The SCG10-related gene family in the developing rat retina: persistent expression of SCLIP and stathmin in mature ganglion cell layer

Timed Notch Inhibition Drives Photoreceptor Fate Specification in Human Retinal Organoids

Purpose

Transplanting photoreceptors from human pluripotent stem cell–derived retinal organoids have the potential to reverse vision loss in affected individuals. However, transplantable photoreceptors are only a subset of all cells in the organoids. Hence, the goal of our current study was to accelerate and synchronize photoreceptor differentiation in retinal organoids by inhibiting the Notch signaling pathway at different developmental time-points using a small molecule, PF-03084014 (PF).

Methods

Human induced pluripotent stem cell– and human embryonic stem cells–derived retinal organoids were treated with 10 µM PF for 3 days starting at day 45 (D45), D60, D90, and D120 of differentiation. Organoids were collected at post-treatment days 14, 28, and 42 and analyzed for progenitor and photoreceptor markers and Notch pathway inhibition by immunohistochemistry (IHC), quantitative PCR, and bulk RNA sequencing (n = 3–5 organoids from three independent experiments).

Results

Retinal organoids collected after treatment showed a decrease in progenitor markers (KI67, VSX2, PAX6, and LHX2) and an increase in differentiated pan-photoreceptor markers (OTX2, CRX, and RCVRN) at all organoid stages except D120. PF-treated organoids at D45 and D60 exhibited an increase in cone photoreceptor markers (RXRG and ARR3). PF treatment at D90 revealed an increase in cone and rod photoreceptors markers (ARR3, NRL, and NR2E3). Bulk RNA sequencing analysis mirrored the immunohistochemistry data and quantitative PCR confirmed Notch effector inhibition.

Conclusions

Timing the Notch pathway inhibition in human retinal organoids to align with progenitor competency stages can yield an enriched population of early cone or rod photoreceptors.

Building Blocks of Functioning Brain: Cytoskeletal Dynamics in Neuronal Development

Neural connectivity requires proper polarization of neurons, guidance to appropriate target locations, and establishment of synaptic connections. From when neurons are born to when they finally reach their synaptic partners, neurons undergo constant rearrangment of the cytoskeleton to achieve appropriate shape and polarity. Of particular importance to neuronal guidance to target locations is the growth cone at the tip of the axon. Growth-cone steering is also dictated by the underlying cytoskeleton. All these changes require spatiotemporal control of the cytoskeletal machinery. This review summarizes the proteins that are involved in modulating the actin and microtubule cytoskeleton during the various stages of neuronal development.

Life-time expression of the proteins peroxiredoxin, beta-synuclein, PARK7/DJ-1, and stathmin in the primary visual and primary somatosensory cortices in rats

Four distinct proteins are regulated in the aging neuroretina and may be regulated in the cerebral cortex, too: peroxiredoxin, beta-synuclein, PARK[Parkinson disease(autosomal recessive, early onset)]7/DJ-1, and Stathmin. Thus, we performed a comparative analysis of these proteins in the the primary somatosensory cortex (S1) and primary visual cortex (V1) in rats, in order to detect putative common development-, maturation- and age-related changes. The expressions of peroxiredoxin, beta-synuclein, PARK[Parkinson disease (autosomal recessive, early onset)]7/DJ-1, and Stathmin were compared in the newborn, juvenile, adult, and aged S1 and V1. Western blot (WB), quantitative reverse-transcription polymerase chain reaction (qRT-PCR), and immunohistochemistry (IHC) analyses were employed to determine whether the changes identified by proteomics were verifiable at the cellular and molecular levels. All of the proteins were detected in both of the investigated cortical areas. Changes in the expressions of the four proteins were found throughout the life-time of the rats. Peroxiredoxin expression remained unchanged over life-time. Beta-Synuclein expression was massively increased up to the adult stage of life in both the S1 and V1. PARK[Parkinson disease (autosomal recessive, early onset)]7/DJ-1 exhibited a massive up-regulation in both the S1 and V1 at all ages. Stathmin expression was massively down regulated after the neonatal period in both the S1 and V1. The detected protein alterations were analogous to their retinal profiles. This study is the first to provide evidence that peroxiredoxin, beta-synuclein, PARK[Parkinson disease (autosomal recessive, early onset)]7/DJ-1, and Stathmin are associated with postnatal maturation and aging in both the S1 and V1 of rats. These changes may indicate their involvement in key functional pathways and may account for the onset or progression of age-related pathologies.

