Developmental changes in interstitial collagens of fetal rat genital ducts

The distribution of interstitial collagen types I and III was studied by immunocytochemistry in the mesenchyme of progressing and regressing mesonephric and paramesonephric ducts of male and female rat fetuses from the age of 15 days until birth. Immunocytochemistry revealed a collagen-poor mesenchymal area around the genital ducts and in continuation with the coelomic epithelium on the lateral edge of the mesonephric ridge of 15-day-old fetuses. Ultrastructurally, collagen fibrils were accumulated along the continuous lamina densa of the mesonephric ducts, whereas they were absent on the medial side of the male and female paramesonephric ducts. In males, the amount of collagen fibrils increased with the histological maturation of the mesenchyme around the mesonephric duct, whereas around the regressing paramesonephric duct collagens disappeared from the basement membrane region and the surrounding mesenchyme of the 16-day-old male duct. After the completion of the paramesonephric regression, the mesenchyme acquired a uniformly collagen containing interstitial matrix. In females, the collagens increased in the mesenchyme around the progressing paramesonephric duct, and the original site of the regressing mesonephric duct became occupied with a collagen-containing mesenchyme by the age of 19 days. The results suggest a close structural linkage between the mesonephric duct and the established early paramesonephric duct. The differences in the developmental maturation of the periductal mesenchyme and the observed changes in the composition of the interstitial matrix probably reflect the functional differences in the regulatory factors acting on the progression and regression of the male and female genital ducts.     

Ultrastructure of the early ovary and testis in pig embryos.

Pig embryos aged 26-27 days were used for an ultrastructural study of the early ovary and testis. Sex was identified by both chromosomal analysis and gonadal histology, with consistent results. The gonads occupied their original site in the medial coelomic angles in both sexes. The female gonad was composed of three tissues: the surface epithelium, the gonadal blastema and the mesenchyme. The gonadal structure was similar to that seen earlier at the age of 24 days. At 26 days the testis had distinctly differentiated into four tissues. The new components were the testicular cords and the interstitium, both derived from the gonadal blastema. The testicular cords resembled anastomosing sheets more than cords. The ultrastructure of the tissues and their cell types are described and compared to the previous indifferent stage at the age of 24 days. The cells of the surface epithelium, of the primitive cords, of the mesenchyme, and the primordial germ cells had an ultrastructure that was similar in both sexes. The sustentacular cells of the testicular cords resembled the primitive cord cells and the spermatogonia were similar to the primordial germ cells. No Leydig cells were present yet. The process of testicular differentiation is described on the basis of the present and a previous study, and a new hypothesis, based on the vascular organization, is presented.     

Fine structure of the human foetal testis

Summary Thirteen male human foetuses ranging in crown-rump length from 29 to 212 mm (ages 8–27 weeks) were studied. Four developmental phases are distinguished. 1. The predifferentiation phase (below 8 weeks): The interstitium contains only undifferentiated mesenchymal cells. 2. The differentiation phase (8–14 weeks): Leydig cells develop and gradually fill the space between the germ cords. 3. The maturity phase (14–18 weeks): The interstitium occupies more than one half of the total area in the testis sections and is filled with mature foetal Leydig cells. 4. The involution phase (18–40 weeks): Most of the Leydig cells gradually degenerate and disappear.The foetal Leydig cells are packed with tubular agranular endoplasmic reticulum (AER). Islets of parallel granular ER membranes and other organelles are embedded in the AER. The mitochondria vary in shape and form, the cristae being mainly tubular. Some mitochondria like organelles contain electron dense inclusions. Dark membrane bound bodies of variable form and resembling the Golgi cisternae are present in most cells. Reinke crystals are never found in the foetal cells. In degenerating Leydig cells the AER appears in vesicular form, membranous whorls are seen in some of them and the cell membrane seems to rupture finally, and cytoplasmic material protrudes outside the cells. The fine structure of the mature foetal Leydig cells is suggested to reflect signs of human chorionic gonadotrophin stimulation.This investigation was supported by the Damon Runyon Memorial Fund (DRG-940) and by the Sigrid Jusélius Foundation.     

Fetal Leydig cells: cellular origin, morphology, life span, and special functional features.

The Leydig cells, responsible for testicular androgen production, have two growth phases during the life-span of mammals. The fetal population appears during fetal life and is responsible for the androgen-induced differentiation of the male genitalia. The fetal Leydig cells disappear after birth, and the other population, the adult Leydig cells, appears during puberty and persists for the whole adult life. The fetal Leydig cells, evidently due to the intrauterine endocrine milieu and their special functional requirements in genital differentiation, differ both morphologically and functionally from the adult population. The purpose of this review is to elucidate the special features of the mammalian fetal Leydig cell population, which presents an intriguing experimental model for studies of function and regulation of steroidogenic cells.     

