Ikaros is expressed in developing striatal neurons and involved in enkephalinergic differentiation

Ikaros is a principal regulator of Aire+ mTEC homeostasis, thymic mimetic cell diversity, and central tolerance

Mutations in the gene encoding the zinc-finger transcription factor Ikaros (IKZF1) are found in patients with immunodeficiency, leukemia, and autoimmunity. Although Ikaros has a well-established function in modulating gene expression programs important for hematopoietic development, its role in other cell types is less well defined. Here, we uncover functions for Ikaros in thymic epithelial lineage development in mice and show that Ikzf1 expression in medullary thymic epithelial cells (mTECs) is required for both autoimmune regulator-positive (Aire+) mTEC development and tissue-specific antigen (TSA) gene expression. Accordingly, TEC-specific deletion of Ikzf1 in mice results in a profound decrease in Aire+ mTECs, a global loss of TSA gene expression, and the development of autoimmunity. Moreover, Ikaros shapes thymic mimetic cell diversity, and its deletion results in a marked expansion of thymic tuft cells and muscle-like mTECs and a loss of other Aire-dependent mimetic populations. Single-cell analysis reveals that Ikaros modulates core transcriptional programs in TECs that correlate with the observed cellular changes. Our findings highlight a previously undescribed role for Ikaros in regulating epithelial lineage development and function and suggest that failed thymic central tolerance could contribute to the autoimmunity seen in humans with IKZF1 mutations.

Signaling pathways and regulation of gene expression in hematopoietic cells

Cellular functions are regulated by signal transduction pathway networks consisting of protein-modifying enzymes that control the activity of many downstream proteins. Protein kinases and phosphatases regulate gene expression by reversible phosphorylation of transcriptional factors, which are their direct substrates. Casein kinase II (CK2) is a serine/threonine kinase that phosphorylates a large number of proteins that have critical roles in cellular proliferation, metabolism and survival. Altered function of CK2 has been associated with malignant transformation, immunological disorders and other types of diseases. Protein phosphatase 1 (PP1) is a serine/threonine phosphatase, which regulates the phosphorylation status of many proteins that are essential for cellular functions. IKAROS is a DNA-binding protein, which functions as a regulator of gene transcription in hematopoietic cells. CK2 directly phosphorylates IKAROS at multiple phosphosites which determines IKAROS activity as a regulator of gene expression. PP1 binds to IKAROS via the PP1-consensus recognition site and dephosphorylates serine/threonine residues that are phosphorylated by CK2. Thus, the interplay between CK2 and PP1 signaling pathways have opposing effects on the phosphorylation status of their mutual substrate - IKAROS. This review summarizes the effects of CK2 and PP1 on IKAROS role in regulation of gene expression and its function as a tumor suppressor in leukemia.

Ikzf1 as a novel regulator of microglial homeostasis in inflammation and neurodegeneration

In the last two decades, microglia have emerged as key contributors to disease progression in many neurological disorders, not only by exerting their classical immunological functions but also as extremely dynamic cells with the ability to modulate synaptic and neural activity. This dynamic behavior, together with their heterogeneous roles and response to diverse perturbations in the brain parenchyma has raised the idea that microglia activation is more diverse than anticipated and that understanding the molecular mechanisms underlying microglial states is essential to unravel their role in health and disease from development to aging. The Ikzf1 (a.k.a. Ikaros) gene plays crucial roles in modulating the function and maturation of circulating monocytes and lymphocytes, but whether it regulates microglial functions and states is unknown. Using genetic tools, here we describe that Ikzf1 is specifically expressed in the adult microglia in brain regions such as cortex and hippocampus. By characterizing the Ikzf1 deficient mice, we observed that these mice displayed spatial learning deficits, impaired hippocampal CA3-CA1 long-term potentiation, and decreased spine density in pyramidal neurons of the CA1, which correlates with an increased expression of synaptic markers within microglia. Additionally, these Ikzf1 deficient microglia exhibited a severe abnormal morphology in the hippocampus, which is accompanied by astrogliosis, an aberrant composition of the inflammasome, and an altered expression of disease-associated microglia molecules. Interestingly, the lack of Ikzf1 induced changes on histone 3 acetylation and methylation levels in the hippocampus. Since the lack of Ikzf1 in mice appears to induce the internalization of synaptic markers within microglia, and severe gliosis we then analyzed hippocampal Ikzf1 levels in several models of neurological disorders. Ikzf1 levels were increased in the hippocampus of these neurological models, as well as in postmortem hippocampal samples from Alzheimer's disease patients. Finally, over-expressing Ikzf1 in cultured microglia made these cells hyporeactive upon treatment with lipopolysaccharide, and less phagocytic compared to control microglia. Altogether, these results suggest that altered Ikzf1 levels in the adult hippocampus are sufficient to induce synaptic plasticity and memory deficits via altering microglial state and function.