Identification of genome-wide SNP-SNP and SNP-clinical Boolean interactions in age-related macular degeneration

We propose here a methodology to uncover modularities in the network of SNP-SNP interactions most associated with disease. We start by computing all possible Boolean binary SNP interactions across the whole genome. By constructing a weighted graph of the most relevant interactions and via a combinatorial optimization approach, we find the most highly interconnected SNPs. We show that the method can be easily extended to find SNP/environment interactions. Using a modestly sized GWAS dataset of age-related macular degeneration (AMD), we identify a group of only 19 SNPs, which include those in previously reported regions associated to AMD. We also uncover a larger set of loci pointing to a matrix of key processes and functions that are affected. The proposed integrative methodology extends and overlaps traditional statistical analysis in a natural way. Combinatorial optimization techniques allow us to find the kernel of the most central interactions, complementing current methods of GWAS analysis and also enhancing the search for gene-environment interaction.

Artemin augments survival and axon regeneration in axotomized retinal ganglion cells

Artemin, a recently discovered member of the glial cell line-derived neurotrophic factor (GDNF) family, has neurotrophic effects on damaged neurons, including sympathetic neurons, dopamine neurons, and spiral ganglion neurons both in vivo and in vitro. However, its effects on retinal cells and its intracellular signaling remain relatively unexplored. During development, expression of GFRα3, a specific receptor for artemin, is strong in the immature retina and gradually decreases during maturation, suggesting a possible role in the formation of retinal connections. Optic nerve damage in mature rats causes levels of GFRα3 mRNA to increase tenfold in the retina within 3 days. GFRα3 mRNA levels continue to rise within the first week and then decline. Artemin, a specific ligand for GFRα3, has a neuroprotective effect on axotomized retinal ganglion cells (RGCs) in vivo and in vitro via activation of the extracellular signal-related kinase- and phosphoinositide 3-kinase-Akt signaling pathways. Artemin also has a substantial effect on axon regeneration in RGCs both in vivo and in vitro, whereas other GDNF family members do not. Therefore, artemin/GFRα3, but not other GDNF family members, may be of value for optic nerve regeneration in mature mammals.

Using evolutionary conserved modules in gene networks as a strategy to leverage high throughput gene expression queries

BACKGROUND

Large-scale gene expression studies have not yielded the expected insight into genetic networks that control complex processes. These anticipated discoveries have been limited not by technology, but by a lack of effective strategies to investigate the data in a manageable and meaningful way. Previous work suggests that using a pre-determined seed-network of gene relationships to query large-scale expression datasets is an effective way to generate candidate genes for further study and network expansion or enrichment. Based on the evolutionary conservation of gene relationships, we test the hypothesis that a seed network derived from studies of retinal cell determination in the fly, Drosophila melanogaster, will be an effective way to identify novel candidate genes for their role in mouse retinal development.

METHODOLOGY/PRINCIPAL FINDINGS

Our results demonstrate that a number of gene relationships regulating retinal cell differentiation in the fly are identifiable as pairwise correlations between genes from developing mouse retina. In addition, we demonstrate that our extracted seed-network of correlated mouse genes is an effective tool for querying datasets and provides a context to generate hypotheses. Our query identified 46 genes correlated with our extracted seed-network members. Approximately 54% of these candidates had been previously linked to the developing brain and 33% had been previously linked to the developing retina. Five of six candidate genes investigated further were validated by experiments examining spatial and temporal protein expression in the developing retina.

CONCLUSIONS/SIGNIFICANCE

We present an effective strategy for pursuing a systems biology approach that utilizes an evolutionary comparative framework between two model organisms, fly and mouse. Future implementation of this strategy will be useful to determine the extent of network conservation, not just gene conservation, between species and will facilitate the use of prior biological knowledge to develop rational systems-based hypotheses.

Characterization of the retinal proteome during rod photoreceptor genesis

Background

The process of rod photoreceptor genesis, cell fate determination and differentiation is complex and multi-factorial. Previous studies have defined a model of photoreceptor differentiation that relies on intrinsic changes within the presumptive photoreceptor cells as well as changes in surrounding tissue that are extrinsic to the cell. We have used a proteomics approach to identify proteins that are dynamically expressed in the mouse retina during rod genesis and differentiation.

