Quantitative analysis of spermatogenic DNA synthesis in the rat using a monoclonal anti-5-bromodeoxyuridine antibody

Summary. The utility of the 5-bromodeoxy-uridine (BrdUrd) labelling technique for the quantitative analysis of spermatogenic deoxyribonucleic acid (DNA) synthesis was investigated in the rat. Rat testicles were labelled by a single intraperitoneal injection of 100 mg kg⁻¹ of BrdUrd. The testicles were removed 1 h after injection, fixed in Bouin's fluid and embedded in paraffin. BrdUrd-labelled cells were detected by immunohistochemical staining using a monoclonal anti-BrdUrd antibody. The number of BrdUrd-labelled tubules per total number of tubules (percent L.T.), the number of BrdUrd-labelled cells per total number of tubules (tubular ratio) and the number of BrdUrd-labelled cells per number of Sertoli cells (Sertoli cell ratio in BrdUrd-labelled cells) were calculated as indices of spermatogenic DNA synthesis during each stage of the seminiferous epithelial wave. BrdUrd labelling was found exclusively in the nuclei of spermatogonia and in preleptotene spermatocytes in the seminiferous epithelium. The percent L.T. was generally greater than 50%, except in stages VI, VII and XIV, and the tubular as well as Sertoli cell ratios in BrdUrd-labelled cells was greater than 2.0 and 0.15, respectively, in stages I, II-III, V, VIII, X, and XII. The tubular ratio and Sertoli cell ratio in BrdUrd-labelled cells along the seminiferous epithelial wave had two distinct peaks. The distribution of the tubular ratio using the BrdUrd-labelling technique correlated well with the distribution previously established by measuring tritiated thymidine uptake per tubule. Thus, the BrdUrd labelling technique, which is more efficient than the tritiated thymidine labelling technique, can be used to quantitatively evaluate spermatogenic DNA synthesis.     

Expression of cathepsin L in human testis under diverse infertility conditions

The cathepsin family of proteolytic enzymes play an important role in the remodeling seminiferous epithelia in rodent testis. In an effort to uncover the cathepsin L expression in diverse pathological conditions in human testis, the immunohistochemical localization of cathepsin L was conducted in human testis under diverse male infertility condition including spermatogenic hypoplasia and testis cancer. In seminiferous tubule of normal, non-obstructive azoospermic, decreased spermatogenesis, and maturation arrest conditions, cathepsin L was found in both germ cells and Sertoli cells. In contrast, there was no visible expression of cathepsin L in seminiferous tubule tissues from Sertoli cell-only syndrome, spermatogenic hypoplasia, and testicular cancer. Our result suggests that the cross-talk between germ cells and Sertoli cells is crucial for the control of cathepsin L expression in human testis. The absence of expression of cathepsin L in germ cell cancer emphasizes that cathepsin L expression in Sertoli cells is regulated by functional germ cells in human testis.     

On the Postnatal Development of the Terminal Segment of the Seminiferous Tubules in Normal and Germ Cell Depleted Rat Testes

The development of the terminal segment of the seminiferous tubules was studied in 5 to 50 days old normal rats. At the age of 5, 10, and 15 days the terminal segment contained fewer gonocytes or spermatogonia than did the corresponding seminiferous tubule. The differentiation of the terminal segment was obvious at 20 days of age due to the high number of germ cells in the seminiferous tubules, where the epithelium became stratified at this stage. The blood-testis barrier in the terminal segment was chiefly established between 15 and 20 days of age as revealed by the lanthanum tracer technique.
To study the effect of the germ cells on the differentiation, the germ cell depleted testes of prenatally irradiated rats were also studied. The modified Sertoli cells of the terminal segment were more vacoulated and had fewer lipid droplets and inter-Sertoli cell junctions than did the Sertoli cells of the seminiferous tubules. The ultrastructure of the modified Sertoli cells of the terminal segment was similar in adult normal and adult SCO (Sertoli cell only) rats. The amount of lipid droplets in the Sertoli cells of SCO rats showed considerable variation among different tubular cross-sections within one testis.     

