Taiman acts as a coactivator of Yorkie in the Hippo pathway to promote tissue growth and intestinal regeneration

Tai/NCOA2 suppresses the Hedgehog pathway by directly targeting the transcription factor Ci/GLI

The Hedgehog (Hh) pathway plays diverse roles in cellular processes by activating the transcription factor Cubitus interruptus (Ci). Abnormal regulation of this pathway has been linked to various human diseases. While previous studies have focused on how Ci is regulated in the cytoplasm, the control of nuclear Ci remains poorly understood. In this study, we have found that the transcriptional cofactor Taiman (Tai) functions as an inhibitor of the Hh pathway. Tai interferes with the response of Hh signal, rather than Hh secretion. Our epistatic analyses reveal that Tai works in parallel with Ci to reduce its activity, thereby counteracting organ overgrowth and the activation of target genes caused by Ci overexpression. Specifically, Tai interacts with Ci to decrease its binding to target gene promoters. The Hh signal weakens the interaction between Ci and Tai, releasing the inhibition on Ci. Importantly, this regulatory mechanism is conserved from Drosophila to mammalian cells. Moreover, NCOA1-3 are the mammalian ortholog of Drosophila protein Tai, but only NCOA2 plays a similar role in inhibiting the Hh pathway. These findings reveal an additional way to modulate the transcriptional activity of nuclear Ci.

The Drosophila EcR-Hippo component Taiman promotes epithelial cell fitness by control of the Dally-like glypican and Wg gradient

Rapidly dividing cells can eliminate slow growing neighbors through the apoptotic process of cell competition. This process ensures that only high fitness cells populate embryonic tissues and is proposed to underlie the ability of oncogene-transformed cells to progressively replace normal cells within a tissue. Patches of cells in the Drosophila wing disc overexpressing the oncogenic Taiman (Tai) transcriptional coactivator kill normal neighbors by secreting Spz ligands that trigger pro-apoptotic Toll signaling in receiving cells. However, extracellular signaling mechanisms responsible for elimination of slow growing cells by normal neighbors remain poorly defined. Here we show that slow growing cells with reduced Tai (Tailow) are killed by normal neighbors through a mechanism involving competition for the Wingless (Wg/Wnt) ligand. Elevated Wg signaling significantly rescues elimination of Tailow cells in multiple organs, suggesting that Tai may normally promote Wg activity. Examining distribution of Wg components reveals that Tai promotes extracellular spread of the Wg ligand from source cells across the wing disc, thus ensuring patterned expression of multiple Wg-regulated target genes. Tai controls Wg spread indirectly through the extracellular glypican Dally-like protein (Dlp), which binds Wg and promotes its extracellular diffusion and capture by receptors. Data indicate that Tai likely controls Dlp at two levels: transcription of dlp mRNA and Dlp intracellular trafficking. Overall, these data indicate that the Tai acts through Dlp to enable Wg transport and signaling, and that cell competition in the Tailow model arises due to inequity in the ability of epithelial cells to sequester limiting amounts of the Wg growth factor.

The roles of the native cell differentiation program aberrantly recapitulated in Drosophila intestinal tumors

Many tumors recapitulate the developmental and differentiation program of their tissue of origin, a basis for tumor cell heterogeneity. Although stem-cell-like tumor cells are well studied, the roles of tumor cells undergoing differentiation remain to be elucidated. We employ Drosophila genetics to demonstrate that the differentiation program of intestinal stem cells is crucial for enabling intestinal tumors to invade and induce non-tumor-autonomous phenotypes. The differentiation program that generates absorptive cells is aberrantly recapitulated in the intestinal tumors generated by activation of the Yap1 ortholog Yorkie. Inhibiting it allows stem-cell-like tumor cells to grow but suppresses invasiveness and reshapes various phenotypes associated with cachexia-like wasting by altering the expression of tumor-derived factors. Our study provides insight into how a native differentiation program determines a tumor's capacity to induce advanced cancer phenotypes and suggests that manipulating the differentiation programs co-opted in tumors might alleviate complications of cancer, including cachexia.

