Biomedical subjects

T A Reh

Publications and source records attributed to T A Reh.

At least 37 records · Page 2Linked to original sources

PubMed1998

The nuclear receptor transcription factor, retinoid-related orphan receptor beta, regulates retinal progenitor proliferation.

We examined the role of retinoid-related orphan receptor (ROR)beta, a member of the nuclear receptor family of transcription factors, in retinal neurogenesis. In situ hybridization studies showed that RORbeta is expressed in retinal progenitor cells in the embryonic rat retina. Further studies demonstrated that RORbeta colocalizes with Chx10, a transcription factor thought to influence retinal progenitor proliferation (Burmeister, M., Novak, J., Liang, M-Y., Basu, S., Ploder, L., Hawes, N.L. Vidgen, D., Hoover, F., Goldman, D. , Kalnins, V.I., Roderick, T.H., Taylor, B.A., Hankin, M.H. and McInnes, R.R., 1996. Ocular retardation mouse caused by Chx10 homeobox null allele: impaired retinal progenitor proliferation and bipolar cell differentiation. Nature Genetics 12, 376-383). Northern analysis reveals that RORbeta expression is dramatically decreased in the ocular retardationJ mutant, which possesses a defect in the Chx10 gene. Overexpression of RORbeta in retinal progenitors by biolistic transfection results in an increase in the number of large cell clones. These data support a role for RORbeta in regulating retinal progenitor proliferation, possibly via the Chx10 gene.

Animals↗

PubMed1998

Multipotential stem cells and progenitors in the vertebrate retina.

The vertebrate retina is derived from paired evaginations from the neural tube in embryonic development and is initially produced by progenitor cells similar to those that generate the neurons and glia of other areas of the central nervous system. In some amphibians and fish, the retina continues to grow along with the eye throughout the life of the animal. The new retinal cells are added at the ciliary margin of the eye from the mitotic activity of neural/glial stem cells in a region known as the germinal zone and are seamlessly incorporated into the existing retinal circuitry. Little is known about the cell or molecular biology of these stem cells; however, studies of retinal progenitor cells in chick and mammalian embryos have led to the identification of several factors that control their proliferation. Moreover, studies of retinal regeneration have shown that retinal stem cells can also be derived from two or perhaps three additional sources after retinal damage: (a) the retinal pigmented epithelium (RPE) in amphibians and embryonic chicks and mammals; (b) a specialized rod progenitor in fish; and (c) the Müller glial cells. While there is currently no evidence for a neural/glial stem cell in the adult mammalian retina, and the retina of the mature mammal does not show regenerative capacity after damage, there is a possibility for the reinitiation of stem cell potential at the peripheral retinal margin, from the RPE or from the Müller glial cells. The application of information derived from the studies of retinal progenitor cells in developing organisms should soon provide a test of these possibilities.

Aging↗

PubMed1997

Sonic hedgehog promotes rod photoreceptor differentiation in mammalian retinal cells in vitro.

The hedgehog gene family encodes secreted proteins important in many developmental patterning events in both vertebrates and invertebrates. In the Drosophila eye disk, hedgehog controls the progression of photoreceptor differentiation in the morphogenetic furrow. To investigate whether hedgehog proteins are also involved in the development of the vertebrate retina at stages of photoreceptor differentiation, we analyzed expression of the three known vertebrate hedgehog genes. We found that Sonic hedgehog and Desert hedgehog are expressed in the developing retina, albeit at very low levels, whereas Indian hedgehog (Ihh) is expressed in the developing and mature retinal pigmented epithelium, beginning at embryonic day 13. To determine whether hedgehog proteins have activities on developing retinal cells, we used an in vitro system in which much of retinal histogenesis is recapitulated. N-terminal recombinant Sonic Hedgehog protein (SHH-N) was added to rat retinal cultures for 3-12 d, and the numbers of retinal cells of various phenotypes were analyzed by immunohistochemistry. We found that SHH-N caused a transient increase in the number of retinal progenitor cells, and a 2- to 10-fold increase in the number of photoreceptors differentiating in the cultures when analyzed with three different photoreceptor-specific antigens. In contrast, the numbers of retinal ganglion cells and amacrine cells were similar to those in control cultures. These results show that Hedgehog proteins can regulate mitogenesis and photoreceptor differentiation in the vertebrate retina, and Ihh is a candidate factor from the pigmented epithelium to promote retinal progenitor proliferation and photoreceptor differentiation.

