Yorkie and Hedgehog independently restrict BMP production in escort cells to permit germline differentiation in the Drosophila ovary

Gap junction-transported cAMP from the niche controls stem cell progeny differentiation

The niche has been shown to control stem cell self-renewal in different tissue types and organisms. Recently, a separate niche has been proposed to control stem cell progeny differentiation, called the differentiation niche. However, it remains poorly understood whether and how the differentiation niche directly signals to stem cell progeny to control their differentiation. In the Drosophila ovary, inner germarial sheath (IGS) cells contribute to two separate niche compartments for controlling both germline stem cell (GSC) self-renewal and progeny differentiation. In this study, we show that IGS cells express Inx2 protein, which forms gap junctions (GJs) with germline-specific Zpg protein to control stepwise GSC lineage development, including GSC self-renewal, germline cyst formation, meiotic double-strand DNA break formation, and oocyte specification. Germline-specific Zpg and IGS-specific Inx2 knockdowns cause similar defects in stepwise GSC development. Additionally, secondary messenger cAMP is transported from IGS cells to GSCs and their progeny via GJs to activate PKA signaling for controlling stepwise GSC development. Therefore, this study demonstrates that the niche directly controls GSC progeny differentiation via the GJ-cAMP-PKA signaling axis, which provides important insights into niche control of stem cell differentiation and highlights the importance of GJ-transported cAMP in tissue regeneration. This may represent a general strategy for the niche to control adult stem cell development in various tissue types and organisms since GJs and cAMP are widely distributed.

Cyromazine affects the ovarian germ cells of Drosophila via the ecdysone signaling pathway

Cyromazine, an insect growth regulator, has been extensively used against the insect pests of livestock and households. Previously, it was observed that the continuous selection of cyromazine from the larval to the adult stage decreased the number of germline stem cells (GSCs) and cystoblasts (CBs) in the adult ovary. In addition, in this study, we observed that the number of primordial germ cells (PGCs) was also decreased in the larval ovary after treatment with cyromazine. However, the mechanism by which it affects the germ cells is yet to be explored. Consequently, to deeply investigate the effects of cyromazine on the germ cells, we performed tissue-specific RNA sequencing. Bioinformatics analysis revealed that the ecdysone signaling pathway was significantly influenced under cyromazine stress. Based on that, we screened and selected 14 ecdysone signaling responsive genes and silenced their expression in the germ cells only. Results of that showed a considerable reduction in the number of germ cells. Furthermore, we mixed exogenous 20E with the cyromazine-containing diet to rescue the ecdysone signaling. Our results supported that the application of exogenous 20E significantly rescued the germ cells in the transgenic lines. Therefore, this implies that the cyromazine decreased the number of germ cells by affecting the ecdysone signaling pathway.

Therapeutic Effect of Melatonin in Premature Ovarian Insufficiency: Hippo Pathway Is Involved

Objective

Premature ovarian insufficiency (POI) is a female reproductive disorder of unknown etiology with no definite pathogenesis. Melatonin (MT) is an endogenous hormone synthesized mainly by pineal cells and has strong endogenous effects in regulating ovarian function. To systematically explore the pharmacological mechanism of MT on POI therapy, a literature review approach was conducted at the signaling pathways level.

Methods

Relevant literatures were searched and downloaded from databases, including PubMed and China National Knowledge Infrastructure, using the keywords “premature ovarian insufficiency,” “Hippo signaling pathways,” and “melatonin.” The search criteria were from 2010 to 2022. Text mining was also performed.

Results

MT is involved in the regulation of Hippo signaling pathway in a variety of modes and has been correlated with ovarian function.

Conclusions

The purpose of this review is to summarize the research progress of Hippo signaling pathways and significance of MT in POI, the potential crosstalk between MT and Hippo signaling pathways, and the prospective therapy.

