Current concepts in the embryology of anorectal malformations

Today, the normal and abnormal development of the hindgut is still a matter of speculation. However, owing to recent studies in appropriate animal models, most embryological events that finally lead to abnormal hindgut development are better known than in the past: (1) The process of maldevelopment starts early in the embryo. (2) The cloacal membrane always is too short in its dorsal part. Thus the dorsal cloaca is missing too. (3) As a result, the hindgut remains attached to the sinus urogenitalis, thus forming the recto-urethral fistula. In the past, an impaired process of septation was believed to be the main cause of abnormal hindgut development. In contrast to this, our results indicate that the development of the septum is more passive than active. Further results of our studies in normal and abnormal development indicate that (1) the embryonic cloaca never passes through a stage that is similar to any form of anorectal malformation in neonates, including the so-called "cloacas" in females, and (2) to explain abnormal development, studies in abnormal embryos are mandatory.

Persistent cloaca and caudal spinal agenesis in calves: three cases

Three newborn calves were affected by caudal spinal dysgenesis or agenesis (coccygeal vertebra) and persistent cloaca. The cloacas were lined by a mixture of transitional and colonic epithelium. The vertebral column of one calf was internalized into the cloaca. The association of persistent cloaca and caudal spinal anomalies is thought to be related to cell loss in the caudal cell mass, which affects caudal spinal column formation and cleavage of the cloaca by the urorectal septum. This association is well documented in humans and has been reported in Manx cats. By extrapolation, it appears likely to exist also in neonatal calves. Identification of cloacal lesions in neonatal animals should be cause for careful examination of the vertebral column because many of the associated spinal lesions are occult.

Apoptosis removes chick embryo tail gut and remnant of the primitive streak

Removal of transient features in morphogenesis of chick embryo tail is by programmed cell death. We used ApopTagTM (Oncor, Gaithersburg, MD) with the peroxidase/diaminobenzidine (DAB) procedure to correlate apoptosis with earlier reports of patterns of cell death in stage HH17-25 embryos, and our results suggest that the cell death inferred with supravital staining and appearance of cells in morphogenesis of the tail bud is programmed cell death called apoptosis. Apoptosis markers in tail bud are most abundant in the median cell cord of occluded degenerating tail gut. Tail bud mesenchyme marks for apoptosis most frequently in the ventrum of older stages, where cell death has been reported. Cells of the remnant of the primitive streak (Hensen's node) mark for apoptosis, suggesting that programmed cell death is a stop signal for axial organization at the caudal terminus. Apoptosis markers in postmembrane cloacal endoderm anticipate the transient cloacal fenestra. Lack of apoptosis markers in neural tube, notochord, and somites supports the suggestion of Schoenwolf ([1981] Anat, Embryol. (Beri.) 162:183-197) that cells of those areas in the tail bud are assimilated into the growing rump of the chick embryo. Lack of markers in neural tube of tail bud formed by secondary neurulation suggests that apoptosis is not involved in cavitation of medullary cord, but further investigation is necessary. A limited investigation of pharyngeal membranes and midgut, where cell death has not been reported to be as important in morphogenesis, did not show apoptosis markers in those tissues (Miller and Briglin [1994] "Cell Death in Development and Cancer," Houston: University of Texas MD Anderson Cancer Center, pp, 82-83). Absence of apoptosis markers in roof of gut tube suggests that the lower frequency of thymidine labeling reported for those cells (Miller [1986] Anat. Rec. 214: 87A) is not a result of apoptosis. Clearly marked cells correlated with expected locations of migrating neural crest and primordial germ cells in these stages, but distribution of apoptosis markers was not abundant or general for either cell type.

