Molecular Pathways and Animal Models of Semilunar Valve and Aortic Arch Anomalies.

The great arteries of the vertebrate carry blood from the heart to the systemic circulation and are derived from the pharyngeal arch arteries. In higher vertebrates, the pharyngeal arch arteries are a symmetrical series of blood vessels that rapidly remodel during development to become the asymmetric aortic arch arteries carrying oxygenated blood from the left ventricle via the outflow tract. At the base of the aorta, as well as the pulmonary trunk, are the semilunar valves. These valves each have three leaflets and prevent the backflow of blood into the heart. During development, the process of aortic arch and valve formation may go wrong, resulting in cardiovascular defects, and these may, at least in part, be caused by genetic mutations. In this chapter, we will review models harboring genetic mutations that result in cardiovascular defects affecting the great arteries and the semilunar valves.

A role for Retinoblastoma 1 in hindbrain morphogenesis by regulating GBX family.

The hindbrain, which develops from the anterior end of the neural tube expansion, can differentiate into the metencephalon and myelencephalon, with varying sizes and functions. The midbrain-hindbrain boundary (MHB) and hindbrain myelencephalon/ventral midline (HMVM) are known to be the source of the progenitors for the anterior hindbrain and myelencephalon, respectively. However, the molecular networks regulating hindbrain morphogenesis in these structures remain unclear. In this study, we show that retinoblastoma 1 (rb1) is highly expressed at the MHB and HMVM in zebrafish. Knocking out rb1 in mice and zebrafish results in an enlarged hindbrain due to hindbrain neuronal hyperproliferation. Further study reveals that Rb1 controls the hindbrain morphogenesis by suppressing the expression of Gbx1/Gbx2, essential transcription factors for hindbrain development, through its binding to E2f3/Hdac1, respectively. Interestingly, we find that Gbx1 and Gbx2 are expressed in different types of hindbrain neurons, suggesting distinct roles in hindbrain morphogenesis. In summary, our study clarifies the specific role of RB1 in hindbrain neural cell proliferation and morphogenesis by regulating the E2f3-Gbx1 axis and the Hdac1-Gbx2 axis. These findings provide a research paradigm for exploring the differential proliferation of neurons in various brain regions.

Oncogenic GBX2 promotes the malignant behaviors of bladder cancer cells by binding to the ITGA5 promoter and activating its transcription.

In bladder cancer patients, metastasis after surgical resection and serious adverse reactions brought by cisplatin-based systemic chemotherapy make it urgent to explore novel therapeutic methods for improving the clinical outcomes of patients with unsuccessful first-line chemotherapy and disease progression. In this study, GBX2 has been recognized as a differentially expressed transcriptional factor between bladder cases with response to treatment and progressive disease based on online expression profile analysis. Higher GBX2 expression was correlated with poorer OS, DSS, and PFS in bladder cancer patients. GBX2 co-expressed genes were enriched in ECM regulation. ITGA5 was positively correlated with GBX2. GBX2 and ITGA5 were notably elevated in bladder cancer cells. GBX2 and ITGA5 similarly affected bladder cancer cell phenotypes via facilitating cell viability, migration, and invasion. By binding to the promoter region of ITGA5, GBX2 activated ITGA5 transcription, upregulating ITGA5 expression. In bladder cancer cells co-transfected with sh-GBX2 and ITGA5 oe, the inhibitory effects of GBX2 knockdown on bladder cancer cell malignant behaviors were partially eliminated by ITGA5 overexpression. In conclusion, GBX2 and ITGA5 serve as oncogenic factors, promoting the viability, migration, and invasion of bladder cancer cells. GBX2 exerts its functions by targeting the ITGA5 promoter region to activate ITGA5 transcription.

An Update on the Molecular Mechanism of the Vertebrate Isthmic Organizer Development in the Context of the Neuromeric Model.