Nucleoporin107 mediates female sexual differentiation via Dsx

We recently identified a missense mutation in Nucleoporin107 (Nup107; D447N) underlying XX-ovarian-dysgenesis, a rare disorder characterized by underdeveloped and dysfunctional ovaries. Modeling of the human mutation in Drosophila or specific knockdown of Nup107 in the gonadal soma resulted in ovarian-dysgenesis-like phenotypes. Transcriptomic analysis identified the somatic sex-determination gene doublesex (dsx) as a target of Nup107. Establishing Dsx as a primary relevant target of Nup107, either loss or gain of Dsx in the gonadal soma is sufficient to mimic or rescue the phenotypes induced by Nup107 loss. Importantly, the aberrant phenotypes induced by compromising either Nup107 or dsx are reminiscent of BMP signaling hyperactivation. Remarkably, in this context, the metalloprotease AdamTS-A, a transcriptional target of both Dsx and Nup107, is necessary for the calibration of BMP signaling. As modulation of BMP signaling is a conserved critical determinant of soma-germline interaction, the sex and tissue specific deployment of Dsx-F by Nup107 seems crucial for the maintenance of the homeostatic balance between the germ cells and somatic gonadal cells.

Neofunctionalization of an ancient domain allows parasites to avoid intraspecific competition by manipulating host behaviour

Intraspecific competition is a major force in mediating population dynamics, fuelling adaptation, and potentially leading to evolutionary diversification. Among the evolutionary arms races between parasites, one of the most fundamental and intriguing behavioural adaptations and counter-adaptations are superparasitism and superparasitism avoidance. However, the underlying mechanisms and ecological contexts of these phenomena remain underexplored. Here, we apply the Drosophila parasite Leptopilina boulardi as a study system and find that this solitary endoparasitic wasp provokes a host escape response for superparasitism avoidance. We combine multi-omics and in vivo functional studies to characterize a small set of RhoGAP domain-containing genes that mediate the parasite's manipulation of host escape behaviour by inducing reactive oxygen species in the host central nervous system. We further uncover an evolutionary scenario in which neofunctionalization and specialization gave rise to the novel role of RhoGAP domain in avoiding superparasitism, with an ancestral origin prior to the divergence between Leptopilina specialist and generalist species. Our study suggests that superparasitism avoidance is adaptive for a parasite and adds to our understanding of how the molecular manipulation of host behaviour has evolved in this system.

A Progressive Somatic Cell Niche Regulates Germline Cyst Differentiation in the Drosophila Ovary

In the germarium of the Drosophila ovary, developing germline cysts are surrounded by a population of somatic escort cells that are known to function as the niche cells for germline differentiation;¹ however, the underlying molecular mechanisms of this niche function remain poorly understood. Through single-cell gene expression profiling combined with genetic analyses, we here demonstrate that the escort cells can be spatially and functionally divided into two successive domains. The anterior escort cells (aECs) specifically produce ecdysone, which acts on the cystoblast to promote synchronous cell division, whereas the posterior escort cells (pECs) respond to ecdysone signaling and regulate soma-germline cell adhesion to promote the transition from 16-cell cyst-to-egg chamber formation. The patterning of the aEC and pEC domains is independent of the germline but is dependent on JAK/STAT signaling activity, which emanates from the posterior. Thus, a heterogeneous population of escort cells constitutes a stepwise niche environment to orchestrate cystoblast division and differentiation toward egg chamber formation.

Analysis of ovarian transcriptomes reveals thousands of novel genes in the insect vector Rhodnius prolixus

Rhodnius prolixus is a Triatominae insect species and a primary vector of Chagas disease. The genome of R. prolixus has been recently sequenced and partially assembled, but few transcriptome analyses have been performed to date. In this study, we describe the stage-specific transcriptomes obtained from previtellogenic stages of oogenesis and from mature eggs. By analyzing ~ 228 million paired-end RNA-Seq reads, we significantly improved the current genome annotations for 9206 genes. We provide extended 5' and 3' UTRs, complete Open Reading Frames, and alternative transcript variants. Strikingly, using a combination of genome-guided and de novo transcriptome assembly we found more than two thousand novel genes, thus increasing the number of genes in R. prolixus from 15,738 to 17,864. We used the improved transcriptome to investigate stage-specific gene expression profiles during R. prolixus oogenesis. Our data reveal that 11,127 genes are expressed in the early previtellogenic stage of oogenesis and their transcripts are deposited in the developing egg including key factors regulating germline development, genome integrity, and the maternal-zygotic transition. In addition, GO term analyses show that transcripts encoding components of the steroid hormone receptor pathway, cytoskeleton, and intracellular signaling are abundant in the mature eggs, where they likely control early embryonic development upon fertilization. Our results significantly improve the R. prolixus genome and transcriptome and provide novel insight into oogenesis and early embryogenesis in this medically relevant insect.