Findings

A series of six developmental ages from E13 to P5 were used to define changes in retinal protein expression during rod photoreceptor genesis and early differentiation. Retinal proteins were separated by isoelectric focus point and molecular weight. Gels were analyzed for changes in protein spot intensity across developmental time. Protein spots that peaked in expression at E17, P0 and P5 were picked from gels for identification. There were 239 spots that were picked for identification based on their dynamic expression during the developmental period of maximal rod photoreceptor genesis and differentiation. Of the 239 spots, 60 of them were reliably identified and represented a single protein. Ten proteins were represented by multiple spots, suggesting they were post-translationally modified. Of the 42 unique dynamically expressed proteins identified, 16 had been previously reported to be associated with the developing retina.

Conclusions

Our results represent the first proteomics study of the developing mouse retina that includes prenatal development. We identified 26 dynamically expressed proteins in the developing mouse retina whose expression had not been previously associated with retinal development.

The microtubule network and neuronal morphogenesis: Dynamic and coordinated orchestration through multiple players

Nervous system function and plasticity rely on the complex architecture of neuronal networks elaborated during development, when neurons acquire their specific and complex shape. During neuronal morphogenesis, the formation and outgrowth of functionally and structurally distinct axons and dendrites require a coordinated and dynamic reorganization of the microtubule cytoskeleton involving numerous regulators. While most of these factors act directly on microtubules to stabilize them or promote their assembly, depolymerization or fragmentation, others are now emerging as essential regulators of neuronal differentiation by controlling tubulin availability and modulating microtubule dynamics. In this review, we recapitulate how the microtubule network is actively regulated during the successive phases of neuronal morphogenesis, and what are the specific roles of the various microtubule-regulating proteins in that process. We then describe the specific signaling pathways and inter-regulations that coordinate the different activities of these proteins to sustain neuronal development in response to environmental cues.

Involvement of acidic fibroblast growth factor in spinal cord injury repair processes revealed by a proteomics approach

Acidic fibroblast growth factor (aFGF; also known as FGF-1) is a potent neurotrophic factor that affects neuronal survival in the injured spinal cord. However, the pathological changes that occur with spinal cord injury (SCI) and the attribution to aFGF of a neuroprotective effect during SCI are still elusive. In this study, we demonstrated that rat SCI, when treated with aFGF, showed significant functional recovery as indicated by the Basso, Beattie, and Bresnahan locomotor rating scale and the combined behavior score (p < 0.01-0.001). Furthermore proteomics and bioinformatics approaches were adapted to investigate changes in the global protein profile of the damaged spinal cord tissue when experimental rats were treated either with or without aFGF at 24 h after injury. We found that 51 protein spots, resolvable by two-dimensional PAGE, had significant differential expression. Using hierarchical clustering analysis, these proteins were categorized into five major expression patterns. Noticeably proteins involved in the process of secondary injury, such as astrocyte activation (glial fibrillary acidic protein), inflammation (S100B), and scar formation (keratan sulfate proteoglycan lumican), which lead to the blocking of injured spinal cord regeneration, were down-regulated in the contusive spinal cord after treatment with aFGF. We propose that aFGF might initiate a series of biological processes to prevent or attenuate secondary injury and that this, in turn, leads to an improvement in functional recovery. Moreover the quantitative expression level of these proteins was verified by quantitative real time PCR. Furthermore we identified various potential neuroprotective protein factors that are induced by aFGF and may be involved in the spinal cord repair processes of SCI rats. Thus, our results could have a remarkable impact on clinical developments in the area of spinal cord injury therapy.

