Crosstalk of EGFR signalling with Notch and Hippo pathways to regulate cell specification, migration and proliferation in cockroach panoistic ovaries

CHMP4B contributes to maintaining the follicular cells integrity in the panoistic ovary of the cockroach Blattella germanica

BACKGROUND

The Endosomal Sorting Complex Required for Transport (ESCRT) is a highly conserved cellular machinery essential for many cellular functions, including transmembrane protein sorting, endosomal trafficking, and membrane scission. CHMP4B is a key component of ESCRT-III subcomplex and has been thoroughly studied in the meroistic ovaries of Drosophila melanogaster showing its relevance in maintaining this reproductive organ during the life of the fly. However, the role of the CHMP4B in the most basal panoistic ovaries remains elusive.

RESULTS

Using RNAi, we examined the function of CHMP4B in the ovary of Blattella germanica in two different physiological stages: in last instar nymphs, with proliferative follicular cells, and in vitellogenic adults when follicular cells enter in polyploidy and endoreplication. In Chmp4b-depleted specimens, the actin fibers change their distribution, appearing accumulated in the basal pole of the follicular cells, resulting in an excess of actin bundles that surround the basal ovarian follicle and modifying their shape. Depletion of Chmp4b also determines an actin accumulation in follicular cell membranes, resulting in different cell morphologies and sizes. In the end, these changes disrupt the opening of intercellular spaces between the follicular cells (patency) impeding the incorporation of yolk proteins to the growing oocyte and resulting in female sterility. In addition, the nuclei of follicular cells appeared unusually elongated, suggesting an incomplete karyokinesis.

CONCLUSIONS

These results proved CHMP4B essential in preserving the proper expression of cytoskeleton proteins vital for basal ovarian follicle growth and maturation and for yolk protein incorporation. Moreover, the correct distribution of actin fibers in the basal ovarian follicle emerged as a critical factor for the successful completion of ovulation and oviposition.

SIGNIFICANCE

The overall results, obtained in two different proliferative stages, suggest that the requirement of CHMP4B in B. germanica follicular epithelium is not related to the proliferative stage of the tissue.

Notch Signaling in Insect Development: A Simple Pathway with Diverse Functions

Notch signaling is an evolutionarily conserved pathway which functions between adjacent cells to establish their distinct identities. Despite operating in a simple mechanism, Notch signaling plays remarkably diverse roles in development to regulate cell fate determination, organ growth and tissue patterning. While initially discovered and characterized in the model insect Drosophila melanogaster, recent studies across various insect species have revealed the broad involvement of Notch signaling in shaping insect tissues. This review focuses on providing a comprehensive picture regarding the roles of the Notch pathway in insect development. The roles of Notch in the formation and patterning of the insect embryo, wing, leg, ovary and several specific structures, as well as in physiological responses, are summarized. These results are discussed within the developmental context, aiming to deepen our understanding of the diversified functions of the Notch signaling pathway in different insect species.

Egfr signaling promotes juvenile hormone biosynthesis in the German cockroach

BACKGROUND

In insects, an interplay between the activities of distinct hormones, such as juvenile hormone (JH) and 20-hydroxyecdysone (20E), regulates the progression through numerous life history hallmarks. As a crucial endocrine factor, JH is mainly synthesized in the corpora allata (CA) to regulate multiple physiological and developmental processes, including molting, metamorphosis, and reproduction. During the last century, significant progress has been achieved in elucidating the JH signal transduction pathway, while less progress has been made in dissecting the regulatory mechanism of JH biosynthesis. Previous work has shown that receptor tyrosine kinase (RTK) signaling regulates hormone biosynthesis in both insects and mammals. Here, we performed a systematic RNA interference (RNAi) screening to identify RTKs involved in regulating JH biosynthesis in the CA of adult Blattella germanica females.

RESULTS

We found that the epidermal growth factor receptor (Egfr) is required for promoting JH biosynthesis in the CA of adult females. The Egf ligands Vein and Spitz activate Egfr, followed by Ras/Raf/ERK signaling, and finally activation of the downstream transcription factor Pointed (Pnt). Importantly, Pnt induces the transcriptional expression of two key enzyme-encoding genes in the JH biosynthesis pathway: juvenile hormone acid methyltransferase (JHAMT) and methyl farnesoate epoxidase (CYP15A1). Dual-luciferase reporter assay shows that Pnt is able to activate a promoter region of Jhamt. In addition, electrophoretic mobility shift assay confirms that Pnt directly binds to the - 941~ - 886 nt region of the Jhamt promoter.

