Ultrastructural study of seminiferous tubules in the rat after prenatal irradiation

Summary Is the presence of germinal cells necessary for the Sertoli cells to acquire normal features? To respond to this question we have studied the development of the Sertoli cells in rats irradiated at the end of the foetal life.In the prenatal irradiated rats, the lumen of the seminiferous tubules appears later than in the control rats. The Sertoli cells show numerous flexuous apical processes, with central microtubule bundles. These processes regress progressively after the 40th day of life when the tubular lumen appears; numerous junctional complexes differentiate with the same structure as those of control animals. There are important dilatations of the intercellular spaces. The cytoplasmic organelles show a normal development up to the 40th day of life. After this period, the rough endoplasmic reticulum and the Golgi apparatus clearly regress while important dilatations appear in the smooth endoplasmic reticulum and persist in the adult animal. From the 35th day on, the basal lamina of the seminiferous tubules is irregular and multilayered.The differentiation of the Sertoli cells seems to be independent of the presence of germinal cells until the 40th day of life and presents several particularities; thereafter the Sertoli cells show signs of regression.     

Ultrastructure of melanocytes in the dark cell area of human vestibular organs: Functional implications of gap junctions,isolated cilia,and annulate lamellae

Background: It is known that melanocytes exist in almost all parts of the inner ear, such as the cochlear duct, stria vascularis, Reissner's membrane, modiolus, vestibular organs in the region surrounding the cristae and maculae, semicircular canals, and pars rugosa of the endolymphatic sac. But there have been few studies using human materials, because of the difficulty of obtaining materials. We attempted to investigate the detailed ultrastructure of melanocytes in the vestibular organs of human inner ear. Methods: Eight surgical specimens obtained from patients with vestibular schwannoma were studied by light microscopy and electron microscopy. Results: Melanocytes were found in the subepithelial layer of the dark cell area. Melanocytes had round or spindle-shaped nuclei and clear cytoplasm with brown pigment granules. Besides melanocytes, there were melanophages, fibroblasts, and small blood vessels. Through electron microscopy we found melanocytes with round-shaped melanosomes in various stages of pigmentation, well-developed Golgi apparatus and endoplasmic reticulum in the cytoplasm, and many cytoplasmic processes. Gap junctions were occasionally found between the cytoplasmic processes. And there were pinocytotic vesicles just under the limiting membrane of melanocytes, and intermediate filaments were abundant in the cytoplasm. Isolated cilia of melanocytes, annulate lamellae, and fusiform banded structures in the connective tissue area around melanocytes were found. Conclusions: Melanocytes in human vestibular organs actively synthesize melanosomes. Frequent findings of isoalted cilia and fusiform banded structures and the incidental existence of annulate lamellae may be an indicator of this metabolically activated state of melanocytes. Moreover, monitoring environmental changes by isolated cilia, melanocytes in the human inner ear could act not only as one cell but also as a group to achieve their physiological functions by means of information transmission through gap junctions. © 1994 Wiley-Liss, Inc.     

Adenocarcinoma of the fallopian tube

Summary A case of fallopian tube adenocarcinoma was studied by light and transmission electron microscopy. The neoplastic cells contained abundant mitochondria, moderate to large amounts of rough endoplasmic reticulum (RER) arranged in parallel arrays and often containing amorphous material, annulate lamellae, possible secretory vesicles, and glycogen. The presence of stacked RER and annulate lamellae together is unusual in papillary serous cystadenocarcinoma of the ovary, and has not been described in Fallopian tube adenocarcinoma. Golgi complexes were are. Small acini with projecting microvilli as well as junctional complexes were present, but cilia were not found. The electron microscopic findings suggest secretory activity, and are remarkably similar to those found in papillary serous cystadenocarcinomas of the ovary. The findings also support the hypothesis that ovarian serous tumors and adenocarcinomas of the Fallopian tube are derived from coelomic epithelium.     

Spermatogonial intercellular bridges in whole-mounted seminiferous tubules from normal and irradiated rodent testes

Whole-mounted seminiferous tubules from normal and irradiated rodent testes were examined by light microscopy. These studies reveal the presence of intercellular bridges in all classes of spermatogonia except for the single A_s stem cells. It was demonstrated that A_s stem cells divide to produce new A_s spermatogonia or paired daughter cells that are united by a cytoplasmic bridge. Evidence was given that all subsequent progeny of these paired A's up to and including the production of type B spermatogonia remain linked by cytoplasmic bridges in increasingly larger and more complex syncytial networks. It is proposed that the intercellular bridges mediate both differentiation and degeneration of spermatogonia. The maintenance of synchronous development within cohorts of spermatogonia is attributed to the bridges. Moreover, the fact that spermatogonia in both normal and irradiated testes degenerate in clusters is determined by the presence of intercellular bridges. Lastly, the integrity of the bridges appears essential for normal germ cell development.     

