Biomedical subjects

G Halder

Publications and source records attributed to G Halder.

12 recordsLinked to original sources

PubMed1999

Ultrabithorax function in butterfly wings and the evolution of insect wing patterns.

BACKGROUND: . The morphological and functional evolution of appendages has played a critical role in animal evolution, but the developmental genetic mechanisms underlying appendage diversity are not understood. Given that homologous appendage development is controlled by the same Hox gene in different organisms, and that Hox genes are transcription factors, diversity may evolve from changes in the regulation of Hox target genes. Two impediments to understanding the role of Hox genes in morphological evolution have been the limited number of organisms in which Hox gene function can be studied and the paucity of known Hox-regulated target genes. We have therefore analyzed a butterfly homeotic mutant 'Hindsight', in which portions of the ventral hindwing pattern are transformed to ventral forewing identity, and we have compared the regulation of target genes by the Ultrabithorax (Ubx) gene product in Lepidopteran and Dipteran hindwings. RESULTS: . We show that Ubx gene expression is lost from patches of cells in developing Hindsight hindwings, correlating with changes in wing pigmentation, color pattern elements, and scale morphology. We use this mutant to study how regulation of target genes by Ubx protein differs between species. We find that several Ubx-regulated genes in the Drosophila haltere are not repressed by Ubx in butterfly hindwings, but that Distal-less (Dll) expression is regulated by Ubx in a unique manner in butterflies. CONCLUSIONS: . The morphological diversification of insect hindwings has involved the acquisition of different sets of target genes by Ubx in different lineages. Changes in Hox-regulated target gene sets are, in general, likely to underlie the morphological divergence of homologous structures between animals.

Animals↗

PubMed1999

twin of eyeless, a second Pax-6 gene of Drosophila, acts upstream of eyeless in the control of eye development.

The Drosophila Pax-6 gene eyeless (ey) plays a key role in eye development. Here we show tht Drosophila contains a second Pax-6 gene, twin of eyeless (toy), due to a duplication during insect evolution. Toy is more similar to vertebrate Pax-6 proteins than Ey with regard to overall sequence conservation, DNA-binding function, and early expression in the embryo, toy and ey share a similar expression pattern in the developing visual system, and targeted expression of Toy, like Ey, induces the formation of ectopic eyes. Genetic and biochemical evidence indicates, however, that Toy functions upstream of ey by directly regulating the eye-specific enhancer of ey. Toy is therefore required for initiation of ey expression in the embryo and acts through Ey to activate the eye developmental program.

Amino Acid Sequence↗

PubMed1999

Signaling by the TGF-beta homolog decapentaplegic functions reiteratively within the network of genes controlling retinal cell fate determination in Drosophila.

Retinal cell fate determination in Drosophila is controlled by an interactive network of genes, including eyeless, eyes absent, sine oculis and dachshund. We have investigated the role of the TGF-beta homolog decapentaplegic in this pathway. We demonstrate that, during eye development, while eyeless transcription does not depend on decapentaplegic activity, the expression of eyes absent, sine oculis and dachshund are greatly reduced in a decapentaplegic mutant background. We also show that decapentaplegic signaling acts synergistically with and at multiple levels of the retinal determination network to induce eyes absent, sine oculis and dachshund expression and ectopic eye formation. These results suggest a mechanism by which a general patterning signal such as Decapentaplegic cooperates reiteratively with tissue-specific factors to determine distinct cell fates during development.

Animals↗

PubMed1998

The Vestigial and Scalloped proteins act together to directly regulate wing-specific gene expression in Drosophila.

