The embryo of the silky shrew opossum, Caenolestes fuliginosus (Tomes, 1863): First description of the embryo of Paucituberculata.

The development of caenolestid marsupials (order Paucituberculata) is virtually unknown. We provide here the first description of Caenolestes fuliginosus embryos collected in the Colombian Central Andes. Our sample of four embryos comes from a single female caught during a fieldtrip at Río Blanco (Manizales, Caldas), in 2014. The sample was processed for macroscopic description using a Standard Event System and for histological descriptions (sectioning and staining). The grade of development of the lumbar flexure and coelomic closure differed between embryos, two of them being more advanced than the others (similar to McCrady's stages 30 and 29, respectively). The pericardial and peritoneal cavities were present, the hepatic anlage was organized in hepatic cords, the heart was in its final position, and the mesonephros was functional. Compared to other Neotropical marsupials, an early appearance of the frontonasal-maxillary fusion and the cervical growth (thickness) was observed; however, absorption of the pharyngeal arches into the body and lung development was delayed. Besides these differences, embryos were similar to equivalent stages in Didelphis virginiana and Monodelphis domestica. Previous proposals of litter size of four for C. fuliginosus are supported.

Mesonephric origin of the gonadal primitive medulla in chick embryos.

The development of the gonadal primitive medulla in embryonic chick gonads was studied with the light microscope, using serial longitudinal sections from 72 h to 108 h of incubation. The sex of embryos was established from karyotypes. At 72 h, the germinal epithelium in the genital ridges was thickened. The nephrogenic cord was not differentiated into nephrons underneath, although the surrounding mesonephros displayed renal corpuscles and tubules. Clusters and trabeculae of mobilized mesonephric cells piled up under the germinal epithelium, forming the rudiment of the primitive medulla. From 78 h onwards, nephrotome-like structures existed in the mesenchyme underlying the germinal epithelium. Mesonephric cells became detached from their ventral walls and incorporated into the rudiment of the medulla. Finally, at 90 h, when the gonads were constituted, the primitive medulla was definitively formed without any contribution of the germinal epithelium. Adrenal cortical cells, also originating from the mesonephric blastema, showed tight relationships with the gonadal medullarian structures. Our observations support the concept of the mesonephric origin of the gonadal components having male potentialities in birds.

Morphology of the epididymis of the cock (Gallus domesticus) and its effect upon the steroid sex hormone synthesis. I. Ontogenesis, morphology and distribution of the epididymis.

The epididymis of the cock is divided into a main part and an appendix epididymidis. The main part of the epididymis is firmly connected to the testis. The sperm transporting tubes open into the ductus epididymidis along its entire length. The rete testis, as the most proximal part of the epididymis, develops from mesenchym cells. The rete testis connects the tubuli seminiferi with the ductuli efferentes proximales which develop from the Bowman's capsules of the mesonephros. The ductuli efferentes distales develop from the proximal tubules, conducting segments (loops of Henle), and the distal tubules of the mesonephros. The short ductuli conjugentes which open into the ductus epididymidis, originate from the connecting segments of the mesonephros. In the sexually mature cock the rete testis, the ductuli efferentes proximales, and the ductus epididymidis all show an enlargement in the lumen. In the ductuli efferentes proximales and in the ductus epididymidis one can observe a formation of globuli and cell protrusion which lead to a loss of the surface structure of the epithelial cells. The appendix epididymidis and the capsula fibrosa of the adrenal gland are joined by connective tissue. The appendix epididymidis consists of the blindly ending ductus aberrans (the crainal continuation of the ductus epididymidis) and the ductuli aberrantes which open into the ductus aberrans. The blind ends of the ductuli aberrantes end in the capsula fibrosa of the adrenal gland.

Sexual differentiation of the urogenital system of the fetal and neonatal tammar wallaby, Macropus eugenii.

