Patterns of expression of sperm flagellar genes: early expression of genes encoding axonemal proteins during the spermatogenic cycle and shared features of promoters of genes encoding central apparatus proteins*

Dnali1 is required for sperm motility and male fertility in mice

BACKGROUND

The sperm flagellum is an evolutionarily conserved specialized organelle responsible for sperm motility and male fertility. Deleterious mutations in genes involved in the sperm flagellum assembly can often cause sperm motility defects and male infertility. The murine Dnali1 gene encodes a protein that is known to interact with the cytoplasmic dynein heavy chain 1.

RESULTS

A Dnali1-mutated mouse model was generated by inducing a nonsense mutation in the Dnali1 gene. The Dnali1-mutated male mice presented impaired sperm motility and were completely infertile. Although no obviously abnormal sperm morphology was observed in Dnali1-mutated male mice, the ultrastructural structure of sperm flagellum was disrupted, displaying as an asymmetrical distribution of the longitudinal columns (LCs). Notably, infertile Dnali1-mutated male mice were able to obtain offspring via ICSI.

CONCLUSIONS

Our results uncover a role of DNALI1 in sperm motility and male fertility in mice, and demonstrate that ICSI overcomes Dnali1-associated male infertility, thus providing guidance for the diagnosis and genetic counseling of DNALI1-associated human infertility.

Deficiency of the Tmem232 Gene Causes Male Infertility with Morphological Abnormalities of the Sperm Flagellum in Mice

The axoneme and accessory structures of flagella are critical for sperm motility and male fertilization. Sperm production needs precise and highly ordered gene expression to initiate and sustain the many cellular processes that result in mature spermatozoa. Here, we identified a testis enriched gene transmembrane protein 232 (Tmem232), which is essential for the structural integrity of the spermatozoa flagella axoneme. Tmem232 knockout mice were generated for in vivo analyses of its functions in spermatogenesis. Phenotypic analysis showed that deletion of Tmem232 in mice causes male-specific infertility. Transmission electron microscopy together with scanning electron microscopy were applied to analyze the spermatozoa flagella and it was observed that the lack of TMEM232 caused failure of the cytoplasm removal and the absence of the 7th outer microtubule doublet with its corresponding outer dense fiber (ODF). Co-IP assays further identified that TMEM232 interacts with ODF family protein ODF1, which is essential to maintain sperm motility. In conclusion, our findings indicate that TMEM232 is a critical protein for male fertility and sperm motility by regulating sperm cytoplasm removal and maintaining axoneme integrity.

WDR87 interacts with CFAP47 protein in the middle piece of spermatozoa flagella to participate in sperm tail assembly

Spermatogenesis is a complex process that includes spermatogonia self-renewal, spermatocyte meiosis and spermatozoa assembly. Recent studies have revealed that WD40-repeat domain-containing (WDR) proteins play important roles in spermatocyte division, spermatozoa flagella assembly and head shaping. In this study, we investigated the expression pattern of WDR87 and found that it was highly expressed in the testis of both humans and mice. Immunofluorescence staining revealed that mouse WDR87 was distributed in the perinuclear cytoplasm of primary spermatocytes, secondary spermatocytes and round spermatids. In the spermiogenesis stage, with extension of the nucleus, WDR87 migrated to the manchette and finally localized to the middle piece of the spermatozoa tail. Furthermore, we identified a cilia- and flagella-associated protein, CFAP47, which interacted with WDR87 in the flagellar midpiece of the spermatozoa, suggesting that WDR87 may be associated with multiple morphological abnormalities of the flagella (MMAF). Subsequently, we screened gene mutations in seven MMAF individuals and found two novel mutations in CFAP47 (c.706G>A, Val236Met; c.1337C>T, Thr446Met) in one case. Immunoblotting and immunofluorescence revealed that CFAP47 was dramatically reduced in spermatozoa from the CFAP47-mutated man. Meanwhile, the expression of WDR87 was also significantly decreased, and weak signals were detected adjacent to the spermatozoa nuclei, indicating that CFAP47 was necessary for WDR87 transportation during spermatozoa flagella biogenesis. These data indicate that WDR87 is located in the middle piece of the sperm tail and interacts with CFAP47 to form a complex which is involved in spermatozoa tail assembly.

Essential Role of CFAP53 in Sperm Flagellum Biogenesis

The sperm flagellum is essential for male fertility. Despite vigorous research progress toward understanding the pathogenesis of flagellum-related diseases, much remains unknown about the mechanisms underlying the flagellum biogenesis itself. Here, we show that the cilia and flagella associated protein 53 (Cfap53) gene is predominantly expressed in testes, and it is essential for sperm flagellum biogenesis. The knockout of this gene resulted in complete infertility in male mice but not in the females. CFAP53 localized to the manchette and sperm tail during spermiogenesis, the knockout of this gene impaired flagellum biogenesis. Furthermore, we identified two manchette and sperm tail-associated proteins that interacted with CFAP53 during spermiogenesis. Together, our results suggest that CFAP53 is an essential protein for sperm flagellum biogenesis, and its mutations might be associated with multiple morphological abnormalities of the flagella (MMAF).

Planar cell polarity defects and hearing loss in sperm-associated antigen 6 (Spag6)-deficient mice

Spag6 encodes an axoneme central apparatus protein that is required for normal flagellar and cilia motility. Recent findings suggest that Spag6 also plays a role in ciliogenesis, orientation of cilia basal feet, and planar polarity. Sensory cells of the inner ear display unique structural features that underlie their mechanosensitivity. They represent a distinctive form of cellular polarity, known as planar cell polarity (PCP). However, a role for Spag6 in the inner ear has not yet been explored. In the present study, the function of Spag6 in the inner ear was examined using Spag6-deficient mice. Our results demonstrate hearing loss in the Spag6 mutants, associated with abnormalities in cellular patterning, cell shape, stereocilia bundles, and basal bodies, as well as abnormally distributed Frizzled class receptor 6 (FZD6), suggesting that Spag6 participates in PCP regulation. Moreover, we found that the subapical microtubule meshwork was disrupted. Our observations suggest new functions for Spag6 in hearing and PCP in the inner ear.