Novel approaches to fertility restoration in women with premature ovarian insufficiency

The diagnosis of premature ovarian insufficiency (POI) brings with it the loss of fertility, an immediate concern for many affected women, and a future one for many others. While there is a low natural conception rate, for most the choice is between oocyte donation and alternative methods of family building such as adoption. There is, however, a lot of research into novel methods for increasing or restoring the fertility of women with POI, which are discussed in this review. Many approaches involve the use of mesenchymal stem cells, from a variety of sources including bone marrow, placenta and umbilical cord, and menstrual blood. These seem to have efficacy in animal models of POI, although through unclear mechanisms. Activation of remaining primordial follicles is also being explored, through physical or chemical manipulation of key regulatory pathways, notably the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) and Hippo pathways. Much of the clinical data are uncontrolled, and mostly in women with a reduced ovarian reserve rather than POI, as are the results thus far for administration of platelet-rich plasma. Clinical studies with appropriate controls are needed to substantiate the preliminary claims of effectiveness of these approaches.

Multiple Niche Compartments Orchestrate Stepwise Germline Stem Cell Progeny Differentiation

The niche controls stem cell self-renewal and progenitor differentiation for maintaining adult tissue homeostasis in various organisms. However, it remains unclear whether the niche is compartmentalized to control stem cell self-renewal and stepwise progeny differentiation. In the Drosophila ovary, inner germarial sheath (IGS) cells form a niche for controlling germline stem cell (GSC) progeny differentiation. In this study, we have identified four IGS subpopulations, which form linearly arranged niche compartments for controlling GSC maintenance and multi-step progeny differentiation. Single-cell analysis of the adult ovary has identified four IGS subpopulations (IGS1-IGS4), the identities and cellular locations of which have been further confirmed by fluorescent in situ hybridization. IGS1 and IGS2 physically interact with GSCs and mitotic cysts to control GSC maintenance and cyst formation, respectively, whereas IGS3 and IGS4 physically interact with 16-cell cysts to regulate meiosis, oocyte development, and cyst morphological change. Finally, one follicle cell progenitor population has also been transcriptionally defined for facilitating future studies on follicle stem cell regulation. Therefore, this study has structurally revealed that the niche is organized into multiple compartments for orchestrating stepwise adult stem cell development and has also provided useful resources and tools for further functional characterization of the niche in the future.

Mud Loss Restricts Yki-Dependent Hyperplasia in Drosophila Epithelia

Tissue development demands precise control of cell proliferation and organization, which is achieved through multiple conserved signaling pathways and protein complexes in multicellular animals. Epithelia are a ubiquitous tissue type that provide diverse functions including physical protection, barrier formation, chemical exchange, and secretory activity. However, epithelial cells are also a common driver of tumorigenesis; thus, understanding the molecular mechanisms that control their growth dynamics is important in understanding not only developmental mechanisms but also disease. One prominent pathway that regulates epithelial growth is the conserved Hippo/Warts/Yorkie network. Hippo/Warts inactivation, or activating mutations in Yorkie that prevent its phosphorylation (e.g., YkiS168A), drive hyperplastic tissue growth. We recently reported that loss of Mushroom body defect (Mud), a microtubule-associated protein that contributes to mitotic spindle function, restricts YkiS168A-mediated growth in Drosophila imaginal wing disc epithelia. Here we show that Mud loss alters cell cycle progression and triggers apoptosis with accompanying Jun kinase (JNK) activation in YkiS168A-expressing discs. To identify additional molecular insights, we performed RNAseq and differential gene expression profiling. This analysis revealed that Mud knockdown in YkiS168A-expressing discs resulted in a significant downregulation in expression of core basement membrane (BM) and extracellular matrix (ECM) genes, including the type IV collagen gene viking. Furthermore, we found that YkiS168A-expressing discs accumulated increased collagen protein, which was reduced following Mud knockdown. Our results suggest that ECM/BM remodeling can limit untoward growth initiated by an important driver of tumor growth and highlight a potential regulatory link with cytoskeleton-associated genes.

