RARβ isoform-specific regulation of DARPP-32 gene expression: an ectopic expression study in the developing rat telencephalon

Darpp-32 and t-Darpp protein products of PPP1R1B: Old dogs with new tricks

The PPP1R1B gene is located on chromosome 17q12 (39,626,208-39,636,626[GRCh38/hg38]), which codes for multiple transcripts and two experimentally-documented proteins Darpp-32 and t-Darpp. Darpp-32 (Dopamine and cAMP Regulated Phosphoprotein), discovered in the early 1980s, is a protein whose phosphorylation is upregulated in response to cAMP in dopamine-responsive tissues in the brain. It's phosphorylation profile modulates its ability to bind and inhibit Protein Phosphatase 1 activity, which, in turn, controls the activity of hundreds of phosphorylated proteins. PPP1R1B knockout mice exhibit subtle learning defects. In 2002, the second protein product of PPP1R1B was discovered in gastric cancers: t-Darpp (truncated Darpp-32). The start codon of t-Darpp is amino acid residue 37 of Darpp-32 and it lacks the domain responsible for modulating Protein Phosphatase 1. Aside from gastric cancers, t-Darpp and/or Darpp-32 is overexpressed in tumor cells from breast, colon, esophagus, lung and prostate tissues. More than one research team has demonstrated that these proteins, through mechanisms that to date remain cloudy, activate AKT, a protein whose phosphorylation leads to cell survival and blocks apoptosis. Furthermore, in Her2 positive breast cancers (an aggressive form of breast cancer), t-Darpp/Darpp-32 overexpression causes resistance to the frequently-administered anti-Her2 drug, trastuzumab (Herceptin), likely through AKT activation. Here we briefly describe how Darpp-32 and t-Darpp were discovered and report on the current state of knowledge of their involvement in cancers. We present a case for the development of an anti-t-Darpp therapeutic agent and outline the unique challenges this endeavor will likely encounter.

An Overview of Neural Differentiation Potential of Human Adipose Derived Stem Cells

There is wide interest in application of adult stem cells due to easy to obtain with a minimal patient discomfort, capable of producing cell numbers in large quantities and their immunocompatible properties without restriction by ethical concerns. Among these stem cells, multipotent mesenchymal stem cells (MSCs) from human adipose tissue are considered as an ideal source for various regenerative medicine. In spite of mesodermal origin of human adipose-derived stem cells (hADSCs), these cells have differentiation potential toward mesodermal and non-mesodermal lineages. Up to now, several studies have shown that hADSCs can undergo transdifferentiation and produce cells outside of their lineage, especially into neural cells when they are transferred to a specific cell environment. The purpose of this literature review is to provide an overview of the existing state of knowledge of the differentiation potential of hADSCs, specifically their ability to give rise to neuronal cells. The following review discusses different protocols considered for differentiation of hADSCs to neural cells, the neural markers that are used in each procedure and possible mechanisms that are involved in this differentiation.

Role of Nuclear Receptors in Central Nervous System Development and Associated Diseases

The nuclear hormone receptor (NHR) superfamily is composed of a wide range of receptors involved in a myriad of important biological processes, including development, growth, metabolism, and maintenance. Regulation of such wide variety of functions requires a complex system of gene regulation that includes interaction with transcription factors, chromatin-modifying complex, and the proper recognition of ligands. NHRs are able to coordinate the expression of genes in numerous pathways simultaneously. This review focuses on the role of nuclear receptors in the central nervous system and, in particular, their role in regulating the proper development and function of the brain and the eye. In addition, the review highlights the impact of mutations in NHRs on a spectrum of human diseases from autism to retinal degeneration.

