My laboratory investigates molecular and cellular mechanisms that regulate spermatogenesis, sperm motility and fertilization. A major focus of our current research is sperm energy metabolism, particularly the function of glycolytic isozymes with restricted expression in the male germline. Our gene targeting studies of two germ cell-specific isozymes provide compelling evidence that glycolysis is essential for sperm motility and male fertility in the mouse. Males lacking either glyceraldehyde 3-phosphate dehydrogenase-S (GAPDHS) or phosphoglycerate kinase 2 produce sperm with severe motility defects and very low ATP levels. GAPDHS has a unique N-terminus that is required for targeting this isozyme to the fibrous sheath, a cytoskeletal structure in the sperm flagellum that defines the limits of the principal piece (see figure). We recently identified three new aldolase isoforms in mouse sperm, including two isoforms with novel N-terminal extensions that are tightly bound to the fibrous sheath. Distinctive features of the germ cell-specific glycolytic enzymes may be important for compartmentalization of glycolysis in the principal piece and/or altered activity of this key metabolic pathway.

We are using homology modeling, X-ray crystallography, and in silico docking studies to determine if the germ cell-specific glycolytic enzymes have distinct enzymatic properties. Two compounds identified in these analyses selectively inhibit GAPDHS. These studies underscore the utility of structure-based drug design and support the concept that sperm-specific glycolytic enzymes may be excellent contraceptive targets.

We investigate several proteins with restricted expression during spermatogenesis, with the goal of identifying key regulators of this developmental process. One current focus is speriolin, a unique protein that associates with activators of the anaphase promoting complex. Expressed only in the late meiotic and post-meiotic stages of spermatogenesis, speriolin is localized in the centrosome and is present in the connecting piece of the sperm flagellum. Our gene targeting studies indicate that speriolin has important functions in spermatogenesis, sperm structure and male fertility.

Sawyer GM, Monzingo AF, Poteet EC, O’Brien DA, Robertus JD (2007) X-ray analysis of phosphoglycerate kinase 2, a sperm specific isoform from Mus musculus, Proteins, published online Nov 14, DOI: 10.1002/prot.21801

Vemuganti SA, Bell TA, Scarlett CO, Parker CE, Pardo-Manuel de Villena F, O’Brien DA (2007) Three male germline-specific aldolase A isozymes are generated by alternative splicing and retrotransposition. Dev Biol 309: 18-31

Buchold GM, Magyar PL, O’Brien DA (2007) Mice lacking cyclin-dependent kinase inhibitor p19Ink4d show strain-specific effects on male reproduction. Mol Reprod Dev 74: 1008-1020

Buchold GM, Magyar PL, Arumugam R, Lee M, O’Brien DA (2007) Cyclin-dependent kinase inhibitors in the male reproductive axis. Mol Reprod Dev 74: 997-1007

Yuan W, Leisner T, McFadden AW, Clark S, Hiller S, Maeda N, O’Brien DA, Parise L (2006) CIB1 is essential for mouse spermatogenesis. Mol Cell Biol, 26: 8507-8514

Krisfalusi M, Miki K, Magyar PL, O’Brien DA (2006) Multiple glycolytic enzymes are tightly bound to the fibrous sheath of mouse spermatozoa. Biol Reprod 75:270-278

Welch JE, Barbee RR, Magyar PL, Bunch DO, O’Brien DA (2006) Expression of the spermatogenic cell-specific glyceraldehyde 3-phosphate dehydrogenase (GAPDS) in rat testis. Mol Reprod Dev 73(8):1052-1060

Holsberger DR, Buchold GM, Leal MC, Kiesewetter SE, O’Brien DA, Hess RA, Franca LR, Kiyokawa H, Cooke PS (2005) Cell cycle inhibitors p27Kip1 and p21Cip1 regulate Sertoli cell proliferation. Biol Reprod 72:1429-1436

Miki K, Qu W, Goulding EH, Willis WD, Bunch DO, Strader LF, Perreault SD, Eddy EM, O’Brien DA (2004) Glyceraldehyde 3-phosphate dehydrogenase-S, a sperm-specific glycolytic enzyme, is required for sperm motility and male fertility. Proc Natl Acad Sci USA 101:16501-16506

Yang G, Zhang Y-L, Buchold GM, Jetten AM, O’Brien DA (2003) Analysis of germ cell nuclear factor transcripts and protein expression during spermatogenesis. Biol Reprod 68:1620-1630

Eddy EM, Toshimori K, O’Brien DA (2003) Fibrous sheath of mammalian spermatozoa. Microsc Res Tech 61:103-115

Akama TO, Nakagawa H, Sugihara K, Narisawa S, Ohyama C, Nishimura S-I, O’Brien DA, Moremen KW, Millán JL, Fukuda MN (2002) Germ cell survival through carbohydrate-mediated interaction with Sertoli cells. Science 295:124-127