Parvalbumin-immunoreactive neurons in the inner nuclear layer of zebrafish retina

The anti-melanogenic properties of Swietenia macrophylla king

Fair flawless skin is the goal for some cultures and the development of irregular skin pigmentation is considered an indication of premature skin aging. Hence, there is a rising demand for skin whitening cosmetics. Thus, this research will be focusing on discovering the anti-pigmentation properties of Swietenia macrophylla seeds. Firstly, the seeds were extracted with ethanol and further fractionate based on their polarity before testing them on zebrafish embryos. The ethanolic extract of the seed demonstrated significant inhibition of both tyrosinase activity and melanin production in the embryos. However, after fractionation, the anti-melanogenic ability was observed to have decreased, signifying that the phytocompounds may be synergistic in nature. Still in the proteomic studies the ethanolic extract and its hexane fraction both induced the downregulation of cathepsin LB and cytoskeletal proteins that have connections to the melanogenic pathway, confirming that S. macrophylla seeds do indeed have anti-pigmentation properties that can be exploited for cosmetic use. Next, limonoids (tetranortriterpenoids found in the seed) were tested for their inhibitory effect against human tyrosinase related protein 1 (TYRP-1) via molecular docking. It was found that limonoids have a stronger binding affinity to TYRP-1 than kojic acid, suggesting that these phytocompounds may have the potential in inhibiting pigmentation. However, this still needs further confirmation before these phytocompounds can be developed into a skin whitening agent. Other assays like ex-vivo or 3D human skin culture can also be used to better study the seeds anti-pigmentation effect on humans.

Dynamic functional and structural remodeling during retinal regeneration in zebrafish

Introduction

Zebrafish regenerate their retinas following damage, resulting in restoration of visual function. Here we evaluate recovery of retinal function through qualitative and quantitative analysis of the electroretinogram (ERG) over time following retinal damage, in correlation to histological features of regenerated retinal tissue.

Methods

Retinas of adult zebrafish were lesioned by intravitreal injection of 10 μM (extensive lesion; destroys all neurons) or 2 μM (selective lesion; spares photoreceptors) ouabain. Unlesioned contralateral retinas served as controls. Function of retinal circuitry was analyzed at selected timepoints using ERG recordings from live zebrafish, and whole eyes were processed for histological analyses immediately thereafter.

Results

Qualitative and quantitative assessment of waveforms during retinal regeneration revealed dynamic changes that were heterogeneous on an individual level within each sampling time, but still followed common waveform recovery patterns on a per-fish and population-level basis. Early in the regeneration period (13-30 days post injury; DPI), for both lesion types, b-waves were essentially not detected, and unmasked increased apparent amplitudes, implicit times, and half-widths of a-waves (vs. controls). In control recordings, d-waves were not obviously detected, but apparent d-waves (OFF-bipolar responses) from regenerating retinas of several fish became prominent by 30DPI and dominated the post-photoreceptor response (PPR). Beyond 45DPI, b-waves became detectable, and the ratio of apparent d- to b-wave contributions progressively shifted with most, but not all, fish displaying a b-wave dominated PPR. At the latest timepoints (extensive, 90DPI; selective, 80DPI), recordings with measurable b-waves approached a normal waveform (implicit times and half-widths), but amplitudes were not restored to control levels. Histological analyses of the retinas from which ERGs were recorded showed that as regeneration progressed, PKCa + ON-bipolar terminals and parvalbumin + amacrine cell processes became more stereotypically positioned within the deep sublaminae of the INL over recovery time after each lesion type, consistent with the shift in PPR seen in the ERG recordings.

Discussion

Taken together, these data suggest that photoreceptor-OFF-bipolar component/connectivity may functionally recover and mature earlier during regeneration compared to the photoreceptor-ON-bipolar component, though the timeframe in which such recovery happens is heterogeneous on a per-fish basis. Collectively our studies suggest gradual restoration of ON-bipolar functional circuitry during retinal regeneration.

Spatial regulation of amacrine cell genesis by Semaphorin 3f

PURPOSE

The axonal projections of retinal ganglion cells (RGCs) of the eye are topographically organized so that spatial information from visual images is preserved. This retinotopic organization is established during development by secreted morphogens that pattern domains of transcription factor expression within naso-temporal and dorso-ventral quadrants of the embryonic eye. Poorly understood are the downstream signaling molecules that generate the topographically organized retinal cells and circuits. The secreted signaling molecule Semaphorin 3fa (Sema3fa) belongs to the Sema family of molecules that provide positional information to developing cells. Here, we test a role for Sema3fa in cell genesis of the temporal zebrafish retina.