Stathmin expression during newt retina regeneration

Japanese common newts (Cynops pyrrhogaster) have high ability to regenerate their injured organs including neural tissues, for example, the neural retina belonging to central nervous system. We attempted to clarify the molecular mechanism underlying the formation of a neural network during newt retina regeneration, and focused on the microtubule dynamics controlled by stathmin family proteins. Stathmin is a small cytoplasmic phosphoprotein known to be a microtubule regulator. We isolated a clone encoding stathmin from the newt. The expression level of stathmin is higher in lung and spleen than in the adult intact retina where stathmin was localized on plexiform layers, the ganglion layer and in photoreceptor inner segments. However, in a regenerating process of the retina, stathmin was upregulated from an early regenerating stage until the retinal layered structure was formed. Immunohistochemical analyses revealed that stathmin existed all around the regenerating retina consisting of retinal progenitor cells. These results suggest that stathmin plays important roles in the construction and maintenance of retinal structure and its neural network, by controlling the proliferation of retinal progenitor cells and the microtubule dynamics of retinal neurons. Moreover, stathmin may function in the dedifferentiating process of retinal pigment epithelium cells.

Pitavastatin prevents NMDA-induced retinal ganglion cell death by suppressing leukocyte recruitment

Excitotoxicity is a major cause of retinal ganglion cell (RGC) death during ischemic diseases such as vessel occlusion and diabetic retinopathy. However, the underlying mechanisms are not well understood. Statins, inhibitors of the HMG-CoA reductase, have neuroprotective effects in addition to their original role in lowering cholesterol. We hypothesize that pitavastatin, a recently introduced potent statin, is protective against N-methyl-d-aspartic acid (NMDA)-induced RGC death. Pitavastatin, administered by gavage, abolished NMDA-induced loss of RGCs. To elucidate the mechanisms underlying the neuroprotective effect of pitavastatin, we investigated its impact on inflammation. NMDA increased the expression of interleukin-1beta and TNF-alpha, and endothelial adhesion molecules, including ICAM-1, and induced leukocyte accumulation in the retinal vessels. Pitavastatin significantly reduced NMDA-induced leukocyte accumulation and up-regulation of endothelial adhesion molecules, whereas cytokine expression was unaffected. Systemic blockade of ICAM-1 in wild-type mice or absence of CD18 in gene-deficient (CD18(-/-)) mice significantly suppressed NMDA-induced leukocyte accumulation and RGC death. These findings suggest a novel and causative role for inflammatory leukocyte recruitment in NMDA-induced excitotoxicity. Furthermore, we show the novel neuroprotective effect of statins against excitotoxicity-induced RGC death. Statins or other anti-inflammatory agents may thus have therapeutic benefits in excitotoxicity-associated neuronal diseases through blockade of leukocyte recruitment.

GAP-43 expression is upregulated in retinal ganglion cells after ischemia/reperfusion-induced damage

In response to injury, the adult mammalian retina shows signs of structural remodeling, possibly in an attempt to preserve or regain some of its functional neural connections. In order to study the mechanisms involved in injury-induced plasticity, we have studied changes in growth associated protein 43 (GAP-43) after retinal ischemia/reperfusion in the rat. GAP-43 is a marker for neuronal remodeling and is involved in synapse formation. Ischemic injury of the rat retina was induced by 60 min of ischemia followed by reperfusion times varying from 2h up to 4 weeks. GAP-43 mRNA levels were significantly increased between 12h and 72 h reperfusion with a peak around 24h. GAP-43 specific antibodies showed that the total amount of GAP-43 labeling in the inner plexiform layer was diminished after 12h of reperfusion by approximately 35% and remained at this level up to 1 week postischemia despite the reduction in thickness of this layer during this period resulting from the ischemia-induced cell loss. At 2 and 4 weeks reperfusion, the amount of labeling was reduced by 70%, simultaneously with a decrease of GAP-43 transcript level. Between 72 h up to 2 weeks postischemia, the induction of intense GAP-43 labeling was observed in NeuN- and beta-tubulin-positive ganglion cell somata and in horizontally and vertically oriented processes in the inner plexiform layer. Ischemia also induced GAP-43 expression in some GFAP-positive Müller cells. Double-labeling showed that in controls and after ischemia GAP-43 was expressed by some amacrine cells of the glycinergic (glycine transporter 1), calretinin-positive, and dopaminergic (tyrosine hydroxylase) subpopulations. No increase of GAP-43 expression levels was found in these amacrine cells. The results demonstrate that ganglion cells show an elevated expression of GAP-43 after ischemia-inflicted damage. These findings suggest a temporal window during which ganglion cells may remodel their neuronal network in the damaged retina.