Conserved and Unique Roles of bHLH-PAS Transcription Factors in Insects - From Clock to Hormone Reception

A dozen bHLH-PAS transcription factors have evolved since the dawn of the animal kingdom; nine of them have mutual orthologs between arthropods and vertebrates. These proteins are master regulators in a range of developmental processes from organogenesis, nervous system formation and functioning, to cell fate decisions defining identity of limbs or photoreceptors for color vision. Among the functionally best conserved are bHLH-PAS proteins acting in the animal circadian clock. On the other side of the spectrum are fundamental physiological mechanisms such as those underlying xenobiotic detoxification, oxygen homeostasis, and metabolic adaptation to hypoxia, infection or tumor progression. Predictably, malfunctioning of bHLH-PAS regulators leads to pathologies. Performance of the individual bHLH-PAS proteins is modulated at multiple levels including dimerization and other protein-protein interactions, proteasomal degradation, and by binding low-molecular weight ligands. Despite the vast evolutionary gap dividing arthropods and vertebrates, and the differences in their anatomy, many functions of orthologous bHLH-PAS proteins are remarkably similar, including at the molecular level. Our phylogenetic analysis shows that one bHLH-PAS protein type has been lost during vertebrate evolution. This protein has a unique function as a receptor of the sesquiterpenoid juvenile hormones of insects and crustaceans. Although some other bHLH-PAS proteins are regulated by binding small molecules, the juvenile hormone receptor presents an unprecedented case, since all other non-peptide animal hormones activate members of the nuclear receptor family. The purpose of this review is to compare and highlight parallels and differences in functioning of bHLH-PAS proteins between insects and vertebrates.

The Drosophila ecdysone receptor promotes or suppresses proliferation according to ligand level

The steroid hormone 20-hydroxy-ecdysone (20E) promotes proliferation in Drosophila wing precursors at low titer but triggers proliferation arrest at high doses. Remarkably, wing precursors proliferate normally in the complete absence of the 20E receptor, suggesting that low-level 20E promotes proliferation by overriding the default anti-proliferative activity of the receptor. By contrast, 20E needs its receptor to arrest proliferation. Dose-response RNA sequencing (RNA-seq) analysis of ex vivo cultured wing precursors identifies genes that are quantitatively activated by 20E across the physiological range, likely comprising positive modulators of proliferation and other genes that are only activated at high doses. We suggest that some of these "high-threshold" genes dominantly suppress the activity of the pro-proliferation genes. We then show mathematically and with synthetic reporters that combinations of basic regulatory elements can recapitulate the behavior of both types of target genes. Thus, a relatively simple genetic circuit can account for the bimodal activity of this hormone.

Juvenile hormone membrane signaling phosphorylates USP and thus potentiates 20-hydroxyecdysone action in Drosophila

Juvenile hormone (JH) and 20-hydroxyecdysone (20E) coordinately regulate development and metamorphosis in insects. Two JH intracellular receptors, methoprene-tolerant (Met) and germ-cell expressed (Gce), have been identified in the fruit fly Drosophila melanogaster. To investigate JH membrane signaling pathway without the interference from JH intracellular signaling, we characterized phosphoproteome profiles of the Met gce double mutant in the absence or presence of JH in both chronic and acute phases. Functioning through a potential receptor tyrosine kinase and phospholipase C pathway, JH membrane signaling activated protein kinase C (PKC) which phosphorylated ultraspiracle (USP) at Ser35, the PKC phosphorylation site required for the maximal action of 20E through its nuclear receptor complex EcR-USP. The usp^S35A mutant, in which Ser was replaced with Ala at position 35 by genome editing, showed decreased expression of Halloween genes that are responsible for ecdysone biosynthesis and thus attenuated 20E signaling that delayed developmental timing. The usp^S35A mutant also showed lower Yorkie activity that reduced body size. Altogether, JH membrane signaling phosphorylates USP at Ser35 and thus potentiates 20E action that regulates the normal fly development. This study helps better understand the complex JH signaling network.

Hippo-Independent Regulation of Yki/Yap/Taz: A Non-canonical View

Initially identified in Drosophila, the Hippo signaling pathway has emerged as an evolutionarily conserved tumor suppressor pathway that controls tissue growth and organ size by simultaneously inhibiting cell proliferation and promoting cell death. Deregulation of Hippo pathway activity has been implicated in a wide range of human cancers. The core Hippo pathway consists of a kinase cascade: an upstream kinase Hippo (Hpo)/MST1/2 phosphorylates and activates a downstream kinase Warts (Wts)/Lats1/2, leading to phosphorylation and inactivation of a transcriptional coactivator Yki/YAP/Taz. Many upstream signals, including cell adhesion, polarity, mechanical stress, and soluble factors, regulate Hippo signaling through the kinase cascade, leading to change in the cytoplasmic/nuclear localization of Yki/YAP/Taz. However, recent studies have uncovered other mechanisms that regulate Yki/YAP/Taz subcellular localization, stability, and activity independent of the Hpo kinase cascade. These mechanisms provide additional layers of pathway regulation, nodes for pathway crosstalk, and opportunities for pathway intervention in cancer treatment and regenerative medicine.

