The mammalian testis possesses a special immunological environment because of its properties of remarkable immune privilege and effective local innate immunity. Testicular immune privilege protects immunogenic germ cells from systemic immune attack, and local innate immunity is important in preventing testicular microbial infections. The breakdown of local testicular immune homeostasis may lead to orchitis, an etiological factor of male infertility. The mechanisms underlying testicular immune privilege have been investigated for a long time. Increasing evidence shows that both a local immunosuppressive milieu and systemic immune tolerance are involved in maintaining testicular immune privilege status. The mechanisms underlying testicular innate immunity are emerging based on the investigation of the pattern recognition receptor-mediated innate immune response in testicular cells. This review summarizes our current understanding of testicular defense mechanisms and identifies topics that merit further investigation.

During spermatogenesis, diploid stem cells differentiate, undergo meiosis and spermiogenesis, and transform into haploid spermatozoa. Various factors have been demonstrated to regulate this marvelous process of differentiation, but the expression of only a few genes specifically involved in spermatogenesis has been studied. In the present study, different types of spermatogenic cells were isolated from Balb/c mice testes of different ages using the velocity sedimentation method, and we determined the expression profiles of 1176 known mouse genes in six different types of mouse spermatogenic cells (primitive type A spermatogonia, type B spermatogonia, preleptotene spermatocytes, pachytene spermatocytes, round spermatids, and elongating spermatids) using Atlas cDNA arrays. Of the 1176 genes on the Atlas Mouse 1.2 cDNA Expression Arrays, we detected 181 genes in primitive type A spermatogonia, 256 in type B spermatogonia, 221 in preleptotene spermatocytes, 160 in pachytene spermatocytes, 141 in round spermatids, and 126 in elongating spermatids. A number of genes were detected as differential expression (up-regulation or down-regulation). Fourteen of the differentially expressed genes have been further confirmed by reverse transcription-polymerase chain reaction for their expression characterizations in different types of spermatogenic cells. These results provide more information for further studies into spermatogenesis-related genes and may lead to the identification of genes with potential relevance to spermatogenesis.

Tyro 3 family receptors contain three members—Tyro 3, Axl, and Mer—that are essential regulators of mammalian spermatogenesis. However, their exact expression patterns in testis are unclear. In this study, we examined the localizations of Tyro 3, Axl, Mer, and their ligand Gas6 in postnatal mouse testes by immunohistochemistry. All three members and their ligand were continuously expressed in different testicular cells during postnatal development. Tyro 3 was expressed only in Sertoli cells with a varied distribution during testis development. At day 3 postnatal, Tyro 3 was distributed in overall cytoplasmic membrane and cytoplasm of Sertoli cells. From day 14 to day 35 postnatal, Tyro 3 appeared on Sertoli cell processes toward the adlumenal compartment of seminiferous tubules. A stage-dependent Tyro 3 immunoexpression in Sertoli cells was shown by adulthood testis at day 56 postnatal with higher expression at stages I-VII and lower level at stages IX-XII. Axl showed a similar expression pattern to Tyro 3, except for some immunopositive Leydig cells detected in mature testis. In contrast, immunostaining of Mer was detected mainly in primitive spermatogonia and Leydig cells, whereas a relative weak signal was found in Sertoli cells. Gas6 was strongly expressed in Leydig cells, and a relative weak staining signal was seen in primitive spermatogonia and Sertoli cells. These immunoexpression patterns of Tyro 3 family receptors and ligand in testis provide a basis to further study their functions and mechanisms in regulating mammalian spermatogenesis.

