Perinatal development of gubernacular cones in rats and rabbits: effect of exposure to anti-androgens

The role of the gubernaculum in the descent and undescent of the testis

Testicular descent to the scrotum involves complex anatomical rearrangements and hormonal regulation. The gubernaculum remains the key structure, undergoing the 'swelling reaction' in the transabdominal phase, and actively migrating out of the abdominal wall to the scrotum in the inguinoscrotal phase. Insulin-like hormone 3 (Insl3) is the primary regulator of the first phase, possibly augmented by Müllerian inhibiting substance/anitmüllerian hormone (MIS/AMH), and regression of the cranial suspensory ligament by testosterone. The inguinoscrotal phase is controlled by androgens acting both directly on the gubernaculum and indirectly via the genitofemoral nerve, and release of calcitonin gene-related peptide from its sensory fibres. Outgrowth of the gubernaculum and elongation to the scrotum has many similarities to an embryonic limb bud.Cryptorchidism occurs because of both failure of migration congenitally, and failure of elongation of the spermatic cord postnatally. Germ cell development postnatally is disturbed in congenital cryptorchidism, but our current understanding of germ cell biology suggests that early orchidopexy, around 6 months of age, should provide a significant improvement in prognosis compared with a previous generation. Hormone treatment is not currently recommended. Acquired cryptorchid testes may need orchidopexy once they no longer reach the scrotum, although this remains controversial.

Cryptorchidism in common eutherian mammals

Cryptorchidism is failure of one or both testes to descend into the scrotum. Primary fault lies in the testis. We provide a unifying cross-species interpretation of testis descent and urge the use of precise terminology. After differentiation, a testis is relocated to the scrotum in three sequential phases: abdominal translocation, holding a testis near the internal inguinal ring as the abdominal cavity expands away, along with slight downward migration; transinguinal migration, moving a cauda epididymidis and testis through the abdominal wall; and inguinoscrotal migration, moving a s.c. cauda epididymidis and testis to the bottom of the scrotum. The gubernaculum enlarges under stimulation of insulin-like peptide 3, to anchor the testis in place during gradual abdominal translocation. Concurrently, testosterone masculinizes the genitofemoral nerve. Cylindrical downward growth of the peritoneal lining into the gubernaculum forms the vaginal process, cremaster muscle(s) develop within the gubernaculum, and the cranial suspensory ligament regresses (testosterone not obligatory for latter). Transinguinal migration of a testis is rapid, apparently mediated by intra-abdominal pressure. Testosterone is not obligatory for correct inguinoscrotal migration of testes. However, normally testosterone stimulates growth of the vaginal process, secretion of calcitonin gene-related peptide by the genitofemoral nerve to provide directional guidance to the gubernaculum, and then regression of the gubernaculum and constriction of the inguinal canal. Cryptorchidism is more common in companion animals, pigs, or humans (2–12%) than in cattle or sheep (≤1%). Laboratory animals rarely are cryptorchid. In respect to non-scrotal locations, abdominal testes predominate in cats, dogs, and horses. Inguinal testes predominate in rabbits, are common in horses, and occasionally are found in cats and dogs. S.c. testes are found in cattle, cats and dogs, but are most common in humans.

Testicular descent, cryptorchidism and inguinal hernia: the Melbourne perspective

Cryptorchidism is the commonest congenital genitourinary anomaly in males and results when the testis does not descend into its normal intrascrotal position during development. In full-term infants, the incidence is approximately 3% at birth. Cryptorchidism results in several abnormalities, including attenuated spermatogenesis, infertility and a greater risk of malignancy. The normal mechanism of testicular descent appears to be multi-staged, with various anatomical factors and hormonal influences, but the exact process is still unclear. In this article we review the current theories of normal testicular descent, with a focus on the hormones and anatomical factors, and current treatments for undescended testis.

Gubernacular cell division in different rodent models of cryptorchidism supports indirect androgenic action via the genitofemoral nerve

PURPOSE

The role of the "gubernaculum" in testicular descent remains controversial. Androgens are proposed to act indirectly by the genitofemoral nerve (GFN) releasing calcitonin gene-related peptide. The authors studied the effects of sensory nerve ablation and androgen blockade on mitosis in the gubernacular tip to determine whether androgens act directly or indirectly.