The transcription factor of the Hippo signaling pathway, LmSd, regulates wing development in Locusta migratoria

Scalloped (Sd) is transcription factor that regulates cell proliferation and organ growth in the Hippo pathway. In the present research, LmSd was identified and characterized, and found to encode an N-terminal TEA domain and a C-terminal YBD domain. qRT-PCR showed that the LmSd transcription level was highest in the fifth-instar nymphs and very little was expressed in embryos. Tissue-specific analyses showed that LmSd was highly expressed in the wing. Immunohistochemistry indicated that LmSd was highly abundant in the head, prothorax, and legs during embryonic development. LmSd dsRNA injection resulted in significantly down-regulated transcription and protein expression levels compared with dsGFP injection. Gene silencing of LmSd resulted in deformed wings that were curved, wrinkled, and failed to fully expand. Approximately 40% of the nymphs had wing pads that were not able to close normally during molting from fifth-instar nymphs into adults. After silencing of LmSd, the transcription levels of cell division genes were suppressed and the expression levels of apoptosis genes were significantly up-regulated. Our results reveal that LmSd plays an important role in wing formation and development by controlling cell proliferation and inhibiting apoptosis.

Taiman negatively regulates the expression of antimicrobial peptides by promoting the transcription of cactus in Macrobrachium nipponense

In insects, Taiman (Tai) participates in the juvenile hormone, 20-hydroxyecdysone, insulin, and Hippo signaling pathways. However, the role of Tai in crustacean innate immunity is less known. In this study, four Tai isoforms (MnTai-A, MnTai-B, MnTai-C, and MnTai-D) produced by alternative splicing were identified from Macrobrachium nipponense. The obtained genome sequences indicated that MnTai DNA has more than 20 exons and 19 introns. The second to last (-exon2) and the third to last (-exon3) exons can be alternatively spliced. The loss of -exon2 or -exon3 produces MnTai-B or MnTai-C, respectively. Both exons are absent in MnTai-D. The full-length cDNA of MnTai-A (including all exons) was 6894 bp with an open reading frame of 4998 bp that encoded a protein of 1665 amino acids. MnTaiA contains the conservative structure of the Tai family and clustered with nuclear receptor coactivator from shrimp. All these four isoforms were widely distributed in a variety of tissues with the highest expression level in the hepatopancreas except MnTaiC. The transcriptional levels of total Tai genes (designated as MnTaiT) in the hepatopancreas and gills were regulated by bacterial or viral challenge. Knockdown of MnTaiT increased the expression of anti-microbial peptides (AMPs) during Vibrio parahaemolyticus infection. Further study indicated that the negative regulation of AMP gene expression by prawn Tai was mediated through its positive regulation of cactus. Our research provides valuable information that prawn Tai isoforms are involved in innate immunity.

Loss of ANCO1 repression at AIB1/YAP targets drives breast cancer progression

Transcription factors critical for the transition of normal breast epithelium to ductal carcinoma in situ (DCIS) and invasive breast cancer are not clearly defined. Here, we report that the expression of a subset of YAP-activated and YAP-repressed genes in normal mammary and early-stage breast cancer cells is dependent on the nuclear co-activator AIB1. Gene expression, sequential ChIP, and ChIP-seq analyses show that AIB1 and YAP converge upon TEAD for transcriptional activation and repression. We find that AIB1-YAP repression of genes at the 1q21.3 locus is mediated by AIB1-dependent recruitment of ANCO1, a tumor suppressor whose expression is progressively lost during breast cancer progression. Reducing ANCO1 reverts AIB1-YAP-dependent repression, increases cell size, and enhances YAP-driven aberrant 3D growth. Loss of endogenous ANCO1 occurs during DCIS xenograft progression, a pattern associated with poor prognosis in human breast cancer. We conclude that increased expression of AIB1-YAP co-activated targets coupled with a loss of normal ANCO1 repression is critical to patterns of gene expression that mediate malignant progression of early-stage breast cancer.

Silencing Taiman impairs larval development in Leptinotarsa decemlineata

An exploration of novel control strategies for Leptinotarsa decemlineata is becoming more pressing given rapid evolution of insecticide resistance and rise of production loss of potato. Dietary delivery of bacterially expressed double-stranded RNA (dsRNA) is a promising alternative for management. An important first step is to uncover possible RNA-interference (RNAi)-target genes effective against both young and old larvae. Taiman (Tai) is a basic-helix-loop-helix/Per-Arnt-Sim transcription factor that is involved in the mediation of both juvenile hormone (JH) and 20-hydroxyecdysone (20E) signaling. In the present paper, we found that continuous ingestion of dsTai for three days by third (penultimate)-instar larvae caused approximately 20% larval mortality and 80% pupation failure. The larval lethality resulted from failed cuticle and tracheae shedding, which subsequently reduced foliage consumption and nutrient absorption, and depleted lipid stores. In contrast, pupation failure derived from disturbed JH and 20E signals, and disordered nutrient homeostasis including, among others, inhibition of trehalose metabolism and reduction of chitin content. Knockdown of LdTai caused similar larval lethality and pupation impairment in second and fourth (final) larval instars. Therefore, LdTai is among the most attractive candidate genes for RNAi to control L. decemlineata larvae.

