Immunocytochemical localization of the alpha-, beta I-, beta II- and gamma-subspecies of protein kinase C in the monkey visual pathway

Dystrophin Is Required for the Proper Timing in Retinal Histogenesis: A Thorough Investigation on the mdx Mouse Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a lethal X-linked muscular disease caused by defective expression of the cytoskeletal protein dystrophin (Dp427). Selected autonomic and central neurons, including retinal neurons, express Dp427 and/or dystrophin shorter isoforms. Because of this, DMD patients may also experience different forms of cognitive impairment, neurological and autonomic disorders, and specific visual defects. DMD-related damages to the nervous system are established during development, suggesting a role for all dystrophin isoforms in neural circuit development and differentiation; however, to date, their function in retinogenesis has never been investigated. In this large-scale study, we analyzed whether the lack of Dp427 affects late retinogenesis in the mdx mouse, the most well studied animal model of DMD. Retinal gene expression and layer maturation, as well as neural cell proliferation, apoptosis, and differentiation, were evaluated in E18 and/or P0, P5, P10, and adult mice. In mdx mice, expression of Capn3, Id3 (E18-P5), and Dtnb (P5) genes, encoding proteins involved in different aspects of retina development and synaptogenesis (e.g., Calpain 3, DNA-binding protein inhibitor-3, and β-dystrobrevin, respectively), was transiently reduced compared to age-matched wild type mice. Concomitantly, a difference in the time required for the retinal ganglion cell layer to reach appropriate thickness was observed (P0–P5). Immunolabeling for specific cell markers also evidenced a significant dysregulation in the number of GABAergic amacrine cells (P5–P10), a transient decrease in the area immunopositive for the Vesicular Glutamate Transporter 1 (VGluT1) during ribbon synapse maturation (P10) and a reduction in the number of calretinin⁺ retinal ganglion cells (RGCs) (adults). Finally, the number of proliferating retinal progenitor cells (P5–P10) and apoptotic cells (P10) was reduced. These results support the hypothesis of a role for Dp427 during late retinogenesis different from those proposed in consolidated neural circuits. In particular, Dp427 may be involved in shaping specific steps of retina differentiation. Notably, although most of the above described quantitative alterations recover over time, the number of calretinin⁺ RGCs is reduced only in the mature retina. This suggests that alterations subtler than the timing of retinal maturation may occur, a hypothesis that demands further in-depth functional studies.

Investigation of Visual System Involvement in Spinocerebellar Ataxia Type 14

Spinocerebellar ataxia type 14 (SCA-PRKCG, formerly SCA14) is a rare, slowly progressive disorder caused by conventional mutations in protein kinase Cγ (PKCγ). The disease usually manifests with ataxia, but previous reports suggested PRKCG variants in retinal pathology. To systematically investigate for the first time visual function and retinal morphology in patients with SCA-PRKCG. Seventeen patients with PRKCG variants and 17 healthy controls were prospectively recruited, of which 12 genetically confirmed SCA-PRKCG patients and 14 matched controls were analyzed. We enquired a structured history for visual symptoms. Vision-related quality of life was obtained with the National Eye Institute Visual Function Questionnaire (NEI-VFQ) including the Neuro-Ophthalmic Supplement (NOS). Participants underwent testing of visual acuity, contrast sensitivity, visual fields, and retinal morphology with optical coherence tomography (OCT). Measurements of the SCA-PRKCG group were analyzed for their association with clinical parameters (ataxia rating and disease duration). SCA-PRKCG patients rate their vision-related quality of life in NEI-VFQ significantly worse than controls. Furthermore, binocular visual acuity and contrast sensitivity were worse in SCA-PRKCG patients compared with controls. Despite this, none of the OCT measurements differed between groups. NEI-VFQ and NOS composite scores were related to ataxia severity. Additionally, we describe one patient with a genetic variant of uncertain significance in the catalytic domain of PKCγ who, unlike all confirmed SCA-PRKCG, presented with a clinically silent epitheliopathy. SCA-PRKCG patients had reduced binocular vision and vision-related quality of life. Since no structural retinal damage was found, the pathomechanism of these findings remains unclear.

Differential expression of PKCα and -β in the zebrafish retina

The retina is a complex neural circuit, which processes and transmits visual information from light perceiving photoreceptors to projecting retinal ganglion cells. Much of the computational power of the retina rests on signal integrating interneurons, such as bipolar cells. Commercially available antibodies against bovine and human conventional protein kinase C (PKC) α and -β are frequently used as markers for retinal ON-bipolar cells in different species, despite the fact that it is not known which bipolar cell subtype(s) they actually label. In zebrafish (Danio rerio) five prkc genes (coding for PKC proteins) have been identified. Their expression has not been systematically determined. While prkcg is not expressed in retinal tissue, the other four prkc (prkcaa, prkcab, prkcba, prkcbb) transcripts were found in different parts of the inner nuclear layer and some as well in the retinal ganglion cell layer. Immunohistochemical analysis in adult zebrafish retina using fluorescent in situ hybridization and PKC antibodies showed an overlapping immunolabeling of ON-bipolar cells that are most likely of the BON s6 and BON s6L or RRod type. However, comparison of transcript expression with immunolabeling, implies that these antibodies are not specific for one single zebrafish conventional PKC, but rather detect a combination of PKC -α and -β variants.

