Biomedical subjects

J M Emmen

Publications and source records attributed to J M Emmen.

7 recordsLinked to original sources

PubMed2001

Developing animal models for analyzing SERM activity.

Estrogens have effects on many organ systems, beyond the reproductive system, in both females and males. Estrogen effects are exerted through specific receptors, of which there are two types: estrogen receptor (ER) alpha and estrogen receptor (ER) beta. To study the roles of each receptor in vivo, a series of mice were generated lacking either a functional ER alpha or ER beta or both. These mice, labeled alphaERKO, betaERKO, or alphabetaERKO, respectively, have been useful in defining the tissue specificities, localization, and functions of each of the estrogen receptors. These mouse models also show great promise for use in defining the effectiveness of putative SERMs.

Animals↗

PubMed2000

The role of the testicular factor INSL3 in establishing the gonadal position.

INSL3, also designated Leydig insulin-like (Ley I-L) or relaxin-like factor (RLF), belongs to the insulin-like hormone superfamily. It is expressed in pre- and postnatal Leydig cells of the testis and in postnatal theca cells of the ovary. This sexual dimorphic pattern of INSL3 expression during development led us to suggest that the INSL3 factor could play an essential role in sexual differentiation, gonadal function and germ cell development. Key insights into the role of INSL3 came from analyses of INSL3 knockout mice. These mice showed impaired development of the gubernaculum ligament, a structure that is believed to mediate transabdominal descent of the testis during male embryogenesis. In double mutant XY-mice lacking INSL3 and a functional androgen receptor, it was demonstrated that both are essential for establishment of the sexual dimorphic position of the gonads through regulation of gubernaculum development and regression of the cranial suspensory ligament (CSL) during fetal life. Defects in this developmental process can cause cryptorchidism in the male, which is a most common disorder of sexual differentiation in human.

Androgens↗

PubMed2000

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.

Androgens↗

PubMed2000

Involvement of insulin-like factor 3 (Insl3) in diethylstilbestrol-induced cryptorchidism.

Recently, it has been shown that targeted inactivation of the Insl3 gene in male mice results in cryptorchidism. The Insl3 gene encodes insulin-like factor 3 (Insl3), which is expressed in fetal Leydig cells. The testicular factor Insl3 appears to play an important role in the transabdominal phase of testis descent, which involves development of the gubernaculum. Other studies have demonstrated that in utero exposure to diethylstilbestrol (DES), a synthetic estrogen, can lead to cryptorchidism both in humans and in animal models. The present study was undertaken to investigate whether prenatal DES-exposure might interfere with testicular Insl3 mRNA expression. Furthermore, the effect of DES on steroidogenic factor 1 (SF-1) mRNA expression level was determined, since it has been shown that SF-1 plays an essential role in transcriptional activation of the Insl3 gene promoter. Timed pregnant mice were treated with DES (100 microg/kg body weight) or vehicle alone on days E9 (gestational day 9) through E17. Control and DES-exposed mouse fetuses were collected at E16, E17 and E18, when transabdominal testis descent is taking place. Lack of gubernaculum development in DES-exposed animals was confirmed by histological analyses at E17. Expression of Insl3 and SF-1 mRNAs was studied in testes of control and DES-exposed fetuses at E16 and E18 by RNase protection assay. Prenatal DES-exposure resulted in a three-fold decrease in Insl3 mRNA expression level (P<0.005), at both E16 and E18. In contrast, DES treatment had no effect on the expression of SF-1 mRNA. These results support our hypothesis that DES may interfere with gubernaculum development by altering Insl3 mRNA expression, providing a possible mechanism by which DES may cause cryptorchidism.

Animals↗

PubMed1999

Targeted disruption of the Insl3 gene causes bilateral cryptorchidism.