METHODS

We compare retinal cell genesis in wild type and sema3fa CRISPR zebrafish mutants by in situ hybridization and immunohistochemistry.

RESULTS

We find that mRNAs for sema3fa and known receptors, neuropilin2b (nrp2b) and plexina1a (plxna1a), are expressed by progenitors of the temporal, but not nasal zebrafish embryonic retina. In the sema3fa^ca304/ca304 embryo, initially the domains of expression for atoh7 and neurod4, transcription factors necessary for the specification of RGCs and amacrine cells, respectively, are disrupted. Yet, post-embryonically only amacrine cells of the temporal retina are reduced in numbers, with both GABAergic and glycinergic subtypes affected.

CONCLUSIONS

These data suggest that Sema3fa acts early on embryonic temporal progenitors to control in a spatially-dependent manner the production of amacrine cells, possibly to allow the establishment of neural circuits with domain-specific functions. We propose that spatially restricted extrinsic signals in the neural retina control cell genesis in a domain-dependent manner.

From random to regular: Variation in the patterning of retinal mosaics

The various types of retinal neurons are each positioned at their respective depths within the retina where they are believed to be assembled as orderly mosaics, in which like-type neurons minimize proximity to one another. Two common statistical analyses for assessing the spatial properties of retinal mosaics include the nearest neighbor analysis, from which an index of their "regularity" is commonly calculated, and the density recovery profile derived from autocorrelation analysis, revealing the presence of an exclusion zone indicative of anti-clustering. While each of the spatial statistics derived from these analyses, the regularity index and the effective radius, can be useful in characterizing such properties of orderly retinal mosaics, they are rarely sufficient for conveying the natural variation in the self-spacing behavior of different types of retinal neurons and the extent to which that behavior generates uniform intercellular spacing across the mosaic. We consider the strengths and limitations of these and other spatial statistical analyses for assessing the patterning in retinal mosaics, highlighting a number of misconceptions and their frequent misuse. Rather than being diagnostic criteria for determining simply whether a population is "regular," they should be treated as descriptive statistics that convey variation in the factors that influence neuronal positioning. We subsequently apply multiple spatial statistics to the analysis of eight different mosaics in the mouse retina, demonstrating conspicuous variability in the degree of patterning present, from essentially random to notably regular. This variability in patterning has both a developmental as well as a functional significance, reflecting the rules governing the positioning of different types of neurons as the architecture of the retina is assembled, and the distinct mechanisms by which they regulate dendritic growth to generate their characteristic coverage and connectivity.

Color Processing in Zebrafish Retina

Zebrafish (Danio rerio) is a model organism for vertebrate developmental processes and, through a variety of mutant and transgenic lines, various diseases and their complications. Some of these diseases relate to proper function of the visual system. In the US, the National Eye Institute indicates >140 million people over the age of 40 have some form of visual impairment. The causes of the impairments range from refractive error to cataract, diabetic retinopathy and glaucoma, plus heritable diseases such as retinitis pigmentosa and color vision deficits. Most impairments directly affect the retina, the nervous tissue at the back of the eye. Zebrafish with long or short-wavelength color blindness, altered retinal anatomy due to hyperglycemia, high intraocular pressure, and reduced pigment epithelium are all used, and directly applicable, to study how these symptoms affect visual function. However, many published reports describe only molecular/anatomical/structural changes or behavioral deficits. Recent work in zebrafish has documented physiological responses of the different cell types to colored (spectral) light stimuli, indicating a complex level of information processing and color vision in this species. The purpose of this review article is to consolidate published morphological and physiological data from different cells to describe how zebrafish retina is capable of complex visual processing. This information is compared to findings in other vertebrates and relevance to disorders affecting color processing is discussed.