The "SCG10-LIke Protein" SCLIP is a novel regulator of axonal branching in hippocampal neurons, unlike SCG10

Stathmin family phosphoproteins participate in the control of microtubule dynamics and have been proposed to be involved in the control of neuronal differentiation. We examined the biological properties and functions of SCLIP, the stathmin family protein most similar to SCG10, a widely studied and recognized neuronal differentiation marker. SCLIP, like SCG10, is present from the earliest stages of hippocampal neuron differentiation in culture at vesicle-like structures following dynamic microtubules. Its inhibition by RNA interference resulted in increased axonal branching, revealing a novel biological role for SCLIP, distinct from SCG10 whose down-regulation in the same conditions promoted growth cone expansion. The enhanced axonal branching resulted from the formation of collateral lamellar protrusions, with cytoskeleton reorganization typical of normal branching. In addition to revealing a novel function for SCLIP in axonal morphogenesis, our results demonstrate for the first time that stathmin family proteins fulfill different and complementary roles during neuronal differentiation.

Estrogen has a neuroprotective effect on axotomized RGCs through ERK signal transduction pathway

The neuroprotective effects of estrogen on neuronal cells in central nervous system have been described previously, however, the mechanisms of neuroprotective effect of estrogen against retinal ganglion cell (RGC) death has not been well identified. To examine the role of endogenous sex steroids produced in ovary, retina samples were prepared from female rats with or without ovariectomy and the density of RGC was calculated. Ovariectomy alone had no effect on the density of fluorogold (FG)-labeled RGC without injury, while the density of surviving RGC after optic nerve axotomy with ovariectomy was significantly decreased compared to that without ovariectomy. To examine the role of exogenous sex steroids, 17beta-estradiol was injected into the vitreous cavity in ovariectomized rats and showed neuroprotective effect on axotomy-induced RGC death while exogenous progesterone showed no effect. Immunoblot and immunohistochemical analysis demonstrated that ERK-c-Fos signal transduction pathway was activated by exogenous 17beta-estradiol in ganglion cell layer. U0126, an ERK inhibitor, inhibited the neuroprotective effect of estrogen on axotomized RGC death. These data suggest that estrogen has neuroprotective effect through activation of ERK-c-Fos signaling pathway on axotomy-induced RGC death. The neuroprotective effect of estrogen may have therapeutic benefits in retinal diseases associated with RGC death such as glaucoma.

SCG10, a microtubule destabilizing factor, stimulates the neurite outgrowth by modulating microtubule dynamics in rat hippocampal primary cultured neurons

Microtubule dynamics, one of the key elements in neurite outgrowth, is regulated by various regulatory factors to determine the behavior of the neuronal growth cone and to form the specialized neuronal shape. SCG10 is a neuron-specific stathmin protein with a potent microtubule destabilizing factor and is enriched in the growth cones of the developing neurons. We investigated the functional role of SCG10 in neurite outgrowth using rat hippocampal primary cultured neurons. Genetic manipulation of SCG10 using a short-interfering RNA duplex markedly decreased the SCG10 expression level and significantly suppressed neurite outgrowth. This result was confirmed by immunodepletion experiments. On the other hand, the protein transduction of SCG10 using a polyarginine tag stimulated neurite outgrowth. Such manipulation of the SCG10 expression level affected microtubule morphology within the growth cones. A decrease in the SCG10 level converted the morphology to a more stable state, while an increase converted the morphology to a more dynamic state. However, an excess of SCG10 induced neurite retraction due to an excess of microtubule disassembly. These results suggest that SCG10 serves as an important regulatory factor of growth cone motility by enhancing microtubule dynamics, possibly through increasing the catastrophe frequency.