Ultrastructural study of Sertoli cells in rat seminiferous tubules during intrauterine life and the postnatal period

Summary Sertoli cells have various functions: mechanical (creation of two compartments in the seminiferous tubules, migration of germinal cells), secretory (secretion of anti-Müllerian hormone, inhibin, androgen-binding-protein and estrogen) and phagocytic.We report an ultrastructural study of the rat Sertoli cell during maturation and consider possible correlations between the acquisition of certain morphological characteristics and certain functions.During fetal life, the Sertoli cell possesses differentiated zones of junction with the gonocytes and seems to have a role in the migration of the gonocytes towards the periphery of the seminiferous tubule. The Sertoli cell performs the phagocytosis of the gonocytes which degenerate during their migration, and seems to be the site of production of protein granules, whose presence can be related to the synthesis of anti-Müllerian hormone.After birth and before puberty, when the inclusions resembling secretory granules disappear, the Sertoli cell membranes in contact with spermatocytes II and spermatids differentiate, forming, through the differentiated junctional complexes, two compartments (adluminal and luminal) in the seminiferous tubules. Finally, they acquire the characteristics of active secretory cells, capable, in particular, of steroid synthesis.     

Morphological and quantitative analysis of spermatogonia in mouse testes using whole mounted seminiferous tubules. II. The irradiated testes

In adult male mice exposed to 300 R X-irradiation, the sper-matogonial population was selectively killed except for the radioresistant type A_s stem cells. Type A spermatogonia were minimal two days after irradiation, when only 20% of the control population was present in stages 5-6; these were predominately single and paired undifferentiated cells. When multiple injections of ³HTdR were given between 2 and 3.5 days post-irradiation, 90–95% of these survivors in stages 4-6 became labeled. Enhanced proliferation of these stem cells, and at times when they were normally quiescent, led to restoration of all classes of spermatogonia by 11 days after irradiation. Several autoradiographic studies were undertaken to better characterize the radioresistant cells. In mice given single or multiple injections of ³HTdR prior to irradiation, there was appreciable retention of label by those type A_s sper-matogonia that had originally incorporated ³HTdR in stages 2-4. This labeling pattern was identical to that of the long-cycling A_s stem cells in nonirradiated testes. Since the long-cycling A_s stem cells are thought to be characterized by a prolonged G₁ or “A-phase” which is known to be a highly radioresistant portion of the cell cycle, it was clear why these cells could preferentially survive irradiation doses that killed other spermatogonial types. It was proposed that following germ cell depletion, as after irradiation injury, the long-cycling A_s survivors could be prematurely triggered from A-phase into DNA synthesis, thereby, initiating restoration of the germ cell population.     

Morphogenesis of the bovine rete testis: the intratesticular rete and its connection to the seminiferous tubules

The development of the intragonadal rete testis and the establishment of the connection between seminiferous and straight testicular tubules was studied using ultrastructural and histochemical methods in 60 bovine embryos and fetuses ranging from day 39 through day 225 post conceptionem. The methodology included a modified acetylcholinesterase (AChE) reaction as a selective marker for pre-Sertoli cells and a modified microsomal aminopeptidase (MAP) reaction as a selective marker for the epithelia of rete testis and straight testicular tubules. Between 40 and 45 days, the rete testis is predominantly an extratesticular rete situated in the cranial peduncle of the gonadal fold and in broad contact with the pro/mesonephric giant corpuscle. During this period, the intragonadal rete enters the gonad proper from its craniodorsal pole and extends into the cranial fourth of the testis. Between 60 and 110 days the rete testis attains its definitive position, extending into the central longitudinal axis as far as to the caudal fourth of the testis. For the caudal expansion of the rete testis the preceding proliferation of the mediastinal stroma is an important prerequisite. In the 40 to 45-day-old embryo the area of the testicular cords may be divided into two zones. A narrow outer zone contains plate-like cords with a thick diameter, and a larger central zone is filled with a network of thinner cords. Only the thick outer cords transform into the permanent seminiferous tubules, whereas the thinner cords in the central zone are transitory structures that disappear between 45 and 110 days. One important function of these transitory cords is to establish a continuous system of basal laminae that allows a direct connection between the central ends of the growing seminiferous tubules and the peripheral extensions of the rete testis (future straight testicular tubules). The first true straight testicular tubules become visible between 85 and 110 days. Due to a strong proliferation of the tubulus rectus-cells the straight testicular tubules elongate continuously, and the border between the rete system and the seminiferous tubules is slowly shifted towards the testicular periphery. This shift is not restricted to the prenatal period, but proceeds until after birth. At the cytological level, the formation and elongation of the straight testicular tubules is effected by proliferating cells that advance along the continuous basal lamina into the area of the seminiferous tubules. The pre-Sertoli and germ cells in this zone of invasion are separated from each other and overgrown by the tubulus rectus-cells. Exposed to the special milieu of the straight testicular tubules, pre-Sertoli and germ cells apparently cannot survive and finally disappear. Accepted: 31 July 2000     

