The role of cremaster muscle in testicular descent in humans and animal models

Could cremaster muscle spasticity cause retractile or undescended testis in cerebral palsy? Implications for assessment and management

This commentary is on the original article by Bortnick et al. on pages 82–86 of this issue.

Loss of WNT4 in the gubernaculum causes unilateral cryptorchidism and fertility defects

Undescended testis (UDT) affects 6% of male births. Despite surgical correction, some men with unilateral UDT may experience infertility with the contralateral descended testis (CDT) showing no A-dark spermatogonia. To improve our understanding of the etiology of infertility in UDT, we generated a novel murine model of left unilateral UDT. Gubernaculum-specific Wnt4 knockout (KO) mice (Wnt4-cKO) were generated using retinoic acid receptor β2-cre mice and were found to have a smaller left-unilateral UDT. Wnt4-cKO mice with abdominal UDT had an increase in serum follicle-stimulating hormone and luteinizing hormone and an absence of germ cells in the undescended testicle. Wnt4-cKO mice with inguinal UDT had normal hormonal profiles, and 50% of these mice had no sperm in the left epididymis. Wnt4-cKO mice had fertility defects and produced 52% fewer litters and 78% fewer pups than control mice. Wnt4-cKO testes demonstrated increased expression of estrogen receptor α and SOX9, upregulation of female gonadal genes, and a decrease in male gonadal genes in both CDT and UDT. Several WNT4 variants were identified in boys with UDT. The presence of UDT and fertility defects in Wnt4-cKO mice highlights the crucial role of WNT4 in testicular development.

Clinically Differentiated Abnormalities of the Architecture and Expression of Myosin Isoforms of the Human Cremaster Muscle in Cryptorchidism and Retractile Testis

AIM

To describe architecture and expression of myosin isoforms of the human cremaster muscle (CM) and to individuate changes in clinically differentiated abnormalities of testicular descent: cryptorchidism or undescended testis (UDT) and retractile testis (RT).

BACKGROUND

The CM is a nonsomitic striated muscle differentiating from mesenchyme of the gubernaculum testis. Morphofunctional and molecular peculiarities linked to its unique embryological origin are not yet completely defined. Its role in abnormalities of testicular descent is being investigated.

SUBJECTS AND METHODS

Biopsy samples were obtained from corrective surgery in cases of cryptorchidism, retractile testis, inguinal hernia, or hydrocele. Muscle specimens were processed for morphology, histochemistry, and immunohistology.

RESULTS AND CONCLUSIONS

The CM differs from the skeletal muscles both for morphological and molecular characteristics. The presence of fascicles with different characterization and its myosinic pattern suggested that the CM could be included in the specialized muscle groups, such as the extrinsic ocular muscles (EOMs) and laryngeal and masticatory muscles. The embryological origin from the nonsomitic mesoderm is, also for the CM, the basis of distinct molecular pathways. In UDT, the histological alterations of CM are suggestive of denervation; the genitofemoral nerve and its molecular messengers directed to this muscle are likely defective. Compared with the other samples, RT has a distinct myosinic pattern; therefore, it has been considered a well-defined entity with respect to the other testicular descent abnormalities.

An extremely rare case of indirect hernia type co-existing with testicular ectopia

We present an extremely rare case of inguinal hernia coexisting with testicular ectopia in a child. Male infant 9.5 month old presented with an empty scrotum and the ipsilateral intravaginal testis lying in a high iliac crest position. When crying a moving right inguinal bulge appeared on clinical examination. This grew bigger in moments of increased abdominal pressure and seemed to move upwards towards the right ileac crest. No abdominal wall defect could be palpated. At operation a large hernia sac fixed in the area of the right iliac crest was identified. Adjacent was the fixation point of the gubernaculum and the testis was found in an ectopic location. We removed the large sac after separating the vas and vessels and the testis and we strengthened the dorsal inguinal wall and fixed the testis in a subdartos scrotal pouch. No postoperative complications happened. An undescended testis may present as an iliac crest ectopy, coexisting with moving inguinal hernia. In our case we propose that the higher position of the aponeurosis of the external oblique in combination with ectopia of gubernacular fixation in the ipsilateral scrotum may have caused the ectopic fixation of the sac in the ipsilateral inguinal crest.

