Louis Hermo

Endocrine Regulation of Male Fertility by the Skeleton

Interactions between bone and the reproductive system have until now been thought to be limited to the regulation of bone remodeling by the gonads. We now show that, in males, bone acts as a regulator of fertility. Using coculture assays, we demonstrate that osteoblasts are able to induce testosterone production by the testes, though they fail to influence estrogen production by the ovaries. Analyses of cell-specific loss- and gain-of-function models reveal that the osteoblast-derived hormone osteocalcin performs this endocrine function. By binding to a G protein-coupled receptor expressed in the Leydig cells of the testes, osteocalcin regulates in a CREB-dependent manner the expression of enzymes that is required for testosterone synthesis, promoting germ cell survival. This study expands the physiological repertoire of osteocalcin and provides the first evidence that the skeleton is an endocrine regulator of reproduction.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 1: Background to spermatogenesis, spermatogonia, and spermatocytes

Spermatogenesis, a study of germ cell development, is a long, orderly, and well‐defined process occurring in seminiferous tubules of the testis. It is a temporal event whereby undifferentiated spermatogonial germ cells evolve into maturing spermatozoa over a period of several weeks. Spermatogenesis is characterized by three specific functional phases: proliferation, meiosis, and differentiation, and it involves spermatogonia, spermatocytes, and spermatids. Germ cells at steps of development form various cellular associations or stages, with 6, 12, and 14 specific stages being identified in human, mouse, and rat, respectively. The stages evolve over time in a given area of the seminiferous tubule forming a cycle of the seminiferous epithelium that has a well‐defined duration for a given species. In this part, we discuss the proliferation and meiotic phase whereby spermatogonia undergo several mitotic divisions to form spermatocytes that undergo two meiotic divisions to form haploid spermatids. In the rat, spermatogonia can be subdivided into several classes: stem cells (As), proliferating cells (Apr, Aal), and differentiating cells (A1–A4, In, B). They are dependent on a specific microenvironment (niche) contributed by Sertoli, myoid, and Leydig cells for proper development. Spermatogonia possess several surface markers whereby they can be identified from each other. During meiosis, spermatocytes undergo chromosomal pairing, synapsis, and genetic exchange as well as transforming into haploid cells following meiosis. The meiotic cells form specific structural entities such as the synaptonemal complex and sex body. Many genes involved in spermatogonial renewal and the meiotic process have been identified and shown to be essential for this event. Microsc. Res. Tech., 2010.

Secretion and endocytosis in the male reproductive tract: a role in sperm maturation

Publisher Summary The epithelial cells of the entire male reproductive duct system, from the testis to the vas deferens, contribute to a proper milieu for sperm maturation through two distinct activities: secretion and endocytosis. Examples are provided in the chapter of these activities by following the origin and fate of SGP-1, SGP-2, and immobilin in the excurrent duct system. These proteins typify the regional variations that exist for the secretion and endocytosis of proteins along the reproductive duct. The reasons for such regional variations in secretion and endocytosis of different proteins ultimately lies in the genetic regulatory factors for each protein, the type of association of each protein with the spermatozoa, if any, and the functional contributions that each protein plays in the final maturation of spermatozoa. An important concept discussed in this chapter is that the spermatozoon itself may contribute to its own maturation (i.e., glycosylation) providing that the appropriate conditions of its external milieu are met by the secretory and endocytic activities along the excurrent reproductive duct system.

Epididymal Cell Types and Their Functions

The mammalian epididymis is a highly coiled duct that links the efferent ducts to the vas deferens. Overwhelming evidence points to the importance of this tissue in transforming spermatozoa leaving the testis as immotile cells, not having the ability to fertilize oocytes, into fully mature cells that have both the ability to swim and to recognize and fertilize eggs (Orgebin-Crist et al., 1975; Turner, 1995; Jones, 1999). Although under pathological conditions, it would appear that spermatozoa can undertake these functions very high up in the excurrent duct system (Silber, 1989; see Schoysman, this volume), under normal conditions, the acquisition of these functions is essentially completed in most species only by the time sperm enter the proximal cauda epididymidis (Robaire and Hermo, 1988; Cooper, 1986; Hermo et al. 1994a; Turner, 1995). In addition to sperm maturation, the epididymis also plays an important role in sperm transport, concentration, protection, and storage (Setchell et al., 1993; Hinton and Palladino, 1995; Cornwall and Hann, 1995; Robaire and Viger, 1995; Turner, 1995; Orgebin-Crist et al., 1996; Jones, 1999; Kirchhoff, 1999; Cooper and Yeung, 1999).

Claudin-1 Is Not Restricted to Tight Junctions in the Rat Epididymis1

The blood-epididymal barrier creates a unique microenvironment critical for sperm maturation. There is little information on proteins comprising epididymal tight and adhering junctions or on factors regulating their expression. Claudins are a family of transmembrane proteins reported to be exclusively localized to tight junctions. In the present study the expression of claudin-l (Cl-1) was examined with respect to the different cell types of the epididymis and its various regions as well as its expression during postnatal development and regulation by testicular factors, using both immunocytochemistry and Northern blot analysis. RT-PCR of adult epididymal and testicular RNA (positive control) indicated that Cl-1 messenger RNA (mRNA) transcripts were present in all regions of the epididymis. In the adult, Cl-1 was localized immunocytochemically along the entire length of the lateral plasma membranes between adjacent principal cells, including apical areas containing tight junctions, as well as at the inter...

Aquaporin-1 and -9 are differentially regulated by oestrogen in the efferent ductule epithelium and initial segment of the epididymis.