Challenging the embryogenesis of cloacal exstrophy

As presently understood, cloacal exstrophy results from a migration failure of the lateral mesodermal folds of the infraumbilical anterior abdominal wall, and rupture of the resulting enlarged, persistent cloacal membrane before the eighth week of gestation. The authors present ultrasonographic evidence that disputes this embryological theory. Routine ultrasonography of a twin gestation at 18 weeks showed that one twin had a dilated cloacal abnormality, bilateral hydronephrosis, and oligohydramnios. Repeat ultrasonography at 24 weeks demonstrated rupture of the cloacal anomaly, with resolution of both the hydronephrosis and oligohydramnios. This twin was born with classic cloacal exstrophy. This striking ultrasound evidence of an intact cloacal membrane at 18 weeks, which ruptured before 24 weeks, relieving the urinary tract outlet obstruction, forces us to rethink how this surgically correctable anomaly develops.

Embryonic development of the ventral body wall and its congenital malformations

Congenital abdominal wall defects, frequently associated with other anomalies, are found in many forms. Consequently, there is still controversy in the literature concerning nomenclature, classification, and pathogenesis. Recently, we proposed a new nomenclature and classification of abdominal wall defects based on the early development of the umbilical cord and of the ventral body wall. According to this classification the complete spectrum of abdominal wall defects, including cloacal exstrophy, bladder exstrophy, and epispadias, can be subdivided into four types: primary (thoraco-)abdominoschisis, omphalocele, body wall dysplasia, and secondary (thoraco-)abdominoschisis. Each type is characterized by its specific configuration of the placenta, the membranes, the umbilical cord, and the fetus. Anomalies such as urachal remnants and omphalomesenteric duct malformations can be explained by disturbances during later stages of umbilical cord development.

[Urogenital sinus and cloacal malformations in infancy and childhood: surgical considerations]

The relative rarity of urogenital sinus and cloacal anomalies, the wide range of their anatomical variants furthermore the number of different surgical options makes the successful management of a child with such urogenital abnormality one of the greatest challenges to the paediatric surgeon. Based on their own experience and the literature the authors give a review of embryology, pathology, and diagnosis of urogenital sinus and cloacal abnormality. They detail the new surgical therapy developed by Hendren and Pena which has been adopted in their routine. This therapy has significantly improved the functional outcome and prognosis of these anomalies. Over the past 20 years 25 patients with urogenital sinus and cloacal abnormalities were surgically treated in the author's institute.

Ventral ectodermal ridge and ventral ectodermal groove: two distinct morphological features in the developing rat embryo tail

The ventral ectodermal ridge (VER) is a thickening of the surface ectoderm on the ventral side of the embryonic tail which resembles the apical ectodermal ridge of the limb bud. The morphological characteristics of the ventral part of the embryo tail were investigated in 10.5- to 14-day rat embryos by light microscopy of serial semithin sections and by scanning and transmission electron microscopy. In 10.5- to 11.5-day embryos the thickening of the ventral surface ectoderm includes the complete ventral midline of the tail and can be divided into two parts. The posterior part is elevated and represents the ventral ectodermal ridge. The anterior part is, in contrast to the ridge, concave, and we have termed it the ventral ectodermal groove (VEG). The cloacal membrane is located at its anterior end. Contacts between the VER and the mesenchymal cells are visible until an intact basal lamina is formed at 11.5 days. Similarly, the VEG is connected by elongated cell processes with the ventral part of the tail gut. Gap junctions are present between the apical parts of ridge and groove cells. The VEG flattens and disappears in 12-day embryos. At this stage the ridge is at its maximum height, simultaneously undergoing extensive cell death. The VER is no longer visible in 14-day rat embryos.

The principles of normal and abnormal hindgut development

In the past, several theories have been proposed to explain the occurrence of anorectal malformations. Most investigators believe that these malformations are the result of an impaired process of septation. However, in 1986 vd Putte challenged all theories that tried to explain anorectal malformations by a faulty fusion of lateral ridges of the cloaca. To elucidate the principles of normal and abnormal cloacal development, the authors studied the morphology of this region in normal embryos of rats and abnormal embryos of SD mice, which often have abnormal cloacas. Using scanning electron microscopy (SEM), 245 normal rat embryos and 80 abnormal SD-mice embryos were observed. The results were as follows. (1) In normal embryos the region of the future anal opening can be identified soon after the establishment of the cloacal membrane. This part is a fixed point in cloacal development. (2) In abnormal embryos the cloacal membrane is too short. The region of the future anal opening is missing. (3) In abnormal embryos a spectrum of malformed cloacas can be observed. This is in accordance with the spectrum of anorectal malformations clinically observed in humans. (4) The authors' observations support recent findings that the "fistula" in anorectal malformations resembles a normal anus at an ectopic position.