Upregulation of the pathogenic transcription factor SPI1/PU.1 in tuberous sclerosis complex and focal cortical dysplasia by oxidative stress

Tuberous sclerosis complex (TSC) is a congenital disorder characterized by cortical malformations and concomitant epilepsy caused by loss‐of‐function mutations in the mTOR suppressors TSC1 or TSC2. While the underlying molecular changes caused by mTOR activation in TSC have previously been investigated, the drivers of these transcriptional change have not been fully elucidated. A better understanding of the perturbed transcriptional regulation could lead to the identification of novel pathways for therapeutic intervention not only in TSC, but other genetic epilepsies in which mTOR activation plays a key role, such as focal cortical dysplasia 2b (FCD). Here, we analyzed RNA sequencing data from cortical tubers and a tsc2^−/− zebrafish. We identified differential expression of the transcription factors (TFs) SPI1/PU.1, IRF8, GBX2, and IKZF1 of which SPI1/PU.1 and IRF8 targets were enriched among the differentially expressed genes. Furthermore, for SPI1/PU.1 these findings were conserved in TSC zebrafish model. Next, we confirmed overexpression of SPI1/PU.1 on the RNA and protein level in a separate cohort of surgically resected TSC tubers and FCD tissue, in fetal TSC tissue, and a Tsc1^GFAP−/− mouse model of TSC. Subsequently, we validated the expression of SPI1/PU.1 in dysmorphic cells with mTOR activation in TSC tubers. In fetal TSC, we detected SPI1/PU.1 expression prenatally and elevated RNA Spi1 expression in Tsc1^GFAP−/− mice before the development of seizures. Finally, in vitro, we identified that in astrocytes and neurons SPI1 transcription was driven by H₂O₂‐induced oxidative stress, independent of mTOR. We identified SPI1/PU.1 as a novel TF involved in the pro‐inflammatory gene expression of malformed cells in TSC and FCD 2b. This transcriptional program is activated in response to oxidative stress and already present prenatally. Importantly, SPI1/PU.1 protein appears to be strictly limited to malformed cells, as we did not find SPI1/PU.1 protein expression in mice nor in our in vitro models.

Helios modulates the maturation of a CA1 neuronal subpopulation required for spatial memory formation

Currently, molecular, electrophysiological and structural studies delineate several neural subtypes in the hippocampus. However, the precise developmental mechanisms that lead to this diversity are still unknown. Here we show that alterations in a concrete hippocampal neuronal subpopulation during development specifically affect hippocampal-dependent spatial memory. We observed that the genetic deletion of the transcription factor Helios in mice, which is specifically expressed in developing hippocampal calbindin-positive CA1 pyramidal neurons (CB-CA1-PNs), induces adult alterations affecting spatial memory. In the same mice, CA3-CA1 synaptic plasticity and spine density and morphology in adult CB-CA1-PNs were severely compromised. RNAseq experiments in developing hippocampus identified an aberrant increase on the Visinin-like protein 1 (VSNL1) expression in the hippocampi devoid of Helios. This aberrant increase on VSNL1 levels was localized in the CB-CA1-PNs. Normalization of VSNL1 levels in CB-CA1-PNs devoid of Helios rescued their spine loss in vitro. Our study identifies a novel and specific developmental molecular pathway involved in the maturation and function of a CA1 pyramidal neuronal subtype.

