Testis Function

Bartles, James | Goldberg, Erwin | Scarpulla, Richard

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James Bartles, Ph.D.
Department of Cell and Molecular Biology
Ph.D., Washington University

The plasma membrane is the interface between the cell and the environment; it is a site where one can find a host of specializations that appear to be remarkably well-tailored to the needs of the cell. Examples include: plasma membrane domains; diffusion barriers; projections such as microvilli and stereocilia; invaginations such as coated pits and caveolae; and junctions of various types. Although these plasma membrane specializations differ from one another in many respects, they share a common structural organization: they are sites where elements of the cortical cytoskeleton are linked, directly or indirectly, to transmembrane proteins of the overlying plasma membrane. The result is to tether or cluster integral plasma membrane proteins, peripheral membrane proteins and cytoskeletal proteins at these specific sites and afford paths along which signals can be relayed between the cell surface and interior. The objective of our research is to identify and characterize novel membrane and cytoskeletal proteins of plasma membrane specializations. Much of our recent work has centered on an analysis of the plasma membrane specializations of the cells of the male reproductive system, in particular the domains and diffusion barriers present within the plasma membrane overlying the tail of the mammalian spermatozoon and the intercellular junctions formed between Sertoli cells and developing spermatids in the seminiferous epithelium.

Recent Publications:

Petruszak JAM, Nehme CL, Bartles JR 1991 Endoproteolytic cleavage in the extracellular domain of the integral plasma membrane protein CE9 precedes its redistribution from the posterior to the anterior tail of the rat spermatozoon during epididymal maturation. J Cell Biol 114: 917-927.

Nehme CL, Cesario MM, Myles DG, Koppel DE, Bartles JR 1993 Breaching the diffusion barrier that compartmentalizes the transmembrane glycoprotein CE9 to the posterior-tail plasma membrane domain of the rat spermatozoon. J Cell Biol 120: 687-694.

Cesario MM, Bartles JR 1994 Compartmentalization, processing and redistribution of the plasma membrane protein CE9 on rodent spermatozoa: relationship of the annulus to domain boundaries in the plasma membrane of the tail. J Cell Sci 107: 561-570.

Cesario MM, Ensrud K, Hamilton DW, Bartles JR 1995 Biogenesis of the posterior-tail plasma membrane domain of the mammalian spermatozoon: targeting and lateral redistribution of the posterior-tail domain-specific transmembrane protein CE9 during spermiogenesis. Dev Biol 169:473-486.

Bartles JR 1995 The spermatid plasma membrane comes of age. Trends Cell Biol 5: 400-404.

Bartles JR, Wierda A, Zheng L 1996 Identification and characterization of espin, an actin-binding protein localized to the F-actin-rich junctional plaques of Sertoli cell ectoplasmic specializations. J Cell Sci 109:1229-1239.
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Erwin Goldberg, Ph.D.
Departrment of Biochemistry, Molecular Biology and Cell Biology
Ph.D., State University of Iowa

Mammalian spermatogenesis is a complex process of cellular differentiation, encompassing unique cytological and molecular changes that culminate in the formation of spermatozoa. We are particularly interested in enzymes and proteins that appear during mammalian spermatogenesis and are unique to the spermatozoon. The best-studied example is lactate dehydrogenase (LDH-X; LDH-C4), which is synthesized in the primary spermatocyte during the midpachytene phase of the first meiotic division.

To understand the mechanisms regulating this remarkable time- and cell-specific process, we have cloned and sequenced the promoter region of the ldh-c gene. We are investigating the roles of both cis- and trans-acting regulatory elements. Differential methylation of the CpG-rich promoter has been shown to regulate expression negatively in tissues lacking LDH-C4.

We are also exploiting the restricted cell-type expression of LDH-C4 to tackle problems in contraception technology and fertility control. LDH-C4 has been successfully used as an antigen to provoke antibodies against sperm. These antibodies interact with sperm in the female reproductive tract and effectively block fertilization. Ongoing work is directed toward developing a contraceptive vaccine using both synthetic peptides (comprising unique epitopes of the native protein) and recombinant viruses encoding the human LDH-C gene as potential immunogens. We are identifying and characterizing additional antigens capable of inducing infertility using sera derived from infertile patients.