Loss of Drosophila E3 Ubiquitin Ligase Hyd Promotes Extra Mitosis in Germline Cysts and Massive Cell Death During Oogenesis

The Drosophila hyperplastic disc (hyd) gene is the ortholog of mammalian tumor suppressor EDD, which is implicated in a wide variety of cellular processes, and its regulation is impaired in various tumors. It is a member of the highly conserved HECT family of E3 ubiquitin ligases, which directly attach ubiquitin to targeted substrates. In early works, it was shown that Drosophila Hyd may be a tumor suppressor because it is involved in the control of imaginal-disc cell proliferation and growth. In this study, we demonstrated that Hyd is also important for the regulation of female germ cell proliferation and that its depletion leads to additional germline cell mitoses. Furthermore, we revealed a previously unknown Hyd function associated with the maintenance of germ cells' viability. A reduction in hyd expression by either mutations or RNA interference resulted in large-scale germ cell death at different stages of oogenesis. Thus, the analysis of phenotypes arising from the hyd deficiency points to Hyd's role in the regulation of germline metabolic processes during oogenesis.

Role of Hippo-YAP1/TAZ pathway and its crosstalk in cardiac biology

The Hippo pathway undertakes a pivotal role in organ size control and the process of physiology and pathology in tissue. Its downstream effectors YAP1 and TAZ receive upstream stimuli and exert transcription activity to produce biological output. Studies have demonstrated that the Hippo pathway contributes to maintenance of cardiac homeostasis and occurrence of cardiac disease. And these cardiac biological events are affected by crosstalk among Hippo-YAP1/TAZ, Wnt/β-catenin, Bone morphogenetic protein (BMP) and G-protein-coupled receptor (GPCR) signaling, which provides new insights into the Hippo pathway in heart. This review delineates the interaction among Hippo, Wnt, BMP and GPCR pathways and discusses the effects of these pathways in cardiac biology.

Coordinating Proliferation, Polarity, and Cell Fate in the Drosophila Female Germline

Gametes are highly specialized cell types produced by a complex differentiation process. Production of viable oocytes requires a series of precise and coordinated molecular events. Early in their development, germ cells are an interconnected group of mitotically dividing cells. Key regulatory events lead to the specification of mature oocytes and initiate a switch to the meiotic cell cycle program. Though the chromosomal events of meiosis have been extensively studied, it is unclear how other aspects of oocyte specification are temporally coordinated. The fruit fly, Drosophila melanogaster, has long been at the forefront as a model system for genetics and cell biology research. The adult Drosophila ovary continuously produces germ cells throughout the organism’s lifetime, and many of the cellular processes that occur to establish oocyte fate are conserved with mammalian gamete development. Here, we review recent discoveries from Drosophila that advance our understanding of how early germ cells balance mitotic exit with meiotic initiation. We discuss cell cycle control and establishment of cell polarity as major themes in oocyte specification. We also highlight a germline-specific organelle, the fusome, as integral to the coordination of cell division, cell polarity, and cell fate in ovarian germ cells. Finally, we discuss how the molecular controls of the cell cycle might be integrated with cell polarity and cell fate to maintain oocyte production.

Signal transduction pathways regulating Drosophila ovarian germline stem cells

Drosophila female germline stem cells (GSCs) serve as one of the best understood stem cell types. GSCs reside in a special microenvironment, the stem cell niche, and their activity is tightly regulated by niche-derived signals. In addition to the stemness-promoting signaling molecules, the niche also generates other signaling molecules that regulate GSC differentiation. Recent studies are beginning to appreciate the intricate interactions among these signaling molecules in the niche and their effects on GSC behaviour. This review summarizes recent advances to demonstrate how the niche functions as a signaling hub to integrate these niche-derived local signals as well as other organ-produced systemic signals to control GSC self-renewal and differentiation.