Lamination of the lateral geniculate nucleus of catarrhine primates

The lateral geniculate nucleus (LGN) of catarrhine primates - with the exception of gibbons - is typically described as a 6-layered structure, comprised of 2 ventral magnocellular layers, and 4 dorsal parvocellular layers. The parvocellular layers of the LGN are involved in color vision. Therefore, it is hypothesized that a 6-layered LGN is a shared-derived trait among catarrhines. This might suggest that in gibbons the lack of further subdivisions of the parvocellular layers is a recent change, and could be related to specializations of visual information processing in this taxon. To address these hypotheses, the lamination of the LGN was investigated in a range of catarrhine species, including several taxa not previously described, and the evolution of the LGN was reconstructed using phylogenetic information. The findings indicate that while all catarrhine species have 4 parvocellular leaflets, two main patterns of LGN parvocellular lamination occur: 2 undivided parvocellular layers in some species, and 4 parvocellular leaflets (with occasional subleaflets) in other species. LGN size was not found to be related to lamination pattern. Both patterns were found to occur in divergent clades, which is suggestive of homoplasy within the catarrhines in LGN morphology.

PKC{alpha} is essential for the proper activation and termination of rod bipolar cell response

PURPOSE

Protein kinase (PKC)-α is abundant in retinal bipolar cells. This study was performed to explore its role in visual processing.

METHODS

PKCα-knockout (Prkca(-/-)) mice and control animals were examined by using electroretinography (ERG), light microscopy, and immunocytochemistry.

RESULTS

The Prkca(-/-) mice showed no signs of retinal degeneration up to 12 months of age, but ERG measurements indicated a decelerated increase in the ascending limb of the scotopic (rod-sensitive) b-wave as well as a delayed return to baseline. These results suggest that PKCα is an important modulator that affects bipolar cell signal transduction and termination. Confocal microscopy of retinal sections showed that PKCα co-localized with calbindin, which indicates a PKCα localization in close proximity to the horizontal cell terminals. In addition, the implicit time of the ERG c-wave originating from the retinal pigment epithelium (RPE) and the recovery of photoreceptors from bleaching conditions were substantially faster in the knockout mice than in the wild-type control animals.

CONCLUSIONS

These results suggest that PKCα is a modulator of rod-bipolar cell function by accelerating glutamate-driven signal transduction and termination. This modulation is of importance in the switch between scotopic and photopic vision. Furthermore, PKCα seems to play a role in RPE function.

Role of protein kinase C in selective inhibition of mouse retinal neurites during contacts with chondroitin sulfates

Chondroitin sulfate proteoglycans elicit a selective inhibition to neurite growth from ventrotemporal (VT) but not dorsonasal (DN) retina, potentiating the bilateral routing of axons in the mouse optic chiasm. We examined whether this selective response is mediated by a difference in protein kinase C (PKC) expression. Effects of suppressing PKC activity in explant preparations of embryonic day 14 retinae with inhibitor Gö6976 or Ro-32-0432 abolished the chondroitin sulfate inhibition to the VT neurites but had no effect to the DN neurites. Whether these responses rely on a difference in expression of PKC in the growth cones was examined using antibodies against six isozymes of PKC. Among these the alpha, betaI and epsilon isozymes were expressed prominently in the retinal growth cones; whilst the betaII, delta and gamma isozymes were barely detected. Moreover, while the alpha and epsilon isozymes were abundant in the filopodial and lamellipodial processes, the betaI isozyme was restricted largely in the core region of the growth cones. Despite these subtype specific localization, there was no significant difference in expression of any of these PKC isozymes between growth cones from VT and DN retina, indicating that the selective response to chondroitin sulfates is not likely generated by a regulation of PKC expression, but by expression of surface molecules that interact with chondroitin sulfate proteoglycans.

The koniocellular pathway in primate vision

A neurochemically distinct population of koniocellular (K) neurons makes up a third functional channel in primate lateral geniculate nucleus. As part of a general pattern, K neurons form robust layers through the full representation of the visual hemifield. Similar in physiology and connectivity to W cells in cat lateral geniculate nucleus, K cells form three pairs of layers in macaques. The middle pair relays input from short-wavelength cones to the cytochrome-oxidase blobs of primay visual cortex (V1), the dorsal-most pair relays low-acuity visual information to layer I of V1, and the ventral-most pair appears closely tied to the function of the superior colliculus. Throughout each K layer are neurons that innervate extrastriate cortex and that are likely to sustain some visual behaviors in the absence of V1. These data show that several pathways exist from retina to V1 that are likely to process different aspects of the visual scene along lines that may remain parallel well into V1.