Isolation and characterization of myogenic precursor cells from human cremaster muscle

Human myogenic precursor cells have been isolated and expanded from a number of skeletal muscles, but alternative donor biopsy sites must be sought after in diseases where muscle damage is widespread. Biopsy sites must be relatively accessible, and the biopsied muscle dispensable. Here, we aimed to histologically characterize the cremaster muscle with regard number of satellite cells and regenerative fibres, and to isolate and characterize human cremaster muscle-derived stem/precursor cells in adult male donors with the objective of characterizing this muscle as a novel source of myogenic precursor cells. Cremaster muscle biopsies (or adjacent non-muscle tissue for negative controls; N = 19) were taken from male patients undergoing routine surgery for urogenital pathology. Myosphere cultures were derived and tested for their in vitro and in vivo myogenic differentiation and muscle regeneration capacities. Cremaster-derived myogenic precursor cells were maintained by myosphere culture and efficiently differentiated to myotubes in adhesion culture. Upon transplantation to an immunocompromised mouse model of cardiotoxin-induced acute muscle damage, human cremaster-derived myogenic precursor cells survived to the transplants and contributed to muscle regeneration. These precursors are a good candidate for cell therapy approaches of skeletal muscle. Due to their location and developmental origin, we propose that they might be best suited for regeneration of the rhabdosphincter in patients undergoing stress urinary incontinence after radical prostatectomy.

Structural study of the cremaster muscle in patients with retractile testis

OBJECTIVE

To analyze the structure of the cremaster in patients with retractile testis (RT), comparing the distribution of nerves, elastic system and muscles with patients having cryptorchidism and inguinal hernia (IH).

PATIENTS AND METHODS

We studied 31 patients, 17 with RT (mean age=5.17years); 9 with IH (mean age=2.6) and 5 with cryptorchidism (mean age=3). A cremaster biopsy was performed and submitted to routine histological processing and studied using histochemistry and immunohistochemistry. The samples were photographed under an Olympus BX51 microscope. The images were processed with the Image J software and the cremaster muscle structures were quantified. Means were compared statistically using ANOVA and the unpaired t-test (p<0.05).

RESULTS

There were no differences (p=0.08) in diameter of muscle fiber between the groups. The muscle fiber density differed between patients with RT and IH (p=0.02): RT (mean=17.71%, SD=16.67), IH (mean=38.06%, SD=14) and cryptorchidism (mean=21.47%, SD=16.18). There was no difference (p=0.07) in the density of elastic fibers in the three groups. We observed a lower concentration of cremaster nerves of patients with RT compared with IH (p=0.0362): RT (mean=1.72%, SD=0.58), IH (mean=3.28% SD=0.94) and cryptorchidism (mean=2.52%, SD=0.53).

CONCLUSIONS

Retractile testis is not a normal variant, and presented a similar cremaster muscle structure as in patients with cryptorchidism.

LEVEL OF EVIDENCE

II; prospective comparative study.

Anatomy and histology of the scrotal ligament in adults: inconsistency and variability of the gubernaculum testis

PURPOSE

The anatomy of gubernaculum testis (GT) is often discussed; however, the postnatal anatomy of the GT or scrotal ligament (SL) is rarely described. Hence, we performed an anatomical and histological study to analyze histologically the structures between testis and scrotum.

METHODS

We performed anatomical dissections on 25 human fresh cadavers' testes. Each testis was removed with its envelopes and macroscopically analyzed. Then samples were included for histological study. Finally, they were analyzed under microscope, looking for attachments between testis, epididymis and scrotal envelopes.

RESULTS

The absence of proximal and distal attachment was found in 56.0% of cases. Looking at the proximal attachment of the SL, the main one found is the epididymal attachment (28.0%), whereas no cases of testis attachment was found. Distally, there are more variations with scrotal attachment (12%) and cremaster attachment (12.0%). We found a significant prevalence of multiple adherences in 16.0% of cases too. Finally, in 15 cases (57.7%) an attachment is present between testis and epididymis, as it is commonly described.

CONCLUSIONS

In the majority of cases there is no attachment of the lower pole of the testis and epididymis and these structures remain free. So it seems that the SL disappears with aging. Moreover, there is not only one kind of ligamentous attachment, but a high variability of attachments at the lower pole of the testiculo-epididymal structure. When it exists, this structure is never a real ligament and it seems more appropriate to use the term "attachments".

Fetal Rat Gubernaculum Mesenchymal Cells Adopt Myogenic and Myofibroblast-Like Phenotypes

PURPOSE

Gubernaculum-cremaster complex development is hormonally regulated and abnormal in a cryptorchid rat model. Using cell tracking techniques and imaging we studied myogenic phenotypes and fates in the fetal rat gubernaculum-cremaster complex.

MATERIALS AND METHODS

Embryonic day 17 gubernaculum-cremaster complexes were labeled with CellTracker™ or the DNA synthesis marker EdU (5-ethynyl-2'-deoxyuridine), or immobilized in Matrigel® and grown in culture. Embryonic day 17 to 21 gubernaculum-cremaster complex sections and cells were imaged using wide field and deconvolution immunofluorescence microscopy, and muscle and/or myofibroblast specific antibodies. Deconvolved image stacks were used to create a 3-dimensional model of embryonic day 21 gubernaculum-cremaster complex muscle.