In male tammar wallabies, the scrotum is the first organ to become sexually differentiated, 4-5 days before birth (day 22 of gestation). This is followed by enlargement of the gubernaculum and processus vaginalis one day before birth. However the indifferent gonad does not show any signs of testicular cord formation or androgen production until later, at around the time of birth; this is more pronounced at 2 days post-partum (p.p.), when the testis takes on a characteristic rounded appearance. Primordial germ cells proliferate throughout the testis at this time, although the testis does not become significantly heavier than the ovary until around 80 days p.p.. In females, the appearance of the mammary glands is the first sign of sexual differentiation 4-5 days before birth. The indifferent gonad first shows signs of developing an ovarian cortex and medulla 7 days after birth. The migrating germ cells are confined to the cortex, and first start to enter meiosis about 25 days after birth. The Wolffian (mesonephric) ducts are patent to the urogenital sinus in fetuses at day 21 of gestation. In the female they have started to regress by 10 days p.p. and only rudiments remain by day 25 p.p.. The Müllerian (paramesonephric) ducts develop adjacent to the cranial pole of the mesonephros at about day 25 of gestation and grow caudally to meet the urogenital sinus between days 2 and 7 p.p.. The Müllerian duct of the female develops a prominent ostium abdominale by day 9 p.p., but this structure has completely regressed in males by day 13 p.p.. The testis and ovary both migrate caudally, together with the adjacent mesonephros, at about day 10 p.p.. The ovaries remain around the level of lumbar vertebra 4 after about day 7 p.p., while the testes continue to descend. The testes enter the internal inguinal ring at about day 25 p.p., about the time that prostatic buds first appear in the urogenital sinus, and are in the inguinal canal from days 25 to 36 p.p.. They enter the scrotum at around day 36 p.p., and testicular descent is complete by days 65-72 p.p.. Melanin develops in the tunica vaginalis 72 days after birth. The overall development of the urogenital system in this marsupial is similar to that of eutherians but the sequence of events differs, with some aspects of genital differentiation preceding gonadal differentiation, apparently because they are directly controlled by X-linked genes, rather than indirectly controlled by gonadal steroids.

Developmental changes in paramesonephric and mesonephric ducts and the external genitalia in swine fetuses during sexual differentiation.

The paramesonephric (Müllerian) duct was first observed in the vicinity of the mesonephric (Wolffian) duct in 30-day-old swine fetuses of both sexes at the level close to the gonad. The paramesonephric duct extended caudally in parallel with the mesonephric duct on day 35 of gestation. By day 40 the paramesonephric duct reached the urogenital sinus. At this stage, the paramesonephric duct began to degenerate in the male, while it continued to develop in the female. This suggests that an anti-Müllerian duct hormone (AMH) is produced before day 40 of gestation. By day 45 of gestation, the mesonephric duct began to decrease in diameter and was accompanied with the involution of the mesonephros in both sexes. By day 60, the male and female mesonephric ducts reduced in their diameter by 70%. Thereafter, the female mesonephric ducts disappeared, while the male ducts developed again. The sex differences was first observed on day 35 in the differentiation of the external genitalia when a small circular urogenital orifice and the anogenital raphe appeared at the sites caudal to the genital tubercle in the male. Such structures were not present in the female. These results suggest that the fetal pig testis is activated to secrete androgen before day 35 of gestation.

The haemocytology and histology of the haemopoietic organs of South African fresh water fish. I. The haemopoietic organs of Clarias gariepinus and Sarotherodon mossambicus.

The haemopoietic organs of the catfish, Clarias gariepinus, and the Mozambique bream, Sarotherodon mossambicus, were studied. In both species the primary haemopoietic organs are the pronephros, the mesonephros and the spleen. The peritoneum and, particularly in catfish, the omentum are of secondary importance in haemopoiesis.

Renal development: a complex process dependent on inductive interaction.

Renal development begins in-utero and continues throughout childhood. Almost one-third of all developmental anomalies include structural or functional abnormalities of the urinary tract. There are three main phases of in-utero renal development: Pronephros, Mesonephros and Metanephros. Within three weeks of gestation, paired pronephri appear. A series of tubules called nephrotomes fuse with the pronephric duct. The pronephros elongates and induces the nearby mesoderm, forming the mesonephric (Woffian) duct. The metanephros is the precursor of the mature kidney that originates from the ureteric bud and the metanephric mesoderm (blastema) by 5 weeks of gestation. The interaction between these two components is a reciprocal process, resulting in the formation of a mature kidney. The ureteric bud forms the major and minor calyces, and the collecting tubules while the metanephrogenic blastema develops into the renal tubules and glomeruli. In humans, all of the nephrons are formed by 32 to 36 weeks of gestation. Simultaneously, the lower urinary tract develops from the vesico urethral canal, ureteric bud and mesonephric duct. In utero, ureters deliver urine from the kidney to the bladder, thereby creating amniotic fluid. Transcription factors, extracellular matrix glycoproteins, signaling molecules and receptors are the key players in normal renal development. Many medications (e.g., aminoglycosides, cyclooxygenase inhibitors, substances that affect the renin-angiotensin aldosterone system) also impact renal development by altering the expression of growth factors, matrix regulators or receptors. Thus, tight regulation and coordinated processes are crucial for normal renal development.

