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In The Origin of Species, Darwin proposed that the complex eyes of animals evolved from a simple prototype consisting of two cells only, a photoreceptor cell and a pigment cell shielding the light from one side and allowing for a directional vision. The discovery of Pax6 as a master control gene for eye development in bilateria lends considerable support to the hypothesis of a monophyletic origin of the metazoan eyes from a Darwinian prototype. Pax6 is found in all bilateria and it is capable of inducing ectopic eyes in both vertebrates and invertebrates. The Darwinian prototype eyes have been found in nature in certain planarians and in the trochophora larvae of Platynereis, an annelid worm, where they were found to express Pax6. The prototypic eye must have evolved from a single cell. Such a single-celled pigmented photoreceptor has been found in the larvae of Tripedalia, a jellyfish, whereas the adult has multicellular lens eyes. We propose that the evolution of the prototypic eye started with a first step of cellular differentiation from a single-celled pigmented photoreceptor, into two cell types: a photoreceptor cell specified by Pax6, and a pigment cell specified by the microphthalmia transcription factor (Mitf), which is also conserved from jellyfish to humans. From the prototypic eye more complex eyes can evolve by intercalating additional genes into the eye developmental pathway by gene duplication and subsequent divergence or by enhancer fusion. [ABSTRACT FROM AUTHOR]

Abstract: The homeobox gene orthodenticle (otd) controls the process of regional specification that takes place in the Drosophila eye-antennal disc during ocelli development. Mutations that reduce or abolish otd expression in the ocelli primordium give rise to ocelliless flies. We have identified the cis-regulatory sequence (ocelliless enhancer) that controls otd expression during ocelli development and studied its regulation at the molecular level. The ocelliless enhancer is initially activated by the combined action of Wingless (Wg) and Hedgehog (Hh) signaling pathways. Later, a positive autoregulatory feedback loop sets in to maintain otd expression. Moreover, we have analyzed the role of otd during ocelli primordium development and determined its involvement in the expression of the retinal determination gene eyes absent (eya). otd indirectly regulates eya in ocellar precursor cells through the inhibition of wg, an eya repressor, and the maintenance of hh expression in the ocelli primordium. Hh signaling is necessary for eya activation in ocellar precursor cells and this activation is mediated by the full-length activator form of the transcription factor Cubitus interruptus. [Copyright &y& Elsevier]

In Drosophila, the sine oculis (so) gene is important for the development of the entire visual system, including Bolwig's organ, compound eyes and ocelli. Together with twin of eyeless, eyeless, eyes absent and dachshund, so belongs to a network of genes that by complex interactions initiate eye development. Although much is known about the genetic interactions of the genes belonging to this retinal determination network, only a few such regulatory interactions have been analysed down to the level of DNA-protein interactions. Previous work in our laboratory identified an eye/ocellus specific enhancer of the sine oculis gene that is directly regulated by eyeless and twin of eyeless. We further characterized this regulatory element and identified a minimal enhancer fragment of so that sets up an autoregulatory feedback loop crucial for proper ocelli development. By systematic analysis of the DNA-binding specificity of so we identified the most important nucleotides for this interaction. Using the emerging consensus sequence for SO-DNA binding we performed a genome-wide search and have thereby been able to identify eyeless as well as the signalling gene hedgehog as putative targets of so. Our results strengthen the general assumption that feedback loops among the genes of the retinal determination network are crucial for proper development of eyes and ocelli. [ABSTRACT FROM AUTHOR]

We reported previously the identification of three homeobox-containing genes, proxl, prox2 and prox3, in sponges [Seimiya, M., Ishiguro, H, Miura, K., Watanabe, Y. & Kurosawa, Y. (1994) Eur: J. Biochem. 221, 219-225]. The transcripts of prox1 and prox2 were identified in cells at all stages of differentiation. In the present study, we have identified two POU-class homeobox genes, designated spou-I and spou-2, in a freshwater sponge (Ephydatia fluviatilis). These genes each encode a POU-specific domain and a POU-type homeodomain. The amino acid sequences of the POU-specific domain and the POU-type homeodomain encoded by the spou-1 gene were 76 % and 67 % similar to those of the human Pit-1 gene, respectively. The amino acid sequence of the POU-specific domain encoded by the spou-2 gene was also most similar to that encoded by the human Pit-1 gene among all the POU-class homeobox genes that have been sequenced to date. in contrast to the results for prox1 and prox2, transcripts of the spou-1 and spou-2 genes were identified in cells only at specific stages during the diferentiation of the sponge. [ABSTRACT FROM AUTHOR]