Animals↗

PubMed1997

Expression of neurogenic basic helix-loop-helix genes in primitive neuroectodermal tumors.

The basic helix-loop-helix (bHLH) class of transcription factors plays a pivotal role in tissue-specific determination and differentiation. Moreover, dysregulated expression or loss of function of these factors contributes to leukemogenesis and solid tumor development. Neurogenesis is regulated by genes of the NEUROD/atonal and ACHAETE SCUTE families. We analyzed expression of human NEUROD1, NEUROD2, NEUROD3, and ACHAETE SCUTE 1 (HASH1) in cerebellar and cerebral primitive neuroectodermal tumors (PNETs), gliomas, and cell lines derived from a variety of neuroectodermal tumors by Northern analysis and in situ hybridization. NEUROD1 was expressed in each of the 12 medulloblastoma specimens, whereas NEUROD2 and NEUROD3/neurogenin were expressed in partly overlapping subsets of medulloblastomas. All of the tumors that presented with distant metastases expressed NEUROD3. The only other NEUROD3-positive tumor progressed early in treatment. Human ACHAETE SCUTE homologue (HASH1) was not expressed in medulloblastomas (infratentorial PNETs) but was expressed in three of five supratentorial PNETs. Neuroectodermal tumor cell lines derived from other sites (e.g., neuroblastoma and retinoblastoma) expressed NeuroD and ACHAETE SCUTE family members. No NEUROD message was detected in glial tumors or cell lines. Neurogenic bHLH transcription factor expression patterns suggest that specific family members may contribute to or reflect biological differences that arise during malignant transformation.

Brain Neoplasms↗

PubMed1997

Basic fibroblast growth factor (FGF-2) induced transdifferentiation of retinal pigment epithelium: generation of retinal neurons and glia.

In the present study we report that basic fibroblast growth factor (bFGF, FGF-2) promotes the transdifferentiation of Xenopus laevis larval retinal pigment epithelium (RPE) into neural retina. Using specific antibodies we have examined the cellular composition of the regenerated retinal tissue. Our results show that, in addition to retinal neurons and photoreceptors, glial cells were also regenerated from the transdifferentiated RPE. These results were specific to FGF-2, since other factors that were tested, including acidic FGF (aFGF, FGF-1), epidermal growth factor (EGF), laminin, ECL, and Matrigel, exhibited no activity in inducing retinal regeneration. These results are the first in amphibians demonstrating the functional role of FGF-2 in inducing RPE transdifferentiation. Transplantation studies were carried out to investigate retinal regeneration from the RPE in an in vivo environment. Sheets of RPE implanted into the lens-less eyes of larval hosts transformed into neurons and glial cells only when under the influence of host retinal factors. In contrast, no retinal transdifferentiation occurred if the RPE was implanted into the enucleated orbit. Taken together, these results show that the amphibian RPE is capable of transdifferentiation into neuronal and glial cell-phenotypes and implicate FGF-2 as an important factor in inducing retinal regeneration in vitro.

Animals↗

PubMed1997

Fibroblast growth factors are necessary for neural retina but not pigmented epithelium differentiation in chick embryos.