METHODS

Five rat models were examined for bromodeoxyuridine (BUdR)-labeling: (i) Sprague-Dawley (SD) rats (controls), (ii) prenatal flutamide-treated rats (75 mg/kg to dams on D16-19 gestation), (iii) neonatal capsaicin-treated rats (50 mg/kg, subcutaneous on day 0), (iv) congenitally cryptorchid transcrotal (TS) rats, and (v) capsaicin-treated TS rats (50 mg/kg, subcutaneous on day 0). Newborn rats were collected at days 0, 2, 4, 6, 8, and 10 (age, n = 5/model, n = 30) and were injected intraperitoneally with 1 mg/kg BUdR, 2 hours before killing. Histological sections of gubernaculum were examined immunohistochemically for BUdR labeling.

RESULTS

In SD (control) rats, DNA synthesis in the gubernacular tip was high at birth, reached a peak at day 2, and then decreased progressively until day 10. A similar pattern was observed in TS rats. However, quantitatively, the levels were significantly higher. In flutamide-treated rats, DNA synthesis was suppressed until day 6, similar suppression was observed in capsaicin-treated SD, and TS rats until day 4.

CONCLUSIONS

Flutamide, a competitive androgen receptor blocker, reduces gubernacular mitosis to basal levels until day 6, highlighting the importance of androgen receptor. Excess DNA accumulation in TS rats is consistent with the known excess of GFN fibers and calcitonin gene-related peptide in this mutant. Capsaicin-inhibited mitosis in both day 2 SD and TS rats suggests that the GFN mediates androgen action on early postnatal gubernacular DNA synthesis and growth.

Role of the gubernacular bulb in cremaster muscle development of the rat

The role of the gubernaculum during the inguino-scrotal phase of testicular descent remains controversial. Some authors propose involution and eversion while others suggest active migration, although the site of growth is unknown. We aimed to determine whether the gubernacular bulb is actively proliferating or regressing during inguino-scrotal testicular descent in the rat. Gubernacula were removed from Sprague-Dawley rats and congenitally-cryptorchid TS mutant rats. Animals (0, 3, 7, 10, and 11 days of age) were treated with bromodeoxyuridine (BUdR) 2 hr before they were killed. BUdR incorporation into newly synthesized DNA served as a marker of cell division. The gubernacula were histologically processed for hematoxylin-eosin (H&E) and immunoperoxidase staining. Four different areas within the gubernaculum were examined for BUdR-positive cells: area 1: plica gubernaculi (cord); area 2: pars infravaginalis gubernaculi (bulb); area 3: distal part of the cremaster muscle; and area 4: proximal part of the cremaster muscle. The rate of cell division for each of these areas was determined by counting the number of BUdR-positive cells per 100 cells. The highest rate of BUdR labeling in both types of rats was in area 2, which is the tip of the gubernacular bulb, and this was significantly greater (P < 0.0001) than in the gubernacular cord or developing cremaster muscle. The mitotic activity was also noted to be significantly greater (P < 0.0001) at the distal end of the cremaster muscle than at the proximal end. The amount of mitosis decreased significantly (P < 0.01) in areas 2 and 4 of the gubernaculum in Sprague-Dawley rats across the period studied. This trend was not observed in TS rats. Our results suggest that the bulb actively proliferates after birth, with possible differentiation into new cremaster muscle cells. We propose that the bulb is the growing end of the elongating gubernaculum, analogous to the growth of a limb bud.

Hormonal control of gubernaculum development during testis descent: gubernaculum outgrowth in vitro requires both insulin-like factor and androgen

The gubernaculum connects the gonad to the inguinoscrotal region and is involved in testis descent. It rapidly develops in the male fetus, whereas development in the female fetus is lacking. Possible factors involved in gubernaculum development are androgens, anti-Müllerian hormone (AMH), and insulin-like factor (Insl3). Sexual dimorphism in gubernaculum development correlated with the mitotic activity of cells in the gubernacular bulbs from male and female fetuses. Androgen receptor expression was restricted to the mesenchymal core of the gubernacular bulb, whereas skeletal muscle was detected in its outer layer. In an organ culture system devised to further study gubernaculum development in vitro, morphology of gubernacular explants grown in the presence of testes was comparable with that of gubernacula developed in vivo. Testicular tissue or medium containing R1881, a synthetic androgen, had a growth stimulatory effect on gubernacular explants compared with ovarian tissue or basal medium only. Moreover, Amh-/-, Amh+/-, and Insl3+/- testes stimulated the growth of gubernacular explants to the same extent as control testes. Insl3-/- testes, however, did not produce such an activity. This study reveals an essential role for both androgen and Insl3 in the gubernaculum outgrowth during transabdominal testis descent.

Does the gubernaculum migrate during inguinoscrotal testicular descent in the rat?