Spermatogenesis occurs in successive mitotic, meiotic, and post-meiotic phase, and involves a number of unique processes including meiosis and dramatic morphological changes. The unique differentiation mechanisms of spermatogenesis suggest the existence of germ-cell-specific molecules. The most straight forward strategy to elucidate differentiation mechanisms is to identify and characterize differentiation-specific molecules and their associated genes in germ cells. However, only a few genes specifically involved in spermatogenesis have been studied. In the present study, six different types of spermatogenic cells (primitive type A spermatogonia, type B spermatogonia, preleptotene spermatocytes, pachytene spermatocytes, round spermatids, and elongating spermatids) were isolated from Balb/c mice testes using velocity sedimentation and Atlas cDNA arrays containing 1,176 known mouse genes were used to determine the gene expression profiles of the spermatogenic cells. The expression of 260 genes were detected in six different stages of spermatogenic cells and a number of genes showed differential expression. The 23 differentially expressed genes were further analysed by reverse transcription polymerase chain reaction (RT-PCR) for their stage-specific and tissue-specific expression characteristics. Based on the results of RT-PCR, six genes highly express in both primitive type A and type B spermatogonia, four genes up-regulate in type B spermatogonia, two genes up-regulate in spermatocytes, two genes up-regulate in spermatids, three genes express constantly from primitive A spermatogonia to elongating spermatids, two genes express constantly from primitive A spermatogonia to round spermatids, two genes do not change in their expression during spermatogenesis, two genes can be detected highly in adult testis, but are undetectable in spermatogenic cells. The tissue-specific expression characteristics of the 23 genes showed that some of them specifically expressed in testes or other tissues. These data provide new information for further studies into spermatogenesis-related genes and may lead to the identification of genes with potential relevance to the differentiation of spermatogenic cells. In addition, some of these genes could be considered to be used as the molecular markers for different stages of spermatogenic cells.

Dishevelled (Dsh in Drosophila or DVL in mice) is a member of the highly conserved Wg/Wnt signaling pathway, which regulates important processes such as cell proliferation, polarity, and specification of cell fate. Three orthologous genes of Dishevelled (Dvl-1, Dvl-2, and Dvl-3) have been found in both humans and mice. They play pivotal roles in regulating cell morphology and a variety of changes in cell behaviors. In the present study, we show that the expression of Dvl-1 is stage-dependent during mouse spermatogenesis, although Dvl-2 and Dvl-3 show relative consistent expression. The expression of Dvl-1 mRNA first appears in pachytene spermatocytes, increases in round and elongating spermatids, and then turns to an undetectable level in mature sperm cells. Analyses of immunohistochemistry and immunofluorescence staining show that DVL-1 is present diffusely in the cytoplasm of pachytene spermatocytes and exhibits mainly a vesicular pattern and perinuclear distribution and a weak diffusely cytoplasmic signal in round and elongating spermatids. The vesicular pattern of DVL-1 has been observed by previous studies in somatic cells, and suggested to play roles in signal transduction. Immunoprecipitation experiments show that DVL-1 coimmunprecipitates with spermatogenic cells beta-actin rather than alpha-tubulin. These results indicate that DVL-1 may be involved in spermatid morphological changes during mouse spermiogenesis through mediating signal transduction and/or regulating actin cytoskeleton organization.

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Transplantation of spermatogonial stem cells in cross-species has been widely used to study the function of Sertoli cells and the effect of phylogenetic distance between donor and recipient animals on the outcome of spermatogonial transplantation, whereas there have been only a few reports on the transplantation of testis tissue. The objective of the present study was to examine the development of grafted testes and the kinetics of spermatogenesis following syngeneic testicular transplantation in both male and female recipient Balb/c mice in an effort to establish an in vivo culture system and to compare the effects of host sex on spermatogenesis. The testes from 5-day-old Balb/c mice were transplanted under the dorsal skin of four-week-old mice. Twenty male and twenty female Balb/c mice were used as the hosts and each host received 4 grafts. The recipient mice were killed at 1, 2, 3, 5, 7, 9, 12 and 15 weeks after transplantation. The graft survival rate and graft size were measured. The status of spermatogenesis was assessed by histological analyses. The expression of the spermatid-specific Protamine-2 gene was examined by RT-PCR. Overall, 70.3% of the testicular grafts in male hosts and 67.2% in female hosts survived. All recovered grafts had increased in volume, some of them had increased by more than 30-fold. The architecture of the seminiferous tubules in female hosts appeared to be better than that in male hosts. The round spermatids were the most advanced germ cells until 15 weeks after transplantation, and no complete spermatozoon was observed in any of the grafts. The expression of protamine-2 was detected in grafts from 5 weeks posttransplantation in both male and female hosts, confirming that the spermatogenic cells differentiated into spermatids. In contrast to grafts, the testes of male hosts had a normal histological appearance. The results showed the schedule of spermatogenesis following syngeneic testicular transplantation in both male and female hosts. This model could be useful for further studies involving the endocrinology of the testis and the mechanisms of spermatogenesis.