title: The acroplaxome is the docking site of Golgi-derived myosin Va/Rab27a/b- containing proacrosomal vesicles in wild-type and Hrb mutant mouse spermatids.
abstract: Acrosome biogenesis involves the transport and fusion of Golgi-derived proacrosomal vesicles along the acroplaxome, an F-actin/keratin 5-containing cytoskeletal plate anchored to the spermatid nucleus. A significant issue is whether the acroplaxome develops in acrosomeless mutant mice. Male mice with a Hrb null mutation are infertile and both spermatids and sperm are round-headed and lack an acrosome. Hrb, a protein that contains several NPF motifs (Asn-Pro-Phe) and interacts with proteins with Eps15 homology domains, is regarded as critical for the docking and/or fusion of Golgi-derived proacrosomal vesicles. Here we report that the lack of an acrosome in Hrb mutant spermatids does not prevent the development of the acroplaxome. Yet the acroplaxome in the mutant contains F-actin but is deficient in keratin 5. We also show that the actin-based motor protein myosin Va and its receptor, Rab27a/b, known to be involved in vesicle transport, are present in the Golgi and Golgi-derived proacrosomal vesicles in wild-type and Hrb mutant mouse spermatids. In the Hrb mutant, myosin-Va-bound proacrosome vesicles tether to the acroplaxome, where they flatten and form a flat sac, designated pseudoacrosome. As spermiogenesis advances, round-shaped spermatid nuclei of the mutant display several nuclear protrusions, designated nucleopodes. Nucleopodes are consistently found at the acroplaxome- pseudoacrosome site. Our findings support the interpretation that the acroplaxome provides a focal point for myosin-Va/ Rab27a/b-driven proacrosomal vesicles to accumulate, coalesce, and form an acrosome in wild-type spermatids and a pseudoacrosome in Hrb mutant spermatids. We suggest that nucleopodes develop at a site where a keratin 5-deficient acroplaxome may not withstand tension forces operating during spermatid nuclear shaping.
authors.affiliation: Department of Cell Biology and Anatomical Sciences, The Sophie Davis School of Biomedical Education/City University of New York Medical School, New York, New York 10031, USA. kier@med.cuny.edu
authors.forename: Abraham L
authors.initials: AL
authors.lastname: Kierszenbaum
authors.forename: Laura L
authors.initials: LL
authors.lastname: Tres
authors.forename: Eugene
authors.initials: E
authors.lastname: Rivkin
authors.forename: Ningling
authors.initials: N
authors.lastname: Kang-Decker
authors.forename: Jan M A
authors.initials: JM
authors.lastname: van Deursen
mesh_terms: D000177:Acrosome / Q000502:physiology*; D000199:Actins / Q000378:metabolism; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D019084:Fluorescent Antibody Technique, Indirect; D006056:Golgi Apparatus / Q000378:metabolism*; D007150:Immunohistochemistry; D053569:Keratin-15; D053555:Keratin-5; D007633:Keratins / Q000172:deficiency; D008297:Male; D051379:Mice; D008854:Microscopy, Electron; D016253:Microscopy, Immunoelectron; D009154:Mutation; D018995:Myosin Heavy Chains / Q000378:metabolism*; D024701:Myosin Type V / Q000378:metabolism*; D013087:Spermatids / Q000502:physiology* / Q000648:ultrastructure; D020691:rab GTP-Binding Proteins / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins
chemical_list: D000199:Actins; D033942:Adaptor Proteins, Vesicular Transport; C440904:Agfg1 protein, mouse; D002352:Carrier Proteins; C503940:KRT5 protein, human; D053569:Keratin-15; D053555:Keratin-5; C492053:Krt15 protein, mouse; C513082:Myo5a protein, mouse; D000075745:rab27 GTP-Binding Proteins; D007633:Keratins; D024701:Myosin Type V; C512962:Rab27a protein, mouse; D018995:Myosin Heavy Chains; D020691:rab GTP-Binding Proteins