The regulation of Drosophila ovarian stem cell niches by signaling crosstalk

The Drosophila female ovary is an excellent model for investigating how multiple stem cell types are coordinately regulated in vivo. The ovary contains at least two stem cell types, germline stem cells (GSCs) and somatic follicular stem cells (FSCs). Although GSCs and FSCs are maintained within a distinct extra-cellular microenvironment, known as a niche, they share some common signaling molecules to generate their own niche. To properly maintain these stem cell types, understanding how signaling molecules are regulated is essential. In this review, we summarize the recent understanding of the mechanisms maintaining GSCs and FSCs from the perspective of growth factor regulation and discuss how these regulatory mechanisms contribute to stem cell maintenance, competition, and survival.

Special vulnerability of somatic niche cells to transposable element activation in Drosophila larval ovaries

In the Drosophila ovary, somatic escort cells (ECs) form a niche that promotes differentiation of germline stem cell (GSC) progeny. The piRNA (Piwi-interacting RNA) pathway, which represses transposable elements (TEs), is required in ECs to prevent the accumulation of undifferentiated germ cells (germline tumor phenotype). The soma-specific piRNA cluster flamenco (flam) produces a substantial part of somatic piRNAs. Here, we characterized the biological effects of somatic TE activation on germ cell differentiation in flam mutants. We revealed that the choice between normal and tumorous phenotypes of flam mutant ovaries depends on the number of persisting ECs, which is determined at the larval stage. Accordingly, we found much more frequent DNA breaks in somatic cells of flam larval ovaries than in adult ECs. The absence of Chk2 or ATM checkpoint kinases dramatically enhanced oogenesis defects of flam mutants, in contrast to the germline TE-induced defects that are known to be mostly suppressed by сhk2 mutation. These results demonstrate a crucial role of checkpoint kinases in protecting niche cells against deleterious TE activation and suggest substantial differences between DNA damage responses in ovarian somatic and germ cells.

Local and Physiological Control of Germline Stem Cell Lineages in Drosophila melanogaster

The long-term survival of any multicellular species depends on the success of its germline in producing high-quality gametes and maximizing survival of the offspring. Studies in Drosophila melanogaster have led our growing understanding of how germline stem cell (GSC) lineages maintain their function and adjust their behavior according to varying environmental and/or physiological conditions. This review compares and contrasts the local regulation of GSCs by their specialized microenvironments, or niches; discusses how diet and diet-dependent factors, mating, and microorganisms modulate GSCs and their developing progeny; and briefly describes the tie between physiology and development during the larval phase of the germline cycle. Finally, it concludes with broad comparisons with other organisms and some future directions for further investigation.

Traffic jam regulates the function of the ovarian germline stem cell progeny differentiation niche during pre-adult stage in Drosophila

Stem cell self-renewal and the daughter cell differentiation are tightly regulated by the respective niches, which produce extrinsic cues to support the proper development. In Drosophila ovary, Dpp is secreted from germline stem cell (GSC) niche and activates the BMP signaling in GSCs for their self-renewal. Escort cells (ECs) in differentiation niche restrict Dpp outside the GSC niche and extend protrusions to help with proper differentiation of the GSC daughter cells. Here we provide evidence that loss of large Maf transcriptional factor Traffic jam (Tj) blocks GSC progeny differentiation. Spatio-temporal specific knockdown experiments indicate that Tj is required in pre-adult EC lineage for germline differentiation control. Further molecular and genetic analyses suggest that the defective germline differentiation caused by tj-depletion is partly attributed to the elevated dpp in the differentiation niche. Moreover, our study reveals that tj-depletion induces ectopic En expression outside the GSC niche, which contributes to the upregulated dpp expression in ECs as well as GSC progeny differentiation defect. Alternatively, loss of EC protrusions and decreased EC number elicited by tj-depletion may also partially contribute to the germline differentiation defect. Collectively, our findings suggest that Tj in ECs regulates germline differentiation by controlling the differentiation niche characteristics.