CONCLUSIONS

This study reveals the detailed molecular mechanism of Egfr signaling in promoting JH biosynthesis in the German cockroach, shedding light on the intricate regulation of JH biosynthesis during insect development.

Distinct gene expression dynamics in germ line and somatic tissue during ovariole morphogenesis in Drosophila melanogaster

The survival and evolution of a species is a function of the number of offspring it can produce. In insects, the number of eggs that an ovary can produce is a major determinant of reproductive capacity. Insect ovaries are made up of tubular egg-producing subunits called ovarioles, whose number largely determines the number of eggs that can be potentially laid. Ovariole number in Drosophila is directly determined by the number of cellular structures called terminal filaments, which are stacks of cells that assemble in the larval ovary. Elucidating the developmental and regulatory mechanisms of terminal filament formation is thus key to understanding the regulation of insect reproduction through ovariole number regulation. We systematically measured mRNA expression of all cells in the larval ovary at the beginning, middle, and end of terminal filament formation. We also separated somatic and germ line cells during these stages and assessed their tissue-specific gene expression during larval ovary development. We found that the number of differentially expressed somatic genes is highest during the late stages of terminal filament formation and includes many signaling pathways that govern ovary development. We also show that germ line tissue, in contrast, shows greater differential expression during early stages of terminal filament formation, and highly expressed germ line genes at these stages largely control cell division and DNA repair. We provide a tissue-specific and temporal transcriptomic dataset of gene expression in the developing larval ovary as a resource to study insect reproduction.

Stimulatory roles of epidermal growth factor receptor (EGFR) in ovarian development of mud crab Scylla paramamosain

The epidermal growth factor receptor (EGFR) is a pleiotropic glycoprotein which plays a role in regulating cell proliferation, migration and differentiation. However, to date little is known about its functions in crustaceans. In this study, we successfully identified SpEGFR from mud crab Scylla paramamosain. RT-PCR result showed that SpEGFR was widely distributed in all tested tissues and highly expressed in ovary. In situ hybridization revealed that SpEGFR mainly localized in oocyte perinuclear region with notably obvious signals. In vitro experiments showed that the expression of SpVgR and SpCyclin B in ovary explants from late vitellogenic stage crabs (summer) were significantly increased when treated with 1 nM human EGF (hEGF) for 1 h, while there was no obvious change towards SpEGFR. Interestingly, as for winter crab at the same vitellogenic stage, the expression of SpVgR and SpCyclin B in ovary explants did not show significant increase until treated with higher concentration of 10 nM hEGF and longer incubation time of 12 h. In addition, the hEGF-induced effect could be suppressed by pre-treated with EGFR inhibitor AG1478 and PD153035, respectively, which further indicated that EGF-EGFR pathway played a vital role in ovarian development in mud crab. In conclusion, SpEGFR might promote ovarian development by stimulating the expression of SpVgR and SpCyclin B under hEGF-induced treatment. The different physiological response to hEGF in the same vitellogenic stage crabs between summer and winter might be attributed to the changes in metabolism and physiological sensitivity.

Eyes absent in the cockroach panoistic ovaries regulates proliferation and differentiation through ecdysone signalling

Eyes absent (Eya), is a protein structurally conserved from hydrozoans to humans, for which two basic roles have been reported: it can act as a transcription cofactor and as a protein tyrosine phosphatase. Eya was discovered in the fly Drosophila melanogaster in relation to its function in eye development, and the same function was later reported in other insects. Eya is also involved in insect oogenesis, although studies in this sense are limited to D. melanogaster, which has meroistic ovaries, and where eya mutations abolish gonad formation. In the present work we studied the function of eya in the panoistic ovary of the cockroach Blattella germanica. We show that eya is essential for correct development of panoistic ovaries. In B. germanica, eya acts at different level and in a distinct way in the germarium and the vitellarium. In the germarium, eya contributes to maintain the correct number of somatic and germinal cells by regulating the expression of steroidogenic genes in the ovary. In the vitellarium, eya facilitates follicle cells proliferation and contributes to regulate the cell program, in the context of basal ovarian follicle maturation. Thus, eya-depleted females of B. germanica arrest the growth and maturation of basal ovarian follicles and become sterile.