Odf2 haploinsufficiency causes a new type of decapitated and decaudated spermatozoa, Odf2-DDS, in mice

Outer dense fibre 2 (Odf2 or ODF2) is a cytoskeletal protein required for flagella (tail)-beating and stability to transport sperm cells from testes to the eggs. There are infertile males, including human patients, who have a high percentage of decapitated and decaudated spermatozoa (DDS), whose semen contains abnormal spermatozoa with tailless heads and headless tails due to head-neck separation. DDS is untreatable in reproductive medicine. We report for the first time a new type of Odf2-DDS in heterozygous mutant Odf2+/- mice. Odf2+/- males were infertile due to haploinsufficiency caused by heterozygous deletion of the Odf2 gene, encoding the Odf2 proteins. Odf2 haploinsufficiency induced sperm neck-midpiece separation, a new type of head-tail separation, leading to the generation of headneck sperm cells or headnecks composed of heads with necks and neckless tails composed of only the main parts of tails. The headnecks were immotile but alive and capable of producing offspring by intracytoplasmic headneck sperm injection (ICSI). The neckless tails were motile and could induce capacitation but had no significant forward motility. Further studies are necessary to show that ICSI in humans, using headneck sperm cells, is viable and could be an alternative for infertile patients suffering from Odf2-DDS.

The Emerging Role of Sperm-Associated Antigen 6 Gene in the Microtubule Function of Cells and Cancer

Accumulated evidence shows that sperm-associated antigen 6 (SPAG6) gene has multiple biological functions. It maintains the normal function of a variety of cells including ciliary/flagellar biogenesis and polarization, neurogenesis, and neuronal migration. Moreover, SPAG6 is found to be critically involved in auditory transduction and the fibroblast life cycle. Furthermore, SPAG6 plays an essential role in immuno-regulation. Notably, SPAG6 has been demonstrated to participate in the occurrence and progression of a variety of human cancers. New evidence shows that SPAG6 gene regulates tumor cell proliferation, apoptosis, invasion, and metastasis. Therefore, in this review, we describe the physiological function and mechanism of SPAG6 in human normal cells and cancer cells. We also highlight that SPAG6 gene may be an effective biomarker for the diagnosis of human cancer. Taken together, targeting SPAG6 could be a novel strategy for the treatment of human diseases including cancer.

The sperm-associated antigen 6 interactome and its role in spermatogenesis

Mammalian SPAG6, the orthologue of Chlamydomonas reinhardtii PF16, is a component of the central apparatus of the '9 + 2' axoneme that controls ciliary/flagellar motility, including sperm motility. Recent studies revealed that SPAG6 has functions beyond its role in the central apparatus. Hence, we reexamined the role of SPAG6 in male fertility. In wild-type mice, SPAG6 was present in cytoplasmic vesicles in spermatocytes, the acrosome of round and elongating spermatids and the manchette of elongating spermatids. Spag6-deficient testes showed abnormal spermatogenesis, with abnormalities in male germ cell morphology consistent with the multi-compartment pattern of SPAG6 localization. The armadillo repeat domain of mouse SPAG6 was used as a bait in a yeast two-hybrid screen, and several proteins with diverse functions appeared multiple times, including Snapin, SPINK2 and COPS5. Snapin has a similar localization to SPAG6 in male germ cells, and SPINK2, a key protein in acrosome biogenesis, was dramatically reduced in Spag6-deficient mice which have defective acrosomes. SPAG16L, another SPAG6-binding partner, lost its localization to the manchette in Spag6-deficient mice. Our findings demonstrate that SPAG6 is a multi-functional protein that not only regulates sperm motility, but also plays roles in spermatogenesis in multiple cellular compartments involving multiple protein partners.

Whole-exome sequencing identifies mutations in FSIP2 as a recurrent cause of multiple morphological abnormalities of the sperm flagella

STUDY QUESTION

Can whole-exome sequencing (WES) of infertile patients identify new genes responsible for multiple morphological abnormalities of the sperm flagella (MMAF)?

SUMMARY ANSWER

WES analysis of 78 infertile men with a MMAF phenotype permitted the identification of four homozygous mutations in the fibrous sheath (FS) interacting protein 2 (FSIP2) gene in four unrelated individuals.

WHAT IS KNOWN ALREADY

The use of high-throughput sequencing techniques revealed that mutations in the dynein axonemal heavy chain 1 (DNAH1) gene, and in the cilia and flagella associated protein 43 (CFAP43) and 44 (CFAP44) genes account for approximately one-third of MMAF cases thus indicating that other relevant genes await identification.

STUDY DESIGN, SIZE, DURATION

This was a retrospective genetics study of 78 patients presenting a MMAF phenotype who were recruited in three fertility clinics between 2008 and 2015. Control sperm samples were obtained from normospermic donors. Allelic frequency for control subjects was derived from large public databases.

PARTICIPANTS/MATERIALS, SETTING, METHODS

WES was performed for all 78 subjects. All identified variants were confirmed by Sanger sequencing. Relative mRNA expression levels for the selected candidate gene (FSIP2) was assessed by quantitative RT-PCR in a panel of normal human and mouse tissues. To characterize the structural and ultrastructural anomalies present in patients' sperm, immunofluorescence (IF) was performed on sperm samples from two subjects with a mutation and one control and transmission electron microscopy (TEM) analyses was performed on sperm samples from one subject with a mutation and one control.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified four unrelated patients (4/78, 5.1%) with homozygous loss of function mutations in the FSIP2 gene, which encodes a protein of the sperm FS and is specifically expressed in human and mouse testis. None of these mutations were reported in control sequence databases. TEM analyses showed a complete disorganization of the FS associated with axonemal defects. IF analyses confirmed that the central-pair microtubules and the inner and outer dynein arms of the axoneme were abnormal in all four patients carrying FSIP2 mutations. Importantly, and in contrast to what was observed in patients with MMAF and mutations in other MMAF-related genes (DNAH1, CFAP43 and CFAP44), mutations in FSIP2 led to the absence of A-kinase anchoring protein 4 (AKAP4).

LIMITATIONS, REASONS FOR CAUTION

The low number of biological samples and the absence of a reliable anti-FSIP2 antibody prevented the formal demonstration that the FSIP2 protein was absent in sperm from subjects with a FSIP2 mutation.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings indicate that FSIP2 is one of the main genes involved in MMAF syndrome. In humans, genes previously associated with a MMAF phenotype encoded axonemal-associated proteins (DNAH1, CFAP43 and CFAP44). We show here that FSIP2, a protein of the sperm FS, is also logically associated with MMAF syndrome as we showed that it is necessary for FS assembly and for the overall axonemal and flagellar biogenesis. As was suggested before in mouse and man, our results also suggest that defects in AKAP4, one of the main proteins interacting with FSIP2, would induce a MMAF phenotype. Finally, this work reinforces the demonstration that WES sequencing is a good strategy to reach a genetic diagnosis for patients with severe male infertility phenotypes.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the following grants: the 'MAS-Flagella' project financed by the French ANR and the DGOS for the program PRTS 2014 (14-CE15) and the 'Whole genome sequencing of patients with Flagellar Growth Defects (FGD)' project financed by the Fondation Maladies Rares for the program Séquençage à haut débit 2012. The authors have no conflict of interest.

