Failure of acrosome formation and globozoospermia in the wobbler mouse, a Vps54 spontaneous recessive mutant

Atg7 is required for acrosome biogenesis during spermatogenesis in mice

The acrosome is a specialized organelle that covers the anterior part of the sperm nucleus and plays an essential role in the process of fertilization. The molecular mechanism underlying the biogenesis of this lysosome-related organelle (LRO) is still largely unknown. Here, we show that germ cell-specific Atg7-knockout mice were infertile due to a defect in acrosome biogenesis and displayed a phenotype similar to human globozoospermia; this reproductive defect was successfully rescued by intracytoplasmic sperm injections. Furthermore, the depletion of Atg7 in germ cells did not affect the early stages of development of germ cells, but at later stages of spermatogenesis, the proacrosomal vesicles failed to fuse into a single acrosomal vesicle during the Golgi phase, which finally resulted in irregular or nearly round-headed spermatozoa. Autophagic flux was disrupted in Atg7-depleted germ cells, finally leading to the failure of LC3 conjugation to Golgi apparatus-derived vesicles. In addition, Atg7 partially regulated another globozoospermia-related protein, Golgi-associated PDZ- and coiled-coil motif-containing protein (GOPC), during acrosome biogenesis. Finally, the injection of either autophagy or lysosome inhibitors into testis resulted in a similar phenotype to that of germ cell-specific Atg7-knockout mice. Altogether, our results uncover a new role for Atg7 in the biogenesis of the acrosome, and we provide evidence to support the autolysosome origination hypothesis for the acrosome.

Pathological changes of testicular tissue in normal adult mice: A retrospective analysis

Mouse testicular experimental models are widely used in the study of andrology, reproductive toxicology and pharmacology. Under physiological conditions, a normal adult mouse is usually considered to have normal testes. However, whether normal adult mouse testes exhibit pathological changes has not been evaluated. The objective of this study was to investigate the pathological changes of testicular tissues in normal adult mice. A retrospective analysis of 720 adult male Kunming mice, used in previous studies as controls, was performed. Bilateral testicular tissues were stained with hematoxylin and eosin for pathological examinations. Among the 720 mice, nine had abnormal testes, an incidence of 1.3%. The nine mice with abnormal testes included two with microrchidia (22.2%) while the others had a normal testicular size. The observed pathological changes associated with microrchidia were seminiferous epithelial vacuolation, spermatogenesis arrest at the spermatocyte stage and the absence of sperm in all tubules. In other abnormal testes, pathological alterations included seminiferous epithelial vacuolation, severe hypospermatogenesis and symplasts composed of collapsed spermatids in tubules. The results demonstrate that normal adult male mice exhibit testicular pathological changes. Therefore, the possibility of abnormal testes in normal adult mice must be considered when using mice to establish a testicular experimental model.

Ubiquitination regulates the morphogenesis and function of sperm organelles

It is now understood that protein ubiquitination has diverse cellular functions in eukaryotes. The molecular mechanism and physiological significance of ubiquitin-mediated processes have been extensively studied in yeast, Drosophila and mammalian somatic cells. Moreover, an increasing number of studies have emphasized the importance of ubiquitination in spermatogenesis and fertilization. The dysfunction of various ubiquitin systems results in impaired sperm development with abnormal organelle morphology and function, which in turn is highly associated with male infertility. This review will focus on the emerging roles of ubiquitination in biogenesis, function and stability of sperm organelles in mammals.

The Arf GAP SMAP2 is necessary for organized vesicle budding from the trans-Golgi network and subsequent acrosome formation in spermiogenesis

SMAP2 is an Arf GAP and modulates clathrin-coated vesicle formation. SMAP2-deficient male mice exhibited globozoospermia due to acrosome deformation. In SMAP2(−/−) spermatids, budding of proacrosomal vesicles from the TGN was distorted and clathrin traffic–related molecules such as CALM and syntaxin2 were mislocated.

The trans-Golgi network (TGN) functions as a hub organelle in the exocytosis of clathrin-coated membrane vesicles, and SMAP2 is an Arf GTPase-activating protein that binds to both clathrin and the clathrin assembly protein (CALM). In the present study, SMAP2 is detected on the TGN in the pachytene spermatocyte to the round spermatid stages of spermatogenesis. Gene targeting reveals that SMAP2-deficient male mice are healthy and survive to adulthood but are infertile and exhibit globozoospermia. In SMAP2-deficient spermatids, the diameter of proacrosomal vesicles budding from TGN increases, TGN structures are distorted, acrosome formation is severely impaired, and reorganization of the nucleus does not proceed properly. CALM functions to regulate vesicle sizes, and this study shows that CALM is not recruited to the TGN in the absence of SMAP2. Furthermore, syntaxin2, a component of the soluble N-ethylmaleimide–sensitive factor attachment protein receptor (SNARE) complex, is not properly concentrated at the site of acrosome formation. Thus this study reveals a link between SMAP2 and CALM/syntaxin2 in clathrin-coated vesicle formation from the TGN and subsequent acrosome formation. SMAP2-deficient mice provide a model for globozoospermia in humans.