Whole-Exome Sequencing in a South American Cohort Links ALDH1A3, FOXN1 and Retinoic Acid Regulation Pathways to Autism Spectrum Disorders

Autism spectrum disorders (ASDs) are a range of complex neurodevelopmental conditions principally characterized by dysfunctions linked to mental development. Previous studies have shown that there are more than 1000 genes likely involved in ASD, expressed mainly in brain and highly interconnected among them. We applied whole exome sequencing in Colombian—South American trios. Two missense novel SNVs were found in the same child: ALDH1A3 (RefSeq NM_000693: c.1514T>C (p.I505T)) and FOXN1 (RefSeq NM_003593: c.146C>T (p.S49L)). Gene expression studies reveal that Aldh1a3 and Foxn1 are expressed in ~E13.5 mouse embryonic brain, as well as in adult piriform cortex (PC; ~P30). Conserved Retinoic Acid Response Elements (RAREs) upstream of human ALDH1A3 and FOXN1 and in mouse Aldh1a3 and Foxn1 genes were revealed using bioinformatic approximation. Chromatin immunoprecipitation (ChIP) assay using Retinoid Acid Receptor B (Rarb) as the immunoprecipitation target suggests RA regulation of Aldh1a3 and Foxn1 in mice. Our results frame a possible link of RA regulation in brain to ASD etiology, and a feasible non-additive effect of two apparently unrelated variants in ALDH1A3 and FOXN1 recognizing that every result given by next generation sequencing should be cautiously analyzed, as it might be an incidental finding.

Retinoic acid receptor beta mediates all-trans retinoic acid facilitation of mesenchymal stem cells neuronal differentiation

All-trans retinoic acid plays an important role in nervous system development. However, the effects of all-trans retinoic acid on the neuronal differentiation of mesenchymal stem cells and the mechanisms through which this differentiation takes place are still poorly understood. Here, we investigated the biological effects of all-trans retinoic acid on the neuronal differentiation of mesenchymal stem cells and the signaling pathways that mediated these effects. We found that the neuronal differentiation efficiency of mesenchymal stem cells following all-trans retinoic acid pre-induction was greater and the axonal length was longer than was observed with mesenchymal stem cells that were not pre-induced. mRNA and protein levels of the neural-markers Nestin, NSE, MAP-2, Tau and Tuj1 were stronger in neural-like cells derived from all-trans retinoic acid-pretreated mesenchymal stem cells than in those not pre-induction. Interestingly, the neuronal excitability of differentiated neural-like cells exhibited the same patterns between these two groups. Clear expression of retinoic acid receptor alpha and gamma in mesenchymal stem cells was observed, while retinoic acid receptor beta was barely detected. However, retinoic acid receptor beta expression in mesenchymal stem cells after neuronal induction increased dramatically, in contrast with retinoic acid receptor alpha and gamma expression, and retinoic acid receptor beta expression in mesenchymal stem cells receiving all-trans retinoic acid pre-induction was even stronger. Next, retinoic acid receptor alpha, beta and gamma were over-expressed by recombinant adenovirus infection prior to neuronal induction. Retinoic acid receptor alpha and gamma over-expression did not impact the neuronal differentiation of mesenchymal stem cells. However, retinoic acid receptor beta over-expression promoted neuronal differentiation to a similar level as observed following all-trans retinoic acid pre-induction. The neuronal differentiation promoting effects of all-trans retinoic acid on mesenchymal stem cells could be inhibited by siRNA silencing of retinoic acid receptor beta and by LE135, an inhibitor of retinoic acid receptor beta. Taken together, these results suggest that all-trans retinoic acid pre-induction facilitates the neuronal differentiation of mesenchymal stem cells. These facilitation effects are achieved by activating the retinoic acid receptor beta signaling pathway.

Retinoic acid and human olfactory ensheathing cells cooperate to promote neural induction from human bone marrow stromal stem cells

The generation of induced neuronal cells from human bone marrow stromal stem cells (hBMSCs) provides new avenues for basic research and potential transplantation therapies for nerve injury and neurological disorders. However, clinical application must seriously consider the risk of tumor formation by hBMSCs, neural differentiation efficiency and biofunctions resembling neurons. Here, we co-cultured hBMSCs exposed to retinoic acid (RA) with human olfactory ensheathing cells (hOECs) to stimulate its differentiation into neural cells, and found that hBMSCs following 1 and 2 weeks of stimulation promptly lost their immunophenotypical profiles, and gradually acquired neural cell characteristics, as shown by a remarkable up-regulation of expression of neural-specific markers (Tuj-1, GFAP and Galc) and down-regulation of typical hBMSCs markers (CD44 and CD90), as well as a rapid morphological change. Concomitantly, in addition to a drastic decrease in the number of BrdU incorporated cells, there was a more elevated synapse formation (a hallmark for functional neurons) in the differentiated hBMSCs. Compared with OECs alone, this specific combination of RA and hOECs was significantly potentiated neuronal differentiation of hBMSCs. The results suggest that RA can enhance and orchestrate hOECs to neural differentiation of hBMSCs. Therefore, these findings may provide an alternative strategy for the repair of traumatic nerve injury and neurological diseases with application of the optimal combination of RA and OECs for neuronal differentiation of hBMSCs.