A crucial event during the development of the central nervous system (CNS) is the early subdivision of the neural tube along its anterior-to-posterior axis to form neuromeres, morphogenetic units separated by transversal constrictions and programed for particular genetic cascades. The narrower portions observed in the developing neural tube are responsible for relevant cellular and molecular processes, such as clonal restrictions, expression of specific regulatory genes, and differential fate specification, as well as inductive activities. In this developmental context, the gradual formation of the midbrain-hindbrain (MH) constriction has been an excellent model to study the specification of two major subdivisions of the CNS containing the mesencephalic and isthmo-cerebellar primordia. This MH boundary is coincident with the common Otx2-(midbrain)/Gbx2-(hindbrain) expressing border. The early interactions between these two pre-specified areas confer positional identities and induce the generation of specific diffusible morphogenes at this interface, in particular FGF8 and WNT1. These signaling pathways are responsible for the gradual histogenetic specifications and cellular identity acquisitions with in the MH domain. This review is focused on the cellular and molecular mechanisms involved in the specification of the midbrain/hindbrain territory and the formation of the isthmic organizer. Emphasis will be placed on the chick/quail chimeric experiments leading to the acquisition of the first fate mapping and experimental data to, in this way, better understand pioneering morphological studies and innovative gain/loss-of-function analysis.

LncRNA FEZF1-AS1 accelerates the migration and invasion of laryngeal squamous cell carcinoma cells through miR-4497 targeting GBX2.

BACKGROUND: MiR-4497 has been previously proved to exert an anti-cancer role in laryngeal squamous cell carcinoma (LSCC) by negatively regulating gastrulation brain homeobox 2 (GBX2). However, the mechanism of miR-4497 in LSCC has yet to be fully elucidated. This study intended to investigate the role of FEZF1-AS1 in the migration and invasion of LSCC cells and clarified its mechanism through miR-4497 and GBX2. METHODS: qPCR evaluated the expression of FEZF1-AS1, miR-4497 and GBX2 in LSCC tissues and cells, compared with controls. Western blotting analyzed GBX2, E-cadherin, N-cadherin and Vimentin. CCK8, wound healing and transwell assays assessed the viability, migration and invasion of TU686 and UM-SCC-17A cells. Luciferase reporter assay affirmed the interplay of miR-4497 with FEZF1-AS1 or GBX2 and Pearson's correlation analysis explored the association between each two genes in both tumor and non-tumor tissues. RESULTS: FEZF1-AS1 was highly expressed in LSCC tissues and cells. Silence or elevation of FEZF1-AS1 inhibited or promoted the migration and invasion of TU686 and UM-SCC-17A cells. FEZF1-AS1 targeted and negatively modulated miR-4497. Inhibition of miR-4497 markedly restored the FEZF1-AS1 silence-repressed cell viability of TU686 and UM-SCC-17A cells. Further, FEZF1-AS1 could positively regulate GBX2 via negative regulation of miR-4497. In these two cells, GBX2 deficiency reversed the promoting impacts of miR-4497 repression on migration and invasion. CONCLUSION: Taken together, FEZF1-AS1, heightened in LSCC tissues and cells, promotes cell migration and invasion of LSCC cells via targeting miR-4497 that inhibits GBX2. The finding may offer new options for the treatment of this cancer.

Gbx2 Is Required for the Migration and Survival of a Subpopulation of Trigeminal Cranial Neural Crest Cells.

The development of key structures within the mature vertebrate hindbrain requires the migration of neural crest (NC) cells and motor neurons to their appropriate target sites. Functional analyses in multiple species have revealed a requirement for the transcription factor gastrulation-brain-homeobox 2 (Gbx2) in NC cell migration and positioning of motor neurons in the developing hindbrain. In addition, loss of Gbx2 function studies in mutant mouse embryos, Gbx2neo, demonstrate a requirement for Gbx2 for the development of NC-derived sensory neurons and axons constituting the mandibular branch of the trigeminal nerve (CNV). Our recent GBX2 target gene identification study identified multiple genes required for the migration and survival of NC cells (e.g., Robo1, Slit3, Nrp1). In this report, we performed loss-of-function analyses using Gbx2neo mutant embryos, to improve our understanding of the molecular and genetic mechanisms regulated by Gbx2 during anterior hindbrain and CNV development. Analysis of Tbx20 expression in the hindbrain of Gbx2neo homozygotes revealed a severely truncated rhombomere (r)2. Our data also provide evidence demonstrating a requirement for Gbx2 in the temporal regulation of Krox20 expression in r3. Lastly, we show that Gbx2 is required for the expression of Nrp1 in a subpopulation of trigeminal NC cells, and correct migration and survival of cranial NC cells that populate the trigeminal ganglion. Taken together, these findings provide additional insight into molecular and genetic mechanisms regulated by Gbx2 that underlie NC migration, trigeminal ganglion assembly, and, more broadly, anterior hindbrain development.