The anatomy of the pelvis in the exstrophy complex

We compared computerized tomography scans of the pelvis of twenty-four patients who had exstrophy of the bladder with scans of age-matched controls in order to analyze the pelvic deformity that accompanies the variably severe manifestations of this condition. The patients who had classic exstrophy of the bladder were found to have a mean of 12 degrees of external rotation of the posterior aspect of the pelvis on each side, retroversion of the acetabula, a mean additional 18 degrees of external rotation and 30 per cent shortening of the pubic rami, and progressive diastasis of the symphysis pubis. The foot-progression angle demonstrated 20 to 30 degrees of external rotation beyond the normal limits seen in early childhood, but this improved with age. The patients who had exstrophy of the cloaca and the bladder not only had all of these pelvic deformities to a greater degree but also had asymmetry of measured parameters between the right and left sides of the pelvis, malformation of the sacro-iliac joints, and occasional dislocation of the hip. An understanding of the pelvic anatomy that accompanies exstrophy is essential when corrective approaches are planned. Such an understanding will improve the rate of success of both closure of the bladder and control of urinary continence postoperatively.

Cloacal and urogenital abnormalities induced by etretinate in mice

Etretinate, a synthetic retinoid, is a potent teratogen. It has previously been shown that acute exposure of gestational day 8 (equivalent to human week 4 post-fertilization) C57BL/6J mouse embryos to this retinoid results in a spectrum of abnormalities that are recognized as constituting caudal regression (dysgenesis). These defects, which include spina bifida, imperforate anus, genitourinary anomalies, omphalocele and limb anomalies, result from a major insult to the primitive streak, that is the gastrulation process. Developmental stages present early on gestational day 9 in mice represent the final stages during which the primitive streak contributes to the trunk of the embryo and, therefore, the last opportunity for abnormalities within the realm of caudal regression to be induced. In fact, acute etretinate exposure on gestational day 9 resulted in anal and urethral atresia, bladder and ureteral dilatation, and tail deficiencies as observed in 251 near-term fetuses in this study. To examine in further detail the gestational day 9 etretinate induced urogenital and anal abnormalities and their pathogenetic basis, analyses were conducted using scanning electron microscopy, light microscopy, antegrade cystourethrograms and a vital staining technique as early as 6 hours following maternal drug administration. It appears that diminution of the caudal cell populations, including those of and those surrounding the cloaca, at this critical stage of embryogenesis accounts for the observed phenotype. We propose that anal and urethral atresia temporally represents the end of the caudal regression (dysgenesis) syndrome.

Current-noise analysis of Na absorption in the embryonic coprodeum: stimulation by aldosterone and thyroxine

The mechanism and regulation of sodium transport in the embryonic coprodeum of chicken were investigated with isolated epithelia in vitro by electrophysiological techniques. Electrogenic sodium transport (INa) was measured in Ussing chambers by the short-circuit current (Isc) technique and identified by the diuretic amiloride or by removal of sodium from the apical medium. Apical sodium channels and the kinetics of amiloride binding were investigated by current-noise analysis. Isc and INa were measured under control conditions and under the influence of in vitro incubation with aldosterone and thyroxine. At 20 days the embryonic coprodeum has an Isc of 12.6 +/- 1.4 microA/cm2 and a transepithelial resistance of 519 +/- 40 omega.cm2. Amiloride blocks 9.0 +/- 1.3 microA/cm2 of the Isc, which represents electrogenic Na+ absorption and can be inhibited by serosal ouabain. Aldosterone does not stimulate Isc or INa, whereas thyroxine increases Isc and INa about threefold. Aldosterone in combination with thyroxine increases Isc and INa further to about five- to sixfold. In both cases the hormonal stimulation can be totally blocked by spironolactone. Current-noise analysis of the apical Na+ entry step reveals amiloride-sensitive Na+ channels with a single-channel current of approximately 2.3 pA and a channel density of 9-16 million/cm2 under stimulated conditions. Half-maximal amiloride block occurs at 0.8-1 microM. The hormones stimulate Na+ absorption by increasing the Na+ channel density and not the single-channel current.(ABSTRACT TRUNCATED AT 250 WORDS)