早期人胎儿睾丸组织异种异体生长发育的研究

目的 采用免疫缺陷小鼠为受体的睾丸组织移植技术,探索小于3月龄的人类胎儿未成熟睾丸组织在异种异位生长发育的可行性,为睾丸移植技术用于人类生精机制研究提供更为易行的供体来源。 方法 将9例10～13周流产胎儿的睾丸组织分别移植到6只雄性去势免疫缺陷小鼠背部皮下,根据移植物的生长状态以及受体的健康状况于不同时间取出移植物。通过对睾丸组织移植前后的组织学观察,对人类未成熟睾丸组织在异种异位的生长发育情况进行分析。 结果 3个月左右的胎儿睾丸约为5～7mg,移植后取出的最大移植物重量为84.1mg。9例未成熟睾丸组织移植后观察到有6例在受体中继续生长发育,其中的生精小管直径由移植时的(44.26±3.14)μm发育成为(77.69±7.47)μm。小管中无规则分布的原始生殖细胞和原始支持细胞开始向基底膜部位迁移,其中部分原始生殖细胞已定位于基底膜处,并具有精原细胞的特征;支持细胞也由幼稚状态发育为具有丰富胞质的成熟型细胞,有序排列在精原细胞周围,形成壁龛样结构。 结论 将较易获得的早期流产胎儿睾丸组织移植到免疫缺陷小鼠体内后,睾丸组织可继续生长发育,因此可作为人类睾丸组织生长发育研究的供体组织。     

Specific expression of the mRNA for 25 kDA heat-shock protein in the spermatocytes of mouse seminiferous tubules

 The 25 kDa heat-shock protein (Hsp25) is a member of the family of small heat-shock proteins. We investigated the expression and cellular localization of Hsp25 mRNA in the testis of adult and developing mice using Northern blotting and in situ hybridization techniques. In the early postnatal days, i.e., before the onset of spermatogenesis, no Hsp25 mRNA was detected in the testis. At around 10 days postpartum, Hsp25 mRNA began to be expressed in the testis in coincidence with the onset of the first wave of spermatogenesis and increased in amount progressively toward adulthood. Throughout the testis development, the signal for Hsp25 mRNA was localized exclusively to germ cells and was not detected in Sertoli or interstitial cells. The testis of W/Wv mutant mice, which lack the germ cell line, exhibited no Hsp25 mRNA expression. In the testis of normal adult mice, the abundance of Hsp25 mRNA differed among the seminiferous tubules in different stages of spermatogenesis. The most intense signal for Hsp25 mRNA was localized to the spermatocytes at leptotene, zygotene and early pachytene phases, which are present in the tubules of stages I–III and IX–XII. The signal decreased in intensity in the late pachytene and diplotene spermatocytes and was not detected in spermatids. Spermatogonia were also devoid of the signal. These results suggested that Hsp25 plays some specific role in the meiotic prophase of the testicular germ cell. Accepted: 27 Oct 1998     

Histochemical demonstration of disulfide-groups in the lamina propria of human seminiferous tubules

Summary The distribution of disulfide-groups was investigated in the tunica propria of human seminiferous tubules by means of a thiosulfation/Alcian Blue+0.8 Mol MgCl₂-staining reaction. Controls had shown the absence of significant amounts of sulfhydryl- or sulfate-groups in the lamina propria, which groups would also be demonstrated by the method employed.The lamina propria of human seminiferous tubules is rich in disulfide-groups. The staining reaction decreases in the region of the tubulus rectus, is only faint in the connective tissue which underlies the epithelium of the rete testis, and is absent in the lamina propria of efferent ducts.It is suggested that microfibrils and type IV collagen (both rich in cystine) are the materials responsible for the histochemical reaction described. The occurrence of multiple layers of basal lamina material (type IV collagen) and bundles of microfibrils is shown in comparative electron microscopic studies.     