Pax9 and Gbx2 Interact in the Pharyngeal Endoderm to Control Cardiovascular Development.

The correct formation of the aortic arch arteries depends on a coordinated and regulated gene expression profile within the tissues of the pharyngeal arches. Perturbation of the gene regulatory networks in these tissues results in congenital heart defects affecting the arch arteries and the outflow tract of the heart. Aberrant development of these structures leads to interruption of the aortic arch and double outlet right ventricle, abnormalities that are a leading cause of morbidity in 22q11 Deletion Syndrome (DS) patients. We have recently shown that Pax9 functionally interacts with the 22q11DS gene Tbx1 in the pharyngeal endoderm for 4th pharyngeal arch artery morphogenesis, with double heterozygous mice dying at birth with interrupted aortic arch. Mice lacking Pax9 die perinatally with complex cardiovascular defects and in this study we sought to validate further potential genetic interacting partners of Pax9, focussing on Gbx2 which is down-regulated in the pharyngeal endoderm of Pax9-null embryos. Here, we describe the Gbx2-null cardiovascular phenotype and demonstrate a genetic interaction between Gbx2 and Pax9 in the pharyngeal endoderm during cardiovascular development.

Gbx1 and Gbx2 Are Essential for Normal Patterning and Development of Interneurons and Motor Neurons in the Embryonic Spinal Cord.

The molecular mechanisms regulating neurogenesis involve the control of gene expression by transcription factors. Gbx1 and Gbx2, two members of the Gbx family of homeodomain-containing transcription factors, are known for their essential roles in central nervous system development. The expression domains of mouse Gbx1 and Gbx2 include regions of the forebrain, anterior hindbrain, and spinal cord. In the spinal cord, Gbx1 and Gbx2 are expressed in PAX2+ interneurons of the dorsal horn and ventral motor neuron progenitors. Based on their shared domains of expression and instances of overlap, we investigated the functional relationship between Gbx family members in the developing spinal cord using Gbx1-/-, Gbx2-/-, and Gbx1-/-/Gbx2-/- embryos. In situ hybridization analyses of embryonic spinal cords show upregulation of Gbx2 expression in Gbx1-/- embryos and upregulation of Gbx1 expression in Gbx2-/- embryos. Additionally, our data demonstrate that Gbx genes regulate development of a subset of PAX2+ dorsal inhibitory interneurons. While we observe no difference in overall proliferative status of the developing ependymal layer, expansion of proliferative cells into the anatomically defined mantle zone occurs in Gbx mutants. Lastly, our data shows a marked increase in apoptotic cell death in the ventral spinal cord of Gbx mutants during mid-embryonic stages. While our studies reveal that both members of the Gbx gene family are involved in development of subsets of PAX2+ dorsal interneurons and survival of ventral motor neurons, Gbx1 and Gbx2 are not sufficient to genetically compensate for the loss of one another. Thus, our studies provide novel insight to the relationship harbored between Gbx1 and Gbx2 in spinal cord development.

GBX2, as a tumor promoter in lung adenocarcinoma, enhances cells viability, invasion and migration by regulating the AKT/ERK signaling pathway.

