Regulation of prostate branching morphogenesis by activin A and follistatin

Bmp7 regulates branching morphogenesis of the lacrimal gland by promoting mesenchymal proliferation and condensation

The lacrimal gland provides an excellent model with which to study the epithelial-mesenchymal interactions that are crucial to the process of branching morphogenesis. In the current study, we show that bone morphogenetic protein 7 (Bmp7) is expressed with a complex pattern in the developing gland and has an important role in regulating branching. In loss-of-function analyses, we find that Bmp7-null mice have distinctive reductions in lacrimal gland branch number, and that inhibition of Bmp activity in gland explant cultures has a very similar consequence. Consistent with this, exposure of whole-gland explants to recombinant Bmp7 results in increased branch number. In determining which cells of the gland respond directly to Bmp7, we have tested isolated mesenchyme and epithelium. We find that, as expected, Bmp4 can suppress bud extension in isolated epithelium stimulated by Fgf10, but interestingly, Bmp7 has no discernible effect. Bmp7 does, however, stimulate a distinct response in mesenchymal cells. This manifests as a promotion of cell division and formation of aggregates, and upregulation of cadherin adhesion molecules, the junctional protein connexin 43 and of alpha-smooth muscle actin. These data suggest that in this branching system, mesenchyme is the primary target of Bmp7 and that formation of mesenchymal condensations characteristic of signaling centers may be enhanced by Bmp7. Based on the activity of Bmp7 in promoting branching, we also propose a model suggesting that a discrete region of Bmp7-expressing head mesenchyme may be crucial in determining the location of the exorbital lobe of the gland.

Mutually antagonistic effects of androgen and activin in the regulation of prostate cancer cell growth

Activin, a member of the TGFbeta superfamily, is expressed in the prostate and inhibits growth. We demonstrate that the effects of activin and androgen on regulation of prostate cancer cell growth are mutually antagonistic. In the absence of androgen, activin induced apoptosis in the androgen-dependent human prostate cancer cell line LNCaP, an effect suppressed by androgen administration. Although activin by itself did not alter the cell cycle distribution, it potently suppressed androgen- induced progression of cells into S-phase of the cell cycle and thus inhibited androgen-stimulated growth of LNCaP cells. Expression changes in cell cycle regulatory proteins such as Rb, E2F-1, and p27 demonstrated a strong correlation with the mutually antagonistic growth regulatory effects of activin and androgen. The inhibitory effect of activin on growth was independent of serine, serine, valine, serine motif phosphorylation of Smad3. Despite their antagonistic effect on growth, activin and androgen costimulated the expression of prostate-specific antigen through a Smad3-mediated mechanism. These observations indicate the existence of a complex cross talk between activin and androgen signaling in regulation of gene expression and growth of the prostate.

Ovarian regulation of endometrial gland morphogenesis and activin-follistatin system in the neonatal ovine uterus

Postnatal development of the ovine uterus between birth and Postnatal Day (PND) 56 involves differentiation of the endometrial glandular epithelium from the luminal epithelium followed by tubulogenesis and branching morphogenesis. Previous results indicated that ovariectomy of ewes at birth did not affect uterine growth or initial stages of endometrial gland genesis on PND 14 but did affect uterine growth after PND 28. Available evidence from a number of species supports the hypothesis that the ovary does not affect endometrial gland morphogenesis in the postnatal uterus. To test this hypothesis in our sheep model, ewes were assigned at birth to a sham surgery as a control or bilateral ovariectomy (OVX) on PND 7. Uteri were removed and weighed on PND 56. Ovariectomy did not affect circulating levels of estradiol-17beta. Uterine weight was 52% lower in OVX ewes. Histomorphological analyses indicated that the thickness of the endometrium and myometrium, total number of endometrial glands, and endometrial gland density in the stratum spongiosum stroma was reduced in uteri of OVX ewes. In contrast, the number of superficial ductal gland invaginations and gland density in the stratum compactum stroma was not affected by ovariectomy. The uteri of OVX ewes contained lower levels of betaA subunit, activin receptor (ActR) type IA, ActRIB, and follistatin protein expression but higher levels of betaB subunit. In the neonatal ovary, follistatin, inhibin alpha subunit, betaA subunit, and betaB subunit were expressed in antral follicles between PNDs 0 and 56. These results led to rejection of the hypothesis that the ovary does not influence endometrial adenogenesis. Rather, the ovary and, thus, an ovarian-derived factor regulates, in part, the coiling and branching morphogenetic stage of endometrial gland development after PND 14 and expression of specific components of the activin-follistatin system in the neonatal ovine uterus that appear to be important for that critical process.