The formation of the pronephric duct in Xenopus involves recruitment of posterior cells by migrating pronephric duct cells

Cell migration and cell-cell interactions play important roles in numerous processes during embryogenesis. One of these is the formation of the pronephric (Wolffian) duct (PD), which connects the pronephros to the cloaca. It is currently accepted that in most amphibians the pronephric duct is formed by active migration of the pronephric duct rudiment (PDR) cells along a predetermined pathway. However, there is evidence that in Xenopus, the PD may be formed entirely by in situ segregation of cells out of the lateral mesoderm. In this study, we show, using PDR ablation and Xenopus laevis-Xenopus borealis chimeras, that PD elongation in Xenopus requires both active cell migration and an induced recruitment of cells from the posterior. We also show that PDR cell migration is limited to only a few stages during development and that this temporal control is due, at least in part, to changes in the competence of the PD pathway to support cell migration.

Abdominal wall defect associated with persistent cloaca. The embryologic clues in autopsy

Three stillborn fetuses are reported in which an abdominal wall defect was associated with defects in the urogenital and anal region. Autopsy of these fetuses provided clues indicative of how and where the embryonic development went wrong. The malformation involved a disturbance of the cell deposition process, occurring in the caudal part of the embryo. During the cell deposition process, which takes place in the neural crest and the body wall placode, ectodermal cells are added to the mesodermal compartment of the embryo, thus contributing to the anlagen of several structures, including the ventral body wall. In addition, a change in the shape of the embryo is generated. The sequence of events resulting from a disturbance of the cell deposition process is explained.

Cloacal extrophy

Extrophic lesions of the ventral abdominal wall are represented by a range of anomalies of which the most severe is cloacal extrophy. By 1986, only 190 cases were reported in the world literature and it is estimated that only 15 cases are seen in the United States of America per year. In Nigeria today, with improvement in antenatal and perinatal services, children who one or two decades ago would have been stillborns or products of miscarriages are now born alive. This paper reports a case of cloacal extrophy in a Nigerian neonate and reviews the current management of the condition.

Allantois as the bursa-equivalent in man

This article proposes the hypothesis that allantois is the anatomical homologue of bursa of Fabricius in mammalia. This hypothesis is based on immunohistochemical study of sections from hematopoietic organs of three fetuses with cloacal exstrophy. In the complex maldevelopment of cloacal exstrophy the common features are absence of distal midgut and exstrophy of cloaca with an exstropic intervening intestinal band. It has been suggested that gut is of dual origin and in addition to the yolk sac, allantois, absent in this maldevelopment, is involved in the embryogenesis of intestines by developing into distal midgut. There was absence of B-lymphocyte in two of three fetuses with rudimentary midgut and aplastic allantois. Meanwhile, B-cells were identified in the hematopoietic tissues and the prominent Peyer's patches of the more developed exstrophic allantois in the third case presented here. Therefore, it is concluded that allantois as the origin of distal midgut and lymphatic-rich ileocecal portion of digestive system is directly involved in the B-cell formation and represents the bursa of Fabricius in man.

Association of congenital vertebral malformations with bladder and cloacal exstrophy

The radiographs of 28 patients with bladder exstrophy and five with cloacal exstrophy were reviewed at an average age of 8 years 3 months to assess congenital vertebral malformations. Fourteen malformations in 11 patients were noted, including abnormal lumbosacral segmentation in five, congenital scoliosis and kyphosis in four, partial sacral agenesis in three, and interpedicular lumbar widenings in two. These findings are explained by an abnormal embryologic development of the spine and cloaca between 4 and 6 weeks of intrauterine life. We recommend entire spinal radiographs in these patients.