BACKGROUND: Increasing evidence shows that gastrulation brain homeobox 2 (GBX2) is involved in multiple cancers. However, whether GBX2 has an effect on the lung adenocarcinoma remains unclear. In the present study, we investigated the functions of GBX2 on lung adenocarcinoma and explored the underlying mechanism. METHODS: Public data were obtained from the TCGA (https://cancergenome.nih.gov) and Oncomine (http://www.oncomine.org) databases. GBX2 expression and its prognostic value were analyzed by bioinformatics methods. Relative mRNA and protein expression levels of GBX2 in lung adenocarcinoma cell lines were evaluated via a quantitative reverse transcriptase polymerase chain reaction and western blotting. Lung adenocarcinoma cell lines LTEP-a-2 and A549, respectively, were selected for gain and loss function of GBX2 assays. Cell viability was detected by CCK8 and clone formation experiments. Cell invasion and migration were assessed by Transwell assays. The effect of GBX2 on the AKT/extracellular signal regulated kinase (ERK) pathway was tested by western blotting. RESULTS: Compared to adjacent tissues, GBX2 expression was up-regulated in lung adenocarcinoma tissues. High expression of GBX2 led to a poor survival and could be seen as an independent predictor for lung adenocarcinoma patients. Furthermore, down-regulation of GBX2 notably restrained the viability, invasion and migration abilities of A549 cells, whereas up-regulation of GBX2 in LTEP-a-2 cells presented the opposite outcomes. Furthermore, western blot indicated that down-regulation of GBX2 decreases the protein levels of phosphorylated (p)-AKT and p-ERK in A549 cells, whereas up-regulation of GBX2 shows the opposite effects in LTEP-a-2 cells. CONCLUSIONS: The results of present study indicate that GBX2 acts a cancer-promoting role to accelerate cell proliferation, invasion and migration partly by modulation of the AKT/ERK pathway in lung adenocarcinoma.

MicroRNA-4497 functions as a tumor suppressor in laryngeal squamous cell carcinoma via negatively modulation the GBX2.

OBJECTIVE: MicroRNAs (miRNAs) are aberrantly expressed in various tumors and play a critical role in the progression and development of tumors. However, there is little information about the role of miR-4497 in laryngeal squamous cell carcinoma (LSCC). The aim of this study is to investigate the role of miR-4497 in LSCC. METHODS: MiR-4497 expression in tumor tissues and adjacent normal tissues was measured by RT-PCR. The effects of miR-4497 on cell viability and apoptosis were evaluated by the MTT assay, Flow cytometry and caspase-3 activity assay. Western blot analysis was used to measure the expression of various proteins. Bioinformatic analysis and luciferase reporter assay were applied to investigate the relationship between miR-4497 and GBX2. RESULTS: We found that miR-4497 expression was downregulated in LSCC tumor tissues and cell lines compared to the normal counterparts. Overexpression of miR-4497 inhibits the proliferation and induces apoptosis of LSCC cells accompanied by the down-regulation of anti-apoptotic Bcl-2 proteins. Mechanisms investigation revealed that GBX2 is a direct target of miR-4497. miR-4497 expression was inversely correlated with GBX2 expression in LSCC tissues. Moreover, overexpression of miR-4497 leads to the activation of ERK, JNK but not p38. Inhibition of ERK by specific inhibitor SCH772984 could interfere the apoptosis induced by overexpression of miR-4497. CONCLUSION: Therefore, our results indicate that miR-4497 may play a suppressive role in LSCC by targeting GBX2, which offer new insights into the tumorigenesis of LSCC.

4D imaging identifies dynamic migration and the fate of gbx2-expressing cells in the brain primordium of zebrafish.

One of the pivotal events in neural development is compartmentalization, wherein the neural tissue divides into domains and undergoes functional differentiation. For example, midbrain-hindbrain boundary (MHB) formation and subsequent isthmus development are key steps in cerebellar development. Although several regulatory mechanisms are known to underlie this event, little is known about cellular behaviors. In this study, to examine the cellular dynamics around the MHB region, we performed confocal time-lapse imaging in zebrafish embryos to track cell populations in the neural tube via 4D analysis. We used a transgenic line wherein enhanced green fluorescent protein (EGFP) expression is driven by the gastrulation brain homeobox 2 (gbx2) enhancer, which is involved in MHB maintenance. 4D time-lapse imaging of 5-20 h revealed a novel pattern in cell migration: a dynamic ventrocaudally directed migration from the MHB region toward the hindbrain. Furthermore, in the hindbrain region, these EGFP-positive cells altered their shapes and extended the axons. Immunohistochemical analysis and retrograde labeling showed that these cells in the hindbrain were in the process of neuronal differentiation, including reticulospinal neurons. These results revealed the dynamic and two-step behavior and possible fate of the cell population, which are linked to brain compartmentalization, leading to a deeper understanding of brain development and formation of neuronal circuits.