The making of a lymphocyte: the choice among disparate cell fates and the IKAROS enigma

In this review from Georgopoulos, the role of the IKAROS gene family in lymphocyte differentiation is discussed in light of recent studies on the lineage-specific transcriptional and epigenetic networks through which IKAROS proteins operate.

Lymphocyte differentiation is set to produce myriad immune effector cells with the ability to respond to multitudinous foreign substances. The uniqueness of this developmental system lies in not only the great diversity of cellular functions that it can generate but also the ability of its differentiation intermediates and mature effector cells to expand upon demand, thereby providing lifelong immunity. Surprisingly, the goals of this developmental system are met by a relatively small group of DNA-binding transcription factors that work in concert to control the timing and magnitude of gene expression and fulfill the demands for cellular specialization, expansion, and maintenance. The cellular and molecular mechanisms through which these lineage-promoting transcription factors operate have been a focus of basic research in immunology. The mechanisms of development discerned in this effort are guiding clinical research on disorders with an immune cell base. Here, I focus on IKAROS, one of the earliest regulators of lymphoid lineage identity and a guardian of lymphocyte homeostasis.

Helios expression coordinates the development of a subset of striatopallidal medium spiny neurons

Here, we unravel the mechanism of action of the Ikaros family zinc finger protein Helios (He) during the development of striatal medium spiny neurons (MSNs). He regulates the second wave of striatal neurogenesis involved in the generation of striatopallidal neurons, which express dopamine 2 receptor and enkephalin. To exert this effect, He is expressed in neural progenitor cells (NPCs) keeping them in the G₁/G₀ phase of the cell cycle. Thus, a lack of He results in an increase of S-phase entry and S-phase length of NPCs, which in turn impairs striatal neurogenesis and produces an accumulation of the number of cycling NPCs in the germinal zone (GZ), which end up dying at postnatal stages. Therefore, He^−/− mice show a reduction in the number of dorso-medial striatal MSNs in the adult that produces deficits in motor skills acquisition. In addition, overexpression of He in NPCs induces misexpression of DARPP-32 when transplanted in mouse striatum. These findings demonstrate that He is involved in the correct development of a subset of striatopallidal MSNs and reveal new cellular mechanisms for neuronal development.

Summary: The transcription factor Helios regulates G1-S transition to promote neuronal differentiation of a striatopallidal neuronal subpopulation involved in motor skill acquisition.

Congenital prosopagnosia is associated with a genetic variation in the oxytocin receptor (OXTR) gene: An exploratory study

Face-recognition deficits, referred to with the term prosopagnosia (i.e., face blindness), may manifest during development in the absence of any brain injury (from here the term congenital prosopagnosia, CP). It has been estimated that approximately 2.5% of the population is affected by face-processing deficits not depending on brain lesions, and varying a lot in severity. The genetic bases of this disorder are not known. In this study we tested for genetic association between single-nucleotide polymorphisms (SNPs) in the oxytocin receptor gene (OXTR) and CP in a restricted cohort of Italian participants. We found evidence of an association between the common genetic variants rs53576 and rs2254298 OXTR SNPs and prosopagnosia. This association was also found when including an additional group of German individuals classified as prosopagnosic in the analysis. Our preliminary data provide initial support for the involvement of genetic variants of OXTR in a relevant cognitive impairment, whose genetic bases are still largely unexplored.

Ikaros and leukaemia

The IKZF1 gene at 7p12.2 codes for IKAROS (also termed IKZF1), an essential transcription factor in haematopoiesis involved primarily in lymphoid differentiation. Its importance is underlined by the fact that deregulation of IKAROS results in leukaemia in both mice and men. During recent years, constitutional as well as acquired genetic changes of IKZF1 have been associated with human disease. For example, certain germline single nucleotide polymorphisms in IKZF1 have been shown to increase the risk of some disorders and abnormal expression and somatic rearrangements, mutations and deletions of IKZF1 (ΔIKZF1) have been detected in a wide variety of human malignancies. Of immediate clinical importance is the fact that ΔIKZF1 occurs in 15% of paediatric B-cell precursor acute lymphoblastic leukaemia (BCP ALL) and that the presence of ΔIKZF1 is associated with an increased risk of relapse and a poor outcome; in some studies such deletions have been shown to be an independent risk factor also when minimal residual disease data are taken into account. However, cooperative genetic changes, such as ERG deletions and CRLF2 rearrangements, may modify the prognostic impact of ΔIKZF1, for better or worse. This review summarizes our current knowledge of IKZF1 abnormalities in human disease, with an emphasis on BCP ALL.