[The development of the early genital anlage and its significance for the development of the large intestine--studies of rat embryos]

The morphology of infraumbilical malformations suggests that the development of the genital anlage is of great importance for the embryology of the cloaca. In rat embryos the development of the genital anlage is documented using scanning electron microscopy. This documentation suggests that the genital anlage develops in three phases. Of these, the development of the unpaired glandular hillock seems to be especially important. The genital anlage affects the development of the cloaca in two ways: firstly its ventral growth causes a ventral shifting of the greater part of the cloaca into the region of the genitalia and secondly the cloaca gains its definite position through the development and growth of the glandular hillock.

Cloacal malformations: embryology, anatomy and principles of management

The cloacal anomaly is characterised by the persistence of a common channel draining the urinary, genital and alimentary tracts via a single orifice. It results from abnormal compartmentalisation of features that are normal in the primitive female embryo. Abnormal embryology and cloacal anatomy are described in detail. Cloacal abnormalities are usually diagnosed promptly in the neonatal period. Management can be divided into three phases: (1) investigating and defining the anatomy, (2) neonatal intervention with relief of obstruction and (3) definitive surgical reconstruction. Successful management of the child with a cloacal abnormality remains one of the greatest challenges to the pediatric surgeon.

Pathogenesis of hypospadias--more questions than answers

Most researchers believe that hypospadias arises from malformation of the penile urethra. However, this concept has been recently rejected, and it has been suggested that the opening of the urethra is "pushed forward" by growth of the perineum. In order to obtain more information on the development of the urethra, late stages of phallic development were studied in 220 rat embryos with scanning electron microscopy (SEM). In our study, signs of rupture of the urogenital membrane or fusion of the urethral folds could not be found. Therefore, we could not confirm the traditional concept for the development of the phallic urethra. A new concept of urethral development is suggested and the pathogenesis of hypospadias is discussed.

Diffusely infiltrated lymphoid areas of the bursa of Fabricius (DIA) and of the cloaca: an embryological study with morphological analogies

The aim of the present experiment was to verify whether the origin of the DIA is ectodermal or endodermal. A rabbit serum against the epithelial cells of the final portion of the cloaca was prepared. The indirect immunofluorescence method was applied to strips obtained with a cryostat, carefully cut in such a way as to include a part of the cloaca, the burso-cloacal stalk, the DIA, and the bursal plicae. In this way, it was possible to demonstrate that the epithelium of the cloaca, of the burso-cloacal stalk, and of the DIA exhibited an intense fluorescence that could not be observed at the level of the epithelium of the bursal plicae. These findings would appear to indicate that the DIA, like the cloaca and the burso-cloacal stalk, is ectodermal in origin. Furthermore, histological study revealed that the DIA exhibits close structural analogies with the dorsal wall of the cloaca. In both areas, unorganized lymphoid infiltrations of the tunica propria can be seen, and the epithelium does not show any follicle-associated epithelial cells. The glands often assume the aspect of dilated crypts containing intestinal transit material. The epithelium of these glands reveals lymphoid infiltrations at various points, and it is not uncommon to detect accumulations of cells in their lumina. Several groups of eosinophilic granulocytes can also be observed in the tunica propria of these two areas, with a clear predominance at the level of the DIA. These similarities between the cloaca and the DIA might lead one to suppose the existence of a functional as well as a morphological correspondence.

Chemotaxis or adhesion gradient? Pronephric duct elongation does not depend on distant sources of guidance information

Previously published experimental studies have led to conflicting interpretations concerning the mechanism guiding pronephric duct elongation in the urodele embryo. Although most studies have led to the conclusion that duct migration is directed by an adhesion gradient (haptotaxis), one set of experiments has been interpreted as supporting chemotactic guidance. We have resolved this conflict by conducting grafting experiments in Ambystoma embryos which distinguish between these two possible mechanisms of cell guidance. Our results provide an alternative explanation for the observations originally interpreted as supporting chemotaxis and add further evidence for adhesive guidance.