The neural border: Induction, specification and maturation of the territory that generates neural crest cells.

The neural crest is induced at the edge between the neural plate and the nonneural ectoderm, in an area called the neural (plate) border, during gastrulation and neurulation. In recent years, many studies have explored how this domain is patterned, and how the neural crest is induced within this territory, that also participates to the prospective dorsal neural tube, the dorsalmost nonneural ectoderm, as well as placode derivatives in the anterior area. This review highlights the tissue interactions, the cell-cell signaling and the molecular mechanisms involved in this dynamic spatiotemporal patterning, resulting in the induction of the premigratory neural crest. Collectively, these studies allow building a complex neural border and early neural crest gene regulatory network, mostly composed by transcriptional regulations but also, more recently, including novel signaling interactions.

The N-terminal domain of gastrulation brain homeobox 2 (Gbx2) is required for iridophore specification in zebrafish.

Although body color pattern formation by pigment cells plays critical roles in animals, pigment cell specification has not yet been fully elucidated. In zebrafish, there are three chromatophores: melanophore, iridophore, and xanthophore, that are derived from neural crest cells (NCCs). A recent study has reported the differentially expressed genes between melanophores and iridophores. Based on transcriptome data, we identified that Gbx2 is required for iridophore specification during development. In support of this, iridophore formation is suppressed by gbx2 knockdown by morpholino antisense oligonucleotide, at 72 h post fertilization (hpf) in zebrafish. Moreover, gbx2 is expressed in sox10-expressing NCCs and guanine crystal plates-containing iridophores during development at 24 and 48 hpf, respectively. In gbx2 knockdown zebrafish embryos, apoptosis of sox10-expressing NCCs was detected at 24 hpf without any effect on the formation of melanophores and xanthophores at 48 hpf. We further observed that the N-terminal domain of Gbx2 is able to rescue the iridophore formation defect caused by gbx2 knockdown. Our study provides insights into the requirement of N-terminal domain of Gbx2 for iridophore specification in zebrafish.

The role of gastrulation brain homeobox 2 (gbx2) in the development of the ventral telencephalon in zebrafish embryos.

During vertebrate brain development, the gastrulation brain homeobox 2 gene (gbx2) is expressed in the forebrain, but its precise roles are still unknown. In this study, we addressed this issue in zebrafish (Danio rerio) first by carefully examining gbx2 expression in the developing forebrain. We showed that gbx2 was expressed in the telencephalon during late somitogenesis, from 18h post-fertilization (hpf) to 24 hpf, and in the thalamic primordium after 26 hpf. In contrast, another gbx gene, gbx1, was expressed in the anterior-most ventral telencephalon after 36 hpf. Thus, the expression patterns of these two gbx genes did not overlap, arguing against their redundant function in the forebrain. Two-color fluorescence in situ hybridization (FISH) showed close relationships between the telencephalic expression of gbx2 and other forebrain-forming genes, suggesting that their interactions contribute to the regionalization of the telencephalon. FISH further revealed that gbx2 is expressed in the ventricular region of the telencephalon. By using transgenic fish in which gbx2 can be induced by heat shock, we found that gbx2 induction at 16 hpf repressed the expression of emx3, dlx2a, and six3b in the ventral telencephalon. Among secreted factor genes, bmp2b and wnt1 were repressed in the vicinity of the gbx2 domain in the telencephalon. The expression of forebrain-forming genes was examined in mutant embryos lacking gbx2, showing emx3 and dlx2a to be upregulated in the subpallium at 24 hpf. Taken together, these findings indicate that gbx2 contributes to the development of the subpallium through its repressive activities against other telencephalon-forming genes. We further showed that inhibiting FGF signaling and activating Wnt signaling repressed gbx2 and affected the regionalization of the telencephalon, supporting a functional link between gbx2, intracellular signaling, and telencephalon development.

