We identified a previously uncharacterized gene, spermatid maturation 1 (Spem1), encoding a protein exclusively expressed in the cytoplasm of steps 14 -16 elongated spermatids in the mouse testis. This protein contains no known functional domains and is highly conserved across mammalian species. Male mice deficient in Spem1 were completely infertile because of deformed sperm characterized by a bent head wrapped around by the neck and the middle piece of the tail. We show that lack of Spem1 causes failure of the cytoplasm to become loose and detach from the head and the neck region of the developing spermatozoa. Retained cytoplasmic components mechanically obstruct the straightening of the sperm head and the stretching of the growing tail, leading to the bending of the head in the neck, followed by the wrapping of the head by the neck or the middle piece of the sperm tail. Our study reveals that proper cytoplasm removal is a genetically regulated process requiring the participation of Spem1 and that lack of Spem1 causes sperm deformation and male infertility. cytoplasmic droplets ͉ gene knockout ͉ spermatogenesis ͉ spermiation ͉ spermiogenesis

"Pinhead sperm," or "acephalic sperm," a type of human teratozoospermia, refers to the condition in which ejaculate contains mostly sperm flagella without heads. Family clustering and homogeneity of this syndrome suggests a genetic basis, but the causative genes remain largely unknown. Here we report that Spata6, an evolutionarily conserved testis-specific gene, encodes a protein required for formation of the segmented columns and the capitulum, two major structures of the sperm connecting piece essential for linking the developing flagellum to the head during late spermiogenesis. Inactivation of Spata6 in mice leads to acephalic spermatozoa and male sterility. Our proteomic analyses reveal that SPATA6 is involved in myosin-based microfilament transport through interaction with myosin subunits (e.g., MYL6).M ale gametes-spermatozoa-are produced in the testis through a process termed spermatogenesis, which can be divided into three phases: mitotic, meiotic, and haploid (1). In the mitotic phase, spermatogonial stem cells proliferate and differentiate into spermatogonia, which subsequently enter the meiotic phase and become spermatocytes. Spermatocytes undergo crossover, followed by two consecutive meiotic cell divisions to produce haploid spermatids. Spermatids then undergo a multistep differentiation process, also called spermiogenesis, to form spermatozoa. Severe disruptions in either the mitotic or the meiotic phase tend to cause azoospermia, whereas spermiogenic defects often lead to reduced sperm counts, aberrant sperm motility, and deformed spermatozoa, a condition termed oligoasthenoteratozoospermia (OAT) in humans (2, 3).OAT accounts for a significant proportion of male idiopathic infertility cases (2, 4). Numerous cases of acephalic spermatozoa have been reported in teratozoospermic patients (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). In these patients, the major anomaly lies in headless spermatozoa in the ejaculate, and the headless spermatozoa were initially called "pinhead sperm" because the investigators mistakenly regarded the retained cytoplasmic droplets, which are usually attached to the midprincipal piece junction of the flagella, as the heads of reduced size (8,13,14). Extensive ultrastructral studies on humans and animals with acephalic spermatozoa suggest that this condition results from defects in formation of the connecting piece of spermatozoa during late spermiogenesis, including failure for the proximal centrioles to attach normally to the caudal portion of the sperm nuclei, leading to abnormal head-midpiece alignment, or a nuclear defect that interferes with formation of the implantation fossa, the normal lodging site for the sperm proximal centriole (16). Aberrant formation of the connecting piece leads to independent development of the sperm heads and flagella, and eventually these structures become separated within the seminiferous tubules or during their transition through the seminal tract as a consequence of increased instability of the head-midpiece junction (16,18)....

Previous studies have shown that the cryptococcal capsule inhibits phagocytosis of Cryptococcus neoformans by macrophages and neutrophils. In this study, the binding sites of potential serum opsonins in immune and nonimmune sera were determined by immunoelectron microscopy, and the results were compared with the results of phagocytosis of the yeasts by mouse peritoneal macrophages and human neutrophils. Immunoglobulin G (IgG) from normal human serum showed low-density binding at the capsular surface and at sites throughout the capsule. Complement component C3 from normal serum bound heavily at the capsular surface. IgG from rabbit capsular antiserum showed relatively dense deposition at the capsular surface and at sites throughout the capsule. Cells opsonized with heat-inactivated human serum were engulfed poorly by both macrophages and neutrophils, indicating that the low-density deposition of IgG produced by normal serum was not adequate for opsonization. Yeasts opsonized with normal human serum were engulfed in large numbers by neutrophils and to a lesser extent by macrophages, indicating that neutrophils in particular were able to effectively utilize the opsonically active C3 which normal human serum deposited at the capsular surface. Yeasts opsonized with rabbit anticapsular serum were engulfed by both macrophages and neutrophils, indicating that the high density of surface IgG produced by capsular antiserum is an effective opsonin for both cells. These results suggest that the complement-neutrophil system is a possible defense mechanism in the nonimmune host.

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The ultrastructure of the mouse esophagus at the level of the diaphragm was studied from embryo day 17 to adult. The transdifferentiation of smooth muscle into skeletal muscle was categorized into seven ultrastructural stages: during phase I normal smooth muscle myogenesis was observed. In phase II subpopulations of cells changed into aggregates of myoblast-like cells. At the center of these cell aggregates, phase III cells appeared that contained condensed myofilaments. Dense bodies and dense bands appeared enlarged by the accumulation of thin filaments. In phase IV the condensed myofilaments organized into sarcomere pretemplate structures. The dense bodies and dense bands formed rudimentary Z-lines. In phase V the sarcomere templates appeared as more defined structures and began to align. An elaborate perinuclear region appeared. During phase VI, skeletal muscle sarcomeres were apparent and myofilaments were arranged in a typical hexagonal array. Phase VII skeletal muscle fibers were unique with sarcomeric bifurcations and anastomoses between adjacent myofibrils. Non-contractile organelles were less organized in these cells than in skeletal muscles such as rectus and vastus lateralis muscles. During the transdifferentiation process, other cell types remained unchanged, except the number of interstitial cells of Cajal became reduced. Immunocytochemical studies with antibodies against smooth and skeletal muscle myosin were also performed during the process of transdifferentiation. An osmium tetroxide/potassium ferricyanide en bloc mordant enabled the use of ultrathin Unicryl sections for immunocytochemistry. Cells exhibited smooth muscle myosin-like immunoreactivity from the smooth muscle stage through the condensed myofilament stage. Cells were immunopositive for skeletal muscle myosin before the formation of sarcomere templates, during the condensed stage, and after development of mature skeletal muscle cells. We also observed a hybrid muscle cell with properties of both smooth and skeletal muscle cells.