A. Yagi et J. Paranko, ACTIN, ALPHA-ACTININ, AND SPECTRIN WITH SPECIFIC ASSOCIATIONS WITH THE POSTACROSOMAL AND ACROSOMAL DOMAINS OF BOVINE SPERMATOZOA, The Anatomical record, 241(1), 1995, pp. 77-87
Background: Characteristic membrane changes in spermatozoa culminating
in acrosome reaction and sperm-egg fusion, and suspected involvement
of actin-containing cytoskeleton in membrane changes in general, promp
ted us to investigate subcellular distribution of actin and actin-bind
ing proteins in bovine spermatozoa subjected to various extractions wh
ich sequentially denude the sperm investments. Methods: Spermatozoa we
re treated with either 1% SDS, 0.1% Triton X-100, 0.1% Hyamine, or 1 M
MgCl2 or were sonicated, Immunostaining of actin, alpha-actinin, spec
trin, and acrosin as well as electron microscopic analysis of extracte
d spermatozoa were carried out. Results: Extractions caused evaginatio
n of the acrosomal lamina which retained focal contacts with the inner
acrosomal membrane. Extractions further revealed lateral prongs at th
e anterior border of the postacrosomal sheath, Labeling for alpha-acti
nin and spectrin was localized in the acrosin-positive acrosomal lamin
a, neck, and principal piece, the latter containing also relatively ex
traction-resistant oligomeric or polymerized actin. In the postacrosom
al area, actin was accumulated in the extraction-resistant posterior r
ing structure and anteriorly at the sites apparently related to the la
teral prongs, Notably, spectrin reactivity was enhanced by MgCl2 in he
ad, neck, and principal piece, and sonication abolished cytoskeletal i
mmunoreactivity in the head. Conclusions: Destabilization of membranes
with selected extractions induces changes in the acrosomal lamina mim
icking acrosomal vesicle formation. The lateral prongs and posterior r
ing structure, respectively, may serve as anterior and posterior ancho
rs for the extraction-resistant postacrosomal sheath. The lateral pron
gs may also be a merger zone for actin, cw-actinin, and spectrin with
important implication on sperm function. The latter two proteins may b
e involved in acrosomal vesicle formation. It is apparent that extract
ions have a significant effect on the detectability of sperm cytoskele
tal elements. (C) 1995 Wiley-Liss, Inc.