A mutation study of sperm head shape and motility in the mouse: lessons for the clinic

Mouse mutants that show effects on sperm head shape, the sperm tail (flagellum), and motility were analysed in a systematic way. This was achieved by grouping mutations in the following classes: manchette, acrosome, Sertoli cell contact, chromatin remodelling, and mutations involved in complex regulations such as protein (de)phosphorylation and RNA stability, and flagellum/motility mutations. For all mutant phenotypes, flagellum function (motility) was affected. Head shape, including the nucleus, was also affected in spermatozoa of most mouse models, though with considerable variation. For the mutants that were categorized in the flagellum/motility group, generally normal head shapes were found, even when the flagellum did not develop or only poorly so. Most mutants are sterile, an occasional one semi-sterile. For completeness, the influence of the sex chromosomes on sperm phenotype is included. Functionally, the genes involved can be categorized as regulators of spermiogenesis. When extrapolating these data to human sperm samples, in vivo selection for motility would be the tool for weeding out the products of suboptimal spermiogenesis and epididymal sperm maturation. The striking dependency of motility on proper sperm head development is not easy to understand, but likely is of evolutionary benefit. Also, sperm competition after mating can never act against the long-term multi-generation interest of genetic integrity. Hence, it is plausible to suggest that short-term haplophase fitness i.e., motility, is developmentally integrated with proper nucleus maturation, including genetic integrity to protect multi-generation fitness. We hypothesize that, when the prime defect is in flagellum formation, apparently a feedback loop was not necessary as head morphogenesis in these mutants is mostly normal. Extrapolating to human-assisted reproductive techniques practice, this analysis would supply the arguments for the development of tools to select for motility as a continuous (non-discrete) parameter.

Testis-specific Fank1 gene in knockdown mice produces oligospermia via apoptosis

Fank1 is exclusively expressed in the testis from the meiosis phase to the haploid phase of spermatogenesis. In this study, we examined the function of Fank1 by establishing a Fank1-knockdown transgenic mouse model. The apoptotic statuses of the testes of the transgenic mice were tested using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) method. The FANK1 consensus DNA-binding sequence was identified using cyclic amplification of sequence target (CAST) analysis. Differentially expressed genes were examined using microarray analysis. A reduction in sperm number and an increase in apoptotic spermatocytes were observed in Fank1-knockdown mice, and the apoptotic cells were found to be primarily spermatogonia and spermatocytes. The CAST results demonstrated that the consensus DNA-binding sequence was AAAAAG, in which the percentage occurrence of each base at each position ranged from 55 to 86%. This sequence was present in the promoter regions of 10 differentially expressed genes that were examined using microarray analysis. In total, 17 genes were differentially expressed with changes in their expression levels greater than twofold. The abnormal expression of Fank1 target genes that were regulated directly or indirectly by Fank1 reduced the number of sperm in the knockdown mice. Thus, FANK1 may play a pivotal role in spermatogenesis as a transcription factor.

Iqcg is essential for sperm flagellum formation in mice

Mammalian spermatogenesis comprises three successive phases: mitosis phase, meiosis phase, and spermiogenesis. During spermiogenesis, round spermatid undergoes dramatic morphogenesis to give rise to mature spermatozoon, including the condensation and elongation of nucleus, development of acrosome, formation of flagellum, and removal of excessive cytoplasm. Although these transformations are well defined at the morphological level, the mechanisms underlying these intricate processes are largely unknown. Here, we report that Iqcg, which was previously characterized to be involved in a chromosome translocation of human leukemia, is highly expressed in the spermatogenesis of mice and localized to the manchette in developing spermatids. Iqcg knockout causes male infertility, due to severe defects of spermiogenesis and resultant total immobility of spermatozoa. The axoneme in the Iqcg knockout sperm flagellum is disorganized and hardly any typical (“9+2”) pattern of microtubule arrangement could be found in Iqcg knockout spermatids. Iqcg interacts with calmodulin in a calcium dependent manner in the testis, suggesting that Iqcg may play a role through calcium signaling. Furthermore, cilia structures in the trachea and oviduct, as well as histological appearances of other major tissues, remain unchanged in the Iqcg knockout mice, suggesting that Iqcg is specifically required for spermiogenesis in mammals. These results might also provide new insights into the genetic causes of human infertility.

Kdm3a lysine demethylase is an Hsp90 client required for cytoskeletal rearrangements during spermatogenesis

The lysine demethylase Kdm3a (Jhdm2a, Jmjd1a) is required for male fertility, sex determination, and metabolic homeostasis through its nuclear role in chromatin remodeling. Many histone-modifying enzymes have additional nonhistone substrates, as well as nonenzymatic functions, contributing to the full spectrum of events underlying their biological roles. We present two Kdm3a mouse models that exhibit cytoplasmic defects that may account in part for the globozoospermia phenotype reported previously. Electron microscopy revealed abnormal acrosome and manchette and the absence of implantation fossa at the caudal end of the nucleus in mice without Kdm3a demethylase activity, which affected cytoplasmic structures required to elongate the sperm head. We describe an enzymatically active new Kdm3a isoform and show that subcellular distribution, protein levels, and lysine demethylation activity of Kdm3a depended on Hsp90. We show that Kdm3a localizes to cytoplasmic structures of maturing spermatids affected in Kdm3a mutant mice, which in turn display altered fractionation of β-actin and γ-tubulin. Kdm3a is therefore a multifunctional Hsp90 client protein that participates directly in the regulation of cytoskeletal components.