Site-specific phosphorylation of SCG10 in neuronal plasticity: role of Ser73 phosphorylation by N-methyl D-aspartic acid receptor activation in rat hippocampus

Accumulated evidence suggests that actin and microtubule regulating proteins contribute to neuronal structural dynamics, which subsequently affect neuronal plasticity. SCG10 is a neuronal-specific stathmin protein with microtubule destabilizing activity that is affected by multiple phosphorylation, at least in vitro. SCG10 has four major phosphorylation sites: Ser50 and Ser97 targeted by protein kinase A (PKA), and Ser62 and Ser73 targeted by mitogen-activated protein kinase (MAPK). To explore the potential roles of site-specific phosphorylation in physiological models, we developed phosphorylation site-specific antibodies and examined the SCG10 status in primary cultured hippocampal neurons and tissues. Although SCG10 is concentrated in growth cones and the Golgi apparatus in primary cultured neurons, the phosphorylated form was also detected in both regions, suggesting that MT dynamics within the growth cone may be regulated by protein phosphorylation. In the adult hippocampus, an intense stimulus such as kainate treatment induced a rapid phosphorylation of Ser73 within 15 min that was sustained for at least 60 min. This response was mediated through the N-methyl D-aspartic acid (NMDA) receptor and was ablated by the antagonist MK-801. The MAPK enzyme Erk2 was simultaneously activated along a similar time course to SCG10, suggesting that Erk2 may directly phosphorylate Ser73. These results demonstrate that changes in the phosphorylation status of SCG10 in vivo, dependent upon neural activity and/or plasticity, could affect the microtubule dynamics in neuronal dendrites.

Selective upregulation of RB3/stathmin4 by ciliary neurotrophic factor following optic nerve axotomy

In this study, we examined the cellular responses of stathmin-related proteins in the rat retina following optic nerve (ON) axotomy. To examine the distribution of stathmin-related gene products, we performed semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), in situ hybridization (ISH) and immunohistochemical analyses. Retrograde labeling using a fluorescein tracer, fluorogold (FG), was used for the identification of retinal ganglion cells (RGCs). RT-PCR and ISH analyses indicated that the expression of RB3 was specifically increased in the ganglion cell layer (GCL) comparing to other members of stathmin-related gene family examined 3 days following the ON axotomy. When brain-derived neurotrophic factor was administrated intravitreously, the induction of RB3 mRNA sustained up to 7 days after axotomy, although the peak induction level was unchanged. In contrast, ciliary neurotrophic factor (CNTF) administration increased the peak level of RB3 mRNA induction significantly at 3 days after axotomy. Immunohistochemistry in combination with the retrograde labeling of axotomized cells by FG revealed that RB3 was increased following axotomy in FG-labeled RGCs. These data suggest that RB3 is the unique response protein in the stathmin-related proteins following ON axotomy and the induced RB3 may play a critical role in the CNTF-induced response on the axotomized RGCs, e.g. axonal regeneration and/or neuroprotection.

L1/Laminin modulation of growth cone response to EphB triggers growth pauses and regulates the microtubule destabilizing protein SCG10

During development, EphB proteins serve as axon guidance molecules for retinal ganglion cell axon pathfinding toward the optic nerve head and in midbrain targets. To better understand the mechanisms by which EphB proteins influence retinal growth cone behavior, we investigated how axon responses to EphB were modulated by laminin and L1, two guidance molecules that retinal axons encounter during in vivo pathfinding. Unlike EphB stimulation in the presence of laminin, which triggers typical growth cone collapse, growth cones co-stimulated by L1 did not respond to EphB. Moreover, EphB exposure in the presence of both laminin and L1 resulted in a novel growth cone inhibition manifested as a pause in axon elongation with maintenance of normal growth cone morphology and filopodial activity. Pauses were not associated with loss of growth cone actin but were accompanied by a redistribution of the microtubule cytoskeleton with increased numbers of microtubules extending into filopodia and to the peripheral edge of the growth cone. This phenomenon was accompanied by reduced levels of the growth cone microtubule destabilizing protein SCG10. Antibody blockade of SCG10 function in growth cones resulted in both changes in microtubule distribution and pause responses mirroring those elicited by EphB in the presence of laminin and L1. These results demonstrate that retinal growth cone responsiveness to EphB is regulated by co-impinging signals from other axon guidance molecules. Furthermore, the results are consistent with EphB-mediated axon guidance mechanisms that involve the SCG10-mediated regulation of the growth cone microtubule cytoskeleton.

Expression and functional properties of unique inward rectifier K+ channel Kir7.1 in the porcine iris and retinal pigment epithelium

PURPOSE

To investigate the membrane functional properties of porcine iris pigment epithelial cells (IPE), and compare the characters of inward rectifier potassium (Kir) channel in the IPE with those in the retinal pigment epithelial cells (RPE).