Distribution of sperm antigen 6 (SPAG6) and 16 (SPAG16) in mouse ciliated and non-ciliated tissues

The cilia and flagella of eukaryotic cells serve many functions, exhibiting remarkable conservation of both structure and molecular composition in widely divergent eukaryotic organisms. SPAG6 and SPAG16 are the homologous in the mice to Chlamydomonas reinhardtii PF16 and PF20. Both proteins are associated with the axonemal central apparatus and are essential for ciliary and flagellar motility in mammals. Recent data derived from high-throughput studies revealed expression of these genes in tissues that do not contain motile cilia. However, the distribution of SPAG6 and SPAG16 in ciliated and non-ciliated tissues is not completely understood. In this work, we performed a quantitative analysis of the expression of Spag6 and Spag16 genes in parallel with the immune-localization of the proteins in several tissues of adult mice. Expression of mRNA was higher in the testis and tissues bearing motile cilia than in the other analyzed tissues. Both proteins were present in ciliated and non-ciliated tissues. In the testis, SPAG6 was detected in spermatogonia, spermatocytes, and in the sperm flagella whereas SPAG16 was found in spermatocytes and in the sperm flagella. In addition, both proteins were detected in the cytoplasm of cells from the brain, spinal cord, and ovary. A small isoform of SPAG16 was localized in the nucleus of germ cells and some neurons. In a parallel set of experiments, we overexpressed EGFP-SPAG6 in cultured cells and observed that the protein co-localized with a subset of acetylated cytoplasmic microtubules. A role of these proteins stabilizing the cytoplasmic microtubules of eukaryotic cells is discussed.

Exploring the Role of Fallopian Ciliated Cells in the Pathogenesis of High-Grade Serous Ovarian Cancer

High-grade serous epithelial ovarian cancer (HGSOC) is the fifth leading cause of cancer death in women and the first among gynecological malignancies. Despite an initial response to standard chemotherapy, most HGSOC patients relapse. To improve treatment options, we must continue investigating tumor biology. Tumor characteristics (e.g., risk factors and epidemiology) are valuable clues to accomplish this task. The two most frequent risk factors for HGSOC are the lifetime number of ovulations, which is associated with increased oxidative stress in the pelvic area caused by ovulation fluid, and a positive family history due to genetic factors. In the attempt to identify novel genetic factors (i.e., genes) associated with HGSOC, we observed that several genes in linkage with HGSOC are expressed in the ciliated cells of the fallopian tube. This finding made us hypothesize that ciliated cells, despite not being the cell of origin for HGSOC, may take part in HGSOC tumor initiation. Specifically, malfunction of the ciliary beat impairs the laminar fluid flow above the fallopian tube epithelia, thus likely reducing the clearance of oxidative stress caused by follicular fluid. Herein, we review the up-to-date findings dealing with HGSOC predisposition with the hypothesis that fallopian ciliated cells take part in HGSOC onset. Finally, we review the up-to-date literature concerning genes that are located in genomic loci associated with epithelial ovarian cancer (EOC) predisposition that are expressed by the fallopian ciliated cells.

SPAG17 Is Required for Male Germ Cell Differentiation and Fertility

Spag17 encodes a protein present in the axoneme central pair complex of motile cilia and flagella. A mutation in this gene has been reported to be associated with infertility caused by defects in sperm motility. Here, we report that Spag17 knockout mice are infertile because of a severe defect in spermatogenesis. The histological evaluation of testis sections from mutant mice revealed seminiferous tubules with spermatogenesis arrested at the spermatid stage and cell debris in the cauda epididymis. The few sperm collected from the cauda epididymis were immotile and displayed abnormal tail and head morphology. Immunofluorescence analysis of Spag17 knockout germ cells showed spermatids with abnormally long manchette structures and morphological defects in the head. Electron microscopy showed altered manchette microtubules, reduced chromatin condensation, irregular nuclear shape, and detached acrosomes. Additionally, the transport of proteins (Pcdp1 and IFT20) along the manchette microtubules was disrupted in the knockout elongating spermatids. Our results show for the first time that Spag17 is essential for normal manchette structure, protein transport, and formation of the sperm head and flagellum, in addition to its role in sperm motility.

The function of sperm-associated antigen 6 in neuronal proliferation and differentiation

Sperm-associated antigen 6 (SPAG6) is initially found in human testis and is essential for sperm motility and male fertility. Later studies indicate that it also express in the chick Central Nervous System and human embryonic stem cells. However, the function of Spag6 in cortical development is still largely unclear. Using in utero electroporation, we showed that overexpression of Spag6 induced the transfected cells excluded from the proliferation zone of the mouse cortex. Ki67 Co-labeling and BrdU incorporation experiment suggested that overexpression of Spag6 inhibited proliferation of neural progenitor cells. Furthermore, we demonstrated that Spag6-overexpressing cells preferred to differentiated into neurons, which could be labeled by Brn2, rather than GFAP positive astrocytes. Taken together, our data indicate that Spag6 plays an essential role in the process of neuronal proliferation and differentiation.

Coiled-coil domain containing 42 (Ccdc42) is necessary for proper sperm development and male fertility in the mouse

Spermiogenesis is the differentiation of spermatids into motile sperm consisting of a head and a tail. The head harbors a condensed elongated nucleus partially covered by the acrosome-acroplaxome complex. Defects in the acrosome-acroplaxome complex are associated with abnormalities in sperm head shaping. The head-tail coupling apparatus (HTCA), a complex structure consisting of two cylindrical microtubule-based centrioles and associated components, connects the tail or flagellum to the sperm head. Defects in the development of the HTCA cause sperm decapitation and disrupt sperm motility, two major contributors to male infertility. Here, we provide data indicating that mutations in the gene Coiled-coil domain containing 42 (Ccdc42) is associated with malformation of the mouse sperm flagella. In contrast to many other flagella and motile cilia genes, Ccdc42 expression is only observed in the brain and developing sperm. Male mice homozygous for a loss-of-function Ccdc42 allele (Ccdc42(KO)) display defects in the number and location of the HTCA, lack flagellated sperm, and are sterile. The testes enriched expression of Ccdc42 and lack of other phenotypes in mutant mice make it an ideal candidate for screening cases of azoospermia in humans.

