Biomedical subjects

G Halder

Publications and source records attributed to G Halder.

6 recordsLinked to original sources

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↗