Development of the seminiferous tubules and rete testis during prenatal human development

The source of origin and particular features of the formation of the seminiferous tubules and tubules of the rete testis during prenatal human development were studied. The seminiferous tubules and tubules of the rete testis were shown to be formed from bands of cells of the celomic epithelium and primordial germ cells, which appear simultaneously in the anlage of the mediastinum testis and the central part of its parenchyma in embryos 13.0–17.0 mm long. It was shown by methods of plastic and graphic reconstruction and fine dissection under the control of the MBS-1 binocular microscope that the seminiferous tubules anastomose with each other both in the same and in adjacent lobules. Tubules of the rete testis do not form anastomoses but are superposed one above the other to give the impression of a network. They merge as the approach the tunica albuginea and continue into the efferent ductules.Department of Human Anatomy, Chernovtsy Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. P. Avtsyn.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 85, No. 2, pp. 227–229, February, 1978.     

Ultrastructure of platelets before and during atrial stimulation

Summary We studied 15 patients with strain-induced angina pectoris performing an ultrastructural analysis of platelets withdrawn simultaneously from the aorta and coronary sinus. In coronary sinus blood, all platelets exhibited shape changes with pseudopod formation but without degranulation.In the aortic blood we observed on average fewer shape changes of the platelets. During tachycardia stress, shape change formation did not increase in most patients. In three patients however, micro-aggregation of the platelets was observed only in the aortic blood. These patients had a paucity of risk factors. They also had fewer critical coronary artery stenoses compared with the other patients. We conclude that there may be minority among the patients with angina pectoris exhibiting hyper-aggregation of the platelets.     

Three-dimensional structure of seminiferous tubules in the Syrian hamster

The hamster is useful for the study of male reproductive biology. However, unlike in the mouse and rat, the gross structure of seminiferous tubules in the hamster is largely unknown. The aim of the present study was to clarify the precise 3-dimensional (3D) structure of seminiferous tubules in hamsters. We reconstructed all seminiferous tubules in 3 and 1 testes from 0-day (P0) and 10-week (adult) Syrian hamsters, respectively, using serial paraffin sections and high-performance 3D reconstruction software. In P0 hamsters, the average numbers of seminiferous tubules, terminating points, branching points, and blind ends per testis were 9.0, 89.7, 93.0, and 0.7, respectively. There were two types of tubules: shorter and dominant ones. The dominant tubules, 2–4 in number per testis and accounting for 86% of the total tubule length, had many terminating and branching points and appeared to be derived from the anastomosis of many shorter tubules. In an adult hamster, there were 11 seminiferous tubules with a total length of 22 m, 98 terminating points, 88 branching points, and 2 blind ends per testis. Three of the 11 tubules were dominant ones, accounting for 83% of the total length, and occupied the testis from the surface over the circumference to the center, while the others were short and occupied only one side of the testis. The amplitude and direction of the curves of tubules were random, and there were no funnel-shaped networks of tubules present, in contrast to the mouse testis. The present study revealed the 3D structure of seminiferous tubules in developing and adult Syrian hamsters, which is different from that in mice and rats.     

Ultrastructure of the normal human aortic media

Summary The ultrastructural organization of the adult human aortic media was studied utilizing aortic biopsies from 14 patients, ranging in age from 28 to 67, who underwent cardiac surgery. Apart from solid elastic elements the tissue spaces contained a vast amount of ill-defined thin streaks of elasin, an observation much facilitated by utilizing a selective elastin staining technique. In favorable sections, these streaks were found to be continuous with the solid elastic laminae. Furthermore, most medial smooth muscle cells were in close contact with the thin streaks, but almost none directly with the elastic laminae. The smooth muscle cells had also virtually no connection with collagen fibers. These observations are in contrast with the organization of elastin and with cell-to-stroma connections in the more extensively studied rodent and porcine aortas; they bring into question the role of the smooth muscle cells in the regulation of the viscoelastic properties of the human aortic wall. Other findings were: large number of nexuses connecting the smooth muscle cells, a very small degree of smooth muscle cell degeneration, and the presence of flocculent, fine-granular material investing all formed elements, but especially associated with the thin streaks of elastin.     