Mammalian Fused is essential for sperm head shaping and periaxonemal structure formation during spermatogenesis

During mammalian spermatogenesis, the diploid spermatogonia mature into haploid spermatozoa through a highly controlled process of mitosis, meiosis and post-meiotic morphological remodeling (spermiogenesis). Despite important progress made in this area, the molecular mechanisms underpinning this transformation are poorly understood. Our analysis of the expression and function of the putative serine-threonine kinase Fused (Fu) provides critical insight into key steps in spermatogenesis. In this report, we demonstrate that conditional inactivation of Fu in male germ cells results in infertility due to diminished sperm count, abnormal head shaping, decapitation and motility defects of the sperm. Interestingly, mutant flagellar axonemes are intact but exhibit altered periaxonemal structures that affect motility. These data suggest that Fu plays a central role in shaping the sperm head and controlling the organization of the periaxonemal structures in the flagellum. We show that Fu localizes to multiple tubulin-containing or microtubule-organizing structures, including the manchette and the acrosome-acroplaxome complex that are involved in spermatid head shaping. In addition, Fu interacts with the outer dense fiber protein Odf1, a major component of the periaxonemal structures in the sperm flagellum, and Kif27, which is detected in the manchette. We propose that disrupted Fu function in these structures underlies the head and flagellar defects in Fu-deficient sperm. Since a majority of human male infertility syndromes stem from reduced sperm motility and structural defects, uncovering Fu׳s role in spermiogenesis provides new insight into the causes of sterility and the biology of reproduction.

Genetics of male fertility

Early in embryogenesis, cells that are destined to become germ cells take on a different destiny from other cells in the embryo. The germ cells are not programmed to perform "vital" functions but to perpetuate the species through the transfer of genetic materials to the next generation. To fulfill their destiny, male germ cells undergo meiosis and extensive morphogenesis that transforms the round-shaped cells into freely motile sperm propelled by a beating flagellum to seek out their missing half. Apparently, extra genes and additional regulatory mechanisms are required to achieve all these unique features, and an estimated 11 % of genes are involved in fertility in Drosophila (Hackstein et al., Trends Genet 16(12):565-572, 2000). If comparative numbers of male fertility genes are needed in mammals, extra risks of male fertility problems are associated with disruptive mutations in those genes. Among human male infertility cases, approximately 22 % were classified as "idiopathic," a term used to describe diseases of unknown causes, with idiopathic oligozoospermia being the most common semen abnormality (11.2 %) (Comhaire et al., Int J Androl (Suppl 7):1-53, 1987). "Idiopathic" is a widely used adjective that is used to reflect our lack of understanding of the genetics of male fertility. Fortunately, after more than two decades of phenotypic studies using knockout mice and identifying genes disrupted in spontaneous mutant mice, we have unveiled new and unexpected aspects of crucial gene functions for fertility. Other efforts to categorize genes involved in male fertility in mammals have suggested a total of 1,188 genes (Hermo et al., Microsc Res Tech 73(4):241-494, 2010). Although intracytoplasmic sperm injection (ICSI) can be used to bypass many fertilization obstacles to achieve fertilization with only a few extracted sperm, the widespread use of ICSI without proper knowledge for genetic testing and counseling could still potentially propagate pleiotropic gene mutations associated with male infertility and other genetic diseases (Alukal and Lamb, Urol Clin North Am 35(2):277-288, 2008). In this chapter, we give a brief account of major events during the development of male germ cells and focus on the functions of several crucial genes that have been studied in mutant mouse models and are potential causes of human male infertility.

Acute versus chronic loss of mammalian Azi1/Cep131 results in distinct ciliary phenotypes