RESULTS

PAX7 (paired box 7) positive and myogenin positive muscle precursors were visible in a desmin-rich myogenic zone between muscle layers that elongated and became thicker during development. Gubernaculum-cremaster complex inner mesenchymal cells expressed desmin and αSMA (α smooth muscle actin) at lower levels than in the myogenic zone. After pulse labeling with CellTracker or EdU mesenchymal cells became incorporated into differentiated muscle. Conversely, mesenchymal cells migrated beyond Matrigel immobilized gubernaculum-cremaster complexes, expressed PAX7 and fused to form striated myotubes. Mesenchymal gubernaculum-cremaster complex cell lines proliferated more than 40 passages and showed contractile behavior but did not form striated muscle. Our 3-dimensional gubernaculum-cremaster complex model had 2 orthogonal ventral layers and an arcing inner layer of muscle.

CONCLUSIONS

Our data suggest that mesenchymal cells in the peripheral myogenic zone of the fetal gubernaculum-cremaster complex contribute to formation of a distinctively patterned cremaster muscle. Nonmyogenic, desmin and αSMA positive gubernaculum-cremaster complex mesenchymal cells proliferate and have a myofibroblast-like phenotype in culture. Intrinsic mechanical properties of these divergent cell types may facilitate perinatal inversion of the gubernaculum-cremaster complex.

The importance of the gubernaculum in testicular migration during the human fetal period

OBJECTIVES

The objective of this review is to study the role of the gubernaculum in the testicular migration process during the human fetal period.

MATERIALS AND METHODS

We performed a descriptive review of the literature about the role of the gubernaculum in testicular migration during the human fetal period.

RESULTS

In the first phase of testicular migration, the gubernaculum enlarges to hold the testis near the groin and in the second phase the gubernaculum migrates across the pubic region to reach the scrotum. The proximal portion of the gubernaculum is attached to the testis and epididymis and the presence of multiple insertions in the distal gubernaculum is extremely rare. The presence of muscle and nerves in the human gubernaculum is very poor. The gubernaculum of patients with cryptorchidism has more fibrous tissue and less collagen and when the patients are submitted to hormonal treatment, the gubernaculum components alter significantly.

CONCLUSIONS

The gubernaculum presents significant structural modifications during testicular migration in human fetuses.

Testicular migration chronology: do the right and the left testes migrate at the same time? Analysis of 164 human fetuses

OBJECTIVE

To determine if the right and the left testes migrate at the same time during the human fetal period.

SUBJECTS AND METHODS

We studied 164 human fetuses (328 testes) ranging in age from 12 to 35 weeks post-conception. The fetuses were carefully dissected with the aid of a stereoscopic lens at ×16/25. The abdomen and pelvis were opened to identify and expose the urogenital organs. Testicular position was classified as: (a) Abdominal, when the testis was proximal to the internal ring; (b) Inguinal, when it was found between the internal and external inguinal rings); and (c) Scrotal, when it was inside the scrotum.

RESULTS

The testes were abdominal in 71% of the cases, inguinal in 9.41%, and scrotal in 19.81%. There was asymmetry in testicular migration in nine cases (5.5%). In three of these nine cases, one testis was situated in the abdomen and the other in the inguinal canal; in another three one testis was situated in the abdomen and the other in the scrotum, and in the remaining three, one testis was in the inguinal canal and the other in the scrotum. In five of the nine cases of asymmetry, the right testis completed the migration first, but this was not statistically significant.

CONCLUSION

Asymmetry in testicular migration is a rare event, accounting for <6% of the cases. The right testis seems to complete migration first.

The regulation of testicular descent and the effects of cryptorchidism

The first half of this review examines the boundary between endocrinology and embryonic development, with the aim of highlighting the way hormones and signaling systems regulate the complex morphological changes to enable the intra-abdominal fetal testes to reach the scrotum. The genitoinguinal ligament, or gubernaculum, first enlarges to hold the testis near the groin, and then it develops limb-bud-like properties and migrates across the pubic region to reach the scrotum. Recent advances show key roles for insulin-like hormone 3 in the first step, with androgen and the genitofemoral nerve involved in the second step. The mammary line may also be involved in initiating the migration. The key events in early postnatal germ cell development are then reviewed because there is mounting evidence for this to be crucial in preventing infertility and malignancy later in life. We review the recent advances in what is known about the etiology of cryptorchidism and summarize the syndromes where a specific molecular cause has been found. Finally, we cover the recent literature on timing of surgery, the issues around acquired cryptorchidism, and the limited role of hormone therapy. We conclude with some observations about the differences between animal models and baby boys with cryptorchidism.