The exocyst functions in niche cells to promote germline stem cell differentiation by directly controlling EGFR membrane trafficking

The niche controls stem cell self-renewal and differentiation in animal tissues. Although the exocyst is known to be important for protein membrane trafficking and secretion, its role in stem cells and niches has never been reported. Here, this study shows that the exocyst functions in the niche to promote germline stem cell (GSC) progeny differentiation in the Drosophila ovary by directly regulating EGFR membrane trafficking and signaling. Inactivation of exocyst components in inner germarial sheath cells, which form the differentiation niche, causes a severe GSC differentiation defect. The exocyst is required for maintaining niche cells and preventing BMP signaling in GSC progeny by promoting EGFR membrane targeting and signaling through direct association with EGFR. Finally, it is also required for EGFR membrane targeting, recycling and signaling in human cells. Therefore, this study reveals a novel function of the exocyst in niche cells to promote stem cell progeny differentiation by directly controlling EGFR membrane trafficking and signaling in vivo, and also provides important insight into how the niche controls stem cell progeny differentiation at the molecular level.

Ectopic Dpp signaling promotes stem cell competition through EGFR signaling in the Drosophila testis

Stem cell competition could select the fittest stem cells and potentially control tumorigenesis. However, little is known about the underlying molecular mechanisms. Here, we find that ectopic Decapentaplegic (Dpp) signal activation by expressing a constitutively active form of Thickveins (Tkv^CA) in cyst stem cells (CySCs) leads to competition between CySCs and germline stem cells (GSCs) for niche occupancy and GSC loss. GSCs are displaced from the niche and undergo differentiation. Interestingly, we find that induction of Tkv^CA results in elevated expression of vein, which further activates Epidermal Growth Factor Receptor (EGFR) signaling in CySCs to promote their proliferation and compete GSCs out of the niche. Our findings elucidate the important role of Dpp signaling in regulating stem cell competition and tumorigenesis, which could be shed light on tumorigenesis and cancer treatment in mammals.

miRNA functions in stem cells and their niches: lessons from the Drosophila ovary

From the very beginning of the miRNA era, Drosophila has served as an excellent model for explanation of miRNA biogenesis. Now Drosophila continues to be used in numerous studies aiming to decipher biological roles of individual miRNAs in a living organism. MiRNAs have emerged as an important regulatory class that adjusts gene expression in response to stress; therefore, it is particularly important to elucidate miRNA-based regulatory networks that appear in response to fluctuations in intrinsic and extrinsic environments. This review explores the major advances in understanding condition-dependent roles of miRNAs in adult stem cell biology using the Drosophila ovarian germline stem cell niche community as a model system.

Biocontrol characteristics of the fruit fly pupal parasitoid Trichopria drosophilae (Hymenoptera: Diapriidae) emerging from different hosts

Trichopria drosophilae (Hymenoptera: Diapriidae) is an important pupal endoparasitoid of Drosophila melanogaster Meigen (Diptera: Drosophilidae) and some other fruit fly species, such as D. suzukii, a very important invasive and economic pest. Studies of T. drosophilae suggest that this could be a good biological control agent for fruit fly pests. In this research, we compared the parasitic characteristics of T. drosophilae reared in D. melanogaster (TD_m) with those reared in D. hydei (TD_h). TD_h had a larger size than TD_m. The number of maximum mature eggs of a female TD_h was 133.6 ± 6.9, compared with the significantly lower value of 104.8 ± 11.4 for TD_m. Mated TD_h female wasp continuously produced female offspring up to 6 days after mating, compared with only 3 days for TD_m. In addition, the offspring female ratio of TD_h, i.e., 82.32%, was significantly higher than that of TD_m, i.e., 61.37%. Under starvation treatment, TD_h survived longer than TD_m. TD_h also survived longer than TD^m at high temperatures, such as 37 °C, although they both survived well at low temperatures, such as 18 °C and 4 °C. Old-age TD_h females maintained a high parasitism rate and offspring female ratio, while they were declined in old-age TD_m. Overall, TD_h had an advantage in terms of body size, fecundity, stress resistance ability and the parasitism rate compared with TD_m. Therefore, T. drosophilae from D. hydei could improve biocontrol efficacy with enormous economic benefits in the field, especially in the control of many frugivorous Drosophilidae species worldwide.