During eye development, optic vesicles evaginate laterally from the neural tube and develop into two bilayered eye cups that are composed of an outer pigment epithelium layer and an inner neural retina layer. Despite their similar embryonic origin, the pigment epithelium and neural retina differentiate into two very distinct tissues. Previous studies have demonstrated that the developmental potential of the pigmented epithelial cells is not completely restricted; until embryonic day 4.5 in chick embryos, the cells are able to switch their phenotype and differentiate into neural retina when treated with fibroblast growth factors (FGF) (Park, C. M., and Hollenberg, M. J. (1989). Dev. Biol. 134, 201-205; Pittack, C., Jones, M., and Reh, T. A. 1991). Development 113, 577-588; Guillemot, F. and Cepko, C. L. (1992). Development 114, 743-754). These studies motivated us to test whether FGF is necessary for neural retina differentiation during the initial stages of eye cup development. Optic vesicles from embryonic day 1.5 chick were cultured for 24 hours as explants in the presence of FGF or neutralizing antibodies to FGF2. The cultured optic vesicles formed eye cups that contained a lens vesicle, neural retina and pigmented epithelium, based on morphology and expression of neural and pigmented epithelium-specific antigens. Addition of FGF to the optic vesicles caused the presumptive pigmented epithelium to undergo neuronal differentiation and, as a consequence, a double retina was formed. By contrast, neutralizing antibodies to FGF2 blocked neural differentiation in the presumptive neural retina, without affecting pigmented epithelial cell differentiation. These data, along with evidence for expression of several FGF family members and their receptors in the developing eye, indicate that members of the FGF family may be required for establishing the distinction between the neural retina and pigmented epithelium in the optic vesicle.

Animals↗

PubMed1996

Temporal and spatial pattern of MASH-1 expression in the developing rat retina demonstrates progenitor cell heterogeneity.

The temporal and spatial pattern of mammalian achaete-scute homolog 1 (MASH-1) expression in the developing rat retina was examined in an effort to correlate achaete-scute homolog expression with the generation of particular cell classes. The expression of MASH-1 was restricted to the latter portion of retinal neurogenesis and was most closely correlated with the appearance of bipolar cells and Müller glia, two cell classes that are generated late in retinogenesis. We also examined the proliferative nature of the MASH-1 -expressing cell type to confirm that MASH-1 is expressed by progenitor cells and to determine the proportion of the proliferating population that expresses MASH-1. MASH-1 was expressed by only 10-30% of the total proliferating population, depending on the age examined. Thus, MASH-1 expression provides a molecular marker of heterogeneity among retinal progenitor cells and may play a role in the commitment and/or differentiation of one or more of the late-appearing retinal phenotypes.

Animals↗

PubMed1996

Growth factors in the treatment of degenerative retinal disorders.

There are currently a number of degenerative conditions, both inherited and acquired, that affect the retina and lead to blindness. Retinal photoreceptors degenerate from inherited conditions, such as retinitis pigmentosa or as a result of light damage or normal ageing; retinal ganglion cells degenerate from optic nerve injury or glaucoma. Current research in this field includes the use of growth factors to: (1) inhibit the degenerative processes; (2) promote regeneration of the retina from the pigmented epithelium; and (3) improve the conditions for transplantation of new cells to the retina by expanding the photoreceptor cell populations in vitro. The results to date have shown that a number of different growth factors promote survival of retinal cells in vitro and in vivo. In addition, some of the same factors can stimulate regeneration in the developing retina and act as mitogens for the retinal progenitor cells. It is likely that a combination of these approaches will ultimately be important for the treatment of the various retinal degenerations.

Animals↗

PubMed1996

Reactive astroglia support primary dendritic but not axonal outgrowth from mouse cortical neurons in vitro.

Reactive astrocytes are thought to be impediments to axon regrowth following injury to the mammalian central nervous system. Axon and dendrite growth, however, appear to be differently controlled by normal astrocytes in vitro. To determine whether reactive astrocytes differ in their ability to support axons or dendrites, embryonic (E18) mouse cortical neurons were cocultured with P4 and P12 rat astroglial cells derived from normal or lesioned cortex. After 5 days in vitro, axon and dendrite outgrowth from isolated neurons was quantified with double-labeling immunohistochemical techniques. Reactive astrocytes were able to maintain primary dendrite growth, principally primary dendrite number. Axon elongation, however, was significantly reduced on both neonatal and more mature reactive astrocytes. These results indicate that reactive astrocytes may exhibit separate mechanisms to control dendrite and axon growth.

Animals↗

PubMed1996

Effects of GGF/neuregulins on neuronal survival and neurite outgrowth correlate with erbB2/neu expression in developing rat retina.