BDNF-TrkB signaling in striatopallidal neurons controls inhibition of locomotor behavior

The physiology of brain-derived neurotrophic factor signaling in enkephalinergic striatopallidal neurons is poorly understood. Changes in cortical Bdnf expression levels, and/or impairment in brain-derived neurotrophic factor anterograde transport induced by mutant huntingtin (mHdh) are believed to cause striatopallidal neuron vulnerability in early-stage Huntington’s disease. Although several studies have confirmed a link between altered cortical brain-derived neurotrophic factor signaling and striatal vulnerability, it is not known whether the effects are mediated via the brain-derived neurotrophic factor receptor TrkB, and whether they are direct or indirect. Using a novel genetic mouse model, here, we show that selective removal of brain-derived neurotrophic factor–TrkB signaling from enkephalinergic striatal targets unexpectedly leads to spontaneous and drug-induced hyperlocomotion. This is associated with dopamine D2 receptor-dependent increased striatal protein kinase C and MAP kinase activation, resulting in altered intrinsic activation of striatal enkephalinergic neurons. Therefore, brain-derived neurotrophic factor/TrkB signaling in striatopallidal neurons controls inhibition of locomotor behavior by modulating neuronal activity in response to excitatory input through the protein kinase C/MAP kinase pathway.

The neurotrophic factor BDNF is implicated in striatal cell long-term survival. Besusso et al. selectively delete BDNF receptors in the striatal circuitry of mice and find that this leads to hyperlocomotion, which is associated with dopamine receptor-dependent increases in specific kinases.

Birth-date dependent arrangement of spinal enkephalinergic neurons: evidence from the preproenkephalin-green fluorescent protein transgenic mice

Enkephalin (ENK) has been postulated to play important roles in modulating nociceptive transmission, and it has been proved that ENKergic neurons acted as a critical component of sensory circuit in the adult spinal cord. Revealing the developmental characteristics of spinal ENKergic neurons will be helpful for understanding the formation and alteration of the sensory circuit under pain status. However, the relationship between the embryonic birth date and the adult distribution of ENKergic neurons has remained largely unknown due to the difficulties in visualizing the ENKergic neurons clearly. Taking advantage of the preproenkephalin-green fluorescent protein (PPE-GFP) transgenic mice in identifying ENKergic neurons, we performed the current birth-dating study and examined the spinal ENKergic neurogenesis. The ENKergic neurons born on different developmental stages and their final location during adulthood were investigated by combining bromodeoxyuridine (BrdU) incorporation and GFP labeling. The spinal ENKergic neurogenesis was restricted at E9.5 to E14.5, and fitted in the same pattern of spinal neurogenesis. Further comparative analysis revealed that spinal ENKergic neurons underwent heterogeneous characteristics. Our study also indicated that the laminar arrangement of ENKergic neurons in the superficial spinal dorsal horn depended on the neurogenesis stages. Taken together, the present study suggested that the birth date of ENKergic neurons is one determinant for their arrangement and function.