BACKGROUND

The role of the gubernaculum in descent of the testis is controversial. The mechanism of testicular descent has been studied in the rat, because inguino-scrotal descent occurs postnatally in this species. Several authors have claimed that the cremasteric sac forms by eversion of the gubernacular cone, whereby regression of the extra-abdominal part of the gubernaculum creates a space into which the gubernacular cone everts to form the processus vaginalis within the scrotum. This postulated lack of any gubernacular migration phase contrasts with the situation in the human, where gubernacular migration appears to be an integral component of testicular descent. This study was designed to determine in the rat whether there is any gubernacular migration toward the scrotum during testicular descent, or whether eversion of the cremasteric sac alone could account for the extension of this sac into the bottom of the scrotum.

METHODS

Oblique sagittal sections of the inguino-perineal region were taken from rats aged 21 days of gestation and days 1, 3, 4, 6, 8, and 10 days postnatally. Histological sections were examined and the following measurements were obtained: gubernacular cone height, gubernaculum-scrotum distance, processus vaginalis length, and pubic symphysis-anus distance.

RESULTS

The gubernaculum was not in close proximity to the developing scrotum at any age. After 21 days of gestation, there was little evidence of a substantial gubernacular bulb distal to the processus vaginalis. At all ages the gubernacular cone height was significantly less than the distance from the gubernaculum to the scrotum.

CONCLUSIONS

These results show that the gubernaculum does not develop in close proximity to the developing scrotum. Even if complete eversion of the gubernaculum takes place, the gubernaculum would still fail to reach the bottom of the scrotum. It is proposed that gubernacular eversion is more apparent than real and that some degree of gubernacular migration is needed for complete extension of the cremasteric sac to the bottom of the scrotum.

Human (and some other primates') uterine teres ligament represents a mammalian developmental novelty

BACKGROUND

The primordia of the structures developing into the mammalian male cremaster sacs emerge as well in females fetuses. In most species the structures developing from these primordia in females remain inconspicuous: the so-called uterine teres ligament consisting of a slender part across the uterine broad ligament and a more or less developed bulbous structure at the site where this ligament inserts into the inguinal abdominal bottom. Not many data are available concerning the growth, development, or function of the uterine teres ligament. In humans--and also in other "higher" female primates--the uterine teres ligament is a major structure consisting mainly of smooth musculature. It is attached to the ventral aspect of the tubo-uterine junction. From there it courses across the uterine broad ligament and extends, retroperitoneally, to the inguinal region where it pierces through the inguinal canal to end in the tissues ventral of the pubic bones.

OBSERVATIONS

Analysis of the fetal development of the human uterine teres ligament, as compared with that of various other non-primate mammals, offers an explanation for its unusual anatomical condition. Evidence is conferred that, in human fetuses, there is no counterpart for the slender ligament across the broad ligament in other mammals. Instead, the homologue of the rudimentary bulbous structure in the abdominal bottom of non-primate females develops into a strong muscular structure which is directly connected to the (para-)menonephric duct wall.

CONCLUSION

It is concluded that the human uterine teres ligament is to be judged a structure different from that of other, non-primate, mammals. It is speculated that the unusual structure of the human teres ligament is related to one or more of the many unusual features of human uterine development: as a single organ (uterus simplex), with a position deep in the abdominal cavity below the pelvic brim, and far away from the posterior abdominal wall. The unusual anatomical position may require an unusual construction of the uterine suspensory apparatus of which the teres ligament is one component.

Foetal genital development in Hyrax capensis, a species with primary testicondia: proposal for the evolution of Hunter's gubernaculum

BACKGROUND

Control of testicular descent is poorly understood. There are a number of mammalian species in which testis descent does not occur, and the phenomenon is called testicondia. Analysis of foetal development of such species could contribute to a better understanding of the key events in anatomical development underlying testis descent. Specific attention is to be given to the development of the so-called gubernaculum of Hunter: a structure of complex architecture and composition, which extends from the caudal pole of the mesonephric remnants into the inguinal abdominal wall and which is present in most mammals but not in submammalian vertebrates.

METHODS

Serially sectioned male and female foetuses of Hyrax capensis, a species in which testes remain close to the caudal pole of the kidneys throughout life, were analysed for architecture of the developing genital apparatus and the immediately surrounding structures. The results of this analysis were compared with those from a similar analysis of reptiles, of monotremata without testis descent, and of mammals with testis descent.

RESULTS

Reptiles and Monotremata showed no gubernacular structures. Mammals with testis descent showed gubernacular growth and differentiation which varied between the sexes and with the stage of foetal development. Hyrax capensis foetuses showed the development of only one component of the gubernaculum: the gubernacular cord as a part of the mesonephric mesentery and extending between the caudal pole of the mesonephros (or mesonephric remnants in older foetuses) and the lateral bladder ligament. No part developed in the inguinal abdominal wall components, which are the primordia of the cremaster sacs in species with testis descent.