The Taiman Transcriptional Coactivator Engages Toll Signals to Promote Apoptosis and Intertissue Invasion in Drosophila

The Drosophila Taiman (Tai) protein is homologous to the human steroid-receptor coactivators SRC1-3 and activates transcription in complex with the 20-hydroxyecdysone (20E) receptor (EcR). Tai has roles in intestinal homeostasis, germline maintenance, cell motility, and proliferation through interactions with EcR and the coactivator Yorkie (Yki). Tai also promotes invasion of tumor cells in adjacent organs, but this pro-invasive mechanism is undefined. Here, we show that Tai expression transforms sessile pupal wing cells into an invasive mass that penetrates the adjacent thorax during a period of high 20E. Candidate analysis confirms a reliance on elements of the 20E and Hippo pathways, such as Yki and the Yki-Tai target dilp8. Screening the Tai-induced wing transcriptome detects enrichment for innate immune factors, including the Spätzle (Spz) family of secreted Toll ligands that induce apoptosis during cell competition. Tai-expressing wing cells induce immune signaling and apoptosis among adjacent thoracic cells, and genetic reduction of spz, Toll, or the rpr/hid/grim pro-apoptotic factors each suppresses invasion, suggesting an intercellular Spz-Toll circuit supports killing-mediated invasion. Modeling these interactions in larval epithelia confirms that Tai kills neighboring cells via a mechanism involving Toll, Spz factors, and the Spz inhibitor Necrotic. Tai-expressing cells evade death signals by repressing the immune deficiency (IMD) pathway, which operates in parallel to Toll to control nuclear factor κB (NF-κB) activity and independently regulates JNK activity. In sum, these findings suggest that Tai promotes competitive cell killing via Spz-Toll and that this killing mechanism supports pathologic intertissue invasion in Drosophila.

Importance of Taiman in Larval-Pupal Transition in Leptinotarsa decemlineata

Insect Taiman (Tai) binds to methoprene-tolerant to form a heterodimeric complex, mediating juvenile hormone (JH) signaling to regulate larval development and to prevent premature metamorphosis. Tai also acts as a steroid receptor coactivator of 20-hydroxyecdysone (20E) receptor heterodimer, ecdysone receptor (EcR) and Ultraspiracle (USP), to control the differentiation of early germline cells and the migration of specific follicle cells and border cells in ovaries in several insect species. In holometabolous insects, however, whether Tai functions as the coactivator of EcR/USP to transduce 20E message during larval-pupal transition is unknown. In the present paper, we found that the LdTai mRNA levels were positively correlated with circulating JH and 20E titers in Leptinotarsa decemlineata; and ingestion of either JH or 20E stimulated the transcription of LdTai. Moreover, RNA interference (RNAi)-aided knockdown of LdTai at the fourth (final) instar stage repressed both JH and 20E signals, inhibited larval growth and shortened larval developing period. The knockdown caused 100% larval lethality due to failure of larval-pupal ecdysis. Under the apolysed larval cuticle, the LdTai RNAi prepupae possessed pupal thorax. In contrast, the process of tracheal ecdysis was uncompleted. Neither JH nor 20E rescued the aforementioned defectives in LdTai RNAi larvae. It appears that Tai mediates both JH and 20E signaling. Our results uncover a link between JH and 20E pathways during metamorphosis in L. decemlineata.

Exploring the Role of Insulin Signaling in Relative Growth: A Case Study on Wing-Body Scaling in Lepidoptera

Adult forms emerge from the relative growth of the body and its parts. Each appendage and organ has a unique pattern of growth that influences the size and shape it attains. This produces adult size relationships referred to as static allometries, which have received a great amount of attention in evolutionary and developmental biology. However, many questions remain unanswered, for example: What sorts of developmental processes coordinate growth? And how do these processes change given variation in body size? It has become increasingly clear that nutrition is one of the strongest influences on size relationships. In insects, nutrition acts via insulin/TOR signaling to facilitate inter- and intra-specific variation in body size and appendage size. Yet, the mechanism by which insulin signaling influences the scaling of growth remains unclear. Here we will discuss the potential roles of insulin signaling in wing-body scaling in Lepidoptera. We analyzed the growth of wings in animals reared on different diet qualities that induce a range of body sizes not normally present in our laboratory populations. By growing wings in tissue culture, we survey how perturbation and stimulation of insulin/TOR signaling influences wing growth. To conclude, we will discuss the implications of our findings for the development and evolution of organismal form.