The development of cancer has been associated with the gradual acquisition of genetic alterations leading to a progressive increase in malignancy. In various cancer types this process is enabled and accelerated by genome instability. While genome sequencing-based analysis of tumor genomes becomes increasingly a standard procedure in human cancer research, the potential necessity of genome instability for tumorigenesis in Drosophila melanogaster has, to our knowledge, never been determined at DNA sequence level. Therefore, we induced formation of tumors by depletion of the Drosophila tumor suppressor Polyhomeotic and subjected them to genome sequencing. To achieve a highly resolved delineation of the genome structure we developed the Deterministic Structural Variation Detection (DSVD) algorithm, which identifies structural variations (SVs) with high accuracy and at single base resolution. The employment of long overlapping paired-end reads enables DSVD to perform a deterministic, i.e. fragment size distribution independent, identification of a large size spectrum of SVs. Application of DSVD and other algorithms to our sequencing data reveals substantial genetic variation with respect to the reference genome reflecting temporal separation of the reference and laboratory strains. The majority of SVs, constituted by small insertions/deletions, is potentially caused by erroneous replication or transposition of mobile elements. Nevertheless, the tumor did not depict a loss of genome integrity compared to the control. Altogether, our results demonstrate that genome stability is not affected inevitably during sustained tumor growth in Drosophila implying that tumorigenesis, in this model organism, can occur irrespective of genome instability and the accumulation of specific genetic alterations. [ABSTRACT FROM AUTHOR]

Cells assemble fibronectin, the major extracellular matrix (ECM) protein, into fibrillar matrices, which serve as 3D architectural scaffolds to provide, together with other ECM proteins tissue-specific environments. Although recent approaches enable to bioengineer 3D fibrillar fibronectin matrices in vitro , it remains elusive how fibronectin can be co-assembled with other ECM proteins into complex 3D fibrillar matrices that recapitulate tissue-specific compositions and cellular responses. Here, we introduce the engineering of fibrillar fibronectin-templated 3D matrices that can be complemented with other ECM proteins, including vitronectin, collagen, and laminin to resemble ECM architectures observed in vivo. For the co-assembly of different ECM proteins, we employed their innate fibrillogenic mechanisms including shear forces, pH-dependent electrostatic interactions, or specific binding domains. Through recapitulating various tissue-specific ECM compositions and morphologies, the large scale multi-composite 3D fibrillar ECM matrices can guide fibroblast adhesion, 3D fibroblast tissue formation, or tissue morphogenesis of epithelial cells. In other examples, we customize multi-composite 3D fibrillar matrices to support the growth of signal propagating neuronal networks and of human brain organoids. We envision that these 3D fibrillar ECM matrices can be tailored in scale and composition to modulate tissue-specific responses across various biological length scales and systems, and thus to advance manyfold studies of cell biological systems. [Display omitted] • We engineer 3D multi-composite fibrillar ECMs of well-defined compositions of key ECM proteins (including fibronectin, laminin, collagen, or vitronectin) such as needed by various tissues. • The multi-composite ECMs are free-standing, easy-to-produce, scalable, transferable for surface functionalization, and mimic the nano-and micro-fibrillar architecture of native ECMs. • The multi-composite ECMs can evoke cellular responses across various biological and temporal scales, from single cells to complex multicellular structures like tissues or organoids, spanning from initial cell attachment to extended culture periods of weeks. [ABSTRACT FROM AUTHOR]

Abstract: The homeobox gene sine oculis (so) is required for the development of the entire visual system in Drosophila, which includes the compound eyes, the ocelli, the optic lobe of the brain and the Bolwig''s organ. During ocelli development, so expression labels, together with eyes absent (eya), the emergence of the ocellar precursor cells in the third instar eye-antennal disc. Footprinting and misexpression studies have led to the proposal that the Pax6 homologue twin of eyeless (toy) directly regulates the initiation of so expression in ocellar precursor cells. However, so expression in a toy loss-of-function mutant background has not been yet analyzed due to the lack of eye-antennal disc development in strong toy mutant alleles. Using an embryonic eye primordium-specific enhancer of toy, we have rescued the developmental defect of a strong toy mutant allele and analyzed so expression in the ocelli primordium of toy loss-of-function eye-antennal discs during third instar larva. The results show that so expression is only marginally affected in the absence of Toy transcriptional activity and that the toy positive effect on so expression is largely eya-mediated. These results suggest that eya is the main factor controlling both initiation and maintenance of so expression in ocellar precursor cells. In addition, we present the characterization of a new minimal eye/ocellus-specific enhancer of the so gene. [Copyright &y& Elsevier]

Pax6 genes encode transcription factors with two DNA-binding domains that are highly conserved during evolution. In Drosophila, two Pax6 genes function in a pathway in which twin of eyeless (toy) directly regulates eyeless (ey), which is necessary for initiating the eye developmental pathway. To investigate the gene duplication of Pax6 that occurred in holometabolous insects like Drosophila and silkworm, we used different truncated forms of toy and small eyes (sey), and tested their capacity to induce ectopic eye development in an ey-independent manner. Even though the Paired domains of TOY and SEY have DNA-binding properties that differ from those of the Paired domain of EY, they all are capable of inducing ectopic eye development in an ey mutant background. We also show that one of the main functional differences between toy and ey lies in the C-terminal region of their protein products, implying differences in their transactivation potential. Furthermore, we show that only the homeodomain (HD) of EY is able to downregulate the expression of Distal-less (Dll), a feature that is required during endogenous eye development. These results suggest distinct functions of the two DNA-binding domains of TOY and EY, and significant evolutionary divergence between the two Drosophila Pax6 genes. [ABSTRACT FROM AUTHOR]