A small number of major regulatory (selector) genes have been identified in animals that control the development of particular organs or complex structures. In Drosophila, the vestigial gene is required for wing formation and is able to induce wing-like outgrowths on other structures. However, the molecular function of the nuclear Vestigial protein, which bears no informative similarities to other proteins, was unknown. Here, we show that Vestigial requires the function of the Scalloped protein, a member of the TEA family of transcriptional regulators, to directly activate the expression of genes involved in wing morphogenesis. Genetic and molecular analyses reveal that Vestigial regulates wing identity by forming a complex with the Scalloped protein that binds sequence specifically to essential sites in wing-specific enhancers. These enhancers also require the direct inputs of signaling pathways, and the response of an enhancer can be switched to another pathway through changes in signal-transducer binding sites. Combinatorial regulation by selector proteins and signal transducers is likely to be a general feature of the tissue-specific control of gene expression during organogenesis.

Animals↗

PubMed1998

Ultrabithorax regulates genes at several levels of the wing-patterning hierarchy to shape the development of the Drosophila haltere.

Arthropods and vertebrates are constructed of many serially homologous structures whose individual patterns are regulated by Hox genes. The Hox-regulated target genes and developmental pathways that determine the morphological differences between any homologous structures are not known. The differentiation of the Drosophila haltere from the wing through the action of the Ultrabithorax (Ubx) gene is a classic example of Hox regulation of serial homology, although no Ubx-regulated genes in the haltere have been identified previously. Here, we show that Ubx represses the expression of the Wingless (Wg) signaling protein and a subset of Wg- and Decapentaplegic-activated genes such as spalt-related, vestigial, Serum Response Factor, and achaete-scute, whose products regulate morphological features that differ between the wing and haltere. In addition, we found that some genes in the same developmental pathway are independently regulated by Ubx. Our results suggest that Ubx, and Hox genes in general, independently and selectively regulate genes that act at many levels of regulatory hierarchies to shape the differential development of serially homologous structures.

Animals↗

PubMed1998

Eyeless initiates the expression of both sine oculis and eyes absent during Drosophila compound eye development.

The Drosophila Pax-6 gene eyeless acts high up in the genetic hierarchy involved in compound eye development and can direct the formation of extra eyes in ectopic locations. Here we identify sine oculis and eyes absent as two mediators of the eye-inducing activity of eyeless. We show that eyeless induces and requires the expression of both genes independently during extra eye development. During normal eye development, eyeless is expressed earlier than and is required for the expression of sine oculis and eyes absent, but not vice versa. Based on the results presented here and those of others, we propose a model in which eyeless induces the initial expression of both sine oculis and eyes absent in the eye disc. sine oculis and eyes absent then appear to participate in a positive feedback loop that regulates the expression of all three genes. In contrast to the regulatory interactions that occur in the developing eye disc, we also show that in the embryonic head, sine oculis acts in parallel to eyeless and twin of eyeless, a second Pax-6 gene from Drosophila. Recent studies in vertebrate systems indicate that the epistatic relationships among the corresponding vertebrate homologs are very similar to those observed in Drosophila.

Animals↗

PubMed1997

Squid Pax-6 and eye development.

Pax-6 in vertebrates and its homolog eyeless in Drosophila are known to be essential for eye development. Here we investigate the role of Pax-6 in eye development in another major systematic group, molluscs. We demonstrate that alternatively spliced RNAs derived from a single Pax-6 gene in the squid (Loligo opalescens) are expressed in the embryonic eye, olfactory organ, brain, and arms. Despite significant sequence differences between squid Pax-6 and Drosophila eyeless in the region outside the paired- and homeodomains, squid Pax-6 is able to induce the formation of ectopic eyes in Drosophila. Our results support the idea that Pax-6 related genes are necessary for eye and olfactory system formation throughout the animal kingdom.

Amino Acid Sequence↗

PubMed1997

PAX-6 in development and evolution.

Pax-6 is a member of the Pax gene class and encodes a protein containing a paired domain and a homeodomain. The molecular characterization of Pax-6 genes from species of different animal phyla and the analysis of Pax-6 function in the developing eyes and central nervous system of vertebrates, Drosophila melanogaster, and Caenorhabditis elegans suggest that Pax-6 homologues share conserved functions. In this review, we present recent data on the structural and functional characterization of Pax-6 homologues from species of different animal phyla. We discuss the implications of these findings for our understanding of the development and evolution of eyes and nervous systems.