Protein kinase C-like immunoreactive cells in embryo and adult chicken retinas

Morphological evidence of a temporal parallelism between the appearance of the alpha isoform of protein kinase C (PKC) and some processes such as synaptogenesis in the plexiform layers of the chicken retina is offered. Immunostaining experiments were performed throughout embryonic, young and adult chicken life. The results help to understand the development of rod bipolar cells.

A zinc-dependent Cl- current in neuronal somata

Extracellular Zn2+ modulates current passage through voltage- and neurotransmitter-gated ion channels, at concentrations less than, or near, those produced by release at certain synapses. Electrophysiological effects of cytoplasmic Zn2+ are less well understood, and effects have been observed at concentrations that are orders of magnitude greater than those found in resting and stimulated neurons. To examine whether and how neurons are affected by lower levels of cytoplasmic Zn2+, we tested the effect of Zn2+-selective chelators, Zn2+-preferring ionophores, and exogenous Zn2+ on neuronal somata during whole-cell patch-clamp recordings. We report here that cytoplasmic zinc facilitates the downward regulation of a background Cl- conductance by an endogenous protein kinase C (PKC) in fish retinal ganglion cell somata and that this regulation is maintained if nanomolar levels of free Zn2+ are available. This regulation has not been described previously in any tissue, as other Cl- currents have been described as reduced by PKC alone, reduced by Zn2+ alone, or reduced by both independently. Moreover, control of cation currents by a zinc-dependent PKC has not been reported previously. The regulation we have observed thus provides the first electrophysiological measurements consistent with biochemical measurements of zinc-dependent PKC activity in other systems. These results suggest that contributions of background Cl- conductances to electrical properties of neurons are susceptible to modulation.

alpha2D/A-adrenergic receptor gene induction in the retina by phorbol ester: involvement of an AP-2 element

BACKGROUND

The alpha2-adrenergic receptor (alpha2-AR) expressed in the bovine retina has been demonstrated to be of the alpha2D subtype. The bovine alpha2D-adrenergic receptor (alpha2D/A-AR) gene has been cloned and characterized. This report describes the induction of this gene by phorbol- 12, 13-myristate acetate (PMA), an activator of protein kinase C (PKC).

RESULTS

Treatment of the bovine retina for 60 min with PMA (1 micrometer) resulted in significant and similar increases in alpha2D/A-AR mRNA level and gene transcription. This indicates that PMA causes alpha2D/A-AR gene induction and that this induction takes place directly at the transcriptional level. In C6 cells, treatment with PMA at a concentration which was as low as 0.1 micrometer induced endogenous alpha2D/A-AR mRNA after 60 min. Luciferase reporter assays in C6 cells mapped the PMA-responsive element to a region between -247 bp and -163 bp on the alpha2D/A-AR promoter. Electrophoretic mobility shift assays showed an increased binding of nuclear factor(s) from PMA-treated bovine retina to this promoter region. Competition assays indicate that an AP-2 element may be involved in the PMA-dependent induction.

CONCLUSION

These findings demonstrate for the first time, the direct induction of the alpha2D/A-AR gene by PMA and support a role for an AP-2 element in the induction mechanism.

Up-regulation of protein kinase C in regenerating optic nerve fibers of goldfish: immunohistochemistry and kinase activity assay

Protein kinase C (PKC) activation has been associated with synaptic plasticity in many projections, and manipulating PKC in the retinotectal projection strongly affects the activity-driven sharpening of the retinotopic map. This study examined levels of PKC in the regenerating retinotectal projection via immunostaining and assay of activity. A polyclonal antibody to the conserved C2 (Ca2+ binding) domain of classical PKC isozymes (anti-panPKC) recognized a single band at 79-80 kD on Western blots of goldfish brain. It stained one class of retinal bipolar cells and the ganglion cells in normal retina, as shown previously. Strong staining was not present in the optic fiber layer of retina or in optic nerve, optic tract, or terminal zone in tectum, with the exception of a single fascicle of optic nerve fibers that by their location and by L1 (E587) staining were identified as those arising from newly added ganglion cells at the retinal margin. Normal tectal sections showed dark staining of a subclass of type XIV neuron with somas at the top of the periventricular layer and an apical dendrite ascending to stratum opticum. In regenerating retina, swollen ganglion cells stained darkly and stained axons were seen in the optic fiber layer. In regenerating optic nerve (2-11 weeks postcrush), all fascicles of optic fibers stained darkly for both PKC and L1(E587). At 5 weeks postcrush, PKC staining could also be seen in the medial and lateral optic tracts and stratum opticum at the front half of the tectum and very lightly over the terminal zones. PKC activity was measured in homogenized tissues dissected from a series of fish with unilateral nerve crush from 1 to 5 weeks previously. Activity levels stimulated by phorbols and Ca2+ were measured by phosphorylation of a specific peptide and referred to levels measured in the opposite control side. Regeneration did not increase overall PKC activity in retina or tectum, but in optic nerve there was an 80% rise after the first week. The increased activity verifies that the increased staining in nerve represented an up-regulation of functional PKC during nerve regeneration.