Ectopic Expression of Cenexin1 S796A Mutant in ODF2(+/-) Knockout Background Causes a Sperm Tail Development Defect

The outer dense fiber 2 (ODF2) protein is an important component of sperm tail outer dense fiber and localizes at the centrosome. It has been reported that the RO072 ES cell derived homozygote knock out of ODF2 results in an embryonic lethal phenotype, and XL169 ES cell derived heterozygote knock out causes severe defects in sperm tail development. The ODF2s splicing variant, Cenexin1, possesses a C-terminal extension, and the phosphorylation of serine 796 residue in an extended C-terminal is responsible for Plk1 binding. Cenexin1 assembles ninein and causes ciliogenesis in early stages of the cell cycle in a Plk1-independent manner. Alternatively, in the late stages of the cell cycle, G2/M phase, Cenexin1 binds to Plk1 and results in proper mitotic progression. In this study, to identify the in vivo function of Plk1 binding to phosphorylated Cenexin1 S796 residue, and to understand the in vivo functional differences between ODF2 and Cenexin1, we generated ODF2/Cenexin1 S796A/Cenexin1 WT expressing transgenic mice in a RO072 ES cell derived ODF2(+/-) knock out background. We observed a severe defect of sperm tail development by ectopic expression of Cenexin1 S796A mutant and no phenotypic differences between the ectopic expression of ODF2/Cenexin1 WT in ODF2(+/-) background and in normal wild type mice.

The effects of Ca2+ and ADP on dynein switching during the beat cycle of reactivated bull sperm models

Calcium regulation of flagellar motility is the basis for chemotaxis, phototaxis, and hyperactivation responses in eukaryotic flagellates and spermatozoa. Ca2+ is the internal messenger for these responses, but the coupling between Ca2+ and the motor mechanism that generates the flagellar beat is incompletely understood. We examined the effects of Ca2+ on the flagellar curvature at the switch-points of the beat cycle in bull sperm. The sperm were detergent extracted and reactivated with 0.1 mM adenosine triphosphate (ATP). With their heads immobilized and their tails beating freely it is possible to calculate the bending torque and the transverse force acting on the flagellum at the switch-points. An increase in the free Ca2+ concentration (pCa 8 to pCa 4) significantly decreased the development of torque and t-force in the principal bending direction, while having negligible effect on the reverse bend. The action of Ca2+ was more pronounced when the sperm were also treated with 4 mM adenosine diphosphate (ADP); it was sufficient to change the direction of bending that reaches the greater curvature. We also observed that the curvature of the distal half of the flagellum became locked in one direction in the presence of Ca2+ . This indicates that a subset of the dynein becomes continuously activated by Ca2+ and fails to switch with the beat cycle. Our evidence suggests this subset of dyneins is localized to doublets #1-4 of the axoneme.

Bower-building behaviour is associated with increased sperm longevity in Tanganyikan cichlids

We investigated the evolutionary relationship between spawning behaviour and sperm motility traits among Tanganyikan mouth-brooding cichlid species that have developed diverse mating behaviours and male sexual traits. Mouth-brooding behaviour is common among these fish, but different species demonstrate a range of spawning behaviours, bower construction, male sexual traits and timing of gamete release. We observed spawning behaviours and compared sperm motility traits of 28 Tanganyikan mouth-brooding cichlids to elucidate the evolutionary correlations between these traits. Sperm longevity was considerably longer in bower-building species that construct crater-shaped spawning sites compared with species that do not build bowers. Male bower builders released sperm in the pit of the bower prior to spawning, and the time from ejaculation to fertilization was longer. Conversely, most mouth-brooding cichlids deposited semen directly into the female buccal cavity, and spawned eggs were immediately picked up to be placed inside the cavity; thus, the time from ejaculation to fertilization was short. These observations suggest that increased sperm longevity is favoured in bower builders. Comparative phylogenetic analyses suggested that bower-building behaviour and greater time from ejaculation to fertilization are associated with the extension of sperm longevity, whereas sperm competition rank does not play a major role. In addition, bower-building behaviour preceded the emergence of increased sperm longevity. These results indicate that the extension of sperm longevity as a result of the emergence of bower builders may have acted as an evolutionary attractor for sperm longevity.

Temporal changes in histomorphology and gene expression in goat testes during postnatal development

Testicular cell proliferation and differentiation is critical for development of normal testicular function and male reproductive maturity. The objective of the current study was to evaluate histoarchitecture and expression of genes marking specific cells and important functions as well as testosterone production of the developing goat testes. Testes were harvested from Alpine bucks at 0, 2, 4, 6, and 8 mo of age (n = 5/age group). Paired testes weight increased from 2 to 4 (P < 0.001) and 4 to 6 mo (P < 0.01). The greatest increases in seminiferous tubule and lumen diameters and height of the seminiferous epithelium occurred between 2 and 4 mo (P < 0.001). Genes expressed in haploid germ cells (Protamine1 [PRM1], Outer Dense Fiber protein 2 [ODF2], and Stimulated by Retinoic Acid gene 8 [STRA8]) increased dramatically at the same time (P < 0.001). Expression of other genes decreased (P < 0.05) during testicular maturation. These genes included P450 side chain cleavage (CYP11A1), Sex determining region Y-box 9 (SOX9), Insulin-like Growth Factor 1 Receptor (IGF1R), and Heat Shock Protein A8 (HSPA8). The Glutathione S-Transferase A3 (GSTA3) gene, whose product was recently recognized as a primary enzyme involved in isomerization of androstenedione in man and livestock species including goats, sheep, cattle, pigs, and horses, uniquely peaked in expression at 2 mo (P < 0.05). Follicle-Stimulating Hormone Receptor (FSHR) mRNA abundance tended to steadily decrease with age (P = 0.1), while Luteinizing Hormone Receptor (LHCGR) mRNA abundance in testes was not significantly different across the ages. Testosterone content per gram of testicular tissue varied among individuals. However, testosterone content per testis tended to increase at 6 mo (P = 0.06). In conclusion, major changes in cellular structure and gene expression in goat testes were observed at 4 mo of age, when spermatogenesis was initiated. Male goats mature rapidly and represent a good model species for the study of agents that enhance or impair development of testicular functions.