The LIM homeobox gene Isl1 is required for the correct development of the striatonigral pathway in the mouse

The mammalian striatum controls the output of the basal ganglia via two distinct efferent pathways, the direct (i.e., striatonigral) and the indirect (i.e., striatopallidal) pathways. The LIM homeodomain transcription factor Islet1 (Isl1) is expressed in a subpopulation of striatal progenitors; however, its specific role in striatal development remains unknown. Our genetic fate-mapping results show that Isl1-expressing progenitors give rise to striatal neurons belonging to the striatonigral pathway. Conditional inactivation of Isl1 in the telencephalon resulted in a smaller striatum with fewer striatonigral neurons and reduced projections to the substantia nigra. Additionally, conditional inactivation in the ventral forebrain (including both the telencephalon and diencephalon) revealed a unique role for Isl1 in diencephalic cells bordering the internal capsule for the normal development of the striatonigral pathway involving PlexinD1-Semaphorin 3e (Sema3e) signaling. Finally, Isl1 conditional mutants displayed a hyperlocomotion phenotype, and their locomotor response to psychostimulants was significantly blunted, indicating that the alterations in basal ganglia circuitry contribute to these mutant behaviors.

Transcriptional regulation of the Ikzf1 locus

Ikaros is a critical regulator of lymphocyte development and homeostasis; thus, understanding its transcriptional regulation is important from both developmental and clinical perspectives. Using a mouse transgenic reporter approach, we functionally characterized a network of highly conserved cis-acting elements at the Ikzf1 locus. We attribute B-cell and myeloid but not T-cell specificity to the main Ikzf1 promoter. Although this promoter was unable to counter local chromatin silencing effects, each of the 6 highly conserved Ikzf1 intronic enhancers alleviated silencing. Working together, the Ikzf1 enhancers provided locus control region activity, allowing reporter expression in a position and copy-independent manner. Only 1 of the Ikzf1 enhancers was responsible for the progressive upregulation of Ikaros expression from hematopoietic stem cells to lymphoid-primed multipotent progenitors to T-cell precursors, which are stages of differentiation dependent on Ikaros for normal outcome. Thus, Ikzf1 is regulated by both epigenetic and transcriptional factors that target its enhancers in both redundant and specific fashions to provide an expression profile supportive of normal lymphoid lineage progression and homeostasis. Mutations in the Ikzf1 regulatory elements and their interacting factors are likely to have adverse effects on lymphopoiesis and contribute to leukemogenesis.

Ikaros promotes early-born neuronal fates in the cerebral cortex

During cerebral cortex development, a series of projection neuron types is generated in a fixed temporal order. In Drosophila neuroblasts, the transcription factor hunchback encodes first-born identity within neural lineages. One of its mammalian homologs, Ikaros, was recently reported to play an equivalent role in retinal progenitor cells, raising the question as to whether Ikaros/Hunchback proteins could be general factors regulating the development of early-born fates throughout the nervous system. Ikaros is also expressed in progenitor cells of the mouse cerebral cortex, and this expression is highest during the early stages of neurogenesis and thereafter decreases over time. Transgenic mice with sustained Ikaros expression in cortical progenitor cells and neurons have developmental defects, including displaced progenitor cells within the cortical plate, increased early neural differentiation, and disrupted cortical lamination. Sustained Ikaros expression results in a prolonged period of generation of deep layer neurons into the stages when, normally, only late-born upper layer neurons are generated, as well as a delayed production of late-born neurons. Consequently, more early-born and fewer late-born neurons are present in the cortex of these mice at birth. This phenotype was observed in all parts of the cortex, including those with minimal structural defects, demonstrating that it is not secondary to abnormalities in cortical morphogenesis. These data suggest that Ikaros plays a similar role in regulating early temporal fates in the mammalian cerebral cortex as Ikaros/Hunchback proteins do in the Drosophila nerve cord.

Exploring the enkephalinergic differentiation potential in adult stem cells for cell therapy and drug screening implications

Stem cell therapy is one of the most promising treatments in neuroregenerative medicine. Considering the role of the endogenous opioid system in controlling the pathophysiology of neurological disorders and behavioral aberrations, current studies have focused on enkephalins as a part of the opioid system. Due to high capability of unrestricted somatic stem cells (USSCs) and human mesenchymal stem cells (hMSCs) for cell therapy and transplantation; here, we examined their enkephalinergic differentiation potential through Ikaros-related pathways in order to develop in vitro models to help drug screening and stem cell therapy for the opioid-related disorders. The authenticity of the stem cells was verified by differentiation experiments along with flow cytometry for surface markers. Later, we confirmed their neurogenic differentiation with semiquantitative and quantitative transcriptional and translational evaluations of the enkephalinergic-related genes such as proenkephalin, CREBZF, Ikaros, and prodynorphin. Our findings supported the enkephalinergic differentiation of these stem cells. Noteworthy, USSCs showed higher potential for differentiating into enkephalinergic neurons under Ikaros activation than hMSCs, which makes them appropriate for neurological therapeutic applications. In conclusion, this study suggests a powerful in vitro model for neurogenesis that may help clarification of enkephalinergic differentiation and related signaling networks along with neural drug screening. Such investigations may be beneficial to ameliorate the neural-related therapeutic approaches.

