Urothelial transformation into functional glandular tissue in situ by instructive mesenchymal induction

Transdifferentiation of adult rat stem Leydig cells into prostatic and uterine epithelium, but not epidermis

Stem Leydig cells (SLCs), precursors of testicular Leydig cells that secrete testosterone required for male sexual differentiation, spermatogenesis, and fertility, were recently identified in rat testes. Various types of stem cells have shown the ability to differentiate into other tissues, but there is no information on the plasticity of adult rat SLCs (rSLCs). This study investigated the ability of rSLCs to transdifferentiate into cell types from all three germ layers-prostatic epithelium (endoderm), uterine epithelium (mesoderm), and epidermis (ectoderm)-under the influence of inductive mesenchyme from fetal and neonatal tissues. To differentiate rSLCs into cells of other lineages, mesenchyme from green fluorescent protein (GFP)-expressing mice was used. Tissue recombinants of urogenital sinus mesenchyme (a potent prostate inducer) and rSLCs grafted into adult male hosts formed ductal structures resembling prostate after 5 weeks. Prostate epithelium was of rSLC origin as determined by absence of GFP expression, and expressed characteristic markers of prostatic epithelium. Similarly, uterine mesenchyme + rSLCs tissue recombinants contained a simple columnar epithelium that was histologically similar to normal uterine epithelium and expressed typical uterine epithelial markers, but was of rSLC origin. In contrast, epidermal tissue was absent in fetal dermis + rSLCs recombinants, suggesting rSLCs did not form skin epithelium. Thus, rSLCs can transdifferentiate into uterine and prostatic epithelium, mesodermal, and endodermal derivatives, respectively, but they may have a limited transdifferentiation potential, as shown by their inability to form epidermis, an ectodermal derivative.

Mesenchymal-epithelial interaction techniques

This paper reviews the importance of mesenchymal-epithelial interactions in development and gives detailed technical protocols for investigating these interactions. Successful analysis of mesenchymal-epithelial interactions requires knowing the ages in which embryonic, neonatal and adult organs can be separated into mesenchymal and epithelial tissues. Methods for separation of mesenchymal and epithelial tissues and preparation of tissue recombinants are described.

Epithelial-mesenchymal crosstalk in Wolffian duct and fetal testis cord development

Interactions between adjacent epithelial and mesenchymal tissues represent a highly conserved mechanism in embryonic organogenesis. In particular, the ability of the mesenchyme to instruct cellular differentiation of the epithelium is a fundamental requirement for the morphogenesis of tubular structures such as those found in the kidneys, lungs, and the developing male reproductive system. Once the tubular structure has formed, it receives signals from the mesenchyme, which can control proliferation, patterning, and differentiation of the epithelium inside the tube. However, the epithelium is not a "silent partner" in this process, and epithelium-derived factors are often required for proper maintenance of the mesenchymal compartment. Although much emphasis has been placed on the characterization of mesenchymally-derived signals required for epithelial differentiation, it is important to note that epithelial-mesenchymal interactions are a two-way street wherein each compartment requires the presence of the other for proper tubule morphogenesis and function. In this review, we discuss epithelial-mesenchymal interactions in the processes of Wolffian duct and fetal testis cord development using the mouse as a model organism and propose inhibin beta A as a conserved mesenchyme-derived regulator in these two male-specific tubular structures.

Down the tube of obstructive nephropathies: the importance of tissue interactions during ureter development

Congenital obstructive malformations of the ureter are amongst the most common human birth defects. To date, the etiology of these diseases has remained largely unexplored, which has preempted any rational approach for therapeutic intervention. Here, we describe that obstructive ureter defects can arise from genetic insults affecting various subprograms of ureter development including formation and patterning of the ureteric bud, differentiation of tissue compartments of the ureter, and junction formation with the bladder and pelvis. New experimental findings have highlighted the importance of epithelial-mesenchymal tissue interactions in all of these subprograms and provided unique insights into the molecular nature of the transcriptional regulators and signaling pathways involved.

Mixed epithelial and stromal tumour (MEST) of the kidney: report of 14 cases with male and PEComatous variants and proposed histopathogenesis

AIMS

This article adds new cases and variants of MEST with discussion of the histopathogenesis.