Developmental and adult characterization of secretagogin expressing amacrine cells in zebrafish retina

Calcium binding proteins show stereotypical expression patterns within diverse neuron types across the central nervous system. Here, we provide a characterization of developmental and adult secretagogin-immunolabelled neurons in the zebrafish retina with an emphasis on co-expression of multiple calcium binding proteins. Secretagogin is a recently identified and cloned member of the F-hand family of calcium binding proteins, which labels distinct neuron populations in the retinas of mammalian vertebrates. Both the adult distribution of secretagogin labeled retinal neurons as well as the developmental expression indicative of the stage of neurogenesis during which this calcium binding protein is expressed was quantified. Secretagogin expression was confined to an amacrine interneuron population in the inner nuclear layer, with monostratified neurites in the center of the inner plexiform layer and a relatively regular soma distribution (regularity index > 2.5 across central–peripheral areas). However, only a subpopulation (~60%) co-labeled with gamma-aminobutyric acid as their neurotransmitter, suggesting that possibly two amacrine subtypes are secretagogin immunoreactive. Quantitative co-labeling analysis with other known amacrine subtype markers including the three main calcium binding proteins parvalbumin, calbindin and calretinin identifies secretagogin immunoreactive neurons as a distinct neuron population. The highest density of secretagogin cells of ~1800 cells / mm² remained relatively evenly along the horizontal meridian, whilst the density dropped of to 125 cells / mm² towards the dorsal and ventral periphery. Thus, secretagogin represents a new amacrine label within the zebrafish retina. The developmental expression suggests a possible role in late stage differentiation. This characterization forms the basis of functional studies assessing how the expression of distinct calcium binding proteins might be regulated to compensate for the loss of one of the others.

Cone signals in monostratified and bistratified amacrine cells of adult zebrafish retina

Strata within the inner plexiform layer (IPL) of vertebrate retinas are suspected to be distinct signaling regions. Functions performed within adult zebrafish IPL strata were examined through microelectrode recording and staining of stratified amacrine types. The stimulus protocol and analysis discriminated the pattern of input from red, green, blue, and UV cones as well as the light-response waveforms in this tetrachromatic species. A total of 36 cells were analyzed. Transient depolarizing waveforms at ON and OFF originated with bistratified amacrine types, whose dendritic planes branched either in IPL sublaminas a & b, or only within sublamina a. Monophasic-sustained depolarizing waveforms originated with types monostratified in IPL s4 (sublamina b). OFF responses hyperpolarized at onset, depolarized at offset, and in some cases depolarized during mid-stimulus. These signals originated with types monostratified in s1 or s2 (sublamina a). Bistratified amacrines received depolarizing signals only from red cones, at both ON and OFF, while s4 stratified ON cells combined red and green cone signals. The s1/s2 stratified OFF cells utilized hyperpolarizing signals from red, red and green, or red and blue cones at ON, but only depolarizing red cone signals at OFF. ON and OFF depolarizing transients from red cones appear widely distributed within IPL strata. "C-type" physiologies, depolarized by some wavelengths, hyperpolarized by others, in biphasic or triphasic spectral patterns, originated with amacrine cells monostratified in s5. Collectively, cells in this stratum processed signals from all cone types. J. Comp. Neurol. 525:1532-1557, 2017. © 2016 Wiley Periodicals, Inc.

Retinal development in the gilthead seabream Sparus aurata

The retinal development of the gilthead seabream Sparus aurata has been analysed from late embryonic development to juvenile stages using classical histological and immunohistological methods. Five significant phases were established. Phases 1 and 2 comprise the late embryonic and hatching stages, respectively. The results indicate that during these early stages the retina is composed of a single neuroblastic layer that consists of undifferentiated retinal progenitor cells. Phase 3 (late prolarval stage) is characterized by the emergence of the retinal layers and the appearance of neurochemical profiles in differentiating photoreceptors, amacrine and ganglion cells. Phases 4 and 5 comprise the late larval and juvenile stages. In these stages, all the retinal cell types can be detected immunohistochemically. All the maturational events described are first detected in the central retina and, as development progresses, spread to the rest of the retina following a central-to-peripheral gradient. The results of this study suggest that S. aurata is an altricial teleost species that hatches with a morphologically undifferentiated retina. The most relevant processes involved in retinogenesis occur during the late prolarval stage (phase 3).

Development of Retinal Amacrine Cells and Their Dendritic Stratification

Themammalian retina containsmultiple neurons, each of which contributes differentially to visual processing. Of these retinal neurons, amacrine cells have recently come to prime light since they facilitate majority of visual processing that takes place in the retina. Amacrine cells are also the most diverse group of neurons in the retina, classified majorly based on the neurotransmitter type they express and morphology of their dendritic arbors. Currently, little is known about the molecular basis contributing to this diversity during development. Amacrine cells also contribute to most of the synapses in the inner plexiform layer and mediate visual information input from bipolar cells onto retinal ganglion cells. In this review, we will describe the current understanding of amacrine cell and cell subtype development. Furthermore, we will address the molecular basis of retinal lamination at the inner plexiform layer. Overall, our review will provide a developmental perspective of amacrine cell subtype classification and their dendritic stratification.