Recent Publications:

Li, S., Zhou, W., Doglio, L. and Goldberg, E. (1998) Transgenic mice demonstrate a testis-specific promoter for lactate dehydrogenase (LDH). J. Biol. Chem. 273:31191-31194.

Goldberg, E. (1998) Human LDH-C peptide as an immunocontraceptive. In: Proceedings of the 10th International Congress of Immunology, New Delhi, India, 1-6 November (Eds. G.P.Talwar, I. Nath, N.K. Ganguly, K.V.S. Rao) Monduzzi Editore, Bologna, Italy, Publ., pp. 1327-1332.

Ambhaikar, M. and Goldberg, E. (1999) DNA-protein interactions in the CCAAT box region of the murine lactate dehydrogenase C promoter. Molec. Reprod. Devel. 52:360-365

Xue, J.-C., and Goldberg, E. (2000) Identification of a novel testis specific leucine rich protein. Biol. of Reprod. 62:1278-1284.

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Richard C. Scarpulla, Ph.D.
Department of Cell and Molecular Biology
Ph.D., Albert Einstein College of Medicine

The capacity for oxidative metabolism is a fundamental property of the differentiated state that varies widely among animal cells and tissues. Differences in respiratory function in both normal cells and in a variety of cellular pathologies are reflected in the number, size, and morphology of mitochondria as well as in the expression of respiratory gene products. A fundamental issue is how the biosynthetic activities of nuclear and mitochondrial genetic systems are coordinated to meet cellular energy demands. Because of the limited coding capacity of the mitochondrial genome, oxidative function relies upon nuclear genes for the majority of respiratory subunits and all of the gene products required for the transcription and replication of mitochondrial DNA (mtDNA). Characterization of mammalian genes encoding the respiratory cytochromes has led to the discovery of nuclear respiratory factors (NRFs). These nuclear transcriptional activators promote the expression of genes encoding both respiratory subunits and key components of the mtDNA transcription and replication machinery. These observations have led to the hypothesis that NRFs may be the targets of extra- and intracellular signaling pathways. As such, they would relay regulatory signals to the mitochondria via their activation of nuclear genes and also communicate the oxidative state of the cytoplasm to the nuclear transcriptional apparatus. In this way NRFs may serve to integrate nuclear and mitochondrial genetic systems to accommodate cellular demands for respiratory energy. Our long term objectives are to further define the molecular interactions and physiological functions of NRFs and related activators.

Recent Publications

Virbasius JV, Scarpulla RC 1994 Activation of the Human Mitochondrial Transcription Factor A Gene by Nuclear Respiratory Factors: A Potential Regulatory Link Between Nuclear and Mitochondrial Gene Expression in Organelle Biogenesis. Proc Natl Acad Sci USA 91:1309-1313.

Gugneja S, Virbasius JV, Scarpulla RC 1995 Four Structurally Distinct, Non-DNA-binding Subunits of Human NRF-2 Share a Conserved Transcriptional Activation Domain. Mol Cell Biol 15:102-111.

Gopalakrishnan L, Scarpulla RC 1995 Structure, Expression and Chromosomal Assignment of the Human Gene Encoding Nuclear Respiratory Factor 1. J Biol Chem 270:18019-18035.

Scarpulla RC 1996 Nuclear Respiratory Factors and the Pathways of Nuclear-Mitochondrial Interaction. Trends in Cardiovascular Medicine 6:39-45.

Gugneja S, Virbasius CA, Scarpulla RC 1996 Nuclear Respiratory Factors 1 and 2 Utilize Similar Glutamine-Containing Clusters of Hydrophobic Residues to Activate Transcription. Mol Cell Biol 16:5708-5716.

Scarpulla RC 1997 Nuclear Control of Respiratory Chain Expression in Mammalian Cells. J Bioenrg Biomemb 29:109-119.

Gugneja S, Scarpulla RC 1997 Serine Phosphorylation within a Concise Amino-Terminal Domain in Nuclear Respiratory Factor 1 Enhances DNA Binding. J Biol Chem 272:18732-18739. 
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