METHODS AND RESULTS

Fourteen MEST were originally diagnosed as cystic nephroma which represents an incidence of 1.6% of renal neoplasms in adults. In females, the stromal component showed areas of müllerian differentiation with positive immunoreactivity for oestrogen (ER) and progesterone receptors (PR) and CD10. Immunoreactivity for HMB45 was identified in a single case having a leiomyomatous appearance. The epithelial component displayed features of müllerian epithelium and reactive renal tubular cells. In two male cases, MEST consisted of fibrous and smooth muscle stroma and cysts lined only by reactive renal tubular cells. Immunoreactivity for ER and PR was focal and weak.

CONCLUSIONS

MEST represents a tumour developing from müllerian-like stromal cells in the kidney. The neoplastic stroma encroaches on the renal tubules and has the potential to stimulate the growth of the renal tubules by contact, with development into cysts. Furthermore, the müllerian stroma likely induces the renal tubules to differentiate into müllerian-like epithelium. Melanocytic differentiation of the stroma may occur which represents the PEComatous variant. MESTs in males were histopathologically slightly different from those in females due to the different hormonal milieu.

Tailbud-derived mesenchyme promotes urinary tract segmentation via BMP4 signaling

Urinary tract morphogenesis requires the sub-division of the ureteric bud (UB) into the intra-renal collecting system and ureter, two tissues with unique structural and functional properties. In this report we investigate the cellular and molecular mechanisms that mediate their differentiation. Fate mapping experiments in the developing chick indicate that the UB is surrounded by two distinct mesenchymal populations: nephrogenic mesenchyme derived from the intermediate mesoderm and tailbud-derived mesoderm, which is selectively associated with the domain of the UB that differentiates into the ureter. Functional experiments utilizing murine metanephric kidney explants show that BMP4, a paracrine factor secreted by tailbud-derived mesenchyme, is required for ureter morphogenesis. Conversely, ectopic BMP4 signaling is sufficient to induce ureter morphogenesis in domains of the UB normally fated to differentiate into the intra-renal collecting system. Collectively, these results indicate that the border between the kidney and ureter forms where mesenchymal tissues originating in two different areas of the early embryo meet. These data raise the possibility that the susceptibility of this junction to congenital defects in humans, such as ureteral-pelvic obstructions, may be related to the complex morphogenetic movements that are required to integrate cells from these different lineages into a single functional structure.

Stromal-epithelial cell interactions and androgen receptor-coregulator recruitment is altered in the tissue microenvironment of prostate cancer

Tissue recombination experiments show that prostate mesenchyma directs prostate epithelial cell growth and development in an androgen-dependent manner, and that functional differentiation of prostate epithelium requires androgen-driven processes in both epithelia and stroma. The androgen induction of target genes in primary cultures of prostate stromal and epithelial cells was determined using an adenoviral expression system, which employed the MMTV-enhancer driven luciferase reporter as an androgen receptor (AR)-mediated transcription assay. These studies indicate that both cell types contain functional AR. Androgen induction of luciferase reporter activity is 3-fold in stromal cells compared with 10-fold in epithelial cells. AR-mediated transcription activity in stroma cells was enhanced by coculture with epithelial cells or epithelial cell-conditioned media. The elevated AR-mediated transcription activity in stromal cells that were exposed to epithelial factors correlated with increased recruitment of coactivators to the AR transcriptional complex. Epithelial cells facilitated interactions of AR with SRC-1 in an androgen-dependent manner. However, AR-mediated transcriptional activity in stromal cells isolated from prostate cancer was reduced compared with stromal cells isolated from benign prostate and continued to be reduced when cocultured with tumor-derived prostate epithelial cells. The occupancy of AR and coregulators on target genes showed that androgen-bound AR in prostate cancer stromal cells was associated with the corepressor silencing mediator for retinoid and thyroid hormone receptor. Thus, the ability of epithelial cells to modulate coregulator recruitment to the AR transcriptional complex on androgen-responsive genes seems altered in the stromal microenvironment of prostate cancer.