The activin-follistatin system in the neonatal ovine uterus

Uterine gland development or adenogenesis in the neonatal ovine uterus involves budding and tubulogenesis followed by coiling and branching morphogenesis of the glandular epithelium (GE) from the luminal epithelium (LE) between birth (Postnatal Day [PND] 0) and PND 56. Activins, which are members of the transforming growth factor beta superfamily, and follistatin, an inhibitor of activins, regulate epithelial branching morphogenesis in other organs. The objective of the present study was to determine effects of postnatal age on expression of follistatin, inhibin alpha subunit, betaA subunit, betaB subunit, activin receptor (ActR) type IA, ActRIB, and ActRII in the developing ovine uterus. Ewes were ovariohysterectomized on PND 0, 7, 14, 21, 28, 35, 42, 49, or 56. The uterus was analyzed by in situ hybridization and immunohistochemistry. Neither inhibin alpha subunit mRNA or protein was detected in the neonatal uterus. Expression of betaA and betaB subunits was detected predominantly in the endometrial LE and GE and myometrium between PND 0 and PND 56. In all uterine cell types, ActRIA, ActRIB, and ActRII were expressed, with the highest levels observed in the endometrial LE and GE and myometrium. Between PND 0 and PND 14, follistatin was detected in all uterine cell types. However, between PND 21 and PND 56, follistatin was only detected in the stroma and myometrium and not in the developing GE. Collectively, the present results indicate that components of the activin-follistatin system are expressed in the developing neonatal ovine uterus and are potential regulators of endometrial gland morphogenesis.

Localization of activin and inhibin subunits, receptors and SMADs in the mouse mammary gland

Activin and inhibin, two closely related protein hormones, are members of the transforming growth factor beta (TGF beta) superfamily of growth factors. Activin and TGF beta have been associated with mouse mammary gland development and human breast carcinogenesis. TGF beta expression in the mammary gland has been previously described, and was found to be expressed in nonparous tissue and during pregnancy, down-regulated during lactation, and then up-regulated during involution. The expression pattern of activin subunits, receptors and cytoplasmic signaling molecules has not been thoroughly described in post-natal mammary gland development. We hypothesize that activin signaling components are dynamically regulated during mammary gland development, thereby permitting activin to have distinct temporal growth regulatory actions on this tissue. To examine the activin signal transduction system in the mammary gland, tissue from CD1 female mice was dissected from nonparous, lactating day 1, 10, and 20 and post-weaning day 4 animals. The expression of the activin receptors (ActRIIA, ActRIIB and ActRIB), the inhibin co-receptor (betaglycan), and ligand subunit (alpha, beta A and beta B), mRNA was measured by semi-quantitative RT-PCR in these tissues. In addition, the cellular compartmentalization of the activin signaling proteins, including the cytoplasmic signaling co-activators, Smads 2, 3 and 4, were examined by immunohistochemistry. Generally, mRNA abundance of activin signaling components was greatest in the nonparous tissue, and then decreased, whereas protein immunoreactivity for activin signaling components increased during lactation and decreased during involution. The alpha-subunit protein was detected in nonparous and lactating day 1 tissue only. Importantly, Smad 3, but not Smad 2, was detected in epithelial cell nuclei during all time points examined, indicating that activin signaling is mediated by Smad 3 at these times. These findings suggest that activin's growth regulatory role during lactation may be distinguished from that of TGF beta during post-natal mammary development. Future studies will focus on determining the exact role this ligand plays in mammary tissue differentiation and neoplasia.