Reduced striatal dopamine D1-D2 receptor heteromer expression and behavioural subsensitivity in juvenile rats

In adult rat striatum the dopamine D1-D2 receptor heteromer is expressed selectively in a subset of medium spiny neurons (MSNs) that coexpress the dopamine D1 and D2 receptors (D1R and D2R) as well as dynorphin (DYN) and enkephalin (ENK), with higher coexpression in nucleus accumbens (NAc) and much lower in the caudate putamen (CP). In the present study we showed that in neonatal striatal cultured neurons >90% exhibited the D1R/D2R-DYN/ENK phenotype. Similarly, in the striatum of juvenile rats (age 26-28 days) coexpression of D1R and D2R was also coincident with the expression of both DYN and ENK. Quantification of the number of striatal MSNs exhibiting coexpression of D1R and D2R in juvenile rats revealed significantly lower coexpression in NAc shell, but not core, and CP than in adult rats. However, within MSNs that coexpressed D1R and D2R, the propensity to form the D1-D2 receptor heteromer did not differ between age groups. Consistent with reduced coexpression of the D1R and D2R, juvenile rats exhibited subsensitivity to D1-D2 receptor heteromer-induced grooming following activation by SKF 83959. Given the proposed role of D1R/D2R-coexpressing MSNs in the regulation of thalamic output, and the recent discovery that these MSNs exhibit both inhibitory and excitatory capabilities, these findings suggest that the functional regulation of neurotransmission by the dopamine D1-D2 receptor heteromer within the juvenile striatum may be significantly different than in the adult.

Helios transcription factor expression depends on Gsx2 and Dlx1&2 function in developing striatal matrix neurons

Development of the nervous system is finely regulated by consecutive expression of cell-specific transcription factors. Here we show that Helios, a member of the Ikaros transcription factor family, is expressed in ectodermal and neuroectodermal-derived tissues. During embryonic development, Helios is expressed by several brain structures including the lateral ganglionic eminence (LGE, the striatal anlage); the cingulated, insular and retrosplenial cortex; the hippocampus; and the accessory olfactory bulb. Moreover, Helios is also expressed by Purkinje neurons during postnatal cerebellar development. Within the LGE, Helios expression follows a dynamic spatio-temporal pattern starting at embryonic stages (E14.5), peaking at E18.5, and completely disappearing during postnatal development. Helios is expressed by a small population of nestin-positive neural progenitor cells located in the subventricular zone as well as by a larger population of immature neurons distributed throughout the mantle zone. In the later, Helios is preferentially expressed in the matrix compartment, where it colocalizes with Bcl11b and Foxp1, well-known markers of striatal projection neurons. In addition, we observed that Helios expression is not detected in Dlx1/2 and Gsx2 null mutants, while its expression is maintained in Ascl1 mutants. These findings allow us to introduce a new transcription factor in the cascade of events that take part of striatal development postulating the existence of at least 4 different neural progenitors in the LGE. An Ascl1-independent but Gsx2- & Dlx1/2-dependent precursor will express Helios defining a new lineage for a subset of matrix striatal neurons.

The Ikaros gene family: transcriptional regulators of hematopoiesis and immunity

The Ikaros family of proteins - comprising Ikaros, Aiolos, Helios, Eos and Pegasus - are zinc finger transcription factors. These proteins participate in a complex network of interactions with gene regulatory elements, other family members and a raft of other transcriptional regulators to control gene expression including via chromatin remodelling. In this way, Ikaros family members regulate important cell-fate decisions during hematopoiesis, particularly in the development of the adaptive immune system. Mutation of several family members results in hematological malignancies,especially those of a lymphoid nature. This review describes the key roles of Ikaros proteins in development and disease, their mechanisms of action and gene targets, as well as explaining their evolutionary origins and role in the emergence of adaptive immunity.

