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Identification and functional characterization of conserved promoter elements from glass: a retinal development gene of Drosophila.

The Drosophila melanogaster glass transcription factor acts in photoreceptor cell development, glass transcription in the developing eye begins in the morphogenetic furrow. We report a deletion analysis which shows that a 5147 bp fragment can confer near wild-type expression in the developing eye. We completed the sequence of a similar Drosophila virilis fragment and comparison of these two genomic sequences reveals seven perfectly conserved sequence elements of 15 bp (or longer). We placed oligomers of each element 5' to an hsp70 promoter-lacZ fusion construct, and examined the patterns of beta-galactosidase expression produced in transgenic files. Three of these elements drive beta-galactosidase expression in the developing eye, and one is inhibitory.

Animals↗

Expression of glia maturation factor during retinal development in the rat.

Glia maturation factor plays important roles in the development and growth of glia and neurons. We investigated the expression and localization of Glia maturation factor-beta (GMFB) and Glia maturation factor-gamma (GMFG) in the rat retina. By northern blot analysis, both GMFB and GMFG mRNAs were detected in retina as early as embryonic day (E) 18 and persisted until adult. The expression of GMFB mRNA was always much greater than that of GMFG mRNA. In situ hybridization showed that the GMFB mRNA signal was positive in the retina from E14 till adult. Immunostaining revealed that GMFB protein was present in the inner layer of retina at E14 and P1, and in Müller cells in adult. GMFG immunoreactivity was observed only in the inner limiting membrane from E14 to P1 rat retina, and was not detected in the adult retina. These results show that GMFs are synthesized and localized mainly in Müller cells in the rat retina, and suggest that they may contribute to the development and growth of glia and neurons.

Animals↗

Tbx12, a novel T-box gene, is expressed during early stages of heart and retinal development.

T-box genes encode transcription factors that regulate many developmental processes. We have cloned a novel mouse T-box gene, Tbx12. Tbx12 is the vertebrate homologue of the Drosophila H15 gene and the Caenorhabditis elegans tbx-12 gene. Tbx12 is expressed in extraembryonic tissues such as the amnion and allantois. In the embryo, Tbx12 is strongly expressed in the neural retina and the heart.

Allantois↗

Chick homeobox gene cbx and its role in retinal development.

Homeobox genes play important roles in animal development. We isolated a chick homeobox gene, cbx, and studied its function during embryonic development. The deduced Cbx protein contained 376 amino acid residues. Its homeodomain was related (with 65-71% sequence identity) to that of human Crx, human Cart-1, and chick Alx-4. On searching the human genome sequence, a human homologue was found, which had 78% overall sequence identity and a 100% identical homeodomain. In the developing chick retina, cbx was expressed in a small fraction of post-mitotic cells residing at anatomical locations typical of bipolar cells. These cells were Goalpha(+) and protein kinase C(-), suggesting that they were probably cone bipolar cells. cbx mRNA was also detected outside the retina, particularly in the tectum and Rathke's pouch. Replication-competent retrovirus was used to drive misexpression of cbx and of an Engrailed repression construct. Engrailed-mediated repression of Cbx was embryonic lethal, while misexpression of cbx itself was tolerated. In the retina, misexpression of cbx resulted in fewer PKC(+) bipolar cells. Our data suggest that cbx is essential for embryonic survival and may participate in the development of bipolar, probably cone bipolar, cells in the retina.

Amino Acid Sequence↗

Retinal development. Waves are swell.

Waves of spontaneous electrical activity and calcium transients occur in the retina during its development. Recent work raises the question of how these waves are produced and propagated.

Animals↗

Tissue culture studies of retinal development.

Because of a limited number of cell types, a series of well-described cell-type-specific markers and a stereotyped sequence of cell development, the retina has been a valuable model of CNS development. Dissociated and explant cultures have been used to help define some of the requirements for differentiation of each major cell class. In addition to mixed-cell cultures it is now possible to use cell purification or selective growth methods to give cultures of single cell types. Alteration of gene expression by viral infection has proved to be a valuable method to help elucidate developmental pathways.

Animals↗

Expression of SNAP-25 during mammalian retinal development: thinking outside the synapse.

The SNARE complex is the core machinery required for vesicle fusion events. Numerous structural, functional, and genetic studies have led to a better understanding of mechanisms that regulate vesicle fusion events during neural development. Studies using the mammalian retina as a model system have increased our understanding of the dynamic patterns of expression of SNARE proteins. In particular, the SNARE complex protein SNAP-25 is expressed in a dynamic fashion during the development of cholinergic amacrine cells in a number of mammalian species. SNAP-25 is also likely to play a crucial role during the development of vertebrate photoreceptors. The integration of comparative studies examining SNARE proteins, such as SNAP-25, provides a powerful approach for the study of CNS development.

Amacrine Cells↗

Regulating proliferation during retinal development.

Recent studies have shown that components of the cell-cycle machinery can have diverse and unexpected roles in the retina. Cyclin-kinase inhibitors, for example, have been implicated as regulators of cell-fate decisions during histogenesis and reactive gliosis in the adult tissue after injury. Also, various mechanisms have been identified that can compensate for extra rounds of cell division when the normal timing of the cell-cycle exit is perturbed. Surprisingly, distinct components of the cell-cycle machinery seem to be used during different stages of development, and different organisms might rely on distinct pathways. Such detailed studies on the regulation of proliferation in complex multicellular tissues during development have not only advanced our knowledge of the ways in which proliferation is controlled, but might also help us to understand the degenerative disorders that are associated with gliosis and some types of tumorigenesis.

Animals↗

Intrinsic changes in developing retinal neurons result in regenerative failure of their axons.

The failure of mature mammalian central nervous system axons to regenerate after transection is usually attributed to influences of the extraneuronal milieu. Using explant cocultures of retina and midbrain tectum from hamsters, we have found evidence that these influences account for failure of regrowth of only a small minority of retinal axons. For most of the axons, there is a programmed loss of ability to elongate in the central nervous system. We show that there is a precipitous decline in the ability of retinal axons to reinnervate tectal targets when the retina is derived from pups on or after postnatal day 2, even when the target is embryonic. By contrast, embryonic retinal axons can regrow into tectum of any age, overcoming growth-inhibiting influences of glial factors.

Age Factors↗

Vesicular acetylcholine transporter (VAChT): a cellular marker in rat retinal development.

A polyclonal goat antiserum against the C-terminal end of the rat vesicular acetylcholine transporter (VAChT) was used to examine the postnatal expression of this protein in the rat retina. The transporter protein was localized in choline acetyltransferase (ChAT)-positive, cholinergic interneurones (so-called starburst amacrine cells) in the inner retina. During postnatal development the VAChT was expressed from postnatal day 1 onward by the two subsets of these cholinergic amacrine cells. The immunocytochemical detection of the VAChT provides a specific marker for the study of developing cholinergic neurones in the rat retina, which so far has only been monitored by ChAT immunoreactivity in the second postnatal week.

Acetylcholine↗