Defects in cilium and centrosome function result in a spectrum of clinically-related disorders, known as ciliopathies. However, the complex molecular composition of these structures confounds functional dissection of what any individual gene product is doing under normal and disease conditions. As part of an siRNA screen for genes involved in mammalian ciliogenesis, we and others have identified the conserved centrosomal protein Azi1/Cep131 as required for cilia formation, supporting previous Danio rerio and Drosophila melanogaster mutant studies. Acute loss of Azi1 by knock-down in mouse fibroblasts leads to a robust reduction in ciliogenesis, which we rescue by expressing siRNA-resistant Azi1-GFP. Localisation studies show Azi1 localises to centriolar satellites, and traffics along microtubules becoming enriched around the basal body. Azi1 also localises to the transition zone, a structure important for regulating traffic into the ciliary compartment. To study the requirement of Azi1 during development and tissue homeostasis, Azi1 null mice were generated (Azi1^Gt/Gt). Surprisingly, Azi1^Gt/Gt MEFs have no discernible ciliary phenotype and moreover are resistant to Azi1 siRNA knock-down, demonstrating that a compensation mechanism exists to allow ciliogenesis to proceed despite the lack of Azi1. Cilia throughout Azi1 null mice are functionally normal, as embryonic patterning and adult homeostasis are grossly unaffected. However, in the highly specialised sperm flagella, the loss of Azi1 is not compensated, leading to striking microtubule-based trafficking defects in both the manchette and the flagella, resulting in male infertility. Our analysis of Azi1 knock-down (acute loss) versus gene deletion (chronic loss) suggests that Azi1 plays a conserved, but non-essential trafficking role in ciliogenesis. Importantly, our in vivo analysis reveals Azi1 mediates novel trafficking functions necessary for flagellogenesis. Our study highlights the importance of both acute removal of a protein, in addition to mouse knock-out studies, when functionally characterising candidates for human disease.

Cilia are slender projections from the surface of most mammalian cells and have sensory and sometimes motile functions. They are essential for mammalian development and defects in cilia lead to a group of human diseases, termed ciliopathies, with variable symptoms including embryonic lethality, lung and kidney defects, blindness and infertility. Cilia are complex structures composed of hundreds of components, whose individual functions are poorly understood. We screened for mammalian genes important in building cilia, and identified Azi1/Cep131, a gene previously shown to be required for cilia formation and function in fish and flies. We show that if we acutely reduce levels of Azi1 in mouse cells, fewer cells form cilia, but if we generate cells chronically lacking all Azi1, cilia form normally. In addition, mice without any Azi1 are healthy and viable, confirming normal cilia function. However, in these mice, the highly specialised ciliary structure of the sperm tail does not form, resulting in male infertility. We suggest Azi1 has conserved trafficking roles in both primary cilia and the specialised sperm flagella. Abruptly removing Azi1 results in instability causing the existing cilia network to collapse, whereas chronic deletion of Azi1 allows the system to re-equilibrate, and cilia to form normally.

Acroframosome-dependent KIFC1 facilitates acrosome formation during spermatogenesis in the caridean shrimp Exopalaemon modestus

Background

Acrosome formation and nuclear shaping are the main events in spermatogenesis. During spermiogenesis in Exopalaemon modestus, a unique microtubular structure called the acroframosome (AFS) forms in spermatids. The AFS links to a temporary organelle called the lamellar complex (LCx) leading to the formation of an everted umbrella-shaped acrosome and a dish-shaped nucleus in the mature sperm. These morphological changes require complex cell motility in which the C-terminal kinesin motor protein called KIFC1 is involved. In this study, we demonstrate that KIFC1 moves along the AFS and plays an important role in acrosome formation and nuclear shaping during spermatogenesis in E. modestus.

Methodology/Principal Findings

We cloned a 3125 bp complete cDNA of kifc1 from the testis of E. modestus by PCR. The predicted secondary and tertiary structures of E. modestus KIFC1 contain three domains: a) the C-terminus, b) the stalk region, and the c) N-terminusl. Semi-quantitative RT-PCR detected the expression of kifc1 mRNA in different tissues of E. modestus. In situ hybridization demonstrated the temporal and spatial expression profile of kifc1 during spermiogenesis. Western blot identified the expression of KIFC1 in different tissues of E. modestus, including the testis. Immunofluorescence localized KIFC1, tubulin, GM130, and mitochondria in order to elucidate their role during spermiogenesis in E. modestus.

Conclusion/Significance

Our results indicate that KIFC1 transports the Golgi complex, mitochondria, and other cellular components that results in acrosome formation and nuclear shaping in E. modestus. The KIFC1 transport function depends upon the microtubular structure called the acroframosome (AFS). This study describes some of the molecular mechanisms involved in the acrosome formation and nuclear shaping in E. modestus. In addition, this study may provide a model for studying the molecular mechanisms involved in spermatogenesis in other crustacean species and lead to a better understanding of the fertilization process in crustaceans.

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.

Dynamics of the mammalian sperm membrane modification leading to fertilization: a cytological study

Fertilization occurs when the sperm penetrates the egg, resulting in the combination of paternal and maternal genomes for the propagation of generations. To perform the task, the mammalian sperm membrane system, constructed during spermatogenesis, undergoes biochemical and cytological modifications. In this review, the following three points are discussed: (i) the nature of the acrosomal membrane disclosed by various types of microscopy, including transmission electron microscopy and the recently developed high-resolution fluorescence microscopy, (ii) the nascent acrosomal membrane dysfunction during acrosome biogenesis and (iii) the modification of the sperm membrane during sperm-egg interaction.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.