Going in circles: conserved mechanisms control radial patterning in the urinary and digestive tracts

Radial patterning in the urinary tract and gut depends on reciprocal signaling between epithelial cells, which form mucosa, and mesenchyme, which forms smooth muscle and connective tissue. These interactions depend on sonic hedgehog (Shh), which is secreted by epithelial cells and induces expression of bone morphogenetic protein 4 (Bmp4), a signaling molecule required for differentiation of smooth muscle progenitors. Patterning of the specialized mucosa lining the anterior-posterior (A-P) axis may be controlled independently by regionally expressed mesenchymal transcription factors. A study by Airik et al. in this issue of the JCI reveals that T-box 18 (Tbx18), a transcription factor selectively expressed in ureteral mesenchyme, regulates smooth muscle differentiation by maintaining Shh1 responsiveness in mesenchymal progenitors (see the related article beginning on page 663). Deletion of Tbx18 resulted in defective urothelial differentiation at the level of the ureter, suggesting that Tbx18 acts via mesenchyme as an important regulator of A-P patterning in the urinary tract.

Molecular, cellular and developmental biology of urothelium as a basis of bladder regeneration

Urinary bladder malfunction and disorders are caused by congenital diseases, trauma, inflammation, radiation, and nerve injuries. Loss of normal bladder function results in urinary tract infection, incontinence, renal failure, and end-stage renal dysfunction. In severe cases, bladder augmentation is required using segments of the gastrointestinal tract. However, use of gastrointestinal mucosa can result in complications such as electrolyte imbalance, stone formation, urinary tract infection, mucous production, and malignancy. Recent tissue engineering techniques use acellular grafts, cultured cells combined with biodegradable scaffolds, and cell sheets. These techniques are not all currently applicable for human bladder reconstruction. However, new avenues for bladder reconstruction maybe facilitated by a better understanding of urogenital development, the cellular and molecular biology of urothelium, and cell-cell interactions, which modulate tissue repair, homeostasis, and disease progression.

Biology of kidney cells: ontogeny-recapitulating phylogeny

Biology of kidney cells can be used as a model for further understanding of ontogeny-recapitulating phylogeny. The common and species-specific structural and functional relationship between blood capillaries and the environment via a filtration barrier of nephrons is a biological phenomenon resulting from renal cell memory acquired through evolution. Genetically programmed development, a subsequent series of gene expression, and inductive interactions played a key role in differentiation and maintenance of specific activities of kidneys in birds and mammals. Various environmental factors may alter kidney development and specific activities at the levels of gene expression, repression, or derepression, and defensive mechanisms involved in reaction to risk factors are developed. Autoimmunity and cancerogenesis are closely dependent on a variety of environmental agents, such as antigens originating from infections with some viruses and toxins, or irradiation, advanced industrialization, and progress of civilization. As a result of gene mutation, delation, rearrangement, and/or susceptibility to different agents, renal cell memory is altered. Instead of cell-specific activities, the abilities for regeneration, and other genetically programmed activities, the genesis of kidney diseases are common. Balkan endemic nephropathy, as regional disease, is an important example of the role, of environmental agents, at the level of genes. Research programs on molecular genetics will contribute to our efforts both to prevent infections and to elucidate the genesis, diagnosis, prognosis, prevention, and therapy of kidney diseases.

The BMP family member Gdf7 is required for seminal vesicle growth, branching morphogenesis, and cytodifferentiation

Epithelial-mesenchymal interactions play an important role in the development of many different organs and tissues. The secretory glands of the male reproductive system, including the prostate and seminal vesicles, are derived from epithelial precursors. Signals from the underlying mesenchyme are required for normal growth, branching, and differentiation of the seminal vesicle epithelium. Here, we show that a member of the BMP family, Gdf7, is required for normal seminal vesicle development. Expression and tissue recombination experiments suggest that Gdf7 is a mesenchymal signal that acts in a paracrine fashion to control the differentiation of the seminal vesicle epithelium.

Changes of phenotypic expression of prostatic antigen in secondary transitional cell carcinoma of the prostate: evidence for induction phenomenon as a mechanism for acquisition of prostatic antigens in prostatic transitional cell carcinoma

BACKGROUND

In vitro and experimental studies of mesenchymal-epithelial interaction for the prostatic stroma have demonstrated that the prostatic stroma is capable of inducing the nonprostatic epithelium to acquire many features of prostatic epithelium. We investigated whether this phenomenon could be observed in vivo in human prostatic stroma. MATERIALS AND METHODS Sixty transitional cell carcinoma (TCC) of the urinary bladder: (a) 20 with glandular lumen; (b) 20 without glandular lumen: (c) 10 mixed TCC-adenocarcinoma (ACA); and (d) 10 with synchronous or metachronous TCC of the prostate; and three primary TCC of the prostate were examined and submitted for immunostaining for prostatic acid phosphatase (PAP) and prostatic specific antigen (PSA).