Molecular regulation of striatal development: a review

The central nervous system is composed of the brain and the spinal cord. The brain is a complex organ that processes and coordinates activities of the body in bilaterian, higher-order animals. The development of the brain mirrors its complex function as it requires intricate genetic signalling at specific times, and deviations from this can lead to brain malformations such as anencephaly. Research into how the CNS is specified and patterned has been studied extensively in chick, fish, frog, and mice, but findings from the latter will be emphasised here as higher-order mammals show most similarity to the human brain. Specifically, we will focus on the embryonic development of an important forebrain structure, the striatum (also known as the dorsal striatum or neostriatum). Over the past decade, research on striatal development in mice has led to an influx of new information about the genes involved, but the precise orchestration between the genes, signalling molecules, and transcription factors remains unanswered. We aim to summarise what is known to date about the tightly controlled network of interacting genes that control striatal development. This paper will discuss early telencephalon patterning and dorsal ventral patterning with specific reference to the genes involved in striatal development.

Pre-activation of retinoid signaling facilitates neuronal differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) can differentiate into neurons in an appropriate cellular environment. Retinoid signaling pathway is required in neural development. However, the effect and mechanism through retinoid signaling regulates neuronal differentiation of MSCs are still poorly understood. Here, we report that all-trans-retinoic acid (ATRA) pre-induction improved neuronal differentiation of rat MSCs. We found that, when MSCs were exposed to different concentrations of ATRA (0.01-100 micromol/L) for 24 h and then cultured with modified neuronal induction medium (MNM), 1 micromol/L ATRA pre-induction significantly improved neuronal differentiation efficiency and neural-cell survival. Compared with MNM alone induced neural-like cells, ATRA/MNM induced cells expressed higher levels of Nestin, neuron specific enolase (NSE), microtubule-associated protein-2 (MAP-2), but lower levels of CD68, glial fibrillary acidic protein (GFAP), and glial cell line-derived neurotrophic factor(GDNF), also exhibited higher resting membrane potential and intracellular calcium concentration, supporting that ATRA pre-induction promotes maturation and function of derived neurons but not neuroglia cells from MSCs. Endogenous retinoid X receptors (RXR) RXRalpha and RXRgamma (and to a lesser extent, RXRbeta) were weakly expressed in MSCs. But the expression of RARalpha and RARgamma was readily detectable, whereas RARbeta was undetectable. However, at 24 h after ATRA treatment, the expression of RARbeta, not RARalpha or RARgamma, increased significantly. We further found the subnuclear redistribution of RARbeta in differentiated neurons, suggesting that RARbeta may function as a major mediator of retinoid signaling during neuronal differentiation from MSCs. ATRA treatment upregulated the expression of Vimentin and Stra13, while it downregulated the expression of Brachyury in MSCs. Thus, our results demonstrate that pre-activation of retinoid signaling by ATRA facilitates neuronal differentiation of MSCs.

Nolz1 promotes striatal neurogenesis through the regulation of retinoic acid signaling

Background

Nolz1 is a zinc finger transcription factor whose expression is enriched in the lateral ganglionic eminence (LGE), although its function is still unknown.