Infertility in rats subjected to genitofemoral nerve section is not associated with testicular damage

This work was aimed at assessing the relationship between testicular ascent and infertility induced by genitofemoral nerve (GFN) section in rats. Eighteen male rats were assigned to three experimental groups as follows: (i) Group SGFN was subjected to surgical section of genitofemoral nerve; (ii) Group Sham; (iii) Control group. The GFN was cut at puberty (28D), and the contralateral testis removed at 90D, with fertility tests at 120D. At 150D, maturity index, epithelial area and histopathological index of seminiferous tubules of all rats were determined and statistically compared between superior and inferior testicle poles, and between groups. There were no differences in testicular parameters, sperm morphology or sperm concentrations (P > 0.05). Section of NGF interfered with fertility (58.3 ± 15.4 in SGFN versus 83.3 ± 10.5 in Sham) and litter size (6.2 ± 1.1 in SGFN versus 10.7 ± 1.4 in Sham). Cremaster of SGFN group showed early neuropathy. The GFN section induced partial testicular ascent and diminished fertility without damage on testicular morphology or spermatic parameters, because, cremaster could affect the contractibility and ejaculation mechanisms in which it participates. The study of the damage on cremaster induced by an injury on GFN could have an overview of the mechanisms inherent in the testicular ascent induced by this iatrogenic alteration and their potential risks on fertility.

Expression of anti-Mullerian hormone receptor on the appendix testis in connection with urological disorders

The female internal sex organs develop from the paramesonephric (Mullerian) duct. In male embryos, the regression of the Mullerian duct is caused by the anti-Mullerian hormone (AMH), which plays an important role in the process of testicular descent. The physiological remnant of the Mullerian duct in males is the appendix testis (AT). In our previous study, we presented evidence for the decreased incidence of AT in cryptorchidism with intraoperative surgery. In this report, the expression of the anti-Mullerian hormone receptor type 2 (AMHR2), the specific receptor of AMH, on the AT was investigated in connection with different urological disorders, such as hernia inguinalis, torsion of AT, cysta epididymis, varicocele, hydrocele testis and various forms of undescended testis. The correlation between the age of the patients and the expression of the AMHR2 was also examined. Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry were used to detect the receptor's mRNA and protein levels, respectively. We demonstrate that AMHR2 is expressed in the ATs. Additionally, the presence of this receptor was proven at the mRNA and protein levels. The expression pattern of the receptor correlated with neither the examined urological disorders nor the age of the patients; therefore, the function of the AT remains obscure.

Reduced expression of androgen receptor and myosin heavy chain mRNA in cremaster muscle of boys with nonsyndromic cryptorchidism

PURPOSE

To better define the developmental mechanisms of nonsyndromic cryptorchidism, we measured the expression of hormone receptor and muscle type specific mRNAs in target tissues of boys with and those without nonsyndromic cryptorchidism.

MATERIALS AND METHODS

Prospectively collected cremaster muscle and/or hernia sac tissues from boys with congenital (79) or acquired (66) nonsyndromic cryptorchidism and hernia/hydrocele (controls, 84) were analyzed for hormone receptor (RXFP2, AR, ESR1, ESR2) and myosin heavy chain specific (MYH1, MYH2, MYH7) mRNA expression using real-time reverse transcriptase polymerase chain reaction. Log transformed mRNA, phenotype and feeding history data were statistically analyzed using Pearson's correlation, ANOVA and 2-sample t tests.

RESULTS

AR mRNA expression was higher in cremaster muscle than in sac tissue, and significantly lower in congenital and acquired nonsyndromic cryptorchidism cases vs controls (p <0.01). Type 1 (slow/cardiac) MYH7 mRNA expression was also significantly reduced in both nonsyndromic cryptorchidism groups (p ≤ 0.002), while a reduction in type 2 (fast) MYH2 expression was more modest and significant only for the congenital cryptorchidism group (p <0.05). Cremasteric MYH7 and AR levels were strongly correlated (r(2) = 0.751, p <0.001). MYH7 and ESR1 mRNA levels were higher and lower, respectively, in boys with nonsyndromic cryptorchidism who were fed soy formula. Expression of other genes was not measurable.

CONCLUSIONS

Our data suggest that boys with congenital and acquired nonsyndromic cryptorchidism differentially express AR and slow twitch specific MYH7 mRNA in the cremaster muscle, and that MYH7 expression is correlated with AR levels and soy formula use. These differences in gene expression may reflect aberrant hormonal signaling and/or innervation during development with the potential for secondary functional effects and failed testicular descent.