Analysis of microRNA expression profiles dynamic in different life stages of Haemaphysalis longicornis ticks by deep sequencing of small RNA libraries

The three-host tick Haemaphysalis longicornis is an obligate blood-sucking ectoparasite. In life-stage transitions, microRNAs (miRNAs) show a variety of expression changes. To investigate these changes, deep sequencing technology was applied to identify the conserved and potentially novel miRNAs expressed during the different life stages of H. longicornis. Total RNA from eggs, unfed larvae, unfed nymphs and unfed adults was extracted for deep sequence analysis. Deep sequencing on a Hiseq 4000 generated a total of 111,192,069 reads, grouped into four small RNA (sRNA) libraries, one for each of the four developmental stages of H. longicornis. Among these sequences, 78 conserved and 55 potentially novel miRNAs were identified, including stage-specific and differentially expressed miRNAs. Gene ontology (GO) analysis indicated significantly enriched GO terms related to cell proliferation and differentiation, including specific terms for the processes of development, growth, metabolism, regulation of biological functions, reproduction, and membrane enzyme regular activity. Kyoto Encyclopedia of Gene and Genomes (KEGG) analysis revealed a significant enrichment of the insulin, notch, Hippo, and Wnt signaling pathways for growth and development. Our data highlight the abundance of miRNA changes (conserved and potentially novel) in the different life stages of H. longicornis. In particular, stage-specific miRNAs, as observed, are essential regulators for the development of H. longicornis.

Downregulation of WW domain-containing oxidoreductase leads to tamoxifen-resistance by the inactivation of Hippo signaling

Acquired tamoxifen-resistance is an important cause of death in patients with hormone-dependent breast tumors. Therefore, understanding the molecular mechanisms underlying the development of tamoxifen-resistance is critical for successful endocrine therapy. This study aimed to define the role of WW domain-containing oxidoreductase (WWOX) in acquired tamoxifen-resistance. Our results show that low WWOX expression was significantly related to tamoxifen-resistance. Moreover, WWOX-knockdown increased resistance to tamoxifen, while WWOX overexpression decreased the resistance. Furthermore, WWOX silencing decreased Yes-associated protein (YAP) phosphorylation and increased YAP nuclear translocation. Finally, YAP silencing decreased tamoxifen-resistance in WWOX-knockdown cells. Our findings demonstrate that WWOX downregulation can lead to the development of tamoxifen-resistance by inactivating Hippo signaling. Thus, WWOX might be a valuable target and prognostic marker for tamoxifen-resistance.

Impact statement

Understanding the molecular pathways leading to the development of tamoxifen-resistance is an important research focus as acquired tamoxifen-resistance is the main cause of death in patients with benign primary prognosis. Although WW domain-containing oxidoreductase (WWOX) has been related to breast tumorigenesis, its role in acquired tamoxifen-resistance has not yet been demonstrated. Our findings show that WWOX might be a valuable therapeutic target and prognostic marker for tamoxifen-resistance.

Screening of acetaminophen-induced alterations in epithelial-to-mesenchymal transition-related expression of microRNAs in a model of stem-like triple-negative breast cancer cells: The possible functional impacts

Current protocols for therapy inefficiently targets triple negative breast cancer and barely eradicate cancer stem cells. Elucidation of the pleiotropic effect of clinically proven therapeutics on cancer cells shed light on novel application of old friends. The pleiotropic effect of acetaminophen (APAP) on breast cancer was previously reported. In a cell model of triple negative breast cancer with stem-like CD44^high/CD24^low phenotype, we screened the impacts of APAP (1 mM, 72 h) on the Epithelial to mesenchymal transition (EMT)-related expression of miRs. APAP significantly overexpressed hsa-miR-130a-3p, 192-5p, 214-3p, 101-3p, 30d-5p, 10a-5p, 99a-5p, 200c-3p, 143-3p, 30b-5p and let-7f-5p showed significant overexpression, but suppressed the expression of hsa-miR-7-5p, 149-3p, 215, 150-5p, 205-5p, 206, 10b-5p, 20b-5p, 145-5p, 26b-5p, 223-3p, 17-5p, 186-5p, 146a-5p and let-7c. It also altered on the expression of selected EMT-related genes, significantly upregulated the expression of KRT19, AKT2, CD24, and TIMP1; but downregulated the expression of MMP2, ALDH1, MMP9, TWIST, NOTCH1, and AKT1. Such shifts in expression profiles increased the population of the cells with CD44^high/CD24^high, and CD44^low/CD24^high phenotypes, significantly reduced the Twist protein and shifted the balance of E-cadherin and Vimentin proteins in favor of differentiation. Treated cells showed a significant reduction of in vitro migration and were significantly chemosensitized to Camptothecin. In conclusion, APAP, at a safe clinical dose, induced a set of targeted alterations in the EMT-related miRs which implicate, even in part, significant mitigation in chemoresistance and in vitro migration. Further studies should also be piloted to elucidate the most crucial miRs and to evaluate its clinical effectiveness.