Results

Here we analyze the role of Nolz1 during LGE development. We show that Nolz1 expression is high in proliferating neural progenitor cells (NPCs) of the LGE subventricular zone. In addition, low levels of Nolz1 are detected in the mantle zone, as well as in the adult striatum. Similarly, Nolz1 is highly expressed in proliferating LGE-derived NPC cultures, but its levels rapidly decrease upon cell differentiation, pointing to a role of Nolz1 in the control of NPC proliferation and/or differentiation. In agreement with this hypothesis, we find that Nolz1 over-expression promotes cell cycle exit of NPCs in neurosphere cultures and negatively regulates proliferation in telencephalic organotypic cultures. Within LGE primary cultures, Nolz1 over-expression promotes the acquisition of a neuronal phenotype, since it increases the number of β-III tubulin (Tuj1)- and microtubule-associated protein (MAP)2-positive neurons, and inhibits astrocyte generation and/or differentiation. Retinoic acid (RA) is one of the most important morphogens involved in striatal neurogenesis, and regulates Nolz1 expression in different systems. Here we show that Nolz1 also responds to this morphogen in E12.5 LGE-derived cell cultures. However, Nolz1 expression is not regulated by RA in E14.5 LGE-derived cell cultures, nor is it affected during LGE development in mouse models that present decreased RA levels. Interestingly, we find that Gsx2, which is necessary for normal RA signaling during LGE development, is also required for Nolz1 expression, which is lost in Gsx2 knockout mice. These findings suggest that Nolz1 might act downstream of Gsx2 to regulate RA-induced neurogenesis. Keeping with this hypothesis, we show that Nolz1 induces the selective expression of the RA receptor (RAR)β without altering RARα or RARγ. In addition, Nozl1 over-expression increases RA signaling since it stimulates the RA response element. This RA signaling is essential for Nolz1-induced neurogenesis, which is impaired in a RA-free environment or in the presence of a RAR inverse agonist. It has been proposed that Drosophila Gsx2 and Nolz1 homologues could cooperate with the transcriptional co-repressors Groucho-TLE to regulate cell proliferation. In agreement with this view, we show that Nolz1 could act in collaboration with TLE-4, as they are expressed at the same time in NPC cultures and during mouse development.

Conclusions

Nolz1 promotes RA signaling in the LGE, contributing to the striatal neurogenesis during development.

Phosphatidylinositide 3-kinase and protein kinase C zeta mediate retinoic acid induction of DARPP-32 in medium size spiny neurons in vitro

Mature striatal medium size spiny neurons express the dopamine and cAMP-regulated phosphoprotein, 32 kDa (DARPP-32), but little is known about the mechanisms regulating its levels, or the specification of fully differentiated neuronal subtypes. Cell extrinsic molecules that increase DARPP-32 mRNA and/or protein levels include retinoic acid (RA), brain-derived neurotrophic factor, and estrogen (E(2)). We now demonstrate that RA regulates DARPP-32 mRNA and protein in primary striatal neuronal cultures. Furthermore, DARPP-32 induction by RA in vitro requires phosphatidylinositide 3-kinase, but is independent of tropomyosin-related kinase B, cyclin-dependent kinase 5, and protein kinase B. Using pharmacologic inhibitors of various isoforms of protein kinase C (PKC), we also demonstrate that DARPP-32 induction by RA in vitro is dependent on PKC zeta (PKCzeta). Thus, the signal transduction pathways mediated by RA are very different than those mediating DARPP-32 induction by brain-derived neurotrophic factor. These data support the presence of multiple signal transduction pathways mediating expression of DARPP-32 in vitro, including a novel, important pathway via which phosphatidylinositide 3-kinase regulates the contribution of PKCzeta.

RAR/RXR and PPAR/RXR signaling in neurological and psychiatric diseases

Retinoids are important signals in brain development. They regulate gene transcription by binding to retinoic acid receptors (RAR) and, as was discovered recently, a peroxisome proliferator-activated receptor (PPAR). Traditional ligands of PPAR are best known for their functions in lipid metabolism and inflammation. RAR and PPAR are ligand-activated transcription factors, which share members of the retinoid X receptor (RXR) family as heterodimeric partners. Both signal transduction pathways have recently been implicated in the progression of neurodegenerative and psychiatric diseases. Since inflammatory processes contribute to various neurodegenerative diseases, the anti-inflammatory activity of retinoids and PPARgamma agonists recommends them as potential therapeutic targets. In addition, genetic linkage studies, transgenic mouse models and experiments with vitamin A deprivation provide evidence that retinoic acid signaling is directly involved in physiology and pathology of motoneurons, of the basal ganglia and of cognitive functions. The activation of PPAR/RXR and RAR/RXR transcription factors has therefore been proposed as a therapeutic strategy in disorders of the central nervous system.