KIF3A is essential for sperm tail formation and manchette function

KIF3A motor protein is responsible for intraflagellar transport, which is required for protein delivery during axoneme formation in ciliated cells. The function of KIF3A during spermatogenesis is not known. In this study, we show that depletion of KIF3A causes severe impairments in sperm tail formation and interestingly, it also affects manchette organization and the shaping of sperm heads. Our results demonstrate the analogy between the mechanisms governing the formation of cilia in somatic cells and the formation of spermatozoa-specific flagella. Furthermore, this study reveals KIF3A as an important regulator of spermatogenesis and emphasizes the crucial role of KIF3A in maintaining male fertility. We also identified several novel interacting partners for KIF3A, including meiosis-specific nuclear structural protein 1 (MNS1) that colocalizes with KIF3A in the manchette and principal piece of the sperm tail. This study highlights the essential role of KIF3A-mediated microtubular transport in the development of spermatozoa and male fertility.

Disruption of Ttll5/stamp gene (tubulin tyrosine ligase-like protein 5/SRC-1 and TIF2-associated modulatory protein gene) in male mice causes sperm malformation and infertility

TTLL5/STAMP (tubulin tyrosine ligase-like family member 5) has multiple activities in cells. TTLL5 is one of 13 TTLLs, has polyglutamylation activity, augments the activity of p160 coactivators (SRC-1 and TIF2) in glucocorticoid receptor-regulated gene induction and repression, and displays steroid-independent growth activity with several cell types. To examine TTLL5/STAMP functions in whole animals, mice were prepared with an internal deletion that eliminated several activities of the Stamp gene. This mutation causes both reduced levels of STAMP mRNA and C-terminal truncation of STAMP protein. Homozygous targeted mutant (Stamp(tm/tm)) mice appear normal except for marked decreases in male fertility associated with defects in progressive sperm motility. Abnormal axonemal structures with loss of tubulin doublets occur in most Stamp(tm/tm) sperm tails in conjunction with substantial reduction in α-tubulin polyglutamylation, which closely correlates with the reduction in mutant STAMP mRNA. The axonemes in other structures appear unaffected. There is no obvious change in the organs for sperm development of WT versus Stamp(tm/tm) males despite the levels of WT STAMP mRNA in testes being 20-fold higher than in any other organ examined. This defect in male fertility is unrelated to other Ttll genes or 24 genes previously identified as important for sperm function. Thus, STAMP appears to participate in a unique, tissue-selective TTLL-mediated pathway for α-tubulin polyglutamylation that is required for sperm maturation and motility and may be relevant for male fertility.

Novel approach for the detection of the vestiges of testicular mRNA splicing errors in mature spermatozoa of Japanese Black bulls

There is a serious problem with the reduction of male reproductive performance of the livestock in the world. We have a hypothesis that the splicing error-caused derivation of aberrant sperm motility-related proteins may be one of its causal factors. It is thought that fresh testicular tissues are necessary for the detection of splicing errors of the mRNA. However, it is difficult to obtain testicular tissues from a number of agriculturally important bulls by surgical methods, because such procedures may have deleterious effects on bulls’ reproductive performance. The aim of this study was to examine the usefulness of mRNA fragments collected from ejaculated spermatozoa as alternative analytical samples for detection of the splicing errors. In the first experiment, we characterized the alternative splicing and splicing error of bull testicular ADCY10 mRNA which coded the synthase of the regulatory molecule for sperm motility “cAMP”. In testes, the exon 11-lacking variant coding the truncated ADCY10 was derived by alternative splicing. However, splicing errors, which accompanied the frame shift in the second cyclase domain, were occasionally observed in the exon 11-lacking variant. This aberrant variant retained intronic nucleotides (4 bases, CCAG) connecting the initial part of exon 10 due to splicing errors and consequently yielded the cleavage site for a restriction enzyme (Cac8I) which recognized the nucleotide sequences (GCNNGC). In the second experiment, we recovered residual testicular mRNA fragments from ejaculated spermatozoa and observed the splicing error-caused derivation of the aberrant variant of ADCY 10. Ejaculated spermatozoa conserved mRNA fragments of the exon 11-lacking variant coding exons 9, 10, 12 and 13. Moreover, the above-mentioned aberrant variant of ADCY10 mRNA fragment was detectable by Cac8I digestion treatment using the sperm mRNAs. These results indicate the utility of sperm mRNA fragments for the detection of splicing errors in bull testicular mRNAs.

Production of chimeras between the Chinese soft-shelled turtle and Peking duck through transfer of early blastoderm cells

Chimeras are useful models for studies of developmental biology and cell differentiation. Intraspecies and interspecies germline chimeras have been produced in previous studies, but the feasibility of producing chimeras between animals of two different classes remains unclear. To address this issue, we attempted to produce chimeras between the Chinese soft-shelled turtle and the Peking duck by transferring stage X blastoderm cells to recipient embryos. We then examined the survival and development of the PKH26-labeled donor cells in the heterologous embryos. At early embryonic stages, both turtle and duck donor cells that were labeled with PKH26 were readily observed in the brain, neural tube, heart and gonads of the respective recipient embryos. Movement of turtle donor-derived cells was observed in the duck host embryos after 48 h of incubation. Although none of the hatchlings presented a chimeric phenotype, duck donor-derived cells were detected in a variety of organs in the hatchling turtles, particularly in the gonads. Moreover, in the hatched turtles, mRNA expression of tissue-specific duck genes MEF2a and MEF2c was detected in many tissues, including the muscle, heart, small and large intestines, stomach and kidney. Similarly, SPAG6 mRNA was detected in a subset of turtle tissues, including the gonad and the small and large intestines. These results suggest that duck donor-derived cells can survive and differentiate in recipient turtles; however, no turtle-derived cells were detected in the hatched ducks. Our findings indicate that chimeras can be produced between animals of two different classes.

Sperm transcriptome profiling in oligozoospermia

PURPOSE

Investigate in what extent sperm transcriptome of infertile men is different from that of fertile individuals.

METHODS

Semen samples were collected for determination of sperm parameters as well as for RNA isolation. Gene expression profile was investigated in spermatozoa of 8 infertile and 3 fertile men by microarray analysis using the Affymetrix Chip HG-U133 Plus 2.0.

RESULT(S)

We observed up to 33-fold reduction expression of genes involved in spermatogenesis and sperm motility. Furthermore, there is an important decrease in expression of genes involved in DNA repair as well as oxidative stress regulation. In this study, we also show a striking drop in expression of histone modification genes.