Fine structure of boundary tissue of the seminiferous tubules in the scrotal and abdominal testes of naturally unilateral cryptorchid West African dwarf goats

The boundary tissue of the seminiferous tubules in the scrotal and abdominal testes of naturally unilateral cryptorchid West African dwarf goats comprised an inner non-cellular, a middle cellular and peripheral cellular lamellae. In the scrotal testes, these components were compact and their arrangement conformed to that described for other domestic ruminants except that here, the basal lamina associated with the seminiferous epithelium was homogeneous and in tact. Alterations due to cryptorchidism as observed in the contralateral abdominal testes include general loss of compactness due to depletion and disorganization of structural extracellular materials like basal lamina coat of myoid cells and collagen fibrils, the splitting of the basal lamina of the seminiferous epithelium into 8-12 thin layers, poor differentiation of the myoid cells and the accumulation of lipid droplets within their cytoplasm. It is concluded that the normal caprine boundary tissue conforms entirely to the characteristics of 'Type C' category in the existing classification. The ultrastructural alterations due to abdominal retention of the testis resemble the testicular changes ascribed to the disturbance of pituitary-testicular hormonal axis.     

Flagellum abnormalities of spermatozoa in seminiferous tubules after a short term vasectomy.

Electron microscopic observation was performed to examine whether spermiogenesis in the hamster might be affected by a short term vasectomy. When viewed by light microscopy, spermiogenesis was temporarily inhibited at 2 weeks, though to a limited extent among individuals, and had apparently recovered to the control level at 4 and 8 weeks after vasectomy in all hamsters. It was revealed at the electron microscopic level that mature spermatozoa with an abnormal flagellum were intermingled among numerous normal spermatozoa. The flagellum of the mature spermatozoa was composed of four different components: a mitochondrial sheath, outer dense fiber, fibrous sheath and axoneme. Abnormalities of the mitochondrial sheath were of three types: its discontinuity, displasia and deformation. The appearance of these abnormalities increased with the time after vasectomy and finally reached 52% as the highest value at 8 weeks. Additional noteworthy findings were the bisectioning of the outer dense fibers 2, 4 and 7, the fusion of two or three fibers, and the partial deletion of the fibrous sheath. These defects were characteristic in the vasectomized hamsters. Possible correlating microenvironmental factors are discussed as to how these abnormalities of the four flagellar components occur in the vasectomized hamsters.     

Ultrastructure of a two-cell human embryo

Summary A two-cell human embryo recovered from the Fallopian tube 82 h following the LH peak in plasma and 37 h after a single episode of intercourse was examined by transmission electron microscopy. At the time of recovery the embryo was denuded of cumulus cells, and both the zona pellucida and the two adjoining blastomeres were intact. The finding of two polar bodies in the perivitelline space, two nucleated blastomeres and remnants of the fertilizing sperm tail within the cytoplasm of one of them, were considered as evidences that the embryo was normally fertilized. Among the most compicuous features found were the presence of very distinct desmosome-like structure between blastomeres, and the cytoplasmic cell organelles distribution in three areas referred as: a sub-cortical, a middle and a perinuclear bands. An outstanding feature was the extensive blebbing of the nuclear envelope. In general, the features seem to correspond to a normally developing two-cell embryo undergoing cleavage at a normal rate.     

Ultrastructure of developing muscle in the upper limbs of the human embryo and fetus

Background: The ultrastructure of the myogenesis, which proceeds along with the appearance of muscle-specific proteins and isozymes, has not been fully described in the upper limb of staged human embryos. Methods: Eight human embryos (Carnegie stage 14–22) and two fetuses (11 and 12 weeks of gestation) were fixed with 5% glutaraldehyde, 4% paraformaldehyde, and 0.2% picric acid in 0.1 M phosphate buffer, pH 7.2. The upper limbs were dissected out and processed for transmission electron microscopy, and sections of the biceps brachii muscle were cut and examined. Results: At stage 14, the myoblasts were loosely scattered in the ventral proximal region of the upper limb bud and had a small amount of cytoplasm with a few intracellular organelles. At stage 16, the myoblasts were spindle shaped and oriented parallel to the axis of the upper limb bud. These cells had irregularly shaped nuclei with prominent nucleoli, rough endoplasmic reticulum (ER), and mitochondria, but no myofilaments were observed. At stages 17–19, rough ER, free ribosomes, and mitochondria increased in number and thick and thin filaments with faint Z-lines appeared in the peripheral cytoplasm of the myotube. The plasma membranes of some neighboring myotubes were continuous, suggesting that these cells were in the initial stages of the fusion process. At stage 22, the striated pattern of the myofilaments became evident and tubular structures appeared around them and near the plasma membrane. In the fetus at the 11th week, the basal lamina began to surround the myotubes, and T-tubules with sarcoplasmic reticulum were observed. Dyads and triads were observed in the myotube of the 12th week fetus. Conclusion: These findings suggest that rapid myogenesis occurs during the late embryonic period in human upper limbs and that the ultrastructural characteristics of mature myotubes are established during the early fetal period. © 1995 Wiley-Liss, Inc.