Modular patterning of structure and function of the striatum by retinoid receptor signaling

Retinoid signaling plays a crucial role in patterning rhombomeres in the hindbrain and motor neurons in the spinal cord during development. A fundamentally interesting question is whether retinoids can pattern functional organization in the forebrain that generates a high order of cognitive behavior. The striatum contains a compartmental structure of striosome (or "patch") and intervening matrix. How this highly complex mosaic design is patterned by the genetic programs during development remains elusive. We report a developmental mechanism by which retinoid receptor signaling controls compartmental formation in the striatum. We analyzed RARbeta(-/-) mutant mice and found a selective loss of striosomal compartmentalization in the rostral mutant striatum. The loss of RARbeta signaling in the mutant mice resulted in reduction of cyclin E2, a cell cycle protein regulating transition from G(1) to S phase, and also reduction of the proneural gene Mash1, which led to defective neurogenesis of late-born striosomal cells. Importantly, during striatal neurogenesis, endogenous levels of retinoic acid were spatiotemporally regulated such that transduction of high levels of retinoic acid through RARbeta selectively expanded the population of late-born striosomal progenitors, which evolved into a highly elaborate compartment in the rostral striatum. RARbeta(-/-) mutant mice, which lacked such enlarged compartment, displayed complex alternations of dopamine agonist-induced stereotypic motor behavior, including exaggeration of head bobbing movement and reduction of rearing activity. RARbeta signaling thus plays a crucial role in setting up striatal compartments that may engage in neural circuits of psychomotor control.

Interplay of leukemia inhibitory factor and retinoic acid on neural differentiation of mouse embryonic stem cells

Embryonic stem (ES) cells have great potential for cell replacement in neurodegenerative disorders. Implantation of these cells into the brain, however, requires their prior differentiation. We examined the interplay between leukemia inhibitory factor (LIF) and retinoic acid (RA) on neural differentiation of mouse ES (mES) cells. Mouse embryonic stem cells were allowed to form cell aggregates, the so-called embryoid bodies (EBs), in the absence or presence of LIF. In the absence of LIF, mES cells downregulated the expression of the undifferentiated mES cell marker Oct-3/4, and increased mRNA levels of two neural precursor markers, Sox-1 and Nestin, as well as the neuronal marker beta-tubulin III. This neuronal differentiation was enhanced by treating EBs with RA. Moreover, RA irreversibly increased the number of postmitotic neurons in culture, as shown by the reduction of proliferating mES cells and the increase in beta-tubulin III-positive cells 6 days after RA removal, which in turn affected mES cell viability. The addition of LIF during EBs formation, however, blocked completely this neuronal differentiation. Our findings also showed that pre-differentiation of mES cells in vitro avoided the teratocarcinoma formation observed when proliferating mES cells were grafted into the brain. In addition, mES cells pre-differentiated with RA in culture showed a reduction in proliferation and the presence of neural phenotypes after grafting. In conclusion, the present results indicate that RA enhances neuronal differentiation of mES cells in the absence of LIF, although it compromises cell viability and transplantation.

Genetic patterning of the mammalian telencephalon by morphogenetic molecules and transcription factors

Patterning centers that produce gradients of morphogenetic molecules, including fibroblast growth factor (FGF), bone morphogenetic proteins (BMP), Wnt, Sonic hedgehog (Shh), and retinoic acid (RA), are located in telencephalic anlage during early stages of development. Genetic evidence based on loss-of-function and gain-of-function studies indicate that they are involved in regional specification of the dorsal, ventral, and lateral telencephalon. For patterning of the dorsal telencephalon, FGF8 controls the anteroposterior patterning, while BMP and Wnt molecules regulate the mediolateral patterning. Shh and retinoic acid regulate patterning of the ventral and the lateral telencephalon. The regionalization of telencephalon is accompanied by expression of region-specific codes of transcription factors, which in turn regulate different phases of neuronal development to generate different cell types in each brain region. Therefore, bioactive signals of morphogenetic molecules are translated into transcription factor codes for regional specification, which subsequently leads to neurogenesis of the diversity of cell types in different regions of the telencephalon.