We have examined the expression of neuregulin and its putative receptors, erbB2/neu, erbB3 and erbB4/tyro2 during retinal development, and tested several potential functions of this class of molecules in dissociated rat retinal cell cultures. At least one form of neuregulin is expressed in the retina, from the earliest stages of retinal development examined; in addition, all three of the known receptors are expressed by retinal neurons in a developmentally regulated manner. When added to cultures of embryonic or neonatal rat retinal cells, neuregulin (rhGGF2) promotes survival and neurite extension from retinal neurons in a dose-dependent manner. These results indicate that in addition to their well described effects on glia, the neuregulins also have direct effects on central nervous system neurons.

Animals↗

PubMed1995

Independent regulation of primary dendritic and axonal growth by maturing astrocytes in vitro.

Whereas axon growth is limited in the mature mammalian central nervous system (CNS), dendritic remodeling occurs throughout life. Since glia can regulate neurite growth during development, we tested whether glia from the mature CNS differ in their ability to support axon and dendrite growth. Cortical neurons were co-cultured with neonatal or mature astroglial, and dendrite and axon outgrowth quantified after 5DIV using immunohistochemical techniques. Primary dendritic growth was supported equally well by mature and immature astrocytes. By contrast, mature astrocytes demonstrated a reduced ability to support axon growth. We propose that the independent regulation of axon and dendrite growth by astrocytes provides a means by which the mature nervous system may adjust its function to activity and the environment.

Animals↗

PubMed1995

Astroglia demonstrate regional differences in their ability to maintain primary dendritic outgrowth from mouse cortical neurons in vitro.

To determine whether glia from different regions of the central nervous system (CNS) initiate or maintain primary dendritic growth, embryonic day 18 mouse cortical neurons were co-cultured with rat (postnatal day 4) astroglial cells derived from retina, spinal cord, mesencephalon, striatum, olfactory bulb, retina, and cortex. Axon and dendrite outgrowth from isolated neurons was quantified using morphological and immunohistochemical techniques at 18 h and 1, 3, and 5 days in vitro. Neurons initially extend the same number of neurites, regardless of the source of glial monolayer; however, glial cells differ in their ability to maintain primary dendrites. Homotypic cortical astrocytes maintain the greatest number of primary dendrites. Glia derived from the olfactory bulb and retina maintained intermediate numbers of dendrites, whereas only a small number of primary dendrites were maintained by glia derived from striatum, spinal cord, or mesencephalon. Longer axons were initially observed from neurons grown on glia that did not maintain dendrite number. Axonal length, however, was similar on the various monolayers after 5 days in vitro. Neurons that were grown in media conditioned by either mesencephalic or cortical glia for the first 24 h followed by culture media from glia of the alternate source for 4 days in vitro confirmed that glia maintained, rather than initiated, the outgrowth of the primary dendritic arbor. These results indicate that glial cells derived from various CNS regions differ in their ability to maintain the primary dendritic arbor from mouse cortical neurons in vitro.

Animals↗

PubMed1995

Transforming growth factor-beta-3 is mitogenic for rat retinal progenitor cells in vitro.

Recent data indicate that the process of neurogenesis in the mammalian central nervous system (CNS) may be regulated by peptide growth factors, such as epidermal growth factor, transforming growth factor-alpha, and acidic or basic fibroblast growth factor. We have investigated whether members of the transforming growth factor-beta (TGF beta) family also play a role in this process and have found that TGF beta-3 is mitogenic for embryonic rat retinal cells in vitro. We also show that TGF beta-3 stimulates production of retinal amacrine cells while photoreceptor production remains unchanged. These data demonstrate that TGF beta-3 can regulate cell proliferation in the CNS during development and can also influence commitment or differentiation, or both, of neural progenitor cells to particular retinal fates.

Animals↗

PubMed1995

Transdifferentiation and retinal regeneration.

The neural retina of amphibians and chick embryos regenerates following damage. Retinal regeneration requires a change in the differentiated state of the cells of the pigmented epithelium of the retina to a neural progenitor phenotype. The molecular mechanisms that control the cell fate decision between these two very different cell types involves soluble growth factors of the fibroblast growth factor family, as well as components of the extracellular matrix. Recent experiments have also begun to detail differences in gene expression between the neural retina and the pigment epithelium that may be critical for their phenotypic distinction.