CONCLUSION

Hyrax capensis shows only partial development of the gubernacular structures, and, specifically, the primordia of the cremaster sacs remain absent. Thus, this species lacks a key anatomical condition for testis descent. Gubernacular architecture in Hyrax capensis seems of a degree intermediate between egg laying monotremata mammals and mammals with testis descent. A model is proposed within which to understand the development of the gubernacular components within the mammalian class.

Development of the gubernaculum and processus vaginalis in freemartinism: further evidence in support of a specific fetal testis hormone governing male-specific gubernacular development

BACKGROUND

Freemartinism occurs in some species of ruminants and affects most female bovine fetuses in heterosexual, multiple pregnancies owing to fusion of the chorionic blood circulations soon after implantation. Maldevelopment of the ovaries and Müllerian ducts have been described and recognized as resulting from exposure of their respective primordia to an excess of anti-Müllerian hormone. The present study aimed to analyse the prenatal growth and development of the gubernaculum in freemartins to find out its possible affliction through foetal testis hormones derived from their male co-twin.

METHODS

Histological sections of young and drawings and photographs of further developed freemartins and control male and female bovine foetuses were analysed. The specimens had been collected earlier for analysis of the time course of male and female gonadal and genital development and its impairment associated with freemartinism.

RESULTS

The gubernaculum of 35-40-day-old male and female fetuses was in the initial stage of development and of similar appearance in all specimens. Gubernacula of 60-70-day-old male fetuses differed from those of females of similar age in various respects: the male gubernaculum size was larger and extension of the processus vaginalis was deeper. Freemartins showed an intermediate development with some individuals resembling male and others resembling female agemates. During further development, gubernacula in males developed into muscular cremaster sacs, whereas those in females generally did not develop beyond the size and structural complexity of 70-day-old foetuses. Beyond day 70 of fetal life, gubernaculum development in freemartins definitely showed male characteristics with respect to size and growth of a processus vaginalis with a cremaster muscular wall. The male-like pattern of the outgrowth of the processus vaginalis changed during the second half of prenatal life. Rather than its further deepening as in males, this structure became inverted to become emerging as a papilla-like structure from the inguinal abdomen bottom. An explanation is proposed for this unprecedented inversion, taking into account: (1) the faster and higher reaching rightsided ascent of the kidneys and gonads, (2) the femalelike outgrowth of the cranial gonadal suspensory ligaments, and (3) the absence of scrotum development. The ovaries and mesonephric remnants in developing freemartins, during their ascent together with the kidneys while remaining attached to the bottom of the developing processus vaginalis sacs via the gubernaculum ligament, are proposed to act together to pull up the bottom of the processus vaginalis sacs. From this action, "inverted hernia sacs" result as the irreversible consequence.

CONCLUSION

The data support the concept that foetal testes act, via as an yet unidentified third hormone, to establish malelike development of gubernacula into muscular cremaster sacs. Further work is required to reveal the identity of this hormone. Furthermore, the apparent similarity of the freemartins' inverted processus vaginalis sacs and the fetal rodents' gubernacular cones suggests that the ruminants' and rodents' processus vaginalis are essentially similar structures. Thus there is no longer an urgent need to distinguish between two different types of gubernaculum development and testis descent in rodents and ruminants, respectively, and involving or not fetal gubernacular cones. The present observations may thus contribute to the development of a unified hypothesis for sexually dimorphic development of the gubernaculum throughout the mammalian class.

Foetal testes control the prenatal growth and differentiation of the gubernacular cones in rabbits--a tribute to the late Professor Alfred Jost

Gubernacular cones develop during foetal life in males of various species, including many of the common small laboratory animals. Postnatally these papilla-like organs invert and develop into the muscular cremaster sacs, providing space for testis descent. The mechanism governing male-specific development of these structures during foetal and postnatal life is unknown but foetal testicular androgens or anti-Mullerian hormone are unlikely to be involved. The present study of gubernacular cone development in 28-day-old rabbit foetuses castrated 5–9 days before questions whether foetal testis hormones play any role in these developmental processes. The study comprised an analysis of the microscopic slides in the legacy of the late Professor Alfred Jost in Paris. Castration at an earlier (19 days) or later (23/24 days) day of foetal life interfered with gubernacular cone growth and differentiation. Unilateral castration partially inhibited ipsilateral gubernacular cone growth. Implantation of a foetal testis close to the ovary could induce male-type gubernacular cone growth in females. Together the data unequivocally support the concept of foetal testicular hormonal control of male-specific gubernacular cone development. Further study is required to unravel the nature of the active foetal testicular agent.