E93 controls adult differentiation by repressing in .

In , successful development relies on the precise coordination of both spatial and temporal regulatory axes. The temporal axis governs stage-specific identity and developmental transitions through a number of genes, collectively forming the . Among these, Ecdysone inducible protein 93F (E93) serves as the critical determinant for adult specification, but its mechanism of action remains unclear.

Evolution of tissue-specific expression of ancestral genes across vertebrates and insects.

Regulation of gene expression is arguably the main mechanism underlying the phenotypic diversity of tissues within and between species. Here we assembled an extensive transcriptomic dataset covering 8 tissues across 20 bilaterian species and performed analyses using a symmetric phylogeny that allowed the combined and parallel investigation of gene expression evolution between vertebrates and insects. We specifically focused on widely conserved ancestral genes, identifying strong cores of pan-bilaterian tissue-specific genes and even larger groups that diverged to define vertebrate and insect tissues.

TGFß/activin-dependent activation of Torso controls the timing of the metamorphic transition in the red flour beetle Tribolium castaneum.

Understanding the mechanisms governing body size attainment during animal development is of paramount importance in biology. In insects, a crucial phase in determining body size occurs at the larva-pupa transition, marking the end of the larval growth period. Central to this process is the attainment of the threshold size (TS), a critical developmental checkpoint that must be reached before the larva can undergo metamorphosis.

Nuclear receptors EcR-A/RXR and HR3 control early embryogenesis in the short-germ hemimetabolous insect .

The role of steroid hormone signaling during insect post-embryonic development has been extensively characterized. However, its function during embryonic development is less understood, particularly in short-germ band hemimetabolous insects. To solve this, we have used to analyze the embryonic functions of the heterodimeric ecdysone receptor, BgEcR-A and BgRXR.

Antagonistic role of the BTB-zinc finger transcription factors Chinmo and Broad-Complex in the juvenile/pupal transition and in growth control.

During development, the growing organism transits through a series of temporally regulated morphological stages to generate the adult form. In humans, for example, development progresses from childhood through to puberty and then to adulthood, when sexual maturity is attained. Similarly, in holometabolous insects, immature juveniles transit to the adult form through an intermediate pupal stage when larval tissues are eliminated and the imaginal progenitor cells form the adult structures.

Activation of EGFR signaling by Tc-Vein and Tc-Spitz regulates the metamorphic transition in the red flour beetle Tribolium castaneum.

Animal development relies on a sequence of specific stages that allow the formation of adult structures with a determined size. In general, juvenile stages are dedicated mainly to growth, whereas last stages are devoted predominantly to the maturation of adult structures. In holometabolous insects, metamorphosis marks the end of the growth period as the animals stops feeding and initiate the final differentiation of the tissues.

How stage identity is established in insects: the role of the Metamorphic Gene Network.

Proper formation of adult insects requires the integration of spatial and temporal regulatory axes. Whereas spatial information confers identity to each tissue, organ and appendage, temporal information specifies at which stage of development the animal is. Regardless of the type of post-embryonic development, either hemimetabolous or holometabolous, temporal specificity is achieved through interactions between the temporal identity genes Kr-h1, E93 and Br-C, whose sequential expression is controlled by the two major developmental hormones, 20-hydroxyecdysone and Juvenile hormone.

Egfr Signaling Is a Major Regulator of Ecdysone Biosynthesis in the Drosophila Prothoracic Gland.

Understanding the mechanisms that determine final body size of animals is a central question in biology. In animals with determinate growth, such as mammals or insects, the size at which the immature organism transforms into the adult defines the final body size, as adult individuals do not grow [1]. In Drosophila, the growth period ends when the immature larva undergoes the metamorphic transition to develop the mature adult [2].

Dual role of FGF in proliferation and endoreplication of Drosophila tracheal adult progenitor cells.

Adult progenitor cells activation is a key event in the formation of adult organs. In Drosophila, formation of abdominal adult trachea depends on the specific activation of tracheal adult progenitors (tracheoblasts) at the Tr4 and Tr5 spiracular branches. Proliferation of these tracheoblasts generates a pool of tracheal cells that migrate toward the posterior part of the trachea by the activation of the branchless/fibroblast growth factor (Bnl/FGF) signaling to form the abdominal adult trachea.

Target of rapamycin (TOR) determines appendage size during pupa formation of the red flour beetle Tribolium castaneum.

The adult body size is species-specific and controlled by complex interactions between hormones and the IIS/TOR pathway. To analyze the role of target of rapamycin (TOR) in the growth and development of the insect, expression levels of TOR were silenced in the model and pest insect red flour beetle, Tribolium castaneum. Injection of dsRNA into the last larval instar decreased pupal mass and size, while the amount of food intake by the larvae was not affected.

Upregulation of E93 Gene Expression Acts as the Trigger for Metamorphosis Independently of the Threshold Size in the Beetle Tribolium castaneum.

Body size in holometabolous insects is determined by the size at which the juvenile larva undergoes metamorphosis to the pupal stage. To undergo larva-pupa transition, larva must reach a critical developmental checkpoint, the threshold size (TS); however, the molecular mechanisms through which the TS cues this transition remain to be fully characterized. Here, we use the flour beetle Tribolium castaneum to characterize the molecular mechanisms underlying entry into metamorphosis.

Differential roles of the Drosophila EMT-inducing transcription factors Snail and Serpent in driving primary tumour growth.

Several transcription factors have been identified that activate an epithelial-to-mesenchymal transition (EMT), which endows cells with the capacity to break through basement membranes and migrate away from their site of origin. A key program in development, in recent years it has been shown to be a crucial driver of tumour invasion and metastasis. However, several of these EMT-inducing transcription factors are often expressed long before the initiation of the invasion-metastasis cascade as well as in non-invasive tumours.