Background information. Efferent ductules reabsorb more than 90% of the rete testis fluid, a process that involves ion transporters and AQP (aquaporin) water channels. Oestrogen has been shown to modulate the expression of the ion transporters involved in this activity, but reports of AQP regulation in the male tract have been confounding. To understand better the regulation of AQP1 and AQP9, we investigated their expression in rat efferent ductules and initial segment of the epididymis after treatment with the pure antioestrogen ICI 182,780 or bilateral efferent duct ligation, or castration, followed by hormone replacement.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: Changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome‐like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species‐specific, and the nuclear chromatin becomes compacted to accommodate the stream‐lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility. Microsc. Res. Tech., 2010.

Unique Features of the Basal Cells of Human Prostate Epithelium

The prostate gland is globally composed of epithelium and stroma. The epithelium plays an important role in the development of both benign and malignant disorders while the stroma is involved in benign prostatic hyperplasia. While the prostatic epithelium of the majority of laboratory animals is well recognized as a pseudostratified columnar, the classification of the human prostatic epithelium is controversial. Moreover, the role of the basal cells of the human prostatic epithelium is still uncertain. These cells have been described as undifferentiated cells, precursors of luminal cells, reserve and myoepithelial cells. The objective of the present study was to assess the similarities and/or differences between the epithelium of the human prostate and that of other laboratory animals and thus derive information about the potential functions of basal cells in the human prostate. In the human, basal cells form a continuous layer of cells resting on the basement membrane and upon which rests a layer of luminal cells. This results in a stratified columnar epithelium of two layers of cells, unlike the sporadic appearance of basal cells observed in other species where it results in a pseudostratified epithelium. In addition, the ratio of basal to luminal cells in the human is about 1:1, while the average ratio in the other animal species examined is about 1:7. Furthermore, the gap junctional proteins connexin 26 and 43, are present between basal and luminal cells in the human, thus suggesting that these cells communicate directly with each other. In addition, the ultrastructure of the human basal cells shows morphological evidence of differentiated but not of undifferentiated cells. Moreover, the presence of junction‐like structures between adjacent basal cells suggests that these cells form a blood‐prostate barrier. In this way, basal cells could prevent substances derived from the blood from directly coming in contact with the luminal cells. Human basal cells could thus regulate functions of the luminal cells by being part of a two‐cell mechanism somewhat analogous to thecal and granulosa cells in the ovary. Microsc. Res. Tech. 51:436–446, 2000.

Germ cell‐specific DNA and RNA binding proteins p48/52 are expressed at specific stages of male germ cell development and are present in the chromatoid body

Proteins homologous to the Xenopus oocyte mRNA binding proteins mRNP3+4 and designated p48/52 have been identified in male mouse germ cells (1993: Dev Biol 158:90–100). Western and Northwestern blots of extracts from testes and isolated germ cells indicate that p48/52 are present during meiosis but reach their highest levels postmeiotically at a time when many mRNAs are stored. Here we analyze the cellular and subcellular distribution of p48/52 in rat and mouse testes by LM and EM immunocytochemistry using an anti‐mRNP3+4 antibody. Immunolabeling was found to be predominantly cytoplasmic and specific to germ cells at certain periods during their development. p48/52 were first detected in early pachytene spermatocytes at stage V of the seminiferous cycle and progressively increased during the remainder of meiotic prophase to a post‐meiotic peak in steps 1–8 round spermatids; thereafter, labeling gradually declined as elongated spermatids underwent nuclear condensation and elongation. A proportionally higher concentration of cytoplasmic immunolabeling was found within the lacunae of the anastomotic granulofilamentous network of the chromatoid body. The pattern of synthesis of these mRNA binding proteins together with their association with the chromatoid body suggests a role as germ cell‐specific mRNA stabilizing and/or storage proteins.

Seminiferous Tubule Degeneration and Infertility in Mice with Sustained Activation of WNT/CTNNB1 Signaling in Sertoli Cells

Abstract WNT/CTNNB1 signaling is involved in the regulation of multiple embryonic developmental processes, adult tissue homeostasis, abd cell fate determination and differentiation. Many WNTs and components of the WNT/CTNNB1 signaling pathway are expressed in the testis, but their physiological roles in this organ are largely unknown. To elucidate the role(s) of WNT/CTNNB1 signaling in the testis, transgenic Ctnnb1tm1Mmt/+;Amhr2tm3(cre)Bhr/+ mice were generated to obtain sustained activation of the WNT/CTNNB1 pathway in both Leydig and Sertoli cells. Male Ctnnb1tm1Mmt/+;Amhr2tm3(cre)Bhr/+ mice were sterile because of testicular atrophy starting at 5 wk of age, associated with degeneration of seminiferous tubules and the progressive loss of germ cells. Although Cre activity was expected in Ctnnb1tm1Mmt/+;Amhr2tm3(cre)Bhr/+ Leydig cells, no evidence of Cre-mediated recombination of the floxed allele or of WNT/CTNNB1 pathway activation could be obtained, and testosterone levels were comparable to age-matched controls, suggesting that genetic recombination was inefficient in Leydig cells. Conversely, sustained WNT/CTNNB1 pathway activation was obtained in Ctnnb1tm1Mmt/+;Amhr2tm3(cre)Bhr/+ Sertoli cells. The latter often exhibited morphological characteristics suggestive of incomplete differentiation that appeared in a manner coincident with germ cell loss, and this was accompanied by an increase in the expression of the immature Sertoli cell marker AMH. In addition, a poorly differentiated, WT1-positive somatic cell population accumulated in multilayered foci near the basement membrane of many seminiferous tubules. Together, these data suggest that the WNT/CTNNB1 pathway regulates Sertoli cell functions critical to their capacity to support spermatogenesis in the postnatal testis.