The role of egr1 in early zebrafish retinogenesis

Proper retinal cell differentiation is essential for establishing a functional retina. The purpose of this study is to investigate the role of early growth response 1 (egr1), a transcription factor (TF) that has been reported to control eye development and function, on retinal differentiation in zebrafish. Specifically, cellular changes in the Egr1-knockdown retinas were characterized by immunohistochemistry at 72 and 120 hours post-fertilization (hpf). The results indicate that Egr1 knockdown specifically suppressed the differentiation of subtypes of amacrine cells (ACs) and horizontal cells (HCs), including Parvalbumin- and GABA-positive ACs as well as Islet1-positive HCs. In addition, the knockdown induced a general delay of development of the other retinal cell types. These differentiation problems, particularly the ones with the ACs and HCs, also compromised the integrity of the inner and outer plexiform layers. In the Egr1-knockdown retinas, the expression of ptf1a, a TF that controls the specification of ACs and HCs, was prolonged and found in ectopic locations in the retina up to 72 hpf. Then, it became restricted to the proliferative marginal zone as in the control retinas at 120 hpf. This abnormal and prolonged expression of ptf1a during retinogenesis might affect the differentiation of ACs and HCs in the Egr1-knockdown retinas.

Biasing amacrine subtypes in the Atoh7 lineage through expression of Barhl2

Within the developing vertebrate retina, particular subtypes of amacrine cells (ACs) tend to arise from progenitors expressing the basic helix-loop-helix (bHLH) transcription factor, Atoh7, which is necessary for the early generation of retinal ganglion cells (RGCs). All ACs require the postmitotic expression of the bHLH pancreas transcription factor Ptf1a; however, Ptf1a alone is not sufficient to give subtype identities. Here we use functional and in vivo time-lapse studies in the zebrafish retina to investigate on the developmental programs leading to ACs specification within the subsequent divisions of Atoh7-positive progenitors. We find evidences that the homeobox transcription factor Barhl2 is an AC subtype identity-biasing factor that turns on within Atoh7-positive descendants. In vivo lineage tracing reveals that particular modes of cell division tend to generate Barhl2-positive precursors from sisters of RGCs. Additionally, Atoh7 indirectly impacts these division modes to regulate the right number of barhl2-expressing cells. We finally find that Atoh7 itself influences the subtypes of Barhl2-dependent ACs. Together, the results from our study uncover lineage-related and molecular logic of subtype specification in the vertebrate retina, by showing that specific AC subtypes arise via a particular mode of cell division and a transcriptional network cascade involving the sequential expression of first atoh7 followed by ptf1a and then barhl2.

Two types of tyrosine hydroxylase-immunoreactive neurons in the zebrafish retina

The purpose of the present study is to identify the dopaminergic amacrine (DA) cells in the inner nuclear layer (INL) of zebrafish retina through immunocytochemistry and quantitative analysis. Two types of tyrosine hydroxylase-immunoreactive (TH-IR) cells appeared on the basis of dendritic morphology and stratification patterns in the inner plexiform layer (IPL). The first (DA1) was bistratified, with branching planes in both s1 and s5 of the IPL. The second (DA2) was diffuse, with dendritic processes branched throughout the IPL. DA1 and DA2 cells corresponded morphologically to A(on)(-s1/s5) and A(diffuse)(-1) (Connaughton et al., 2004). The average number of total TH-IR cells was 1088±79cells per retina (n=5), and the mean density was 250±27cells/mm(2). Their density was highest in the mid central region of ventrotemporal retina and lowest in the periphery of dorsonasal retina. Quantitatively, 45.71% of the TH-IR cells were DA1 cells, while 54.29% were DA2 cells. No TH-IR cells expressed calbindin D28K, calretinin or parvalbumin, markers for the various INL cells present in several animals. Therefore the TH-IR cells in zebrafish are limited to very specific subpopulations of the amacrine cells.

Zebrafish Tg(7.2mab21l2:EGFP)ucd2 transgenics reveal a unique population of retinal amacrine cells

PURPOSE

Amacrine cells constitute a diverse, yet poorly characterized, cell population in the inner retina. Here, the authors sought to characterize the morphology, molecular physiology, and electrophysiology of a subpopulation of EGFP-expressing retinal amacrine cells identified in a novel zebrafish transgenic line.