The ESCRT-deubiquitinating enzyme USP8 in the cervical spinal cord of wild-type and Vps54-recessive (wobbler) mutant mice

Usp8 is a deubiquitinating enzyme that works as regulator of endosomal trafficking and is involved in cell proliferation. "In vivo" USP8 is predominantly expressed in the central nervous system and testis, two organs with highly polarized cells. Considering that neuronal cell functionality is strictly dependent on vesicular traffic and ubiquitin-mediated sorting of the endocytosed cargo, it could be of relevance to investigate about USP8 in neuronal cells, in particular motor neurons. In this study, we found that USP8 is expressed in the gray and white matter of the spinal cord, labeling neuronal cell bodies, axonal microtubules and synaptic terminals. The glia component is essentially USP8-immunonegative. The partial colocalization of USP8 with EEA1 in motor neurons indicates that USP8 is involved in early endosomal trafficking while that with Vps54 suggests an involvement in the retrograde traffic. The variant Vps54(L967Q) is responsible for the wobbler phenotype, a disorder characterized by motor neuron degeneration. We searched for USP8/Vps54 in wobbler spinal cord. The most worth-mention result was that wobbler oligodendrocytes, in contrast to the wild-type, are heavily USP8-immunoreactive; no significant modification was appreciated about the cellular expression of mutated Vps54. On the other hand, as to the neuronal intracellular localization, both USP8 and Vps54(L967Q) did not show the typical spot-like distribution, but seemed to accumulate in proteinaceous aggregates. Collectively, our study suggests that in neuronal cells USP8 could be involved in endosomal trafficking, retrograde transport and synaptic plasticity. In disorders leading to neurodegeneration USP8 is upregulated and could influence the neuron-oligodendrocyte interactions.

The wobbler mouse, an ALS animal model

This review article is focused on the research progress made utilizing the wobbler mouse as animal model for human motor neuron diseases, especially the amyotrophic lateral sclerosis (ALS). The wobbler mouse develops progressive degeneration of upper and lower motor neurons and shows striking similarities to ALS. The cellular effects of the wobbler mutation, cellular transport defects, neurofilament aggregation, neuronal hyperexcitability and neuroinflammation closely resemble human ALS. Now, 57 years after the first report on the wobbler mouse we summarize the progress made in understanding the disease mechanism and testing various therapeutic approaches and discuss the relevance of these advances for human ALS. The identification of the causative mutation linking the wobbler mutation to a vesicle transport factor and the research focussed on the cellular basis and the therapeutic treatment of the wobbler motor neuron degeneration has shed new light on the molecular pathology of the disease and might contribute to the understanding the complexity of ALS.

Absence of Dpy19l2, a new inner nuclear membrane protein, causes globozoospermia in mice by preventing the anchoring of the acrosome to the nucleus

Sperm-head elongation and acrosome formation, which take place during the last stages of spermatogenesis, are essential to produce competent spermatozoa that are able to cross the oocyte zona pellucida and to achieve fertilization. During acrosome biogenesis, acrosome attachment and spreading over the nucleus are still poorly understood and to date no proteins have been described to link the acrosome to the nucleus. We recently demonstrated that a deletion of DPY19L2, a gene coding for an uncharacterized protein, was responsible for a majority of cases of type I globozoospermia, a rare cause of male infertility that is characterized by the exclusive production of round-headed acrosomeless spermatozoa. Here, using Dpy19l2 knockout mice, we describe the cellular function of the Dpy19l2 protein. We demonstrate that the protein is expressed predominantly in spermatids with a very specific localization restricted to the inner nuclear membrane facing the acrosomal vesicle. We show that the absence of Dpy19l2 leads to the destabilization of both the nuclear dense lamina (NDL) and the junction between the acroplaxome and the nuclear envelope. Consequently, the acrosome and the manchette fail to be linked to the nucleus leading to the disruption of vesicular trafficking, failure of sperm nuclear shaping and eventually to the elimination of the unbound acrosomal vesicle. Finally, we show for the first time that Dpy19l3 proteins are also located in the inner nuclear envelope, therefore implying that the Dpy19 proteins constitute a new family of structural transmembrane proteins of the nuclear envelope.

Molecular control of rodent spermatogenesis

Spermatogenesis is a complex developmental process that ultimately generates mature spermatozoa. This process involves a phase of proliferative expansion, meiosis, and cytodifferentiation. Mouse models have been widely used to study spermatogenesis and have revealed many genes and molecular mechanisms that are crucial in this process. Although meiosis is generally considered as the most crucial phase of spermatogenesis, mouse models have shown that pre-meiotic and post-meiotic phases are equally important. Using knowledge generated from mouse models and in vitro studies, the current review provides an overview of the molecular control of rodent spermatogenesis. Finally, we briefly relate this knowledge to fertility problems in humans and discuss implications for future research. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.