Genome editing reveals the function of Yorkie during the embryonic and early larval development in silkworm, Bombyx mori

As a transcriptional coactivator, Yorkie (Yki) is a major downstream target of the Hippo signalling pathway to regulate the organ size during animal development and regeneration. Previous microarray analysis in the silkworm, Bombyx mori, has shown that genes associated with the Hippo pathway were primarily expressed in gonads and imaginal discs. The RNA-interference-mediated silencing of Yki at the early wandering stage delayed B. mori development and ovary maturation, whereas baculovirus-mediated overexpression at the late larval instar facilitated organ growth and accelerated metamorphosis. Here, we employed CRISPR/Cas9-mediated mutagenesis to investigate the function of Yki in B. mori (BmYki) at the embryonic and early larval stages. Knocking out of BmYki led to reduced body size, moulting defects and, eventually, larval lethality. Sequence analysis of CRISPR/Cas9 mutants exhibited an array of deletions in BmYki. As a critical downstream effector of the Hippo kinase cassette, silencing of BmYki at the embryonic stage is indispensable and the consequence is lethal. Given that the Hippo signalling pathway is evolutionarily conserved, Yki has the potential to be a novel molecular target for genetic-based pest management practices.

Cloning and expression analysis of BmYki gene in silkworm, Bombyx mori

The transcriptional coactivator Yorkie(Yki), is a critical downstream effector of the Hippo(Hpo) signaling pathway that controls organ size through the regulation of cell proliferation and apoptosis. During the past ten years the biological function of Yki has been studied extensively in Drosophila and a few other insects, however, little is known about it in the silkworm, Bombyx mori, a major research model of lepidopteran insect. Here, we describe the isolation, characterization and expression of the B. mori Yki ortholog, BmYki. The coding sequence of the BmYki was 1314 bp in length, encoding a protein of 437 amino acids containing two conserved WW domains. BmYki transcripts were ubiquitous but not abundant in all detected tissues and developmental stages. Comparatively, it was expressed at pretty high level in silk glands and at the stage of fifth-instar day-3 larvae. Overexpression of BmYki in cultured B. mori embryonic cells significantly promoted transcription of genes associated with cell proliferation and apoptosis, indicating that BmYki functions in the regulation of organ growth-related biological processes. Interestingly, transcription of silk protein-coding genes and transcription factors regulating the synthesis of silk proteins was downregulated remarkably, suggesting that BmYki was involved in the regulation of silk protein synthesis. This study provides new insights into the role of BmYki in Hpo pathway regulation in silkworm.

The Notch pathway regulates both the proliferation and differentiation of follicular cells in the panoistic ovary of Blattella germanica

The Notch pathway is an essential regulator of cell proliferation and differentiation during development. Its involvement in insect oogenesis has been examined in insect species with meroistic ovaries, and it is known to play a fundamental role in cell fate decisions and the induction of the mitosis-to-endocycle switch in follicular cells (FCs). This work reports the functions of the main components of the Notch pathway (Notch and its ligands Delta and Serrate) during oogenesis in Blattella germanica, a phylogenetically basal species with panoistic ovary. As is revealed by RNAi-based analyses, Notch and Delta were found to contribute towards maintaining the FCs in an immature, non-apoptotic state. This ancestral function of Notch appears in opposition to the induction of transition from mitosis to endocycle that Notch exerts in Drosophila melanogaster, a change in the Notch function that might be in agreement with the evolution of the insect ovary types. Notch was also shown to play an active role in inducing ovarian follicle elongation via the regulation of the cytoskeleton. In addition, Delta and Notch interactions were seen to determine the differentiation of the posterior population of FCs. Serrate levels were found to be Notch-dependent and are involved in the control of the FC programme, although they would appear to play no crucial role in panoistic ovary oogenesis.