Êxpression of inducible nitric oxide synthase (iNOS) in the azoospermic human testis

Azoospermia, which is the absence of spermatozoa in the ejaculate, is not a rare cause of male infertility. Inducible nitric oxide synthase (iNOS) is a calcium-independent NOS, which is present in the testis and involved in spermatogenesis, and apoptosis of Sertoli and germ cells. Twenty idiopathic infertile men presenting nonobstructive azoospermia were enrolled in this study, and testicular sperm extraction procedures were performed. Tissue extracts were dissected, and the fluid samples were investigated to determine the presence of spermatozoa. Histologic evaluation of the spermatozoa-present samples revealed that seminiferous tubules were normal and were lined by Sertoli cells and spermatogenic cells. However, in the spermatozoa-absent samples, the diameter of the seminiferous tubules was small, and Sertoli-cell-only syndrome was determined in most of the tubules. iNOS expression was very weak in Sertoli cells, germ cells, and in Leydig cells in the spermatozoa-present group. In the spermatozoa-absent group, the immunostaining was very intense in Sertoli and Leydig cells. Electron microscopy findings were supported the histologic results. In conclusion, complete germ cell loss and intense expression of iNOS in the Sertoli and Leydig cells in the spermatozoa-absent groups of azoospermic human testis suggest an essential role of iNOS in spermatogenesis.     

Experimental cryptorchidism in the adult mouse: I. Qualitative and quantitative light microscopic morphology

Morphologic changes in the testes of adult mice after experimentally induced cryptorchidism were studied by light microscopy and stereology. Increasing duration of cryptorchidism resulted in a gradual decrease in the volume of seminiferous tubules per testis, and this was associated with germ cell degeneration. The volumes of Sertoli cell lipid droplets increased, and dilations of the intercellular space between the Sertoli cell junctions was observed in the cryptorchid testis. The luminal volume of the seminiferous tubule was reduced by 50% after 28 days of cryptorchidism. However, the volumes of intertubular tissue and Leydig cells in control and cryptorchid testes were not significantly different. Leydig cell number per testis increased, and the average volume of a Leydig cell decreased gradually with the progression of the cryptorchid state. The volume of the connective tissue cells in the intertubular area increased, but no significant volume change was observed in the volume of intertubular macrophages. After 28 days, the cryptorchid testis contained a significantly increased volume of blood vessels and a reduced volume of lymphatic space per testis. These observations clearly demonstrate that, although the mouse is a species closely related to the rat, the morphologic changes that occur in the Leydig cell population after induction of experimental cryptorchidism in this species is different.     

Pattern of Sertoli cell degeneration in cryptorchid prepubertal tests

Seventy-three testicular biopsies from 54 children (aged 2 months-14 years) with undescended testes were examined by light and electron microscopy. The biopsies included abdominal, inguinally fixed, inguinally moveable, and retractile testes. Alterations in Sertoli cell morphology were found in all biopsies. The alterations included dilated elements of rough endoplasmic reticulum, vacuolization of the cytoplasm, mitochondria with poorly preserved cristae, increase in electron density of the matrix, elongation of the nuclei, and irregularities of the nuclear membrane. According to the numerical appearance of these cells and to the extent of lesions in single Sertoli cells, seven phases in the continuous process of tubular alteration were distinguished. The most severe tubular damaged (phase VII) occurred when the seminiferous epithelium consisted exclusively of necrotic cells. All phases of tubular alterations were seen regularly in each of the biopsies investigated. Germ cells occurred only in phases I-IV and were never observed in tubules in phases V-VII. Significant differences became evident between inguinal and retractile testes by morphometric evaluation. It was demonstrated that the number of germ cells per cross-sectioned tubule (S/T value) correlated negatively with the percentage of tubules in phases V-VII. In contrast to inguinal testes, a complete absence of Sertoli cells and an S/T value less than 0.1 were never found in retractile testes and the percentage of tubules in phases V-VII was reduced significantly compared with inguinal testes. Our findings indicate that (i) maldescended testis in patients between 1 and 15 years-of-age is associated with a special pattern of Sertoli cell degeneration; (ii) Sertoli cell degeneration is a continuous process, which can lead eventually to complete dissolution of the seminiferous epithelium; (iii) total degeneration is not related to age but is dependent on testicular position; (iv) a defined phase of degeneration excludes germ cell development, and therefore enhanced Sertoli cell degeneration in cryptorchid testes must also account for the reduction in germ cell number.     