The Temporal Contribution of the Gbx2 Lineage to Cerebellar Neurons.

The cerebellum (Cb) is an exquisite structure that controls elaborate motor behaviors and is essential for sensory-motor learning. During development, the Cb is derived from rhombomere 1 (r1). Within this embryonic compartment, precursors in r1 are patterned by signaling cues originating from the isthmus organizer (IsO) and subsequently undergo complex morphogenic movements to establish their final position in the mature Cb. The transcription factor Gbx2 is expressed in the developing Cb and is intimately involved in organizing and patterning the Cb. Nevertheless, how precursors expressing Gbx2 at specific embryonic time points contribute to distinct cell types in the adult Cb is unresolved. In this study, we used Genetic Inducible Fate Mapping (GIFM) to mark Gbx2-expressing precursors with fine temporal resolution and to subsequently track this lineage through embryogenesis. We then determined the terminal neuronal fate of the Gbx2 lineage in the adult Cb. Our analysis demonstrates that the Gbx2 lineage contributes to the Cb with marking over the course of five stages: Embryonic day 7.5 (E7.5) through E11.5. The Gbx2 lineage gives rise to Purkinje cells, granule neurons, and deep cerebellar neurons across these marking stages. Notably, the contribution of the Gbx2 lineage shifts as development proceeds with each marking stage producing a distinct profile of mature neurons in the adult Cb. These findings demonstrate the relationship between the temporal expression of Gbx2 and the terminal cell fate of neurons in the Cb. Based on these results, Gbx2 is critical to Cb development, not only for its well-defined role in positioning and maintaining the IsO, but also for guiding the development of Cb precursors and determining the identity of Cb neurons.

The transcription factor Gbx2 induces expression of Kruppel-like factor 4 to maintain and induce naïve pluripotency of embryonic stem cells.

The transcription factor Gbx2 (gastrulation brain homeobox 2) is a direct target of the LIF/STAT3 signaling pathway, maintains mouse embryonic stem cell (mESC) self-renewal, and facilitates mouse epiblast stem cell (mEpiSC) reprogramming to naïve pluripotency. However, the mechanism by which Gbx2 mediates its effects on pluripotency remains unknown. Here, using an RNA-Seq approach, we identified Klf4 (Kruppel-like factor 4) as a direct target of Gbx2. Functional studies indicated that Klf4 mediates the self-renewal-promoting effects of Gbx2, because knockdown of Klf4 expression abrogated the ability of Gbx2 to maintain the undifferentiated state of mESCs. We also found that Gbx2 largely depends on Klf4 to reprogram mEpiSCs to a mESC-like state. In summary, our study has uncovered a mechanism by which Gbx2 maintains and induces naïve pluripotency. These findings expand our understanding of the pluripotency control network and may inform the development of culture conditions for improved ESC maintenance and differentiation.

Comprehensive analysis of target genes in zebrafish embryos reveals gbx2 involvement in neurogenesis.

It is well established that the gbx2 homeobox gene contributes to the positioning of the midbrain-hindbrain boundary (MHB) governing the development of adjacent brain regions in vertebrate embryos, but the specific aspects of the gene regulatory network regulated by gbx2 during brain development remain unclear. In the present study, we sought to comprehensively identify gbx2 target genes in zebrafish embryos by microarray analysis around the end of gastrulation, when the MHB is established, using transgenic embryos harboring heat-inducible gbx2. This analysis revealed that a large number of genes were either upregulated or downregulated following gbx2 induction, and the time course of induction differed depending on the genes. The differences in response to gbx2 were found by functional annotation analysis to be related to the functions and structures of the target genes. Among the significantly downregulated genes was her5, whose expression in the midbrain was precisely complementary to gbx2 expression around the MHB, suggesting that gbx2 expression in the anterior hindbrain restricts her5 expression to the midbrain. Because her5 represses neurogenesis, gbx2 may positively regulate neural development in its expression domain. Indeed, we showed further that gbx2 induction upregulated neural marker expression in the midbrain. Quantitative PCR analysis revealed that gbx2 upregulated the expression of the zebrafish proneural gene ebf2, whereas it repressed notch1a, which generally represses neurogenesis. Taken together, these results demonstrate that gbx2 not only functions to position the MHB but also regulates neurogenesis in the anterior hindbrain.