CONCLUSION(S)

We found that transcription profile in germ cells of men with idiopathic infertility is different from that of fertile individuals. Interestingly, about 15% of the regulated genes (Eddy Rev Reprod 4:23-30, 1999) play a role in spermatogenesis.

DNAJB13 is a radial spoke protein of mouse '9+2' axoneme

It has been shown that DNAJB13, a type II heat shock protein 40, is highly expressed in the testis and is an axonemal component of mouse mature spermatozoa. By multi-tissue reverse transcription polymerase chain reaction, we found that Dnajb13 gene was expressed not only in the testis but also in several other ciliated cell-containing tissues like brain, lung and oviduct. Immunohistochemistry on mouse trachea and oviduct sections shown that DNAJB13 was present in the motile cilia of those tissues. To define further its localization in the axoneme, immunoelectron microscopy of mouse sperm flagella was performed and shown that DNAJB13 was localized to radial spokes of the axoneme. Taken together, our data indicate that DNAJB13 is a radial spoke protein of the mouse '9+2' axoneme.

Spag16, an axonemal central apparatus gene, encodes a male germ cell nuclear speckle protein that regulates SPAG16 mRNA expression

Spag16 is the murine orthologue of Chlamydomonas reinhardtii PF20, a protein known to be essential to the structure and function of the "9+2" axoneme. In Chlamydomonas, the PF20 gene encodes a single protein present in the central pair of the axoneme. Loss of PF20 prevents central pair assembly/integrity and results in flagellar paralysis. Here we demonstrate that the murine Spag16 gene encodes two proteins: 71 kDa SPAG16L, which is found in all murine cells with motile cilia or flagella, and 35 kDa SPAG16S, representing the C terminus of SPAG16L, which is expressed only in male germ cells, and is predominantly found in specific regions within the nucleus that also contain SC35, a known marker of nuclear speckles enriched in pre-mRNA splicing factors. SPAG16S expression precedes expression of SPAG16L. Mice homozygous for a knockout of SPAG16L alone are infertile, but show no abnormalities in spermatogenesis. Mice chimeric for a mutation deleting the transcripts for both SPAG16L and SPAG16S have a profound defect in spermatogenesis. We show here that transduction of SPAG16S into cultured dispersed mouse male germ cells and BEAS-2B human bronchial epithelial cells increases SPAG16L expression, but has no effect on the expression of several other axoneme components. We also demonstrate that the Spag16L promoter shows increased activity in the presence of SPAG16S. The distinct nuclear localization of SPAG16S and its ability to modulate Spag16L mRNA expression suggest that SPAG16S plays an important role in the gene expression machinery of male germ cells. This is a unique example of a highly conserved axonemal protein gene that encodes two protein products with different functions.

Transcriptional regulation of an axonemal central apparatus gene, sperm-associated antigen 6, by a SRY-related high mobility group transcription factor, S-SOX5

SOX5 is a transcription factor with homology to the high mobility group box region of the testis-determining factor, SRY. Both the mouse and human SOX5 genes encode a 48-kDa SOX5 protein (S-SOX5) that is only present in tissues containing cells with motile cilia/flagella. The mammalian sperm-associated antigen 6 gene (SPAG6) encodes an axoneme central apparatus protein. Because human and mouse SPAG6 gene promoters contain multiple potential binding sites for SOX5, SPAG6 gene regulation by S-SOX5 was investigated in BEAS-2B cells, a line derived from human bronchial cells. Like FOXJ1, a transcription factor known to be essential for motile ciliogenesis, S-SOX5 stimulated mouse and human SPAG6 promoter function in BEAS-2B cells, but the effect was abrogated when the SOX5 binding sites were mutated or deleted. S-SOX5 and FOXJ1 functioned cooperatively in stimulating SPAG6 promoter activity. The SPAG6 message was up-regulated when S-SOX5 was overexpressed in BEAS-2B cells, and silencing of S-SOX5 by RNA interference down-regulated SPAG6 transcripts. Chromatin immunoprecipitation and EMSA experiments demonstrated that S-SOX5 associates with the SPAG6 promoter directly. The present study demonstrates that SPAG6 is a S-SOX5 target gene, indicating a key role for S-SOX5 in the formation and function of motile cilia.

Expression of SPEF2 during mouse spermatogenesis and identification of IFT20 as an interacting protein

SPEF2 is expressed in all ciliated cells and is essential for correct sperm tail development and male fertility. We have previously identified a mutation within the SPEF2 gene as the cause for infertility because of immotile and malformed sperm tails in pigs. This mutation in pigs alters the testis-specific long SPEF2 isoform and exclusively affects the sperm tail development. In infertile boars, axonemal and all accessory structures of the sperm tail are affected; thus, SPEF2 seems to participate in the organization of these structures. In the present study, we have investigated the expression of SPEF2 during mouse spermatogenesis. SPEF2 mRNA and protein products appear to be localized both in germ cells and in Sertoli cells. In differentiating germ cells, SPEF2 protein is localized in the Golgi complex, manchette, basal body, and midpiece of the sperm tail. In mature murine sperm, SPEF2 is present in the distal part of the sperm tail midpiece. Using yeast two-hybrid assay and coimmunoprecipitation experiments, we identified an interaction between SPEF2 and the intraflagellar transport protein IFT20 in the testis. Furthermore, these two proteins colocalize in differentiating male germ cells. These results support the crucial importance of SPEF2 in sperm differentiation and involvement of SPEF2 in structuring of the sperm tail.

MEIG1 is essential for spermiogenesis in mice

Spermatogenesis can be divided into three stages: spermatogonial mitosis, meiosis of spermatocytes, and spermiogenesis. During spermiogenesis, spermatids undergo dramatic morphological changes including formation of a flagellum and chromosomal packaging and condensation of the nucleus into the sperm head. The genes regulating the latter processes are largely unknown. We previously discovered that a bi-functional gene, Spag16, is essential for spermatogenesis. SPAG16S, the 35 kDa, testis-specific isoform derived from the Spag16 gene, was found to bind to meiosis expressed gene 1 product (MEIG1), a protein originally thought to play a role in meiosis. We inactivated the Meig1 gene and, unexpectedly, found that Meig1 mutant male mice had no obvious defect in meiosis, but were sterile as a result of impaired spermatogenesis at the stage of elongation and condensation. Transmission electron microscopy revealed that the manchette, a microtubular organelle essential for sperm head and flagellar formation was disrupted in spermatids of MEIG1-deficient mice. We also found that MEIG1 associates with the Parkin co-regulated gene (PACRG) protein, and that testicular PACRG protein is reduced in MEIG1-deficient mice. PACRG is thought to play a key role in assembly of the axonemes/flagella and the reproductive phenotype of Pacrg-deficient mice mirrors that of the Meig1 mutant mice. Our findings reveal a critical role for the MEIG1/PARCG partnership in manchette structure and function and the control of spermiogenesis.