A hypothesis on the allantoic origin of the distal midgut

No satisfactory explanation for the absence of the ileocecal portion of the digestive system in the newborns with cloacal exstrophy has been offered previously. This is a report of such a case in which the lymphocytes and plasma cells were used as tissue markers to identify the origin of the lymphatic-rich ileocecal portion of the digestive tract. The absence of these cells, in this case demonstrated immunohistochemically, is suggestive of a dual origin of the midgut. Normal embryogenesis of the digestive system is reviewed and the possibility of participation of the allantois, in addition to the yolk sac, in the embryogenesis of the ileocecal segment of the gastrointestinal tract is discussed.

Normal and abnormal development of the anorectum

A study of the development of hereditary anorectal malformations in pig embryos resulted in major corrections of all current theories concerning normal and abnormal anorectal development. The principal event in anorectal development proved to be a shift of the dorsal part of the cloaca and the adjacent gut to the body surface of the tail groove. Regression of the dorsal part of the cloacal membrane forms an essential part in this process. Agenesis of this part to the membrane blocks the normal shift of the anorectum of the body surface with anorectal malformation as the result. The subtype of anomaly appeared to depend on the size and the form of this defect. Thus, small defects resulted in stenotic, ectopic perineal, and vulvar/vestibular orifices, and larger defects led to anal and anorectal agenesis. In all cases, an ectopic anal communication ("fistula") to the skin or the urogenital system developed but this was eventually lost in some cases by epithelial regression. A basic similarity between man and pig in both the normal development of the anorectum and in the morphology of the anorectal anomalies makes it likely that the same pathogenetic principle also applies to man. Deformities of the cloacal membrane may also form the basis of other congenital malformations of cloaca-derived orifices such as hypospadia, epispadia, vesical and cloacal extrophy, double urethra, and cloacal membrane agenesis.

Induction of cloacal exstrophy in the chick embryo using the CO2 laser

We have developed a model for cloacal exstrophy in the chick embryo using the Cavitron AO 300 CO2 laser. Embryos between 68 and 76 hours of development have been injured caudal to the omphalomesenteric vessels in the region of the tail bud in ovo. This has resulted in the induction of cloacal exstrophy in 5 of 59 chicks that survived ten days after injury. Evidence from this model suggests that cloacal exstrophy is caused by early disruption of the cloacal membrane or that group of cells responsible for its subsequent development.

[Kinetics of cellular populations at different stages of the histogenesis of tissues of the chorio-allantois of the chick embryo]

Changes occurring in indices of cell fractions being at the phase of mitosis (Nm) and at the phase of DNA synthesis (NS) have been studied in the chorio-allantoic tissues and in epithelii of the duodenum and cloaca. Their dynamics differ essentially. In the chorio-allantois, decrease in the Nm up to the 14th day is evidently connected with the transfer of the cells into R2-state, and then decrease of the proliferative pool takes place. This is caused by outcome of the cells from the reproductive cycle into differentiation.

[Effects of cadmium on the development of an amphibian]

The effects of continuous treatment with cadmium on Bufo arenarum embryos from the 2-cell stage onwards, were evaluated by light and scanning electron microscopy. Damages were concentration-dependent (between 0.03 and 4.00 mg Cd++/L in 10% Holtfreter's solution) and ranged between teratogenic effects and lethality. In the 0.50-4.00 mg Cd++/L range high mortality, delayed development and significant alterations in the gastrulation and neurulation processes were observed. In embryos maintained at concentrations between 0.03 and 0.25 mg Cd++/L, lethality was considerably lower and development proceeded to more advanced stages. In this group of embryos the toxicity signs were: retarded growth rate, reduced body size, behavioral disorders and a variety of malformations such as microcephaly, underdevelopment of gills and abnormal fins. The ectodermal tissue exhibited predominance of ciliated cells and/or atypical distribution of them. These findings were compared with the effect of cadmium and other heavy metals on embryos, larvae and adults of several amphibian, fish and mammalian species. The findings were interpreted on the basis of known biochemical effects of cadmium.

