Developmental patterning of rod and cone photoreceptors in embryonic zebrafish

Cone photoreceptors in the zebrafish retina are arranged in a crystalline lattice, with each spectral subtype at a specific position in the array: rod photoreceptors are inserted around the cones. Patterning events and developmental mechanisms that lead to the formation of the cone mosaic are not known. To begin investigating this issue, we examined the initial stages of opsin expression in zebrafish embryos by in situ hybridization with goldfish opsin cRNA probes to determine how and when the cone mosaic pattern arises. We found both differences and similarities in the spatiotemporal patterns of rod and cone development, which suggest the following: (1) Expression of opsin message (including rod opsin, blue and red cone opsins) was initiated at 50–52 hours postfertilization by a few photoreceptors which were consistently found in a ventral patch of retina located nasal to the choroid fissure. (2) The cone mosaic pattern was generated by a crystallization-like process initiated in the precocial ventral patch and secondarily in nasal retina, which then swept like a wave into dorsotemporal retina. (3) The pattern of differentiation of rods in the ventronasal patch differed substantially from that in the remainder of the retina, suggesting that these precocial rods might differ from typical rods. (4) Developmental maturation of rods in zebrafish, as reflected by expression of opsin, may be accelerated compared to cones, which are thought to become postmitotic before rods. These data are consistent with a model in which lateral inductive interactions among differentiating photoreceptors lead to patterning of the array. © 1995 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50066/1/903590403_ftp.pd

Molecular characterization of retinal stem cells and their niches in adult zebrafish

BACKGROUND: The persistence in adult teleost fish of retinal stem cells that exhibit all of the features of true 'adult stem cells' – self-renewal, multipotency, and the capacity to respond to injury by mitotic activation with the ability to regenerate differentiated tissues – has been known for several decades. However, the specialized cellular and molecular characteristics of these adult retinal stem cells and the microenvironmental niches that support their maintenance in the differentiated retina and regulate their activity during growth and regeneration have not yet been elucidated. RESULTS: Our data show that the zebrafish retina has two kinds of specialized niches that sustain retinal stem cells: 1) a neuroepithelial germinal zone at the interface between neural retina and ciliary epithelium, called the ciliary marginal zone (CMZ), a continuous annulus around the retinal circumference, and 2) the microenvironment around some Müller glia in the differentiated retina. In the uninjured retina, scattered Müller glia (more frequently those in peripheral retina) are associated with clusters of proliferating retinal progenitors that are restricted to the rod photoreceptor lineage, but following injury, the Müller-associated retinal progenitors can function as multipotent retinal stem cells to regenerate other types of retinal neurons. The CMZ has several features in common with the neurogenic niches in the adult mammalian brain, including access to the apical epithelial surface and a close association with blood vessels. Müller glia in the teleost retina have a complex response to local injury that includes some features of reactive gliosis (up-regulation of glial fibrillary acidic protein, GFAP, and re-entry into the cell cycle) together with dedifferentiation and re-acquisition of phenotypic and molecular characteristics of multipotent retinal progenitors in the CMZ (diffuse distribution of N-cadherin, activation of Notch-Delta signaling, and expression of rx1, vsx2/Chx10, and pax6a) along with characteristics associated with radial glia (expression of brain lipid binding protein, BLBP). We also describe a novel specific marker for Müller glia, apoE. CONCLUSION: The stem cell niches that support multi-lineage retinal progenitors in the intact, growing and regenerating teleost retina have properties characteristic of neuroepithelia and neurogenic radial glia. The regenerative capacity of the adult zebrafish retina with its ability to replace lost retinal neurons provides an opportunity to discover the molecular regulators that lead to functional repair of damaged neural tissue

Immunolocalization of basic fibroblast growth factor and its receptor in adult goldfish retina

The neural retina of teleost fish can regenerate following surgical or neurotoxic lesions. As a first attempt to uncover the factors important for the regenerative response, we used immunocytochemistry to demonstrate the presence of basic fibroblast growth factor (bFGF) and its receptor in the goldfish retina. The bFGF-immunoreactivity was present throughout the retina, but was most intense in photoreceptor cells, especially cones, and Muller glia. Immunoreactivity for the bFGF receptor was strongest in the axon terminals of photoreceptors, both rods and cones. This pattern of immunolocalization is especially interesting since the proliferating cells that are thought to be responsible for generating the neural regenerate are located among the photoreceptor axon terminals. These proliferating cells have been identified as rod precursors because in the intact retina they give rise only to rod photoreceptors. When the neural retina is damaged, however, rod precursors are thought to be the source of proliferating neuroepithelial cells responsible for generating the retinal regenerate. The role played by bFGF in normal neurogenesis, cell differentiation, and/or neuronal regeneration in the fish retina has yet to be determined.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30286/1/0000688.pd

Anisotropic Müller glial scaffolding supports a multiplex lattice mosaic of photoreceptors in zebrafish retina