Expression of beta-catenin in human testes with spermatogenic defects

beta-catenin is a multifunctional molecule that functions in intercellular adhesion and signal transduction during assembly of AJs between Sertoli cells as well as between Sertoli cells and germ cells. To assess changes in the testicular beta-catenin in male infertility conditions, testicular tissues from obstructive azoospermia with normal spermatogenesis, spermatogenic arrest (SA) and Sertoli cell-only syndrome (SCO) patients were examined for immunohistochemical localization of beta-catenin. In normal spermatogenic tissue, expression of beta-catenin was largely found in the Sertoli cell-germ cell (primarily spermatocytes) contact areas. Interestingly, perinuclear localization of beta-catenin was found in spermatocytes and spermatids. In spermatogenic arrest, beta-catenin in cell contact areas between Sertoli cells and germ cells was greatly decreased, but perinuclear beta-catenin in spermatocytes was not. In SCO, weak or negligible immunoreactivity of beta-catenin was found in cell contacts between Sertoli cells. Nuclear localization of beta-catenin was found in myotubular cells in all samples. Taken together, altered expression of beta-catenin in cell contacts within the seminiferous epithelia in spermatogenic arrest and SCO suggests that interactions between Sertoli cells and germ cell are crucial for expression of beta-catenin, and thus functional development of AJs in seminiferous epithelia in human testis. It should be also emphasized that perinuclear beta-catenin in germ cells may play a specific role in spermatogenesis.     

Morphological evidence for two types of idiopathic ''Sertoli-cell-only'' syndrome

Biopsies of testicular specimens taken from 41 patients that were diagnosed as having idiopathic Sertoli-cell-only syndrome were classified into two types, A and B, on the basis of histological and immunohistochemical findings. Thirty eight specimens that were classified as type A exhibited seminiferous tubules of small diameter and with tubular wall hyalinization, but containing normal adult type Sertoli cells. The other three specimens that were classified as type B showed no seminiferous tubular wall hyalinization, and their Sertoli cells had vimentin distribution localized in the subnuclear cytoplasm and had a pseudostratified lining, features resembling the appearance of fetal Sertoli cells. In one patient with a seminoma, a comparative study of the same testis prior to and post-irradiation was undertaken. Judging from this, postpubertal depletion of the germ cell population was considered to be responsible for the tubular atrophy observed in type A. Type B testes, though small in number, were characterized by a morphology distinct from the type A, but their pathogenesis remains unknown.     

Erdosteine protects rat testis tissue from hypoxic injury by reducing apoptotic cell death

The purpose of this study was to examine the effects of hypobaric hypoxia on testis morphology and the effects of erdosteine on testis tissue. Caspase‐3 and hypoxia‐inducible factor 1α expressions were detected by immunohistochemistry. Adult male Wistar rats were placed in a hypobaric hypoxic chamber. Rats in the erdosteine group were exposed to the same conditions and treated orally with erdosteine (20 mg kg^?1 daily) at the same time from the first day of hypoxic exposure for 2 weeks. The normoxia group was evaluated as the control. The hypoxia group showed decreased height of spermatogenic epithelium in some seminiferous tubules, vacuolisation in spermatogenic epithelial cells, deterioration and gaps in the basal membrane and an increase in blood vessels in the interstitial area. The erdosteine group showed amelioration of both epithelial cell vacuolisation and basal membrane deterioration. Numbers of hypoxia‐inducible factor 1α–immunostained Sertoli and Leydig cells were significantly higher in the hypoxia group than in the erdosteine group. The number of seminiferous tubules with caspase‐3–immunostained germ cells was highest in the hypoxia group and decreased in the erdosteine and normoxia groups respectively. Based on these observations, erdosteine protects testis tissue from hypoxic injury by reducing apoptotic cell death.     

Effects of diazacholesterol dihydrochloride (SC-12937), an avian antifertility agent, on rat testis

The present study was undertaken to evaluate the effectiveness of an avian chemosterilant, 20, 25-diazacholesterol dihydrochloride (SC-12937), on the rat testis. Adult male rats were injected intraperitoneally with 10 mg (Group 1) or 30 mg (Group 2) of SC-12937/kg/d or with vehicle alone (Group 3) for 10 days, and were killed 24 hours after the last injection. A wide range of variation in the appearance of affected seminiferous tubules was observed in the testis of SC-12937-treated rats at both dose levels. This ranged from apparently normal-looking seminiferous tubules to almost completely atrophied tubules with no cells. Affected tubules exhibited intraepithelial vacuoles of varying size, multinucleated giant cells, germ cell exfoliation, and tubular atrophy. The presence of severely damaged and entirely normal seminiferous tubules adjacent to one another in the same section was noteworthy. The changes appeared to be dose-related. A greater number (34.6%) of affected tubules were observed in rats receiving 30 mg of SC-12937 compared with the ones receiving 10 mg of this compound (19.6%). The Sertoli cells also were affected by this drug and exhibited cytoplasmic vacuolation, a marked increase in the accumulation of lipid droplets and myeloid bodies. Necrotic Sertoli cells also were observed in the severely affected tubules. The possible mechanism of antispermatogenic action of SC-12937 in rats has been discussed briefly.     

