Epididymides of sex-reversed XX mice lack the initial segment

Is the Epididymis a Series of Organs Placed Side By Side?

The mammalian epididymis is more than a highly convoluted tube divided into four regions: initial segment, caput, corpus and cauda. It is a highly segmented structure with each segment expressing its own and overlapping genes, proteins, and signal transduction pathways. Therefore, the epididymis may be viewed as a series of organs placed side by side. In this review we discuss the contributions of septa that divide the epididymis into segments and present hypotheses as to the mechanism by which septa form. The mechanisms of Wolffian duct segmentation are likened to the mechanisms of segmentation of the renal nephron and somites. The renal nephron may provide valuable clues as to how the Wolffian duct is patterned during development, whereas somitogenesis may provide clues as to the timing of the development of each segment. Emphasis is also placed upon how segments are differentially regulated, in support of the idea that the epididymis can be considered a series of multiple organs placed side by side. One region in particular, the initial segment, which consists of 2 or 4 segments in mice and rats, respectively, is unique with respect to its regulation and vascularity compared to other segments; loss of development of these segments leads to male infertility. Different ways of thinking about how the epididymis functions may provide new directions and ideas as to how sperm maturation takes place.

Natural exceptions to normal gonad development in mammals

Gonads are the only organs with 2 possible developmental pathways, testis or ovary. A consequence of this unique feature is that mutations in genes controlling gonad development give rise not only to gonadal malformation or dysfunction but also to frequent cases of sex reversal, including XY females, XX males and intersexes. Most of our current knowledge on mammalian sex determination, the genetic process by which the gonadal primordia are committed to differentiate as either testes or ovaries, has derived mainly from the study of sex-reversed mice obtained by direct genetic manipulation. However, there are also numerous cases of natural exceptions to normal gonad development which have been described in a variety of mammals, including both domestic and wild species. Here, we review the most relevant cases of: (1) natural, non-induced sex reversal and intersexuality described in laboratory rodents, including Sxr and B6-Y(DOM) mice; (2) sex reversal in domestic animals, including freemartinism in bovids and pigs, XX sex reversal in pigs, goats and dogs, XY sex reversal in the horse, and sex chromosome chimerism and sex reversal in the cat, and (3) sex reversal in wild mammals, including the generalised true hermaphroditism described in talpid moles, XY sex reversal in Akodon, Microtus and Dicrostonyx species, males lacking a Y chromosome and SRY in Ellobius lutescens, the X* chromosome of Myopus schisticolor, and sex chromosome mosaicism and X0 females in Microtus oregoni. These studies are necessary to elucidate particular aspects of mammalian gonad development in some instances and to understand how the genetic mechanisms controlling gonad development have evolved.

The epididymis as a target for male contraceptive development

The epididymis is an excellent target for the development of a male contraceptive. This is because the process of sperm maturation occurs in this organ; spermatozoa become motile and are able to recognise and fertilise an egg once they have traversed the epididymal duct. However, a number of attempts to interfere in sperm maturation and epididymal function or both have not been successful. The use of transgenic animals has proved useful in identifying a few epididymal targets but has yet to open the doors for drug development. Continuous focus on identifying additional epididymal targets and sperm-specific and epididymal-specific drugs is key to bringing a male contraceptive acting on the epididymis to the public.

Extracellular matrix abnormalities in testis and epididymis of XXSxr ("sex-reversed") mice

Sex-reversed (Sxr) is a duplication of the sex-determining region of the Y chromosome, which gets transposed to a paternal X chromosome. Chromosomally female (XX) zygotes that receive this XSxr chromosome develop as apparent males. Previous work on XXSxr mice (called pseudomales) showed extracellular matrix (ECM) ultrastructural abnormalities in the epididymis and testis. This study examined the biochemical nature of these abnormalities. More hydroxyproline (an indicator of collagen) was noted in the pseudomale testis and epididymis compared to normal male tissues. Western blot analysis showed increased collagen IV in the pseudomale testis and epididymis. In both the hydroxyproline and collagen IV studies, the epididymis was found to contain higher levels of these substances than the testis for both genotypes. There also appeared to be increased messenger RNA for tissue inhibitor of metalloproteinases (Timp), a regulator of collagen, in the pseudomale testis. Data from these studies seem to indicate that the XXSxr genotype influences ECM deposition and/or turnover and exerts a direct genetic influence on the development of the testis and epididymis. According to the existing paradigm of mammalian sexual development, the epididymis is expected to be normal in the presence of adequate androgenization and independent of chromosomal and genetic sex. The results presented here differ from what would be predicted by this paradigm.