METHODS

IPE and RPE were acutely dissociated from porcine eyes. Functional properties of Kir channels were characterized using whole cell patch clamp recording techniques. Expression of Kir7.1 mRNA in both cells was detected by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Whole cell current in the IPE exhibited a mild inward K+ rectification, and showed little dependence on [K+]o. Unusual high (7.04 +/- 1.7) Rb+ to K+ inward conductance ratio indicated that Kir7.1 subunit was expressed in the IPE as the same as RPE cells. Also, Kir7.1 mRNA was detected in both porcine IPE and RPE by RT-PCR. However, functional expression of Kir conductance in IPE cells (21.7 S/F) was much smaller than that in RPE cells (205.6 S/F).

CONCLUSIONS

The Kir7.1 subunit was predominantly expressed in the acutely dissociated porcine IPE and its functional properties are similar to those in the RPE. However, the current density seems too small to fulfill the task of the Kir function of RPE.

Expression of stathmin family genes in human tissues: non-neural-restricted expression for SCLIP

The stathmin family consists of phosphoproteins highly conserved in vertebrates and thought to be implicated in the development and functional regulation of various organs, most notably the nervous system. This family includes stathmin, SCG10, SCLIP, and RB3, phosphoproteins that are related by structural and functional homologies. They all sequester tubulin and interfere with microtubule dynamics, a property due to their shared stathmin-like domain. Little is known about the expression of the stathmin gene family in humans. Herein, we describe for the first time, for a collection of human tissues, the expression of each member of this family, using real-time quantitative RT-PCR. We found that stathmin is ubiquitously expressed, whereas SCG10 and RB3 are neural enriched, expression patterns similar to those reported for other mammals. Surprisingly, SCLIP, whose expression is thought to be neural-specific, exhibits a broader tissue distribution. Analyses of the SCLIP gene (approved symbol STMN3) show that it contains several NRSE-like elements that display low or no affinity for the cognate binding protein NRSF. The substantial expression of SCLIP in most tissues points out a novel function for this protein outside the nervous system and raises the possibility that its coexpression with stathmin could provide some degree of functional redundancy.

SCG10-related neuronal growth-associated proteins in neural development, plasticity, degeneration, and aging

Neuronal growth-associated proteins (nGAPs) are in general neuron-specific gene products whose expression correlates tightly with neuronal process outgrowth and/or regeneration, and are mostly good downstream targets of neurotrophin stimulation. Expression of genes encoding nGAPs such as GAP-43, SCG10, and stathmin is upregulated following lesioning of cortical and hippocampal regions of the adult rat brain. In the brains of aged animals, however, the magnitude of the response is reduced, whereas the time course of the response is mostly unchanged when compared with that for brains of young ones. Expression of GAP-43 and stathmin is reduced by aging, and is also changed in age-related neurodegenerative conditions such as Alzheimer's disease in humans. Certain nGAPs are induced during long-term potentiation (LTP) and also during critical periods of song-learning and ocular dominance column formation in birds and cats, respectively. Recent evidence further supports the idea that functional synaptic modulation is often associated with remodeling of synaptic structures. These results suggest that neurotrophin-responsive nGAPs serve as molecular markers of neuronal plasticity during development and aging, and that the neuronal plasticity decreases, at least in certain neuronal circuits, in the aged brain and neurodegenerative diseases. Recent findings on the roles of stathmin and SCG10-related proteins in microtubule destabilization and its functional block by phosphorylation further support the importance of the SCG10 family proteins in neuronal cytoskeletal regulation, particularly as to microtubule dynamics. We summarize here a decade of research on SCG10 and its related molecules with special interests to brain aging and disease.

