyclin A1 in the male germ line, the kinase partners and substrates of cyclin A1 protein, and the functional redundancy of the two mammalian A-type cyclins. Our current projects include:

* Identifying regulatory elements required for the proper in vivo expression of cyclin A1
* Asking if cyclin A2 can rescue the cyclin A1-deficient phenotype of meiotic arrest in spermatogenesis, in transgenic mice in vivo
* Studying the function of cyclin A1in human spermatogenesis by screening for mutations in the gene for cyclin A1 in infertile men
* Examining the role of p53 in the cell cycle arrest-induced apoptosis that occurs in the absence of cyclin A1
* Determining the downstream effector molecules responsible for the cell death that occurs in the absence of cyclin A1
* Identifying proteins that interact with cyclin A1 in the germ line
* Identifying molecules that could inhibit cyclin A1/Cdk activity

Cyclin A1 and Leukemogenesis

Cyclin A1 is highly expressed in human leukemic cells from patients with acute myeloid leukemia. To test the hypothesis that the aberrant high levels of cyclin A1 were causal in the leukemic phenotype, i.e., acting as an oncogene, we generated transgenic mice in which cyclin A1 was expressed under the direction of the human cathepsin G promoter in myeloid precursor cells. The transgenic animals exhibited abnormal myelopoiesis and developed acute myeloid leukemia. We have also recently observed high levels of cyclin A1 expression in testicular tumors of the highly invasive embryonal carcinoma class but not in the more common and less invasive seminoma. We propose that cyclin A1 represents a novel target for drug intervention in cancer therapy. Our current projects include:

* Asking if inhibiting the expression of cyclin Al in leukemic cells can revert the leukemic phenotype
* Developing in vitro kinase assays for screening pharmacological targets for inhibition specifically for cyclin A1/Cdk function
* Examining the sub-cellular distribution of cyclin A1 in leukemic versus normal cells
* Studying the role of cyclin A1 in normal hematopoiesis in cyclin A1-deficient mice

Retinoid Signaling and Development of the Reproductive System

Dietary retinal is required for spermatogenesis (and vision) in mammals. Studies generating mutations in specific receptors for vitamin A metabolites have clearly shown a role for the retinoid receptors RAR alpha and RXR beta in spermatogenesis. Our current projects include:

* Characterizing the phenotypic abnormalities resulting in male sterility in mice mutated in the RAR alpha gene, with particular emphasis on the developmental etiology of the abnormalities in the testis
* Testing the hypothesis that the mutations in the RAR alpha gene are essentially phenocopied by the effects of vitamin A deficiency by comparing the spermatogenic abnormalities in the mutant mice with those in mice which have been vitamin A-deficient from birth
* Identifying targets of the RAR alpha receptor in specific populations of cells in the testis
* Examining cell-specific functions of RAR alpha by generating conditional mutations in particular cell types

The FSRG Bromodomain-containing Proteins and Reproductive Tissues

We have characterized some properties of Fsrg1, a bromodomain-containing mouse gene that is homologous to the Drosophila gene female sterile homeotic. Fsrg1 is a member of a small sub-family of bromodomain-containing genes that appear to be involved in chromatin remodeling and possibly regulating transcription. Our current projects include:

* Determining the subcellular distribution of the Fsrg2, Fsrg3, and Fsrg4 proteins in reproductive tissues
* Characterizing the biochemical properties of the Fsrg family of proteins by identifying proteins with which they associate in vivo, particularly in the germ line
* Determining the effect of targeted mutagenesis of Fsrg1 and Fsrg3, with particular focus on spermatogenesis and oogenesis

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Genetic Control of mammalian germ cell differentiation.

Research Statement: 

The research interests of the Wolgemuth lab focus on understanding the genetic control of gametogenesis and embryogenesis using mouse models and gene targeting, transgenic, and molecular and cell biological approaches. The first of the three major projects involves understanding the function of the A and E-type cyclins during the mitotic and meiotic cell cycles mainly during spermatogenesis but also in oogenesis. We have demonstrated that cyclin A1 is essential for the progression of spermatocytes into the first meiotic division, that cyclin A2 is required for mitotic divisions of male germ cell stem cells, and that the E-type cyclins have unexpected function during meiosis, notably in the maintenance of telomere integrity. A second area of research involves elucidating the function of the BET family of double bromodomain-containing proteins, proteins that read epigenetic marks, during germ cell differentiation and neural development. We showed that the BET family member BRDT is essential for proper chromatin remodeling and transcriptional regulation during meiotic prophase and again during spermiogenesis and that BRD2 is essential for embryonic survival and neural differentiation and function, in particular in the etiology of seizure susceptibility. We have recently generated a conditional knockout model of Brd2 which will allow determining its function in adult tissues, including the germ line. Finally, the lab is pursuing studies on the role of retinoid signaling during male germ cell differentiation, again in using molecular genetic approaches in the mouse model, and more recently, pharmacologic intervention. We have used a pan-antagonist of the retinoic acid receptors (RARs) to disrupt spermatogenesis and induce sterility, importantly in a reversible manner. Long-term efforts in this project will involve developing RAR-alpha specific antagonists, identifying the target genes of RAR-alpha, and discerning their function in germ cell-Sertoli cell interactions.

Publications: 

1. Liu, D., M.M. Matzuk, W.K. Sung, Q. Guo, P. Wang and D.J. Wolgemuth.: (1998) Cyclin A1 is required for meiosis in the male mouse..  Nat Genet  20: 377-380 

2. Shang, E., H.D. Nickerson, D. Wen, X. Wang and D.J. Wolgemuth.: (2007) The first bromodomain of Brdt, a testis-specific member of the BET sub-family of double-bromodomain-containing proteins, is essential for male germ cell differentiation. .  Development  134: 3507-3515 

3. Shang, E., X. Wang, D. Wen, D.A. Greenberg and D.J. Wolgemuth. : (2009) Double bromodomain-containing gene Brd2 is essential for embryonic development in mouse. .   Dev. Dyn.  238: 908-917 

4. Chung, S.S., X. Wang, S.S. Roberts, S.M. Griffey, P.R. Reczek and D.J. Wolgemuth. : (2011) Oral administration of a retinoic Acid receptor antagonist reversibly inhibits spermatogenesis in mice. 
Our studies were highlighted as a feature article in Endocrine News, the official newsletter of the Endocrine Society and have been the subject of attention in the public media world-wide (since June, 2011). The work was also highlighted in a leading edge previews article in Cell (Bremner WJ Cell, 150, 1-2, 2012) and in a news focus article in Science 338, 318-320 (2012)..  Endocrinology  152: 2492-2502 

5. Berkovits, B.D., L. Wang, P. Guarnieri and D.J. Wolgemuth. : (2012) The testis-specific double bromodomain-containing protein BRDT forms a complex with multiple spliceosome components and is required for mRNA splicing and 3'-UTR truncation in round spermatids. .  Nucleic Acids Res.  40: 7162-7175 

6. Martinerie, L., M. Manterola, S.S. Chung, S.K. Panigrahi, M. Weisbach, A. Vasileva, Y. Geng, P. Sicinski and D.J. Wolgemuth. : (2014) Mammalian E-type cyclins control chromosome pairing, telomere stability and CDK2 localization in male meiosis. .   PLoS Genet.  10: e1004165