Thalamo-cortical axons regulate the radial dispersion of neocortical GABAergic interneurons.

Neocortical GABAergic interneuron migration and thalamo-cortical axon (TCA) pathfinding follow similar trajectories and timing, suggesting they may be interdependent. The mechanisms that regulate the radial dispersion of neocortical interneurons are incompletely understood. Here we report that disruption of TCA innervation, or TCA-derived glutamate, affected the laminar distribution of GABAergic interneurons in mouse neocortex, resulting in abnormal accumulation in deep layers of interneurons that failed to switch from tangential to radial orientation. Expression of the KCC2 cotransporter was elevated in interneurons of denervated cortex, and KCC2 deletion restored normal interneuron lamination in the absence of TCAs. Disruption of interneuron NMDA receptors or pharmacological inhibition of calpain also led to increased KCC2 expression and defective radial dispersion of interneurons. Thus, although TCAs are not required to guide the tangential migration of GABAergic interneurons, they provide crucial signals that restrict interneuron KCC2 levels, allowing coordinated neocortical invasion of TCAs and interneurons.

Early molecular events during retinoic acid induced differentiation of neuromesodermal progenitors.

Bipotent neuromesodermal progenitors (NMPs) residing in the caudal epiblast drive coordinated body axis extension by generating both posterior neuroectoderm and presomitic mesoderm. Retinoic acid (RA) is required for body axis extension, however the early molecular response to RA signaling is poorly defined, as is its relationship to NMP biology. As endogenous RA is first seen near the time when NMPs appear, we used WNT/FGF agonists to differentiate embryonic stem cells to NMPs which were then treated with a short 2-h pulse of 25 nM RA or 1 µM RA followed by RNA-seq transcriptome analysis. Differential expression analysis of this dataset indicated that treatment with 25 nM RA, but not 1 µM RA, provided physiologically relevant findings. The 25 nM RA dataset yielded a cohort of previously known caudal RA target genes including Fgf8 (repressed) and Sox2 (activated), plus novel early RA signaling targets with nearby conserved RA response elements. Importantly, validation of top-ranked genes in vivo using RA-deficient Raldh2-/- embryos identified novel examples of RA activation (Nkx1-2, Zfp503, Zfp703, Gbx2, Fgf15, Nt5e) or RA repression (Id1) of genes expressed in the NMP niche or progeny. These findings provide evidence for early instructive and permissive roles of RA in controlling differentiation of NMPs to neural and mesodermal lineages.

The epigenetic modifier DNMT3A is necessary for proper otic placode formation.

Cranial placodes are thickenings in the ectoderm that give rise to sensory organs and peripheral ganglia of the vertebrate head. At gastrula and neurula stages, placodal precursors are intermingled in the neural plate border with future neural and neural crest cells. Here, we show that the epigenetic modifier, DNA methyl transferase (DNMT) 3A, expressed in the neural plate border region, influences development of the otic placode which will contribute to the ear. DNMT3A is expressed in the presumptive otic region at gastrula through neurula stages and later in the otic placode itself. Whereas neural plate border and non-neural ectoderm markers Erni, Dlx5, Msx1 and Six1 are unaltered, DNMT3A loss of function leads to early reduction in the expression of the key otic placode specifier genes Pax2 and Gbx2 and later otic markers Sox10 and Soho1. Reduction of Gbx2 was first observed at HH7, well before loss of other otic markers. Later, this translates to significant reduction in the size of the otic vesicle. Based on these results, we propose that DNMT3A is important for enabling the activation of Gbx2 expression, necessary for normal development of the inner ear.