Comparative expression profiles of Trk receptors and Shc-related phosphotyrosine adapters during retinal development: potential roles of N-Shc/ShcC in brain-derived neurotrophic factor signal transduction and modulation

Neurotrophins (NTs) have multiple roles in retinal development and survival, which are mediated through their specific receptors and signaling molecules. An emerging family of adapter protein, Shc (Src homology and collagen)-related molecules, i.e., Shc/ShcA, Sck/ShcB, and N-Shc/ShcC, has been implicated in various phosphotyrosine signal transduction mechanisms, including that for NTs. To explore the potential role(s) of Shc-related adapters in NT signaling in the retina, we compared the developmental changes of the mRNA expression of TrkA -B, and -C in the rat retina, on one hand and, on the other hand, studied which members of the Shc family were activated after brain-derived neurotrophic factor (BDNF) application in axotomized rat retinas. Early in development, both TrkA and ShcA were highly expressed, whereas, in late development to adulthood, TrkB/C and ShcB/C were highly expressed. In the mature retinal ganglion cell layer, the expression of ShcB/C and TrkB/C was evident. Immunoreactivity of ShcC was located in the retinal ganglion cells, amacrine cells, and inner plexiform layer. The response of ShcC following retinal axotomy was most profound with the administration of BDNF, and there was some response with neurotrophin-3. These results indicate that ShcC could be a potential phosphotyrosine adapter among the Shc family members for BDNF signaling and function during retinal development and regeneration in vivo.

Ocular development-associated gene (ODAG), a novel gene highly expressed in ocular development

Complementary DNA (cDNA) arrays were used to detect highly expressed messenger RNA (mRNA) at postnatal day 2 (P2) and P10 in the mouse eye, and several clones highly expressed at P2 were isolated. We focused among them on a novel gene, the ocular development-associated gene (ODAG), which was down regulated at P10. The expression around birth was subsequently confirmed by reverse transcription-polymerase chain reaction. Mouse ODAG cDNA encodes a protein of 266 amino acids. Human ODAG cDNA and genomic structure were identified by basic local alignment search tool analysis of the GenBank database with mouse ODAG. Mouse ODAG-specific mRNA expression was detected in various mouse tissues within the eye at P2 and P7, whereas it was not detected anywhere at P14, suggesting that ODAG may play a role in eye development.

Full-sized RanBPM cDNA encodes a protein possessing a long stretch of proline and glutamine within the N-terminal region, comprising a large protein complex

Previously isolated RanBPM, a Ran-binding protein in the microtubule-organizing center, which had been thought to play a role in Ran-stimulated microtubule assembly, turned out to be a truncated protein. To clarify the function of RanBPM, we cloned the full-sized RanBPM cDNA that encodes a 90 kDa protein, compared to the previously isolated cDNA that encoded a 55 kDa protein. The newly cloned 5' coding region contains a great number of cytidine and guanidine nucleotides, like the CpG island. Thus, full-sized RanBPM cDNA encodes a long stretch of proline and glutamine residues in the N-terminal region. It comprises a protein complex of more than 670 kDa. Ran was detected in this complex when RanBPM and Ran were both ectopically expressed. New antibodies to RanBPM were prepared against three different regions of RanBPM. All of them detected a 90 kDa protein that is predominantly localized both in the nucleus and in the cytoplasmic region surrounding the centrosome, but none of them stained the centrosome. In this context, our previous notion that RanBPM is a centrosomal protein should be discarded. RanBPM is well conserved in the animal kingdom. It may play an important role in uncovering Ran-dependent nuclear events.

Stathmin family proteins display specific molecular and tubulin binding properties

Stathmin family phosphoproteins (stathmin, SCG10, SCLIP, and RB3/RB3'/RB3") are involved in signal transduction and regulation of microtubule dynamics. With the exception of stathmin, they are expressed exclusively in the nervous system, where they display different spatio-temporal and functional regulations and hence play at least partially distinct and possibly complementary roles in relation to the control of development, plasticity, and neuronal activities. At the molecular level, each possesses a specific "stathmin-like domain" and, with the exception of stathmin, various combinations of N-terminal extensions involved in their association with intracellular membrane compartments. We show here that each stathmin-like domain also displays specific biochemical and tubulin interaction properties. They are all able to sequester two alpha/beta tubulin heterodimers as revealed by their inhibitory action on tubulin polymerization and by gel filtration. However, they differ in the stabilities of the complexes formed as well as in their interaction kinetics with tubulin followed by surface plasmon resonance as follows: strong stability and slow kinetics for RB3; medium for SCG10, SCLIP, and stathmin; and weak stability and rapid kinetics for RB3'. These results suggest that the fine-tuning of their stathmin-like domains contributes to the specific functional roles of stathmin family proteins in the regulation of microtubule dynamics within the various cell types and subcellular compartments of the developing or mature nervous system.