Role of the mesonephros as a transient haematopoietic organ in the bovine embryo.

During vertebrate embryogenesis, haematopoietic stem cells (HSC) arise in the aorta-gonads-mesonephros (AGM) region. In the present study, we examined serial sections of 22-34 days post-insemination (dpi) bovine embryos, a species with a well-developed and functional mesonephros. We describe the temporo-spatial distribution of presumptive c-kit positive HSC and the occurrence of haematopoietic foci in the mesonephros and fetal liver using specific antibodies directed against haematopoietic cell markers and conventional electron microscopy. In the mesonephros, presumptive HSC were found at 23-24 dpi in the blood stream, in the endothelial lining of the filtering capillaries and in the septal stroma of the cranial part of the mesonephros, the mesonephric giant corpuscle (MGC), suggesting a colonalization via the blood stream from the haematopoietic clusters of the dorsal aorta. From 25 to 30 dpi, presumptive HSC predominate in the septal stroma of the MGC, were they first expand but then decline and disappear following 32 dpi. In parallel, we found ongoing erythropoiesis and myelopoiesis starting in the MGC at 24 dpi and extending during the complete observation period. In the embryonic liver, colonization with presumptive c-kit positive HSC occurs slightly later, at 25 dpi. Active formation of blood cells in the liver increases following 30 dpi. In conclusion, the mesonephros of bovine embryos, in particular its MGC, functions as a primitive haematopoietic organ, temporarily intercalated between extraembryonic erythropoiesis and haematopoiesis within in the fetal liver, thus recapitulating for a short period a phylogenetically old site of blood formation.

Development of the mesonephros in camel (Camelus dromedarius).

The study of the development of the mesonephros in the camel (Camelus dromedarius) was carried out on 16 embryos ranging from 0.9 to 8.6 cm crown vertebral rump length (CVRL). At 0.9 cm CVRL, the mesonephros is represented by a narrow strip along the roof of the thoracolumbar part of the vertebral column. At 1.4 cm CVRL, some of the mesonephric tubules are canalized but others are still solid. The mesonephric corpuscles are well developed at 1.9 cm CVRL and occupy almost the entire abdominal cavity in between the liver and the gut. Histologically, the glomeruli occupy the ventromedial aspect of the mesonephros while the mesonephric tubules become numerous, larger and more coiled. At 3 cm CVRL, the metanephros is invaginated in the caudal pole of the mesonephros, and the mesonephric tubules in some areas are differentiated into secretory and collecting tubules. At 3.5 cm CVRL the mesonephros is related dorsally to the postcardinal vein and ventrally to the subcardinal vein. At 4.7 cm CVRL continuous regression of the mesonephros from cranialwards to caudalwards is observed. At 5.3-5.5 cm CVRL, the cranial part of the mesonephros is divided into medial and lateral regions, and later the medial region completely disappears and is replaced by the primordium of the adrenal gland. At 8.6 cm CVRL, the caudal part of the mesonephros completely disappears.

Sexually dimorphic expression of secreted frizzled-related (SFRP) genes in the developing mouse Müllerian duct.

In developing male embryos, the female reproductive tract primordia (Müllerian ducts) regress due to the production of testicular anti-Müllerian hormone (AMH). Because of the association between secreted frizzled-related proteins (SFRPs) and apoptosis, their reported developmental expression patterns and the role of WNT signaling in female reproductive tract development, we examined expression of Sfrp2 and Sfrp5 during development of the Müllerian duct in male (XY) and female (XX) mouse embryos. We show that expression of both Sfrp2 and Sfrp5 is dynamic and sexually dimorphic. In addition, the male-specific expression observed for both genes prior to the onset of regression is absent in mutant male embryos that fail to undergo Müllerian duct regression. We identified ENU-induced point mutations in Sfrp5 and Sfrp2 that are predicted to severely disrupt the function of these genes. Male embryos and adults homozygous for these mutations, both individually and in combination, are viable and apparently fertile with no overt abnormalities of reproductive tract development.