Lentiviral transfection of ependymal primary cultures facilitates the characterisation of kinocilia-specific promoters

Ependymal primary cultures (EPCs) are an established model for studying ependymal cell biochemistry and the biology of kinocilia-bearing cells. However, the difficulty in causing them to express transgenes at high efficiency has been an important drawback of the system. Indeed plasmid-based transfection attempts remain at an efficiency below 1% and fail to elicit reporter gene expression, namely green fluorescent protein (GFP) synthesis, in any of the kinocilia-bearing cells of the cultures. Human immunodeficiency virus pseudotyped with the vesicular stomatitis virus envelope glycoprotein (HIV/VSV-G) and encoding GFP under the control of the ubiquitously recognised promoter of elongation factor 1 alpha (EF1alpha) also does not cause transgene expression in the kinocilia-bearing cells of an EPC when applied at multiplicities of infection (MOIs) of up to 40 and destroys the culture when the MOI is increased further. In contrast, HIV/VSV-G encoding GFP under the control of a promoter specifically active in kinocilia-bearing cells leads to transgene expression in up to 79% of the kinociliated cells of an EPC when applied at an MOI of 20. This has permitted the initial characterisation of the promoter for the gene specifically transcribed in kinocilia-bearing cells, wdr16. The results have identified two regions of 100 nucleotides length each, which are critical for promoter activity and contain putative binding sites for the transcription factors Foxd1, Sox17 and Spz1. It appears that wdr16 is controlled by a bidirectional promoter also responsible for regulating the syntaxin 8 gene.

Expression profile of male germ cell-associated genes in mouse embryonic stem cell cultures treated with all-trans retinoic acid and testosterone

Cells that morphologically and functionally resemble male germ cells can be spontaneously derived from ES cells. However, this process is inefficient and unpredictable suggesting that the expression pattern of male germ cell associated genes during spontaneous ES cell differentiation does not mimic the in vivo profiles of the genes. Thus, in the present study, the temporal profile of genes expressed at different stages of male germ cell development was examined in differentiating ES cells. The effect of all-trans retinoic acid (RA) which is a known inducer of primordial germ cell (PGC) proliferation/survival in vitro and testosterone which is required for spermatogenesis in vivo on the expression of these genes was also determined. Each of the 12 genes analyzed exhibited one of four temporal expression patterns in untreated differentiating ES cells: progressively decreased (Dppa3, Sycp3, Msy2), initially low and then increased (Stra8, Sycp1, Dazl, Act, Prm1), initially decreased and then increased (Piwil2, Tex14), or relatively unchanged (Akap3, Odf2). RA-treated cells exhibited increased expression of Stra8, Dazl, Act, and Prm1 and suppressed expression of Dppa3 compared to untreated controls. Furthermore, testosterone increased expression of Stra8 while the combination of RA and testosterone synergistically increased expression of Act. Our findings establish a comprehensive profile of male germ cell gene expression during spontaneous differentiation of murine ES cells and describe the capacity of RA and testosterone to modulate the expression of these genes. Furthermore, these data represent an important first step in designing a plausible directed differentiation protocol for male germ cells.

Phosphorylation of mouse sperm axoneme central apparatus protein SPAG16L by a testis-specific kinase, TSSK2

The mammalian protein SPAG16L, the ortholog of Chlamydomonas Pf20, is an axoneme central apparatus protein necessary for flagellar motility. The SPAG16L protein sequence contains multiple potential phosphorylation sites, and the protein was confirmed to be phosphorylated in vivo. A yeast two-hybrid screen identified the testis-specific kinase, TSSK2, to be a potential SPAG16L binding partner. SPAG16L and TSSK2 interactions were confirmed by coimmunoprecipitation of both proteins from testis extracts and cell lysates expressing these proteins, and their colocalization was also noted by confocal microscopy in Chinese hamster ovary cells, where they were coexpressed. TSSK2 associates with SPAG16L via its C-terminal domain bearing WD repeats. The N-terminal domain containing a coiled coil motif does not associate with TSSK2. SPAG16L can be phosphorylated by TSSK2 in vitro. Finally, TSSK2 is absent or markedly reduced from the testes in most of the SPAG16L-null mice. These data support the conclusion that SPAG16L is a TSSK2 substrate.

Accelerated mortality from hydrocephalus and pneumonia in mice with a combined deficiency of SPAG6 and SPAG16L reveals a functional interrelationship between the two central apparatus proteins

SPAG6 and SPAG16L are proteins localized to the "9+2" axoneme central apparatus. Both are essential for sperm motility and male fertility. These two proteins are also expressed in other tissues containing ciliated cells, such as brain and lung. To study the effects of combined deficiency of these two proteins, a double mutant mouse model was created. The double mutant mice displayed a more profound phenotype of growth retardation and hydrocephalus compared to mice nullizygous for SPAG6 and SPAG16L alone. The double mutant mice died younger, and mortality was significantly higher than in single mutant mice. In addition, the double mutant mice demonstrated pneumonia and its complications, including hemorrhage, edema, and atelectasis, phenotypes not observed in mice nullizygous for mutations in the individual genes. No other cilia-related phenotypic change was detected in double mutant mice including lateralization defects. The ultrastructure of cilia in both the brain and lung of the double mutant mice appeared normal. This model of combined SPAG6 and SPAG16L deficiency provides a new platform to study primary ciliary dyskinesia. The findings also demonstrate that SPAG6 and SPAG16L have related roles in controlling the function of cilia in the brain and lung.

Korean ginseng induces spermatogenesis in rats through the activation of cAMP-responsive element modulator (CREM)

The effect of Korean ginseng (ginseng) on spermatogenesis and cAMP-responsive element modulator (CREM) in rat testes was evaluated using sperm analysis, reverse transcription polymerase chain reaction, and Western blot analysis. The ginseng-treated rats exhibited significantly increased sperm count and motility with enhanced levels of CREM messenger RNA and protein. Ginseng appears to induce spermatogenesis via CREM activation in rat testes.