Local regulation of Leydig cells by the seminiferous tubules. Effect of short-term cryptorchidism

Unilateral cryptorchism was induced in adult rats for 24 h, and its effect on testicular morphology and intratesticular testosterone concentration after hCG-stimulation were studied. In seminiferous, tubules from abdominal testes an increased number of degenerating germ cells was noted in stages XIV-III of the spermatogenic cycle and Sertoli cells contained an increased amount of lipid droplets in stages XIV-VIII. However, germ cells and Sertoli cells from tubules at other stages of the cycle appeared unaffected. In scrotal testes the size of peritubular Leydig cells varied in phase with the spermatogenic cycle. The largest cells were found adjacent to stage VII-VIII and the smallest adjacent to stage XI-XII. In abdominal testes no stage-dependent variation in the size of peritubular Leydig cells was seen. Perivascular Leydig cells were of equal size in abdominal and scrotal testes. The testicular testosterone concentration following stimulation with a low dose of hCG was significantly lower in abdominal testes. It is suggested that the seminiferous tubules locally modulate Leydig cell function and that the stage specific stimulatory influence from stage VII-VIII is rapidly lost during experimental cryptorchidism.     

The effect of selective destruction and regeneration of rat Leydig cells on the intratesticular distribution of testosterone and morphology of the seminiferous epithelium

This study was designed to explore the relationship between the intratesticular distribution of testosterone and spermatogenesis by completely destroying the Leydig cells of mature male rats with injection of a single i.p. dose of ethane dimethanesulphonate. After such treatment, testosterone levels in serum, testicular interstitial fluid, seminiferous tubules, and whole testis declined significantly 6 to 24 hours after injection and fell below assay detection limits between 3 and 7 days. At 3 and 7 days, serum LH and FSH levels rose significantly and remained elevated up to 4 and 6 weeks, respectively, in comparison with vehicle-treated controls. Leydig cells disappeared from the interstitium by day 3, but between 2 and 4 weeks postinjection a new generation of fetal-like Leydig cells repopulated the testicular interstitium and, during weeks 6 to 10, were transformed into, or replaced by, Leydig cells with an adult type of morphology. Histologic examination of the seminiferous tubules showed progressive disruption of spermatogenesis between 3 and 14 days post-ethane dimethanesulphonate. The first histologic sign of spermatogenic damage was noted at day 3, with the occurrence of stage-specific degenerating pachytene primary spermatocytes at stages VII to VIII of the spermatogenic cycle. On day 7, these cells and degenerating round, or step 19, spermatids often were observed during stages VII to XI, although qualitatively normal spermatogenesis also was seen in these and all other stages of the cycle. Maximum impairment of spermatogenesis occurred 2 weeks post-ethane dimethane sulphonate, at which time the tubules commonly lacked one or more germ cell generations or, alternatively, showed accumulation of lipid inclusions, extracellular spaces, and variable numbers of degenerating germ cells. Following repopulation of the testis by Leydig cells during weeks 3 and 4, spermatogenesis recovered. By 10 weeks after treatment, qualitatively normal spermatogenesis was seen in the great majority of seminiferous tubules, although a few tubules still remained in which the germ cell complement was severely reduced, and contained only Sertoli cells and spermatogonia.(ABSTRACT TRUNCATED AT 400 WORDS)     

睾丸细胞生物学研究进展

睾丸是男性生殖腺,由生精小管和间质构成。生精小管主要由生精细胞和支持细胞组成,是精子发生场所;间质中主要是间质细胞,间质细胞合成与分泌雄激素。本文介绍睾丸3种细胞的发育分化,以及成年期睾丸细胞的结构和生物学研究进展。     

A quantitative morphological study of age-related changes in the donkey testis in the period between puberty and senium