RESULTS

There was a spectrum of immunostaining for PSA ranging from negative reactivity in TCC without glandular lumen of the urinary bladder, to focal and weak reactivity in single cells with varying degrees of nonmucinous glandular differentiation and to strong reactivity in groups of cells in primary and synchronous or metachronous TCC in the prostate. The areas of carcinoma geographically closest to the prostate and with the most extensive nonmucinous glandular differentiation displayed the most frequent and strongest immunoreactivity for PSA. The immunoreactivity for PAP was usually stronger than for PSA. Four cases of TCC and mixed TCC-ACA were immunoreactive only for PAP. Furthermore, there was a change in the phenotype of TCC in the urinary bladder as it spread into the prostate. For 10 TCC in the urinary bladder with synchronous or metachronous tumor in the prostate, all TCC in the urinary bladder were negative for PAP and PSA, whereas six TCC in the prostate were focally positive.

CONCLUSIONS

The spectrum of immunoreactivity for PAP and PSA and the change in immunoreactivity of TCC of the urinary bladder as it spreads into the prostate are likely induced by the prostatic stroma through the mechanism of mesenchymal-epithelial interaction. Prostate 47:172-182, 2001.

Mesenchymal reprogramming of adult human epithelial differentiation

The objective of this study was to determine whether neonatal rat seminal vesicle mesenchyme (rSVM) can reprogram epithelial differentiation in a fully differentiated adult human bladder epithelium. For this purpose neonatal rSVM was isolated from newborn (0-day) Sprague-Dawley rats, and normal adult human bladder epithelium (hBLE) was isolated from radical cystoprostatectomy specimens to prepare rSVM+hBLE tissue recombinants in vitro. After overnight culture the tissue recombinants were grafted beneath the renal capsule of male athymic rodent hosts and allowed to grow in vivo for 6 months. As controls, rSVM and hBLE were grafted separately and allowed to grow for the same period. Tissue recombinants and control tissue grafts were harvested, and secretions were collected for biochemical studies. Tissues were fixed both for histologic as well as immunohistochemical staining. Neonatal rSVM induced normal adult human bladder urothelium to form glandular structures resembling prostate. The induced prostatic acini were filled with secretions that expressed human prostate-specific secretory proteins. These findings demonstrate that adult human urothelial cells retain a responsiveness to neonatal prostatic mesenchymal inductors. Change in urothelial histodifferentiation was associated with change in functional activity. The ability of the neonatal rat mesenchymal tissues to induce morphologic as well as biochemical changes in normal adult human urothelium provides a basis for human tissue engineering and organ reconstruction.

To clone or not to clone--a Jewish perspective

Many new reproductive methods such as artificial insemination, in vitro fertilisation, freezing of human embryos, and surrogate motherhood were at first widely condemned but are now seen in Western society as not just ethically and morally acceptable, but beneficial in that they allow otherwise infertile couples to have children. The idea of human cloning was also quickly condemned but debate is now emerging. This article examines cloning from a Jewish perspective and finds evidence to support the view that there is nothing inherently wrong with the idea of human cloning. A hypothesis is also advanced suggesting that even if a body was cloned, the brain, which is the essence of humanity, would remain unique. This author suggests that the debate should be changed from "Is cloning wrong?" to "When is cloning wrong?".

Hepatocyte growth factor and the kidney: it is not just for the liver

Mesenchymal-epithelial interactions are important for many biological processes in epithelial organs such as the kidney. Hepatocyte growth factor (HGF) is a mesenchymally derived polypeptide cytokine that acts through its tyrosine kinase c-met receptor and is an important mediator of these interactions. This article reviews data showing the in vitro actions of HGF on renal epithelial cells that result in such diverse responses as mitogenesis, motogenesis, and morphogenesis. It also examines the in vivo evidence linking HGF and the c-met receptor to kidney development, regeneration following injury, and renal disease. Elucidating cellular mechanisms underlying the coordinated control of diverse HGF-induced phenotypic changes in renal epithelia in vitro should contribute to a clearer understanding of complex biological processes such as organogenesis, regeneration, and carcinogenesis in epithelial organs such as the kidney.