Abstract Background The multiplex, lattice mosaic of cone photoreceptors in the adult fish retina is a compelling example of a highly ordered epithelial cell pattern, with single cell width rows and columns of cones and precisely defined neighbor relationships among different cone types. Cellular mechanisms patterning this multiplex mosaic are not understood. Physical models can provide new insights into fundamental mechanisms of biological patterning. In earlier work, we developed a mathematical model of photoreceptor cell packing in the zebrafish retina, which predicted that anisotropic mechanical tension in the retinal epithelium orients planar polarized adhesive interfaces to align the columns as cone photoreceptors are generated at the retinal margin during post-embryonic growth. Methods With cell-specific fluorescent reporters and in vivo imaging of the growing retinal margin in transparent juvenile zebrafish we provide the first view of how cell packing, spatial arrangement, and cell identity are coordinated to build the lattice mosaic. With targeted laser ablation we probed the tissue mechanics of the retinal epithelium. Results Within the lattice mosaic, planar polarized Crumbs adhesion proteins pack cones into a single cell width column; between columns, N-cadherin-mediated adherens junctions stabilize Müller glial apical processes. The concentration of activated pMyosin II at these punctate adherens junctions suggests that these glial bands are under tension, forming a physical barrier between cone columns and contributing to mechanical stress anisotropies in the epithelial sheet. Unexpectedly, we discovered that the appearance of such parallel bands of Müller glial apical processes precedes the packing of cones into single cell width columns, hinting at a possible role for glia in the initial organization of the lattice mosaic. Targeted laser ablation of Müller glia directly demonstrates that these glial processes support anisotropic mechanical tension in the planar dimension of the retinal epithelium. Conclusions These findings uncovered a novel structural feature of Müller glia associated with alignment of photoreceptors into a lattice mosaic in the zebrafish retina. This is the first demonstration, to our knowledge, of planar, anisotropic mechanical forces mediated by glial cells.https://deepblue.lib.umich.edu/bitstream/2027.42/139592/1/13064_2017_Article_96.pd

Expression of rod and cone visual pigments in goldfish and zebrafish: A rhodopsin-like gene is expressed in cones

The primary purpose of the present study was to determine whether a rhodopsin-like gene, which has been postulated to represent the green cone pigment in several species, is in fact expressed in cone photoreceptors instead of rods. The expression patterns of rod opsin and blue and red cone opsins were also examined in both goldfish and zebrafish retinas using colorimetric in situ hybridization. The results demonstrate that the rhodopsin-like gene is expressed in green cones, as predicted. A subset of small cones that do not hybridize with these cRNA probes are tentatively identified as ultraviolet receptors. The results also demonstrate that opsin message in cones is restricted to the perinuclear region, whereas in rods, it is both perinuclear and adjacent to the ellipsoid.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30780/1/0000433.pd

Characterization of the yehUT Two-Component Regulatory System of Salmonella enterica Serovar Typhi and Typhimurium

10.1371/journal.pone.0084567PLoS ONE812-POLN

Coupling Mechanical Deformations and Planar Cell Polarity to Create Regular Patterns in the Zebrafish Retina

<div><p>The orderly packing and precise arrangement of epithelial cells is essential to the functioning of many tissues, and refinement of this packing during development is a central theme in animal morphogenesis. The mechanisms that determine epithelial cell shape and position, however, remain incompletely understood. Here, we investigate these mechanisms in a striking example of planar order in a vertebrate epithelium: The periodic, almost crystalline distribution of cone photoreceptors in the adult teleost fish retina. Based on observations of the emergence of photoreceptor packing near the retinal margin, we propose a mathematical model in which ordered columns of cells form as a result of coupling between planar cell polarity (PCP) and anisotropic tissue-scale mechanical stresses. This model recapitulates many observed features of cone photoreceptor organization during retinal growth and regeneration. Consistent with the model's predictions, we report a planar-polarized distribution of Crumbs2a protein in cone photoreceptors in both unperturbed and regenerated tissue. We further show that the pattern perturbations predicted by the model to occur if the imposed stresses become isotropic closely resemble defects in the cone pattern in zebrafish <em>lrp2</em> mutants, in which intraocular pressure is increased, resulting in altered mechanical stress and ocular enlargement. Evidence of interactions linking PCP, cell shape, and mechanical stresses has recently emerged in a number of systems, several of which show signs of columnar cell packing akin to that described here. Our results may hence have broader relevance for the organization of cells in epithelia. Whereas earlier models have allowed only for unidirectional influences between PCP and cell mechanics, the simple, phenomenological framework that we introduce here can encompass a broad range of bidirectional feedback interactions among planar polarity, shape, and stresses; our model thus represents a conceptual framework that can address many questions of importance to morphogenesis.</p> </div

Simulation results.

<p>Blue bars indicate the axis of cell polarization from PCP; longer bars correspond to stronger polarization. <b>A, B</b>) If all cells assume the cone fate simultaneously, whether under conditions of isotopic or anisotropic global stress, a disordered packing results. <b>C</b>) In the growing retina, cone photoreceptors are generated in a propagating, linear wave. Proliferative precursor cells are shown in white and cone photoreceptors in grey. To mimic growth and differentiation at the germinal zone in the simulations, successive columns of cells are induced to assume the cone fate. <b>D</b>) Induction of cones column-by-column with isotropic mechanical stress leads to a packing that is more ordered than in panel A, but still imperfect. <b>E</b>) Induction of cones column-by-column in the presence of anisotropic mechanical stress yields straight columns. <b>F</b>) When stress anisotropy is added during a simulation, ordering improves. Double-headed arrows indicate regions of the simulated packing where the initial induction of cone fate occurred under the indicated stresses.</p