[Transformation of the kidney pelvis and the major and minor calices during their development]. / Transformatsiia pochechnoi lokhanki, bol'shikh i malykh chashek v protsesse ikh razvitiia.

The investigation has been performed in 28 series of histological sections of human embryos and prefetuses (4-20 weeks of the intrauterine development) and in 17 fetal corpses by means of certain histological methods, preparation of graphic reconstructive models, microscopy and fine preparation. The structural form of the definitive organ renal pelvis is demonstrated to depend on the ramification type of the metanephric duct derivatives. This is stipulated by interinductive processes of the ureteral sprout and metanephrogenic tissue. Quantitative and qualitative characteristics of the diverticulum ramification of the mesonephric duct during embryonic period of the prenatal ontogenesis predetermine the number of the calyces renalis majors and minors in the metanephros.

[Structural organization of the tubular component of the renal countercurrent system]. / Osobennosti strukturnoi organizatsii kanal'tsevogo komponenta protivotochnoi sistemy pochki.

The time course of the developing tubules of the dog kidney in the prenatal period of ontogenesis was studied by the methods of microscopy and three-dimensional reconstruction. It was established that the structural functional unit of the osmoregulatory system is a cone-shaped fascicle whose central axis is a collecting tubule. Henle's loops of three juxtamedullary nephrons and accompanying blood vessels are grouped concentrically along the axis. The tubules are grouped in such a manner that the most central position is occupied by the ascending portions of the loop while the descending ones lie somewhat outwards.

[Development of the ductule system of the epididymis in the prenatal period of human ontogeny]. / Razvitie kanal'tsevoi sistemy pridatka iaichka v prenatal'nom periode ontogeneza cheloveka.

In 285 human embryos, prefetuses, fetuses and newborns by means of a complex of morphological methods, development of the epididymal canalicular system has been studied. The anlage of the epididymal canalicular system is stated to appear in embryos 13.0-17.0 mm long (the 6th week of development) and is presented as an accumulation of epithelial cells and primary germ cells between reducing glomeruli and mesonephric canaliculi. The canalization process of the cellular accumulations and their transformation into real canaliculi takes place during the first half of the prefetal period (the 8th week of development). Further growth and development of the epididymal canaliculi takes place in the craniocaudal direction and by the end of the prefetal period (the 12th week) the canaliculi of the head are already formed, they have a twisted course; within the limits of the body and tail they are yet poorly differentiated and their course is nearly straight. During the fetal period of ontogenesis, further differentiation of the epididymal parts occurs and structure of their canaliculi becomes more complex. They acquire a twisted course in all the parts of the organ; by the end of the fetal period the form and structure of the epididymal canaliculi resemble those of the definitive organ.

Further observations on the corpuscles of Stannius in two Indian hill-stream teleosts.

The corpuscles of Stannius in Glyptothorax pectinopterus and Pseudecheneis sulcatus occur in close proximity to the mesonephros. They are encapsulated structures comprising of secretory cells which make up a homogeneous mass in G. pectinopterus, but are arranged in complete or incomplete lobules in P. sulcatus. Based on their reaction to the aldehyde fuchsin or PAS, two types of corpuscular cells are demonstrable, and the earlier suggestion that CS have a single cell type in these two species is therefore withdrawn. The stainable cells react positively and intensely in contrast to the nonstainable ones which remain more or less colourless. Although a mixture of the two cell types comprise the CS, the stainable cells preponderate.

Ectopic vas deferens.

Two infants with ectopia of the vas deferens are described. To date 11 cases have been reported, comprising a total of 13 ectopic vas insertions, 2 of which are bilateral. A classification of 2 types of ectopic vas is presented with a discussion of their relationship to ureteral ectopias. An embryological hypothesis of a proximal vas precursor segment of the wolffian duct is related closely to Stephens' theory of ureteral development.

3D reconstruction of the mouse's mesonephros.