Animals↗

PubMed1997

Conservation of Pax-6 in a lower chordate, the ascidian Phallusia mammillata.

The Pax-6 genes of vertebrates and invertebrates encode transcription factors with both a paired domain and a homeodomain. They are expressed in the developing eye and in the central nervous system. Loss-of-function mutations in mammals and in flies result in a reduction or absence of eyes and targeted expression of the Drosophila and the mouse Pax-6 genes induces ectopic eye structures in Drosophila. These findings lead to the proposal that the morphogenesis of the different types of eyes is controlled by a Pax-6-dependent genetic pathway and that the various eye types are of monophyletic origin. We have isolated a Pax-6 homologous gene from the ascidian Phallusia mammillata, because ascidians occupy an important position in early chordate evolution. Furthermore, the Phallusia larva has a simple photosensitive ocellus. Phallusia Pax-6 shares extensive sequence identity and conserved genomic organization with the known Pax-6 genes of vertebrates and invertebrates. Expression of Phallusia Pax-6 is first detected at late gastrula stages in distinct regions of the developing neural plate. At the tailbud stage, it is expressed in the spinal cord and the brain vesicle, where the sensory organs (ocellus and otolith) form, suggesting an important function in their development. Ectopic expression of the ascidian Pax-6 gene in Drosophila leads to the induction of supernumerary eyes indicating a highly conserved gene regulatory function for Pax-6 genes.

Amino Acid Sequence↗

PubMed1995

Induction of ectopic eyes by targeted expression of the eyeless gene in Drosophila.

The Drosophila gene eyeless (ey) encodes a transcription factor with both a paired domain and a homeodomain. It is homologous to the mouse Small eye (Pax-6) gene and to the Aniridia gene in humans. These genes share extensive sequence identity, the position of three intron splice sites is conserved, and these genes are expressed similarly in the developing nervous system and in the eye during morphogenesis. Loss-of-function mutations in both the insect and in the mammalian genes have been shown to lead to a reduction or absence of eye structures, which suggests that ey functions in eye morphogenesis. By targeted expression of the ey complementary DNA in various imaginal disc primordia of Drosophila, ectopic eye structures were induced on the wings, the legs, and on the antennae. The ectopic eyes appeared morphologically normal and consisted of groups of fully differentiated ommatidia with a complete set of photoreceptor cells. These results support the proposition that ey is the master control gene for eye morphogenesis. Because homologous genes are present in vertebrates, ascidians, insects, cephalopods, and nemerteans, ey may function as a master control gene throughout the metazoa.

Animals↗

PubMed1995

New perspectives on eye evolution.

The highly complex eyes of vertebrates, insects and molluscs have long been considered to be of independent evolutionary origin. Recently, however, Pax-6, a highly conserved transcription factor, has been identified as a key regulator of eye development in both mammals and flies. Homologues of Pax-6 have also been identified in species from other phyla, including molluscs. The wide variety of eyes in the animal kingdom may, therefore, have evolved from a single ancestral photosensitive origin.

Animals↗

PubMed1994

Muscle LIM protein, a novel essential regulator of myogenesis, promotes myogenic differentiation.

Muscle LIM protein (MLP) is a novel positive regulator of myogenesis. Its expression and that of its Drosophila homolog DMLP1 are enriched in striated muscle and coincide with myogenic differentiation. In the absence of MLP, induced C2 cells express myogenin but fail to exit from the cell cycle and to differentiate. Over-expression of MLP in C2 myoblasts potentiates myogenic differentiation and reduces its sensitivity to TGF beta. Like MLP, single LIM domain deletion mutants of MLP and nonmuscle LIM-only proteins promote myogenic differentiation. In 3T3 fibroblasts, the same LIM proteins prevent phorbol ester-induced inhibition of DNA replication. These results establish MLP as an essential promoter of myogenesis and suggest that LIM-only proteins act via similar mechanisms to regulate aspects of cell differentiation.

Amino Acid Sequence↗