METHODS

After 7.2 kb of the zebrafish mab21l2 promoter was cloned upstream of EGFP, it was used to create the Tg(7.2mab21l2:EGFP)ucd2 transgenic line. Transgenic EGFP expression was analyzed by fluorescence microscopy in whole mount embryos, followed by detailed analysis of EGFP-expressing amacrine cells using fluorescence microscopy, immunohistochemistry, and electrophysiology.

RESULTS

A 7.2-kb fragment of the mab21l2 promoter region is sufficient to drive transgene expression in the developing lens and tectum. Intriguingly, EGFP was also observed in differentiated amacrine cells. EGFP-labeled amacrine cells in Tg(7.2mab21l2:EGFP)ucd2 constitute a novel GABA- and glycine-negative amacrine subpopulation. Morphologically, EGFP-expressing cells stratify in sublamina 1 to 2 (type 1 OFF) or sublamina 3 to 4 (type 1 ON) or branch diffusely (type 2). Electrophysiologically, these cells segregate into amacrine cells with somas in the vitreal part of the INL and linear responses to current injection or, alternatively, amacrine cells with somas proximal to the IPL and active oscillatory voltage signals. CONCLUSIONS; The novel transgenic line Tg(7.2mab21l2:EGFP)ucd2 uncovers a unique subpopulation of retinal amacrine cells.

Neurochemical coding of enteric neurons in adult and embryonic zebrafish (Danio rerio)

Although the morphology and development of the zebrafish enteric nervous system have been extensively studied, the precise neurochemical coding of enteric neurons and their proportional enteric distribution are currently not known. By using immunohistochemistry, we determined the proportional expression and coexpression of neurochemical markers in the embryonic and adult zebrafish intestine. Tyrosine hydroxylase (TH), vasoactive intestinal peptide (VIP), and pituitary adenylate cyclase-activating peptide (PACAP) were observed only in nerve fibers, whereas other markers were also detected in neuronal cell bodies. Calretinin and calbindin had similar distributions. In embryos, all markers, except for choline acetyltransferase (ChAT) and TH, were present from 72 hours postfertilization. Nitrergic neurons, evenly distributed and remaining constant in time, constituted the major neuronal subpopulation. The neuronal proportions of the other markers increased during development and were characterized by regional differences. In the adult, all markers examined were expressed in the enteric nervous system. A large percentage of enteric neurons displayed calbindin and calretinin, and serotonin was the only marker showing significant distribution differences in the three intestinal regions. Colocalization studies showed that serotonin was not coexpressed with any of the other markers. At least five neuronal subpopulations were determined: a serotonergic, a nitrergic noncholinergic, two cholinergic nonnitrergic subpopulations along with one subpopulation expressing both ChAT and neuronal nitric oxide synthase. Analysis of nerve fibers revealed that nitrergic neurons coexpress VIP and PACAP, and that nitrergic neurons innervate the tunica muscularis, whereas serotonergic and cholinergic nonnitrergic neurons innervate the lamina propria and the tunica muscularis.

Distinct retinal deficits in a zebrafish pyruvate dehydrogenase-deficient mutant

Mutations in ubiquitously expressed metabolic genes often lead to CNS-specific effects, presumably because of the high metabolic demands of neurons. However, mutations in omnipresent metabolic pathways can conceivably also result in cell type-specific effects because of cell-specific requirements for intermediate products. One such example is the zebrafish noir mutant, which we found to be mutated in the pdhb gene, coding for the E1 beta subunit of the pyruvate dehydrogenase complex. This vision mutant is described as blind and was isolated because of its vision defect-related darker appearance. A detailed morphological, behavioral, and physiological analysis of the phenotype revealed an unexpected specific effect on the retina. Surprisingly, the cholinergic amacrine cells of the inner retina are affected earlier than the photoreceptors. This might be attributable to the inability of these cells to maintain production of their neurotransmitter acetylcholine. This is reflected in an earlier loss of motion vision, followed only later by a general loss of light perception. Since both characteristics of the phenotype are attributable to a loss of acetyl-CoA production by pyruvate dehydrogenase, we used a ketogenic diet to bypass this metabolic block and could indeed partially rescue vision and prolong survival of the larvae. The noir mutant provides a case for a systemic disease with ocular manifestation with a surprising specific effect on the retina given the ubiquitous requirement for the mutated gene.