Summary. The testis of the donkey was used as a model to study age-related changes in the period between puberty and senium. From the age of 1.5 years to the middle of sexual maturity (5 to 6 years) a number of histophysiological features, all indicative of the spermatogenetic efficiency, increase continuously. Then without a longer-lasting plateau of maximal performance these features undergo continuous retrogression. Thus, the adult testis is an organ in permanent change. During its progressive period (1.5 to 5 years) the average testicular and tubular volumes treble. The increase in tubular volume is due to an increase in tubular length (from 700 m to 1600 m per testis) and tubular diameter (from 205 μm to 250 μ). Parallel to this growth, the spermatogenetic efficiency of the seminiferous epithelium rises: the number of germ cells entering meiosis increases and the cell loss by apoptosis or exfoliation decreases. During the following regressive period of the testis (5–10 years) seminiferous epithelial height and tubular diameter are again gradually reduced to 70 μ and 205 μ, respectively. The absolute number of Sertoli cells per testis decreases continuously from puberty onwards. The tubular lamina propria thickens with advancing age and at the age of 10 years, displays long irregular projections into the seminiferous epithelium.     

大鼠严重烫伤后睾丸的病理变化

对大鼠严重体表烫伤后睾丸组织的病理变化进行了动态观察。大鼠体表３０％ＩＩ度烫伤后睾丸出现明显病变，其病理变化出现早、程度较重、形态变化多样，生精细胞、支持细胞、曲细精管界膜、间质细胞及血管内皮细胞均有不同程度的损伤性改变。生精细胞的病变以精母细胞及精细胞为重，精原细胞无明显损伤，伤后３０天生精上皮基本恢复正常。曲细精管界膜内纤维连接蛋白（Ｆｎ）于伤后早期减少。认为曲细精管界膜及支持细胞的损伤，特别是后者的损伤，改变了生精细胞生长、发育的微环境而可能导致或加重生精细胞的损伤。     

大鼠曲细精管生殖细胞体外共培养和精子发生过程的观察

目的建立体外长期共培养体系和观察方法,为精子发生过程的研究提供细胞模型。方法采用大鼠曲细精管生殖细胞及支持细胞共培养的方法,对睾丸生精细胞作显微镜观察。结果共培养的支持细胞和生精细胞在体外存活超过6个月。在共培养期间,观察到精母细胞、圆形精子细胞和长形精子细胞。结论在不添加任何细胞因子和生长因子的情况下,大鼠曲细精管生殖细胞长期增生分化,不断产生精子细胞。这一结果暗示组织块和共生的支持细胞可为生殖细胞的增生和分化提供必需的细胞因子。该方法为体外研究精子发生过程提供了实验依据。     

Bovine sertoli cells colonize and form tubules in murine hosts following transplantation and grafting procedures

The contribution of somatic cells to nonrodent male germ cell transplantation success has not been well established due to lack of cell type-specific markers to distinguish donor cells from host cells. In the present study, we first screened antibodies and a lectin to identify markers suitable for unequivocal distinction between germ cells and Sertoli cells in bovine testes compared with mouse testes. Anti-vimentin and the Dolichos biflorus agglutinin (DBA) lectin detected only bovine Sertoli cells and spermatogonia, respectively; anti-NONO and anti-GCNA1 detected only mouse Sertoli and germ cells, respectively. The outcome of transplanting bovine testis cells into nude mouse testes was then studied using these markers. Our results clearly showed that immature bovine Sertoli cells survive and colonize mouse testes at 2.5 months after transplantation and that tubular structures composed of donor Sertoli cells formed adjacent to murine tubules within the host mouse testis. Bovine germ cell colonization and survival in mouse testes after transplantation were confirmed, but this was restricted to areas of bovine Sertoli cell colonization. In addition, ectopic grafts of intact bovine testis tissue and cell aggregates from hanging drop cultures were placed under the back skin and testis capsule of nude mice. Bovine Sertoli cells in ectopic grafts and aggregates were able to form tubular structures, and some bovine germ cells were observed around 2 months after implantation. This study therefore identifies a practical strategy to assess the outcome of testicular cell transplantation using different antibodies and a lectin to distinguish bovine cells from mouse cells. It identifies an approach that can readily be adapted to study other nonrodent species.     

Alteración de la densidad del volumen de los componentes testiculares asociada con el cisplatino: ¿pueden los antioxidantes ofrecer protección?

