PARENT SESSION
PLATFORM SESSION 11. GAMETE BIOLOGY AND GAMETOGENESIS II

Monday, August 2, 2004
2:00 PM–4:00 PM
Buchanan A104
Chair: John McCarrey Co-Chair: Barbara Sotolongo

(304) LOCALIZATION OF SAMP14, A NOVEL ACROSOMAL MEMBRANE ASSOCIATED PROTEIN, DURING ACROSOME BIOGENESIS IN THE HUMAN TESTIS.

Vanage, Geeta¹, Shetty, Jagathpala¹, Klotz, Kenneth¹, Westbrook, Vivian¹, Flickinger, Charles¹, Herr, John¹, ¹ Department of Cell Biology, Charlottesville, VA

ABSTRACT- The acrosome of the mature spermatozoon functions as a regulated secretary vesicle, which performs several critical functions in mammalian fertilization. Sperm acrosomal membrane associated protein 14 (SAMP14), a new GPI anchored member of the Ly-6/uPAR super family, was localized to outer and inner acrosomal membranes of ejaculated human sperm. The present study uses a monoclonal antibody to examine the specific testicular cell types involved in the expression of SAMP14 during spermatogenesis. Light microscopic immunofluorescent observations revealed that SAMP14 is expressed first in round spermatids in the nascent acrosomal vesicle and persists throughout the cap and elongation phases of acrosomal biogenesis. Electron microscopic immunolocalization confirmed the association of SAMP14 with the acrosome in Golgi, cap and elongation phases and revealed additional fine structural details. SAMP14 was first detected associated with the acrosomal granule and the membranes of the nascent acrosomal vesicle in early round spermatids. As the acrosomal vesicle spreads and flattens over the nucleus during the cap phase, gold particles indicative of the presence of SAMP14 were visible in the electron dense fibro granular matrix but not in the electron lucent regions of the vesicle interior. In this phase gold particles were also abundant in the subacrosomal perinuclear space. During condensation of the nucleus and elongation of the spermatid, staining was most evident associated with acrosomal membranes, particularly the inner acrosomal membrane, and it was concentrated over the subacrosomal perinuclear space. Staining was also conspicuous on the outer acrosomal membrane and appeared to extend outward towards the spermatid plasmalemma. SAMP14 is an acrosome specific marker that is useful for the study of acrosome biogenesis. A high concentration of SAMP14 between the developing acrosome and the nucleus suggests that it plays a role in the attachment of the acrosome to the nucleus. Its localization also indicates that it may play a role similar to uPAR in the spatial restriction of proteolytic processes at the surface of the inner acrosomal membrane during sperm/egg interaction. The Fogarty International Center D43 TW/HD00654, the Andrew W Mellon Foundation and Schering AG supported the study.

KEY WORDS: acrosome, samp14, biogenesis