Computer analysis of living cells: movements of the chromatoid body in early spermatids compared with its ultrastructure in snap-frozen preparations

 Quantitative analyses of cytoplasmic and nuclear organelle movements in living interphase cells at defined stages of differentiation are few. By phase contrast videomicroscopy and digital imaging techniques, we have traced the path of the chromatoid body (CB) and analysed its rapidly changing positions in relation to the nuclear envelope, Golgi complex and nuclear pale chromatin areas in living early spermatids of the rat. The CB had intimate interactions with the nuclear envelope and moved both in parallel and perpendicular fashion in relation to it. It had successive short contacts with the Golgi complex and nuclear pale chromatin areas. It was also seen to scan between two pale chromatin areas and it had pinocytosis-like transient engulfments during interactions with the pale chromatin. In ultrastructural analysis of snap-frozen preparations, the CB had a large contact area with the nuclear envelope with several intermediate organelles that may be involved in nucleocytoplasmic material transport. It is evident that quantitative image analysis of living cells is a powerful guide for ultrastructural analyses. The snap-freezing technique gives new possibilities for studies of structures that are sensitive to conventional fixation procedures. Accepted: 23 January 1997     

Ultrastructure of subcellular fractions of bull spermatozoa after hyamine treatment

Summary Ejaculated bull spermatozoa (SZ) were washed and incubated with a cationic surface active agent, Hyamine 2389, and centrifuged using 2-step discontinuous sucrose density gradient. The washed SZ, Hyamine-treated SZ and subcellular spermatozoal fractions obtained after centrifugation were prepared for electron microscopy. The washing did not cause any major structural changes in SZ. The Hyamine treatment of SZ disrupted the outer acrosome membranes. The anterior part of acrosome (the acrosomal cap) was detached retaining its integrity, or forming vesicles by fusing with the cell membrane as in true acrosome reaction. Because of this structural similarity in vesicle formation, Hyamine is assumed to be a suitable experimental initiator for acrosome reaction. The loosened acrosomal membranes were harvested almost totally by the centrifugation. The acrosomes were seen as loosened U-shaped unbroken acrosomal caps or as vesicles with fuzzy acrosomal material. The lightest particles were vesicles consisting of smooth membranes, formed evidently of sperm cell membrane. A negligible amount of fibrous sheaths were also among acrosomal membranes but no other sperm parts were encountered.The authors are thankful to Mrs. Marita Aaltonen, Mrs. Sirpa From, Miss Ulla Mäntylä, Mr. Mauno Lehtimäki and Mr. Urpo Reunanen for their skilful technical assistance.     

A streamlined technique for on-grid electron immunocytochemistry

Summary The unlabelled antibody enzyme technique for on-grid immunostaining demands exacting conditions of cleanliness. These can be met with minimal trouble by two technical modifications.Large supplies of all the solutions are millipore-filtered in advance and are then stored frozen in sealed plastic bags and allowed to thaw when required.A disposable, contamination-free surface with depressions to hold drops of staining solution is prepared from a strip of parafilm.     

Structural proteins in sexual differentiation of embryonic gonads

Sexual differentiation of embryonic gonads was studied by immunocytochemical analysis of cytoskeleton, basement membrane and extracellular matrix. The epithelial cells of the prospective gonadal region in both sexes contained vimentin and desmin intermediate filament proteins but not cytokeratin. Basement membrane components laminin, collagen types IV and V, heparan sulfate proteoglycan, and fibronectin were seen in an unorganized form in the extracellular space. The development of the gonads started by proliferation of the pregonadal epithelial cells, which formed separate clusters and loose mesenchyme. In the male gonad the clusters joined together into elongated cords, outlined by basement membrane components. The cord cells became polarized epithelial cells, and cytokeratin appeared with the disappearance of desmin in their cytoplasm. Desmin and vimentin remained in the interstitial cells. In the female gonad the clusters were smaller, and the cords were irregular in shape and size. Desmin disappeared from the cord cells and cytokeratin appeared, but more slowly and less well polarized than in the testis. The present results show that after common early development, the sexual differences in gonads emerge as different organization of the internal epithelial tissue with different timing of changes in intra- and extracellular components.     

Developmental stages of fetal-type Leydig cells in prepubertal rats

Fetal Leydig cells were studied in rats during and after the perinatal-neonatal period by comparing changes in morphology, number and volume with changes in testicular steroids and serum luteinizing hormone (LH) concentration. Stereologic examination indicated regression of fetal Leydig cells in testis by showing that their total volume as well as the average cell volume decreased between prenatal day 20 and postnatal day 3. The total number and total volume of cells both increased between postnatal days 3 and 11 but the average cell volume did not change during the same time period. Determination of serum LH showed a close correlation between an increase in LH concentration and increases in total number and volume of cells. The combined number of fetal- and adult-type Leydig cells on day 20 was more than 20 times the number of fetal cells at 3 days of age. Electron microscopic analysis showed that fetal Leydig cells after birth formed conspicuous clusters, which were surrounded by a layer of envelope cells and extracellular material. Occasional dividing fetal Leydig cells and possible precursors of fetal or adult Leydig cells were observed. Mitoses of spindle-shaped pericordal cells were frequent during the neonatal period. During and after the second postnatal week fetal Leydig cells again showed signs of regression, indicated by disintegration of the cell clusters, a decrease in cell size, accumulation of collagen between the cells and a decrease in steroid content per cell.(ABSTRACT TRUNCATED AT 250 WORDS)