ObjectivesCis-platinum based chemotherapy agents are widely used in treatment of testicular cancer and its deleterious effects on spermatogenesis are well known. Therefore an extensive survey was undertaken to evaluate the effects of antioxidants in combination with Cis-platinum in an attempt to minimize its effects upon spermatogenic function of adult rats.MethodsA short-term prospective study (thirteen days) including twenty-four adult male Wistar rats was performed. Animals were assigned into one of three groups (eight per group): GI-control, GII-Cis-platinum treated and GIII-Cis-platinum plus superoxide dismutase and catalase. Histological analyses included germ cell counts, germ to Sertoli cell ratios and estimation of volume density components as well as the determination of the sperm reserves. Data was examined through one-way analysis of variance at 5% level of significance.ResultsGerm cell numbers, germ cell to Sertoli cell ratios, organ weights (except body weight) and sperm reserves presented no differences among groups. However, the volumetric proportion of some components (tubular epithelium, tunica propria, Leydig cell nuclei and stroma) were affected (p<0.05) by treatment. The most prominent testicular component, the seminiferous epithelium was reduced (p<0.05) in Cis-platinum treated animals (GII).ConclusionThe use of antioxidant in association with Cis-platinum did not affect sperm production (germ cell numbers, germ to Sertoli cell ratios and sperm reserves) of adult rats. However, the deleterious effect of Cis-platinum on the seminiferous tubule epithelium was minimized by antioxidants.     

The effects of aging on the seminiferous epithelium and the blood-testis barrier of the Brown Norway rat.

Steroidogenesis and spermatogenesis decrease in aging Brown Norway rats. We therefore hypothesized that there must be accompanying morphological changes taking place in the seminiferous tubules of the aging testis. The testes of Brown Norway rats ranging in age from 3 to 24 months were prepared for light and electron microscopy. To assess the integrity of the blood-testis barrier with age, a lanthanum nitrate study was done. The normal seminiferous tubules present in rats at 3 and 12 months of age were largely replaced at 24 months by fully regressed tubules that were virtually devoid of germ cells and contained large intercellular spaces. An electron-microscopic study of these regressed tubules showed a complete loss of cyclical variations of the organelles of the Sertoli cells. The nucleus was more irregularly shaped and was present at various levels in the epithelium. The endoplasmic reticulum was a loose, vesiculated network that was unlike the elaborate, tubular, anastomotic network noted in young animals. The lysosomes were large, oddly-shaped, and contained lipidic inclusions, in contrast to the distinct membrane-bound lysosomes and dense core bodies found in the young animals. Adjacent Sertoli cell processes encompassed large, empty intercellular spaces, possibly occupied previously by germ cells. The typical Sertoli-Sertoli junctions of the blood-testis barrier in the young animal were rarely seen at 24 months and were replaced by focal contact points, usually between three Sertoli cell processes. In the aged animals, lanthanum nitrate permeated the basal and adluminal compartments, extending between Sertoli cell processes and entering the intercellular spaces and lumen. In summary, during aging, there is a breakdown of the blood-testis barrier, and there are striking changes in the appearance of Sertoli cells. These results suggest a possible intrinsic limitation that prevents stem cells from renewing themselves, whether because of a degeneration of immunological origin or because of a lack of Sertoli cell support.     

Expression of p50 C-terminal Src kinase (Csk) in mouse testis

C-terminal Src Kinase (Csk) is a cytoplasmic tyrosine kinase that phosphorylates a critical tyrosine residue in each of the Src family kinases to inhibit their activities. To investigate the possible regulation of spermatogenesis by Src-Csk loop, the postnatal changes in the expression of Csk were examined in mouse testes. Semiquantitative RT-PCR analysis revealed that Csk mRNA increased during neonatal development and peaked at 2 weeks of age. Following the decrease during pubertal development, Csk expression re-increased in adult testes. In Western blot, immature testes showed higher expression of Csk protein than the pubertal or adult testes. In immature testis, Csk immunoreactivity was largely found in the Sertoli cell and there was no visible difference in the Csk immunoreactivity among the seminiferous tubules. In adult testis, however, a differential Csk immunoreactivity was found among the seminiferous tubules. Intense signal was found in the adluminal cytoplasm of the Sertoli cells bearing the post-meiotic differentiating germ cells, suggesting that Csk may participate in the remodeling of seminiferous tubule during late phase of spermatogenesis. Csk immunoreactivity was also found in the Leydig cells, suggesting the possible regulation of Leydig cell function. Src-Csk loop may participate in the differentiation of the seminiferous epithelia and Leydig cells in mouse testis.