5 Beta-reductase activity in the brain and cloacal gland of male and female embryos in the Japanese quail (Coturnix coturnix japonica)

Testosterone metabolism was studied by an in-vitro technique in the brain and cloacal gland of young male and female quail at different ages ranging from 7 days of incubation to 2 days after hatching. Very active metabolism, leading almost exclusively to the production of 5 beta-reduced compounds, was observed. 5 beta-Reductase activity remained high throughout the incubation period in the hypothalamus, decreased around the time of hatching in the cerebellum and decreased progressively between days 7 and 15 of incubation in the cloacal gland. These changes could be involved in the control of sexual differentiation: the high 5 beta-reductase in the brain possibly protects males from being behaviourally demasculinized by their endogenous testosterone while the decreasing 5 beta-reductase in the cloacal gland would progressively permit the masculinization of that structure.

Cloacal exstrophy

Although each patient with cloacal exstrophy must be considered as a unique individual and much controversy still remains about the treatment of this complex syndrome, our review of the literature suggests that the previously detailed series of stages in the approach to this patient represents a conservative, individualized, yet successful approach.

The embryology and endocrinology of primary amenorrhoea: a study of one hundred and forty patients

The overwhelming majority of girls presenting with primary amenorrhoea have aetiologies with their roots in disturbances of embryogenesis and/or the endocrinology of sexual differentiation. This review will deal with the fundamentals of embryology and endocrinology relevant to the subject and then discuss the findings in a group of one hundred and forty patients with primary amenorrhoea as they relate to these disturbances.

Sexual differentiation of the urogenital tract in the chicken embryo: autoradiographic localization of sex-steroid target cells during development

The determinant role ascribed to steroid hormones in sexual differentiation of the reproductive tract of the embryo implies the presence of target cells for sex steroids. An autoradiographic technique adapted for diffusible compounds was employed to characterize and localize cells which concentrate either [3H]oestradiol (E2) or [3H]dihydrotestosterone (DHT) in their nuclei. This paper describes the topographical distribution of cells containing receptor sites for oestrogen or androgen in various tissues of the reproductive tract of chicken embryos from day 6 to 15 of incubation. Receptor sites for oestradiol are present in the mesenchyme of the cloaca and in urodeum and vascular body. In the lower part of the Wolffian duct, only epithelial cells display nuclear labelling. In the Müllerian duct, nuclear receptor sites for [3H]oestradiol are observed not before day 15. Receptor sites for DHT are localized in the mesenchyme of the cloacal region from day 7 to 15. The Wolffian, but not the Müllerian duct contains receptor sites for DHT in the nuclei of epithelial and mesenchymal cells. Cross-competition experiments between [3H]E2 or [3H]DHT and unlabelled DHT or E2 respectively, show that 2 different types of receptor sites exist. The observations indicate: (a) complementary roles forffian, but not the Müllerian duct contains receptor sites for DHT in the nuclei of epithelial and mesenchymal cells. Cross-competition experiments between [3H]E2 or [3H]DHT and unlabelled DHT or E2 respectively, show that 2 different types of receptor sites exist. The observations indicate: (a) complementary roles forffian, but not the Müllerian duct contains receptor sites for DHT in the nuclei of epithelial and mesenchymal cells. Cross-competition experiments between [3H]E2 or [3H]DHT and unlabelled DHT or E2 respectively, show that 2 different types of receptor sites exist. The observations indicate: (a) complementary roles for oestrogenic and androgenic hormones in embryonic sexual differentiation; (b) precocity of receptors for sex hormones during embryonic development; (c) importance of mesenchyme in differentiation processes which are sex-steroid dependent.