The present work reports on the three-dimensional reconstruction of the segmented mesonephros during the embryonic development of the mouse. With a light microscope and an automatic reconstruction of surfaces, aspects of the mesonephros are described. These surfaces are obtained by using digitized contour lines. A new interpolation method called DSI (Discrete Smooth Interpolation) enables correction of the distortion induced by microtomy in paraffin sections. After a triangulation step, this method uses a smoothing algorithm, which implies a spatial redistribution of the vertices of the triangles to correct the rotational and translational misalignment. The use of this 3D program improves the understanding of the development patterns and helps us to appreciate changes in the rebuilt mesonephros. By 10.5 embryonic days, tubules emerge from the Wolffian body and begin their formation, then between 11.5 and 13.5 embryonic days, tortuous mesonephric tubules bound to the Wolffian duct form small curls, which grow and finally unwind. At the same time, mesonephric tubules unbound to the Wolffian duct appear, and on 13.5 embryonic days, the Müllerian duct is visible. After 14.5 embryonic days, the segmented mesonephros keeps its general aspect but decreases in size. At this time, each gonad is provided with both Wolffian and Müllerian ducts. Later, the Wolffian duct differentiates into the definitive male duct system, whilst the Müllerian duct regresses. Conversely, the paramesonephric duct differentiates into the definitive female duct system, whilst the mesonephric duct in turn degenerates. By this time degeneration has begun in the cranial portion of the mesonephros and this process progresses caudally. The spatial organization of the mesonephric tubules and the precise organization of all connections between these elements and the ducts may be well defined. Such approach can allow for a high definition of the normal pattern of mesonephros differentiation.

Morphological observations on the mesonephros in the postnatal opossum, Didelphis virginiana.

The mesonephros of the opossum persists for 3-4 weeks into the postnatal period. Based on our observations of its structure, and the vital dye experiments of others, it appears that the opossum mesonephros is functional during the first 10 days of the postnatal period. The mesonephros of the newborn opossum consists of 35-45 nephron units which are structurally very similar to metanephric nephrons except that they lack a loop of Henle. By the end of the first postnatal week, regression which proceeds in a craniocaudal direction, is observed. By the end of the second week most nephrons show some signs of regression. The regressing mesonephric nephrons are replaced by connective tissue.

The mammalian rete ovarii: a literature review.

The rete ovarii is the homologue of the rete testis. It develops from cells of mesonephric origin which immigrate into the developing gonad of the embryo. The mature form of the rete ovarii is generally found to be groups of anastomosing tubules lined by cuboidal or columnar epithelium. These tubules are usually located in the hilus of the ovary, but may extend through the medulla or be isolated in the mesovarium adjacent to the hilus. The rete is often continuous with the transverse ductules through which it contacts the longitudinal duct of the epoophoron. The rete ovarii is important in the control of meiosis in the maturing ovary. Cells of the rete ovarii differentiate to form granulosa cells as well. The rete is also credited with secretory capability, a hypothesis supported by the observation of secretory material in the lumina of the rete tubules in several species. Cysts have been observed in the rete ovarii of several species. The rete ovarii of the adult does not appear to be a functionless vestige as has been previously reported.

Development of sexual dimorphism in human urogenital sinus complex.

The histological differentiation of the human fetal prostatic urethra and the corresponding part of human fetal female urethra was studied during the 10th through 14th weeks of ovulation age. The development of all the prostatic glands started as epithelial outgrowths from the urethral wall of the urogenital sinus during the time covered in this study. These outgrowths grew rapidly in number and size, especially the posterior ones, and no outgrowths were seen from the paramesonephric and mesonephric ducts. However, the more columnar epithelial cells on the colliculus seminalis, from which the middle and posterior lobes developed, may be of different embryonic origin, e.g. mesonephric, paramesonephric and urethral, or may react differently to hormonal factors. The possible differences in the origin and in the morphological differentiation of the epithelial cells may give clues to the differences in localization of neoplastic changes in adult prostate. The gland formation was preceded by mesenchymal changes which progressed during acinic morphogenesis. Mesenchymal cells differentiated into fibroblasts forming a lamina propria the primitive acini. The mesenchymal differentiation in the corresponding part of the female urethra was not equally prominent. However, the increase in urethral epithelial cells density and cell size was more prominent in the females. These morphological differences might be regulated by sex steroids and further strengthen the current view of the role of the mesenchyme in the prostatic morphogenesis.