Subregional specification of embryonic stem cell-derived ventral telencephalic tissues by timed and combinatory treatment with extrinsic signals

During early telencephalic development, the major portion of the ventral telencephalic (subpallial) region becomes subdivided into three regions, the lateral (LGE), medial (MGE), and caudal (CGE) ganglionic eminences. In this study, we systematically recapitulated subpallial patterning in mouse embryonic stem cell (ESC) cultures and investigated temporal and combinatory actions of patterning signals. In serum-free floating culture, the dorsal-ventral specification of ESC-derived telencephalic neuroectoderm is dose-dependently directed by Sonic hedgehog (Shh) signaling. Early Shh treatment, even before the expression onset of Foxg1 (also Bf1; earliest marker of the telencephalic lineage), is critical for efficiently generating LGE progenitors, and continuous Shh signaling until day 9 is necessary to commit these cells to the LGE lineage. When induced under these conditions and purified by fluorescence-activated cell sorter, telencephalic cells efficiently differentiated into Nolz1(+)/Ctip2(+) LGE neuronal precursors and subsequently, both in culture and after in vivo grafting, into DARPP32(+) medium-sized spiny neurons. Purified telencephalic progenitors treated with high doses of the Hedgehog (Hh) agonist SAG (Smoothened agonist) differentiated into MGE- and CGE-like tissues. Interestingly, in addition to strong Hh signaling, the efficient specification of MGE cells requires Fgf8 signaling but is inhibited by treatment with Fgf15/19. In contrast, CGE differentiation is promoted by Fgf15/19 but suppressed by Fgf8, suggesting that specific Fgf signals play different, critical roles in the positional specification of ESC-derived ventral subpallial tissues. We discuss a model of the antagonistic Fgf8 and Fgf15/19 signaling in rostral-caudal subpallial patterning and compare it with the roles of these molecules in cortical patterning.

Ikaros-1 couples cell cycle arrest of late striatal precursors with neurogenesis of enkephalinergic neurons

During central nervous system development, several transcription factors regulate the differentiation of progenitor cells to postmitotic neurons. Here we describe a novel role for Ikaros-1 in the generation of late-born striatal neurons. Our results show that Ikaros-1 is expressed in the boundary of the striatal germinal zone (GZ)/mantle zone (MZ), where it induces cell cycle arrest of neural progenitors by up-regulation of the cyclin-dependent kinase inhibitor (CDKi) p21(Cip1/Waf1). This effect is coupled with the neuronal differentiation of late precursors, which in turn is critical for the second wave of striatal neurogenesis that gives rise to matrix neurons. Consistently, Ikaros(-/-) mice had fewer striatal projecting neurons and, in particular, enkephalin (ENK)-positive neurons. In addition, overexpression of Ikaros-1 in primary striatal cultures increases the number of calbindin- and ENK-positive neurons. Our results also show that Ikaros-1 acts downstream of the Dlx family of transcription factors, insofar as its expression is lost in Dlx1/2 double knockout mice. However, we demonstrate that Ikaros-1 and Ebf-1 independently regulate the final determination of the two populations of striatal projection neurons of the matrix compartment, ENK- and substance P-positive neurons. In conclusion, our findings identify Ikaros-1 as a modulator of cell cycle exit of neural progenitors that gives rise to the neurogenesis of ENK-positive striatal neurons.

Immune and nervous systems: more than just a superficial similarity?