Taurine-stimulated outgrowth from the retina is impaired by protein kinase C activators and phosphatase inhibitors

Taurine increases neurite elongation of post-crush goldfish retinal explants, as well as the number of outgrowing isolated cells from goldfish and rat retina in culture. The trophic effect of taurine is related to an elevation in calcium flux rather than increased cell proliferation. Since taurine regulates phosphorylation in rat retina, we investigated if this process could be involved in the mechanism of taurine action on outgrowth. Control and taurine-supplemented post-crush goldfish retinal explants were cultured in the presence of protein kinase C activators or phosphatase inhibitors, and the length of neurites was measured after five days in culture. In some cases, there was an inhibition of the stimulatory effect of taurine without a modification in basal outgrowth. In others, outgrowth of control explants was also reduced. A certain level of protein phosphorylation seems to be critical for the trophic effect of taurine in the retina.

Layer-specific differential regulation of transcription factors Zif268 and Jun-D in visual cortex V1 and V2 of macaque monkeys

To investigate intracellular mechanisms of cortical layer-specific gene regulation, we quantitatively examined the expression of two transcription factors, Zif268 and JunD, and compared their expression levels in each layer of the primary visual cortex (VI) and visual area 2 (V2) of macaque monkeys (Macaca fuscata). The brain sections were immunohistochemically stained for determination of the percentage of Zif268- or JunD-expressing neurons in the total neuronal population. We found area- and layer-specific expression of these transcription factors; Zif268 tended to be expressed at high levels in layers on the parvocellular pathway in V1, whereas JunD did not show such an expression pattern. In V1, many Zif268-immunopositive neurons were observed in layers II/III, IVC beta and VI. The percentage of Zif268-immunopositive neurons was highest in layer IVC beta and lowest in layer IVC alpha. JunD-immunopositive neurons were fewest in layer IVC beta and most abundant in layer VI. In V2, the level of expression of Zif268 was almost the same as that of JunD in layer II/II. However, layer IV of V2 tended to contain more Zif268-immunopositive neurons than JunD-immunopositive neurons, whereas layer VI contained more JunD-immunopositive neurons than Zif268-immunopositive neurons. Although it has been reported that the same extracellular signals induce both Zif268 and JunD, the present results indicate that the expression of these transcription factors is differentially controlled in each layer of the primate visual cortical areas. Furthermore, the present results suggest that these transcription factors contribute to area- and layer-specific gene regulation by mediating transmission of extracellular signals to the nucleus via different intracellular signalling pathways.

Two classes of bipolar cell in the retina of the skate Raja erinacea

We have used immunoreactions against serotonin and protein kinase C to visualize two distinct classes of bipolar cell in the all-rod retina of the skate, Raja erinacea. To enhance the immunoreaction in serotonin-accumulating bipolar cells, prior to fixation, some retinas were incubated in Ringer's solution containing serotonin and pargyline. We found the somata of serotonin-accumulating bipolar cells to be located slightly distal to the midline of the inner nuclear layer. With increasing eccentricity from the visual streak, the size of the perikarya increases, concomitant with a decline in density of their distribution. Dendrites emanate from stout primary stalks and branch out before reaching the outer plexiform layer. Axons are bistratified within the inner plexiform layer with ramifications at the border of strata 1 and 2 and in stratum 4. The overall morphology of serotonin-accumulating bipolar cells is similar to that of serotonin-accumulating OFF bipolar cells of other non-mammalian vertebrates. Protein kinase C immunoreactive cells display the typical appearance of rod bipolar cells. Somata of protein kinase C immunoreactive bipolar cells are spindle-shaped and located distal to the serotonin-accumulating bipolar cells. Dendrites of these bipolars do not ramify before reaching the outer plexiform layer. Thin axons of protein kinase C immunoreactive bipolar cells end in large, club-shaped terminals in stratum 5 of the inner plexiform layer, bearing a striking similarity to axon terminals of mammalian ON rod bipolar cells. Our findings suggest that the all-rod retina of the skate contains at least two distinct vertical pathways including an OFF bipolar cell pathway in addition to a classical rod ON bipolar pathway.