Zfy is transcribed in the normal mouse epididymis and in the XXSxr ("sex reversed") testis

The presence of the mutation Sex reversed (Sxr), a copy of a Y-chromosomal segment that gets transferred to an X chromosome, causes the resulting XXSxr mice to develop as apparent males. However, several features of male sexual development are abnormal in these animals. The testes are small and aspermatogenic, and the epididymides lack the initial segment. Testes and epididymides show abnormalities of extracellular matrix. In this study we examined transcription of the conserved Y chromosomal gene Zfy, which has an X-chromosomal homologue (Zfx). Northern blotting showed Zfy to be expressed in the testes of XXSxr animals, except for those that carry the coat-marker gene Tabby (Ta), despite the lack of germ cells in XXSxr mice. Reverse transcription polymerase chain reaction (RT-PCR) studies detected Zfy in mRNA in testes even when Ta was present. RT-PCR also demonstrated Zfy transcription in epididymides of normal males, though not in XXSxr mice. Previous authors reported an absence of Zfy transcription in XXSxr testes; Zfy transcription in normal testes has been ascribed to germ cells. Our observation indicates that this idea requires re-evaluation. The occurrence of Zfy transcription in the normal epididymis is similarly a novel finding that may help explain those aspects of epididymal development that occur in the absence of androgen.

Development of the normal XY male and sex-reversed XXSxr pseudomale mouse epididymis

XXSxr pseudomale mice (chromosomally XX animals "sex-reversed" by the Sxr factor) develop testes and produce sufficient androgens for masculinization as assessed at the macroscopic level. However, adult XXSxr pseudomales lack the epididymal initial segment (I.S.). In this study prenatal and postnatal epididymal development was examined histologically and biochemically, and it was found that XXSxr pseudomales are indistinguishable from normal XY males up to day 21 of postnatal life. By 25 days postnatally, before the onset of the pubertal androgen surge, the I.S. precursor is evident in normal animals but absent in XXSxr mutants. No major abnormalities were seen in other segments of the XXSxr epididymis. Our data suggest that androgen levels in testis and epididymis are not higher in normal XY males than in XXSxr pseudomale mice of the same age. Inadequate availability of androgens at the target site is unlikely to be the cause of the epididymal abnormality in XXSxr pseudomale mice.

Ultrastructural abnormalities of epididymal tissues in XXSxr pseudomale (sex-reversed) mice

Sex reversed (Sxr), a duplication of the Y chromosomal testis-determining factor in mice, causes testis development in XXSxr animals. No effects of Sxr on nongonadal organs are expected. However, we have previously shown that the epididymis of XXSxr pseudomale (sex-reversed) mice lacks the Initial Segment. In the present study we examined the ultrastructure of the head of the epididymis of adult and 21-day old XXSxr pseudomale mice. Epithelial cells of both adult and juvenile XXSxr animals contain numerous vesicles, some within mitochondria. The basal lamina is thickened and infolded. The periepithelial layer is abnormally thick, with distorted smooth muscle cells and fibrocytes that also contain lysosomelike vesicles, often in mitochondria, and excessively wide intercellular spaces. Normal collagen fibrils are infrequent; they are in part replaced by wisps of nondiscrete material, possibly immature collagen. Sxr is known to affect spermatogenesis and Sertoli cells. The abnormal conjugation of sex-determining genes in XXSxr appears also to subvert mesenchymal-epithelial development in both epididymis and testis. We believe the most likely explanation of our data is that the XXSxr genotype is not testis specific but also influences the epididymis directly.

Androgen levels and androgenization in sex-reversed (XXSxr pseudomale) mouse: absence of initial segment of epididymis is independent of androgens

The XXSxr pseudomale ("sex-reversed") mouse has an apparently normal male phenotype. This is in accordance with Jost's Principle that, in an animal with androgen-producing testes, phenotype will be fully masculinized, irrespective of chromosomal sex. However, the epididymis of this mutant lacks the Initial Segment. Several alternative explanations were proposed. In the present study we examined the primary of these, viz, androgen insufficiency. We studied androgen levels in serum and tissues of the mutant, and we investigated whether injection of exogenous androgens could induce normal development. The XXSxr pseudomale is not deficient in androgens, nor do exogenous additional androgens induce development of the Initial Segment. It would appear that the abnormal genotype acts on the organ phenotype without intervention of androgens.