Amphibians↗

PubMed1995

Ligands of steroid/thyroid receptors induce cone photoreceptors in vertebrate retina.

The mechanisms by which multipotent progenitor cells are directed to alternative cell identities during the histogenesis of the vertebrate central nervous system are likely to involve several different types of signaling systems. Recent evidence indicates that 9-cis retinoic acid, which acts through members of the steroid/thyroid superfamily of receptors, directs progenitor cells to the rod photoreceptor cell fate. We now report that another effector of this family of receptors, thyroid hormone, induces an increase in the number of cone photoreceptors that develop in embryonic rat retinal cultures, and that combinations of 9-cis retinoic acid and triiodothyronine cause isolated progenitor cells to differentiate as either rods or cones, depending on the relative concentrations of the ligands. These results implicate thyroid hormone in CNS cell fate determination, and suggest that different photoreceptor phenotypes may be modulated through the formation of thyroid/retinoid receptor heterodimers.

Animals↗

PubMed1995

Regulation of proliferation and photoreceptor differentiation in fetal human retinal cell cultures.

PURPOSE: To examine whether fetal human retinal cells can be maintained in vitro over long time periods and to determine whether exogenous growth factors can be used to generate large numbers of photoreceptors within these cultures. METHODS: Fetal human retinas (6 to 13 weeks after conception) were dissected, dissociated, and plated into culture wells. Specific growth factors and steroid/thyroid hormones, which have been shown to influence retinal progenitor cell proliferation and differentiation in rats, were added to the culture medium to determine whether any of these factors had similar effects on human retinal cells. RESULTS: Fetal human retinal cells survived and continued to proliferate for up to 300 days in vitro. Under control conditions, 15 million cells were generated from an initial plating of 100,000 cells; however, the addition of either epidermal growth factor or basic fibroblast growth factor stimulated proliferation and resulted in the generation of more than 100 million cells. A percentage of these cells was induced to differentiate as photoreceptors by adding either retinoic acid or triiodo-thyronine to the culture medium. CONCLUSIONS: Fetal human retinal cells can be maintained and expanded in vitro, indicating that this technique may be useful for generating large numbers of retinal cells. The number and types of cells generated can be influenced by adding exogenous factors to the culture medium. The response of human retinal cells to growth factors and hormones is similar to the response of rodent retinal cells to the same factors, suggesting that the effects of these factors are conserved across species.

Cell Differentiation↗

PubMed1994

Inhibition of retinal regeneration in larval Rana by an antibody directed against a laminin-heparan sulfate proteoglycan.

In vivo and in vitro experiments have demonstrated that the retinal pigmented epithelium can give rise to neuronal precursors during retinal regeneration in amphibians. In vitro experiments have further demonstrated that this process is greatly facilitated by two molecules associated with basement membranes: laminin and fibroblast growth factor. We now report that retinal regeneration can be blocked in vivo by an antibody that inhibits the interaction of cells with the laminin-heparan sulfate proteoglycan complex. These results further support a role for the extracellular matrix in regulating cellular phenotype during retinal regeneration.

Animals↗

PubMed1994

A chicken achaete-scute homolog (CASH-1) is expressed in a temporally and spatially discrete manner in the developing nervous system.

We have identified a basic helix-loop-helix encoding cDNA from embryonic chicken retina which shares sequence similarity with the achaete-scute family of genes of Drosophila. The deduced amino acid sequence of this chicken achaete-scute homolog (CASH-1) is identical, over the region encoding the basic helix-loop-helix domain, to the recently identified mammalian achaete-scute homolog (MASH-1) and to the Xenopus homolog (XASH1), and 70% identical, over the same region, to Drosophila achaete-scute complex members. The expression of CASH-1 is restricted to subsets of neuronal progenitor cells in the developing chicken nervous system, similar in distribution to that reported for MASH-1 and XASH1. In addition, in situ localization in the retina reveals a dynamic character of expression of the gene in a particular region of the CNS, and suggests that the expression of CASH-1 may be important in defining a particular stage in the progenitor cell necessary for the differentiation of particular neuronal phenotypes.

Amino Acid Sequence↗