A gene trap knockout of the abundant sperm tail protein, outer dense fiber 2, results in preimplantation lethality

Outer dense fiber 2 (Odf2) is highly expressed in the testis where it encodes a major component of the outer dense fibers of the sperm flagellum. Furthermore, ODF2 protein has recently been identified as a widespread centrosomal protein. While the expression of Odf2 highlighted a potential role for this gene in male germ cell development and centrosome function, the in vivo function of Odf2 was not known. We have generated Odf2 knockout mice using an Odf2 gene trapped embryonic stem cell (ESC) line. Insertion of a gene trap vector into exon 9 resulted in a gene that encodes a severely truncated protein lacking a large portion of its predicted coil forming domains as well as both leucine zipper motifs that are required for protein-protein interactions with ODF1, another major component of the outer dense fibers. Although wild-type and heterozygous mice were recovered, no mice homozygous for the Odf2 gene trap insertion were recovered in an extended breeding program. Furthermore, no homozygous embryos were found at the blastocyst stage of embryonic development, implying a critical pre-implantation role for Odf2. We show that Odf2 is expressed widely in adults and is also expressed in the blastocyst stage of preimplantation development. These findings are in contrast with early studies reporting Odf2 expression as testis specific and suggest that embryonic Odf2 expression plays a critical role during preimplantation development in mice.

Characteristics of 292 Testis-Specific Genes in Human

To explore their genomic and functional characteristics, 292 human testis-specific genes were obtained from a UniGene library and a full-scale analysis was made. Various bioinformatics tools were applied to analyze the gene ontology and chromosome location, and the expression profiles of eight selected candidates from the 292 genes were analyzed using RT-PCR for 12 adult human tissues. The results showed that of the total 292 genes, 153 were known (114 assigned genes and 39 named genes), and 139 were unknown. Of the 114 assigned genes, 63 were labeled to molecular function, 28 to cellular component, 23 to biological process. All 292 genes are distributed on human chromosomes at different gene density, lower gene density appears on chromosomes 21 (R=0.22), X (R=0.33), 14 (R=0.39), 10 (R=0.61), 8 (R=0.63), and 18 (R=0.67) and higher density on chromosomes 19 (R=3.65), 20 (R=1.83), 16 (R=1.74), and 17 (R=1.64). The expression profile of the eight selected genes in the 12 human tissues showed that five candidate genes: Hs.443729, Hs.115366, Hs.558087, Hs.534501, and Hs.132104 were expressed exclusively in human testis; Hs.132310, Hs.443299 were expressed highly in testis and also expressed weakly in human heart; Hs.160370 was expressed in human testis, ovary, uterus, and not expressed in other tissues. Our study can be a basis for characterization of the function of human testis-specific genes during male mammalian spermatogenesis.

The human cumulus--oocyte complex gene-expression profile

BACKGROUND

The understanding of the mechanisms regulating human oocyte maturation is still rudimentary. We have identified transcripts differentially expressed between immature and mature oocytes and cumulus cells.

METHODS

Using oligonucleotide microarrays, genome-wide gene expression was studied in pooled immature and mature oocytes or cumulus cells from patients who underwent IVF.

RESULTS

In addition to known genes, such as DAZL, BMP15 or GDF9, oocytes up-regulated 1514 genes. We show that PTTG3 and AURKC are respectively the securin and the Aurora kinase preferentially expressed during oocyte meiosis. Strikingly, oocytes overexpressed previously unreported growth factors such as TNFSF13/APRIL, FGF9, FGF14 and IL4 and transcription factors including OTX2, SOX15 and SOX30. Conversely, cumulus cells, in addition to known genes such as LHCGR or BMPR2, overexpressed cell-to-cell signalling genes including TNFSF11/RANKL, numerous complement components, semaphorins (SEMA3A, SEMA6A and SEMA6D) and CD genes such as CD200. We also identified 52 genes progressively increasing during oocyte maturation, including CDC25A and SOCS7.

CONCLUSION

The identification of genes that were up- and down-regulated during oocyte maturation greatly improves our understanding of oocyte biology and will provide new markers that signal viable and competent oocytes. Furthermore, genes found expressed in cumulus cells are potential markers of granulosa cell tumours.

An intronic insertion in KPL2 results in aberrant splicing and causes the immotile short-tail sperm defect in the pig

The immotile short-tail sperm defect is an autosomal recessive disease within the Finnish Yorkshire pig population. This disease specifically affects the axoneme structure of sperm flagella, whereas cilia in other tissues appear unaffected. Recently, the disease locus was mapped to a 3-cM region on porcine chromosome 16. To facilitate identification of candidate genes, we constructed a porcine-human comparative map, which anchored the disease locus to a region on human chromosome 5p13.2 containing eight annotated genes. Sequence analysis of a candidate gene KPL2 revealed the presence of an inserted retrotransposon within an intron. The insertion affects splicing of the KPL2 transcript in two ways; it either causes skipping of the upstream exon, or causes the inclusion of an intronic sequence as well as part of the insertion in the transcript. Both changes alter the reading frame leading to premature termination of translation. Further work revealed that the aberrantly spliced exon is expressed predominantly in testicular tissue, which explains the tissue-specificity of the immotile short-tail sperm defect. These findings show that the KPL2 gene is important for correct axoneme development and provide insight into abnormal sperm development and infertility disorders.

Deficiency of SPAG16L causes male infertility associated with impaired sperm motility

The axonemes of cilia and flagella contain a "9+2" structure of microtubules and associated proteins. Proteins associated with the central doublet pair have been identified in Chlamydomonas that result in motility defects when mutated. The murine orthologue of the Chlamydomonas PF20 gene, sperm-associated antigen 16 (Spag16), encodes two proteins of M(r) approximately 71 x 10(3) (SPAG16L) and M(r) approximately 35 x 10(3) (SPAG16S). In sperm, SPAG16L is found in the central apparatus of the axoneme. To determine the function of SPAG16L, gene targeting was used to generate mice lacking this protein but still expressing SPAG16S. Mutant animals were viable and showed no evidence of hydrocephalus, lateralization defects, sinusitis, bronchial infection, or cystic kidneys-symptoms typically associated with ciliary defects. However, males were infertile with a lower than normal sperm count. The sperm had marked motility defects, even though ultrastructural abnormalities of the axoneme were not evident. In addition, the testes of some nullizygous animals showed a spermatogenetic defect, which consisted of degenerated germ cells in the seminiferous tubules. We conclude that SPAG16L is essential for sperm flagellar function. The sperm defect is consistent with the motility phenotype of the Pf20 mutants of Chlamydomonas, but morphologically different in that the mutant algal axoneme lacks the central apparatus.