Genetic basis for the evolution of organ morphogenesis: the case of spalt and cut in the development of insect trachea.

It is not clear how simple genetic changes can account for the coordinated variations that give rise to modified functional organs. Here, we addressed this issue by analysing the expression and function of regulatory genes in the developing tracheal systems of two insect species. The larval tracheal system of Drosophila can be distinguished from the less derived tracheal system of the beetle Tribolium by two main features.

The Occurrence of the Holometabolous Pupal Stage Requires the Interaction between E93, Krüppel-Homolog 1 and Broad-Complex.

Complete metamorphosis (Holometaboly) is a key innovation that underlies the spectacular success of holometabolous insects. Phylogenetic analyses indicate that Holometabola form a monophyletic group that evolved from ancestors exhibiting hemimetabolous development (Hemimetaboly). However, the nature of the changes underlying this crucial transition, including the occurrence of the holometabolan-specific pupal stage, is poorly understood.

FGF coordinates air sac development by activation of the EGF ligand Vein through the transcription factor PntP2.

How several signaling pathways are coordinated to generate complex organs through regulation of tissue growth and patterning is a fundamental question in developmental biology. The larval trachea of Drosophila is composed of differentiated functional cells and groups of imaginal tracheoblasts that build the adult trachea during metamorphosis. Air sac primordium cells (ASP) are tracheal imaginal cells that form the dorsal air sacs that supply oxygen to the flight muscles of the Drosophila adult.

Specification of differentiated adult progenitors via inhibition of endocycle entry in the Drosophila trachea.

A population of Drosophila adult tracheal progenitor cells arises from differentiated cells of the larval main trachea that retain the ability to reenter the cell cycle and give rise to the multiple adult tracheal cell types. These progenitors are unique to the second tracheal metamere as homologous cells from other segments, express fizzy-related (fzr), the Drosophila homolog of CDH1 protein of the APC complex, and enter endocycle and do not contribute to adult trachea. Here, we examine the mechanisms for their quiescence and show that they reenter the cell cycle by expression of string/cdc25 through ecdysone.

Transcription factor E93 specifies adult metamorphosis in hemimetabolous and holometabolous insects.

All immature animals undergo remarkable morphological and physiological changes to become mature adults. In winged insects, metamorphic changes either are limited to a few tissues (hemimetaboly) or involve a complete reorganization of most tissues and organs (holometaboly). Despite the differences, the genetic switch between immature and adult forms in both types of insects relies on the disappearance of the antimetamorphic juvenile hormone (JH) and the transcription factors Krüppel-homolog 1 (Kr-h1) and Broad-Complex (BR-C) during the last juvenile instar.

Cancer becomes wasteful: emerging roles of exosomes(†) in cell-fate determination.

Extracellular vesicles (EVs), including exosomes, have been widely recognized for their role in intercellular communication of the immune response system. In the past few years, significance has been given to exosomes in the induction and modulation of cell-fate-inducing signalling pathways, such as the Hedgehog (Hh), Wnts, Notch, transforming growth factor (TGF-β), epidermal growth factor (EGF) and fibroblast growth factor (FGF) pathways, placing them in the wider context of development and also of cancer. These protein families induce signalling cascades responsible for tissue specification, homeostasis and maintenance.

Conserved and divergent elements in Torso RTK activation in Drosophila development.

The repeated use of signalling pathways is a common phenomenon but little is known about how they become co-opted in different contexts. Here we examined this issue by analysing the activation of Drosophila Torso receptor in embryogenesis and in pupariation. While its putative ligand differs in each case, we show that Torso-like, but not other proteins required for Torso activation in embryogenesis, is also required for Torso activation in pupariation.

Specific GATA factors act as conserved inducers of an endodermal-EMT.

The epithelial-to-mesenchymal transition (EMT) converts cells from static epithelial to migratory mesenchymal states (Hay, 1995). Here, we demonstrate that EMT in the Drosophila endoderm is dependent on the GATA-factor Serpent (Srp), and that Srp acts as a potent trigger for this transition when activated ectopically. We show that Srp affects endodermal-EMT through a downregulation of junctional dE-Cadherin (dE-Cad) protein, without a block in its transcription.

A genome-wide RNA interference screen identifies two novel components of the metazoan secretory pathway.

Genetic screens in the yeast Saccharomyces cerevisiae have identified many proteins involved in the secretory pathway, most of which have orthologues in higher eukaryotes. To investigate whether there are additional proteins that are required for secretion in metazoans but are absent from yeast, we used genome-wide RNA interference (RNAi) to look for genes required for secretion of recombinant luciferase from Drosophila S2 cells. This identified two novel components of the secretory pathway that are conserved from humans to plants.

Wingless promotes proliferative growth in a gradient-independent manner.

Morphogens form concentration gradients that organize patterns of cells and control growth. It has been suggested that, rather than the intensity of morphogen signaling, it is its gradation that is the relevant modulator of cell proliferation. According to this view, the ability of morphogens to regulate growth during development depends on their graded distributions.

Glypican-mediated endocytosis of Hedgehog has opposite effects in flies and mice.

Glypicans are glycosylphosphatidylinositol-linked heparan sulfate proteoglycans that play an essential part in the regulation of morphogen signalling. Two new reports using Drosophila and mice have highlighted the importance of glypican endocytosis in the regulation of Hedgehog (Hh) signalling and in Wingless gradient formation. One Drosophila glypican, Dally-like, acts positively in Hh signalling, whereas mouse Glypican-3 is a negative regulator.