Inhibition of epithelial ductal branching in the prostate by sonic hedgehog is indirectly mediated by stromal cells

Sonic hedgehog (Shh), a vertebrate homologue of the Drosophila segment-polarity gene hedgehog, has been reported to play an important role during normal development of various tissues. Abnormal activities of Shh signaling pathway have been implicated in tumorigenesis such as basal cell carcinomas and medulloblastomas. Here we show that Shh signaling negatively regulates prostatic epithelial ductal morphogenesis. In organotypic cultures of developing rat prostates, Shh inhibited cell proliferation and promoted differentiation of luminal epithelial cells. The expression pattern of Shh and its receptors suggests a paracrine mechanism of action. The Shh receptors Ptc1 (Patched1) and Ptc2 were found to be expressed in prostatic stromal cells adjacent to the epithelium, where Shh itself was produced. This paracrine model was confirmed by co-culturing the developing prostate in the presence of stromal cells transfected with a vector expressing a constitutively active form of Smoothened, the real effector of the Shh signaling pathway. Furthermore, expression of activin A and TGF-beta1 that were shown previously to inhibit prostatic epithelial branching was up-regulated following Shh treatment in the organotypic cultures. Taken together, these results suggest that Shh negatively regulates prostatic ductal branching indirectly by acting on the surrounding stromal cells, at least partly via up-regulating expression of activin A and TGF-beta1.

New perspectives on growth factor-sex steroid interaction in the prostate

Many organs respond to both sex steroids and growth factors. Regulation of these pathways is integral to cell-cell communications during development and aberrant changes cause disease pathogenesis. Traditionally, paracrine and endocrine actions of growth factors and steroid hormones are considered independently. Recently, new data indicated that activin/TGFbeta and sex steroid signalling are linked; explicitly, that the pathways cross-talk intracellularly. Here we present new perspectives on these interactions, using examples predominantly from the prostate, as it is a well-characterised organ in this context. While this information provides insight to the potential mechanisms behind these interactions, it also presents a new challenge; the action of any of these factors cannot be considered exclusively without considering the impact on the other biological pathways.

Hormonal, cellular, and molecular control of prostatic development

The prostate is a male accessory sex gland found only in mammals that functions to produce a major fraction of seminal fluid. Interest in understanding the biology of the prostate is driven both by the fascinating nature of the developmental processes that give rise to the prostate and by the high incidence in humans of prostatic diseases, including prostatic adenocarcinoma and benign prostatic hyperplasia. This review summarizes the current state of knowledge of the cellular and molecular processes that control prostatic development. Insight into the mechanisms that control prostatic development has come from experimental embryological work as well as from the study of mice and humans harboring mutations that alter prostatic development. These studies have demonstrated a requirement for androgens throughout prostatic development and have revealed a series of reciprocal paracrine signals between the developing prostatic epithelium and prostatic mesenchyme. Finally, these studies have identified several specific gene products that are required for prostatic development. While research in recent years has greatly enhanced our understanding of the molecular control of prostatic development, known genes cannot yet explain in molecular terms the complex biological interactions that descriptive and experimental embryological studies have elucidated in the control of prostatic development.

Activins as regulators of branching morphogenesis

Development of glandular organs such as the kidney, lung, and prostate involves the process of branching morphogenesis. The developing organ begins as an epithelial bud that invades the surrounding mesenchyme, projecting dividing epithelial cords or tubes away from the site of initiation. This is a tightly regulated process that requires complex epithelial-mesenchymal interactions, resulting in a three-dimensional treelike structure. We propose that activins are key growth and differentiation factors during this process. The purpose of this review is to examine the direct, indirect, and correlative lines of evidence to support this hypothesis. The expression of activins is reviewed together with the effect of activins and follistatins in the development of branched organs. We demonstrate that activin has both negative and positive effects on cell growth during branching morphogenesis, highlighting the complex nature of activin in the regulation of proliferation and differentiation. We propose potential mechanisms for the way in which activins modify branching and address the issue of whether activin is a regulator of branching morphogenesis.