The sexual dimorphic position of the gonads in mammals is dependent on differential development of two ligaments, the cranial suspensory ligament (CSL) and the gubernaculum. During male embryogenesis, outgrowth of the gubernaculum and regression of the CSL result in transabdominal descent of the testes, whereas in the female, development of the CSL in conjunction with failure of the gubernaculum development holds the ovaries in a position lateral to the kidneys. Several lines of evidence suggest that regression of the CSL and induction of gubernaculum development are mediated by testosterone and a yet unidentified testicular factor, respectively. The Insl3 gene (originally designated Ley I-L), a member of the insulin-like superfamily, is specifically expressed in Leydig cells of the fetal and postnatal testis and in theca cells of the postnatal ovary. Here we show that male mice homozygous for a targeted deletion of the Insl3 locus exhibit bilateral cryptorchidism with free moving testes and genital ducts. These malformations are due to failure of gubernaculum development during embryogenesis. In double-mutant male mice for Insl3 and androgen receptor genes, testes are positioned adjacent to the kidneys and steadied in the abdomen by the CSL. These findings demonstrate, that the Insl3 induces gubernaculum development in an androgen-independent way, while androgen-mediated regression of the CSL occurs independently from Insl3.

Androgens↗

PubMed1998

Androgen action during male sex differentiation includes suppression of cranial suspensory ligament development.

The cranial suspensory ligament is located on the border of the cranial (mesonephric) mesentery in adult female mammals, which runs between the cranial pole of the internal genitalia and the dorsal abdominal wall. Absence of the cranial suspensory ligament in male mammals depends upon exposure of its primordium to fetal testicular androgens and is a prerequisite for testis descent. Female rats were exposed to 5alpha-dihydrotestosterone propionate at different stages of genital development, and cranial suspensory ligament development was studied in neonatal and in adult animals. Androgens suppressed cranial suspensory ligament development when exposure started during the early stages of genital development, until day 19 postconception (pc). Androgen receptor expression was immunohistochemically detected in the cranial mesentery of both sexes from day 16 pc onwards. A decrease of androgen receptor expression in female fetuses from day 18 pc onwards coincided with the appearance of a differentiated cranial suspensory ligament, as evidenced by the expression of two cell differentiation markers: alpha-smooth muscle (alpha-SM) actin and desmin. alpha-SM actin was located on the outer border of the cranial mesentery of both sexes at day 17 pc, and expression increased only in female fetuses. On day 19 pc, desmin expression was also detectable in the a-SM actin-positive cells. Proliferation and apoptosis indices of cells in the cranial mesentery, as analysed by 5'-bromodeoxyuridine incorporation and by detection of DNA strand breaks (TUNEL method) respectively, did not show any difference between the sexes, neither on day 17 nor on day 18 pc. Since primordial cells of the cranial suspensory ligament highly express the androgen receptor during the period of gestation when androgens can suppress cranial suspensory development, altered morphogenesis of these cells may be a direct consequence of androgen action.

Actins↗

PubMed1996

Bilateral cryptorchidism in a dog with persistent cranial testis suspensory ligaments and inverted gubernacula: report of a case with implications for understanding normal and aberrant testis descent.

The genital system of a dog with bilateral intra-abdominal testes is described. External virilisation was normal except for an empty scrotum. Internally there was a prostate of normal macroscopic and histological appearances and, bilaterally, a fully developed male genital tract. Testicular vasculature was normal. Cranial to each testis, there was a strong ligament lying at the free edge of the gonadal/genital mesentery and running between the cranial tip of the testis/epididymis and the area craniolateral of the ipsilateral kidney. It was impossible to push the testes into the inguinal canal because of this strong ligament. Caudal to each testis, there was an elongated whitish structure between the caudal pole of the epididymis and the area of the internal inguinal ring. On closer inspection this structure appeared to be the inverted and elongated processus vaginalis sac. There was a minor ligament at the free border of the inguinal fold of the genital mesentery between the tip of this inverted processus vaginalis and the adjacent junction of the cauda epididymidis and vas deferens. The findings suggest that persistence of the fetal cranial gonadal suspensory ligaments could have been the major aetiological factor in this case of cryptorchidism. Their persistence could have prevented caudal outgrowth of the processus vaginalis with its consequent development into an intra-abdominal papilla-like structure. Inappropriate persistence of the cranial suspensory ligaments in male rodents, pig, and cattle has been associated with insufficient exposure of their primordia to androgen during fetal life. It is uncertain whether a similar deficiency could underlie persistence of these structures in the present specimen. The findings add further weight to the hypothesis that regression of the cranial gonadal suspensory ligament in males is a key event in the process of testis descent. The human homologue of this ligament deserves more attention in the analysis and treatment of human cryptorchidism.

Animals↗