Strong evidence is emerging that the nervous and immune systems share mechanisms of gene regulation, signaling, cell communication, and supracellular organization. This brings to the fore many questions, not least of which is the developmental and evolutionary origin of the commonalities between the two systems. By providing answers to these questions, immunologists and neurobiologists increasingly expose the mechanistic and conceptual affinities of their respective fields and facilitate the understanding of fundamental principles that govern the organization of complex cellular systems. The current essay and reviews in Immunity and Neuron attempt to communicate to the wider scientific community a series of examples relating to commonalities between the immune and nervous system and enhance the dialog and exchange of ideas between the two fields.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Ikaros confers early temporal competence to mouse retinal progenitor cells

In the developing mouse retina, multipotent retinal progenitor cells (RPCs) give rise to specific retinal cell types at different times, but the molecular mechanisms regulating how RPCs change over time remain unclear. In the Drosophila neuroblast lineage, the zinc finger transcription factor Hunchback (Hb) is both necessary and sufficient to specify early-born neuronal identity. We show here that Ikaros, a mouse ortholog of Hb, is expressed in all early embryonic RPCs, which then give rise to Ikaros-negative RPCs at later stages in the lineage. Remarkably, misexpression of Ikaros in late RPCs is sufficient to confer competence to generate early-born neurons. Conversely, Ikaros mutant mice have reduced numbers of early-born cell types, whereas late-born cell types are not affected. These results suggest a model in which Ikaros expression is both necessary and sufficient to confer early temporal competence to RPCs and raise the possibility that a similar strategy might be used to control the sequential order of cell birth in other parts of the nervous system.

Molecular specification and patterning of progenitor cells in the lateral and medial ganglionic eminences

We characterized intrinsic and extrinsic specification of progenitors in the lateral and medial ganglionic eminences (LGE and MGE). We identified seven genes whose expression is enriched or restricted in either the LGE [biregional cell adhesion molecule-related/downregulated by oncogenes binding protein (Boc), Frizzled homolog 8 (Fzd8), Ankrd43 (ankyrin repeat domain-containing protein 43), and Ikzf1 (Ikaros family zinc finger 1)] or MGE [Map3k12 binding inhibitory protein 1 (Mbip); zinc-finger, SWIM domain containing 5 (Zswim5); and Adamts5 [a disintegrin-like and metallopeptidase (reprolysin type) with thrombospondin type 1 motif, 5]]. Boc, Fzd8, Mbip, and Zswim5 are apparently expressed in LGE or MGE progenitors, whereas the remaining three are seen in the postmitotic mantle zone. Relative expression levels are altered and regional distinctions are lost for each gene in LGE or MGE cells propagated as neurospheres, indicating that these newly identified molecular characteristics of LGE or MGE progenitors depend on forebrain signals not available in the neurosphere assay. Analyses of Pax6(Sey/Sey), Shh(-/-), and Gli3(XtJ/XtJ) mutants suggests that LGE and MGE progenitor identity does not rely exclusively on previously established forebrain-intrinsic patterning mechanisms. Among a limited number of additional potential patterning mechanisms, we found that extrinsic signals from the frontonasal mesenchyme are essential for Shh- and Fgf8-dependent regulation of LGE and MGE genes. Thus, extrinsic and intrinsic forebrain patterning mechanisms cooperate to establish LGE and MGE progenitor identity, and presumably their capacities to generate distinct classes of neuronal progeny.

Isolation and characterization of SATB2, a novel AT-rich DNA binding protein expressed in development- and cell-specific manner in the rat brain

AT-rich DNA elements play an important role in regulating cell-specific gene expression. One of the AT-rich DNA binding proteins, SATB1 is a novel type of transcription factor that regulates gene expression in the hematopoietic lineage through chromatin modification. Using DNA-affinity purification followed by mass spectrometry we identified and isolated a related protein, SATB2 from the developing rat cerebral cortex. SATB2 shows homology to SATB1 and the rat protein is practically identical to the mouse and human SATB2. Using competitive EMSA, we show that recombinant SATB2 protein binds with high affinity and specificity to AT-rich dsDNA. Using RT-PCR, Western analysis and immunohistochemistry we demonstrate that SATB2 expression is restricted to a subset of postmitotic, differentiating neurons in the rat neocortex at ages E16 and P4. We suggest that similar to its homologue SATB1, SATB2 is also involved in regulating gene expression through altering chromatin structure in differentiating cortical neurons.