Embryology of the lower genitourinary tract

The urinary and genital systems are closely related in their development so that dividing them into separate divisions is often artificial. The lower urinary system begins as a cloaca. The urorectal septum then divides the cloaca into a ventral urogenital sinus and a dorsal hindgut. The ureteral bud forms off the mesonephric duct. The male and female genital systems are the same until the gonad assumes characteristics of the testis or ovary in the eighth week of gestation. It is not until the eleventh or twelfth week that the external genitalia assume specific sexual characteristics. Anomalies of the urethra and bladder can vary from a severe epispadias-exstrophy complex to a minimal Type I urethral valve. Ureteral anomalies include duplications, ectopia, and ureteroceles. An undescended testis is probably the most common anomaly in the male genital tract. Female genital anomalies can include a variety of uterine duplication anomalies. Gonadal abnormalities are often created by a chromosomal defect and are ultimately reflected by abnormal sexual differentiation.

Exstrophy and cloacal exstrophy

Classic bladder exstrophy and cloacal exstrophy are grotesque anomalies in the eyes of young parents. An immediate evaluation by an experienced team is required to assess the variations in the condition and to devise a plan of treatment that can reassure the parents as to eventual prognosis and rehabilitation. This plan of treatment must include provisions for renal preservation, urinary control, cosmetic appearance, and sexual function. The newborn is usually normal in respect to nutrition and its cardiopulmonary state, and will tolerate surgery well. Passive parental immunity provides better resistance to intercurrent illness at this time than will be present in the later months of infancy. When applicable, the initial stages of surgery should be undertaken at birth when the pelvic ring can be approximated without osteotomy and the bladder mucosa has not deteriorated from inflammatory changes. Parental attitudes toward the child as well as successful reconstruction may both be best served by immediate surgery to begin reconstruction and reduce the visible defect.

Embryologic basis for lower ureteral anomalies: a hypothesis

A hypothesis for the embryogenesis of lower ureteral anomalies invokes variations in location and number of ureteral buds on the mesonephric duct. Such vagaries determine the length of the common nephric duct and the time of meeting of the ureteral bud (or buds) with the urogenital sinus. These factors in turn affect the density of the mesenchymal tissue and its mass in relation to the adjoining structures and, ultimately, the musculature of the trigone as well as the level of the ureteral hiatus and the musculature of the bladder base. Primary reflux, ureteral ectopy, ureteral duplication, ureterocele, functional ureteral obstruction, and congenital strictures are viewed and possibly explained in the light of the embryonal variations mentioned.

[Development of the cloaca and its ulterior transformations in the polypterids (Pisces)]

Generally spoken cloacae have been but little studied. In Polypterus, a brachiopterygian fish, a cloaca only exists during parts of the embryonal and larval life and it gets replaced by structures consisting of an anus and an urinary sinus. In the beginning of embryonal life the posterior opening of the body seems to be nothing else than the original blastoporus. The wall of this opening acquires evaginations; the anlagen of the excretory ducts come in contact with them, establishing in that way a structure, that merits the name of cloaca. During the elongation of the post-vitellin body, the latter gets shifted from the level of metamere XII to that of metamere XXX. Another migration of the cloaca occurs when the digestive system acquires its development. Finally the cloaca may be found under the 47th and 48th muscular segments (at least in the species Polypterus senegalus senegalus Cuvier). During these stages the excretory ducts have build up an urinary sinus that gets separated from the gut. In adults no communication exists any more between the gut and the urinary sinus; the latter is a very destinct organ that may have an impair or pair aspect according to its being filled up. Because of the establishing of a communication with the genital ducts the sinus becomes an uro-genital sinus in the adult.

On the development of the lymphoid follicles of the bursa of Fabricius

The structural features of the development of the bursa of Fabricius in white Leghorn chick embryos are depicted at carefully timed intervals during embryogenesis, with emphasis on the sequence of events between the ninth and twelfth days of incubation. The direction and character of the migration of lymphoid cell precursors and granulocytes from the intravascular space to intraepithelial sites, where the formation of the primitive lymphoepithelial nodule takes place, is demonstrated. The mechanism of the mode of migration of these cells through the stromal epithelial interface is described and illustrated with electron micrographs and their role in the development of the primitive lymphoid follicles is described and discussed.