Hippo signaling in the ovary and polycystic ovarian syndrome

PURPOSE

To provide a commentary on our understanding of the role that the Hippo signaling pathway may play in patients with polycystic ovarian syndrome (PCOS) and how this understanding may impact the diagnosis of PCOS.

METHODS

We assessed publications discussing the role of the Hippo signaling pathway in the ovary. In particular, we discuss how Hippo signaling disruption after ovarian fragmentation, combined with treating ovarian fragments with phosphatase and tensin homolog (PTEN) inhibitors and phosphoinositide-3-kinase stimulators to augment AKT signaling, has been used in treatment of patients with primary ovarian insufficiency. Furthermore, we discuss our own data on variations in Hippo signaling pathway gene expression in cumulus cells isolated from women undergoing IVF with a previous diagnosis of PCOS.

RESULTS AND CONCLUSIONS

Aberrant Hippo signaling in PCOS patients is likely a contributing mechanism to the multifactorial etiology of the disease. Given the challenge of discerning the underlying etiology of oligo-ovulation in some patients, especially those with normal body mass indices, and the need for customized stimulation protocols for PCOS patients who have an increased risk of over-response and higher percentage of immature oocyte yield, it is important to identify these patients prior to treatment. Hippo gene expression fingerprints could potentially be used to more accurately define patients with PCOS. Additionally, targeting this pathway with pharmacologic agents could lead to non-surgical therapeutic options for PCOS.

Smad-Independent BMP Signaling in Somatic Cells Limits the Size of the Germline Stem Cell Pool

In developing organisms, proper tuning of the number of stem cells within a niche is critical for the maintenance of adult tissues; however, the involved mechanisms remain largely unclear. Here, we demonstrate that Thickveins (Tkv), a type I bone morphogenetic protein (BMP) receptor, acts in the Drosophila developing ovarian soma through a Smad-independent pathway to shape the distribution of BMP signal within the niche, impacting germline stem cell (GSC) recruitment and maintenance. Somatic Tkv promotes Egfr signaling to silence transcription of Dally, which localizes BMP signals on the cell surface. In parallel, Tkv promotes Hh signaling, which promotes escort cell cellular protrusions and upregulates expression of the Drosophila BMP homolog, Dpp, forming a positive feedback loop that enhances Tkv signaling and strengthens the niche boundary. Our results reveal a role for non-canonical BMP signaling in the soma during GSC establishment and generally illustrate how complex, cell-specific BMP signaling mediates niche-stem cell interactions.

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Tkv, a BMP receptor, in the developing ovarian soma controls fertility

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Knockdown Tkv in the developing soma causes ectopic germline stem cell (GSC) accumulation

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Tkv in the soma controls GSC number by limiting BMPs within the GSC niche

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BMP-Tkv signaling in the soma limits GSC number via Egfr and Hh signaling

Self-restrained regulation of stem cell niche activity by niche components in the Drosophila testis

Most, if not all, stem cells reside in a defined microenvironment, called the niche. Short-ranged niche signal must be tightly controlled to be active only inside the niche to maintain the proper balance of stem cell self-renewal verse differentiation. However, how niche components restrict localized niche signal activation remains largely unknown. Here, we find that Thickveins (Tkv, a type I receptor of the Dpp signaling pathway) in cyst stem cells (CySCs) of the testis niche prevents Dpp signaling activation outside of the niche. We show that Tkv functions as Dpp trap/sink to spatially restrain Dpp signaling inside the niche. This self-restrained regulation of niche activity by Tkv in CySCs is independent of the canonical Dpp signaling pathway. Our data demonstrate the critical roles of niche components (CySCs) in the self-restrained regulation of niche activity, which could be shed light on niche activity regulation in general.