A mammalian helix-loop-helix factor structurally related to the product of Drosophila proneural gene atonal is a positive transcriptional regulator expressed in the developing nervous system

Selective induction of neocortical GABAergic neurons by the PDK1-Akt pathway through activation of Mash1

Extracellular stimuli regulate neuronal differentiation and subtype specification during brain development, although the intracellular signaling pathways that mediate these processes remain largely unclear. We now show that the PDK1-Akt pathway regulates differentiation of telencephalic neural precursor cells (NPCs). Active Akt promotes differentiation of NPC into gamma-aminobutyric acid-containing (GABAergic) but not glutamatergic neurons. Disruption of the Pdk1 gene or expression of dominant-negative forms of Akt suppresses insulin-like growth factor (IGF)-1 enhancement of NPC differentiation into neurons in vitro and production of neocortical GABAergic neurons in vivo. Furthermore, active Akt increased the protein levels and transactivation activity of Mash1, a proneural basic helix-loop-helix protein required for the generation of neocortical GABAergic neurons, and Mash1 was required for Akt-induced neuronal differentiation. These results have unveiled an unexpected role of the PDK1-Akt pathway: a key mediator of extracellular signals regulating the production of neocortical GABAergic neurons.

Zinc intake during pregnancy increases the proliferation at ventricular zone of the newborn brain

Neurogenesis involves cell proliferation, cell cycle arrest, differentiation, migration and the natural developmental death of the neural precursors. These processes are highly co-ordinated and governed by cell-cycle genes and neural transcription factors. Zn plays a crucial role as a functional and structural component of enzymes and transcription factors and components of the intracellular signaling pathway associated with the regulation of cell proliferation. The influence of additional Zn intake during pregnancy on the neuronal proliferation at ventricular zone of the developing fetus has been studied. Pups delivered by the group of mice provided with drinking water with 4.0 mM Zn supplement throughout pregnancy contained an increased number of proliferating neurons in the ventricular zone at P0 compared to those delivered by the mice provided with drinking water without any Zn supplement. This finding provides direct evidence to support the notion that maternal Zn levels influence the development of the nervous system of the offspring.

Inhibitory and excitatory subtypes of cochlear nucleus neurons are defined by distinct bHLH transcription factors, Ptf1a and Atoh1

The cochlear nucleus (CN), which consists of dorsal and ventral cochlear nuclei (DCN and VCN), plays pivotal roles in processing and relaying auditory information to the brain. Although it contains various types of neurons, the origins of the distinct subtypes and their developmental molecular machinery are still elusive. Here we reveal that two basic helix-loop-helix transcription factors play crucial roles in specifying neuron subtypes in the CN. Pancreatic transcription factor 1a (Ptf1a) and atonal homolog 1 (Atoh1) were found to be expressed in discrete dorsolateral regions of the embryonic neuroepithelia of the middle hindbrain (rhombomeres 2-5). Genetic lineage tracing using mice that express Cre recombinase from the Ptf1a locus or under the control of the Atoh1 promoter revealed that inhibitory (GABAergic and glycinergic) or excitatory (glutamatergic) neurons of both DCN and VCN are derived from the Ptf1a- and Atoh1-expressing neuroepithelial regions, respectively. In the Ptf1a or Atoh1 null embryos, production of inhibitory or excitatory neurons, respectively, was severely inhibited in the CN. These findings suggest that inhibitory and excitatory subtypes of CN neurons are defined by Ptf1a and Atoh1, respectively and, furthermore, provide important insights into understanding the machinery of neuron subtype specification in the dorsal hindbrain.

Neural differentiation potential of human bone marrow-derived mesenchymal stromal cells: misleading marker gene expression

BACKGROUND

In contrast to pluripotent embryonic stem cells, adult stem cells have been considered to be multipotent, being somewhat more restricted in their differentiation capacity and only giving rise to cell types related to their tissue of origin. Several studies, however, have reported that bone marrow-derived mesenchymal stromal cells (MSCs) are capable of transdifferentiating to neural cell types, effectively crossing normal lineage restriction boundaries. Such reports have been based on the detection of neural-related proteins by the differentiated MSCs. In order to assess the potential of human adult MSCs to undergo true differentiation to a neural lineage and to determine the degree of homogeneity between donor samples, we have used RT-PCR and immunocytochemistry to investigate the basal expression of a range of neural related mRNAs and proteins in populations of non-differentiated MSCs obtained from 4 donors.

RESULTS

The expression analysis revealed that several of the commonly used marker genes from other studies like nestin, Enolase2 and microtubule associated protein 1b (MAP1b) are already expressed by undifferentiated human MSCs. Furthermore, mRNA for some of the neural-related transcription factors, e.g. Engrailed-1 and Nurr1 were also strongly expressed. However, several other neural-related mRNAs (e.g. DRD2, enolase2, NFL and MBP) could be identified, but not in all donor samples. Similarly, synaptic vesicle-related mRNA, STX1A could only be detected in 2 of the 4 undifferentiated donor hMSC samples. More significantly, each donor sample revealed a unique expression pattern, demonstrating a significant variation of marker expression.

CONCLUSION

The present study highlights the existence of an inter-donor variability of expression of neural-related markers in human MSC samples that has not previously been described. This donor-related heterogeneity might influence the reproducibility of transdifferentiation protocols as well as contributing to the ongoing controversy about differentiation capacities of MSCs. Therefore, further studies need to consider the differences between donor samples prior to any treatment as well as the possibility of harvesting donor cells that may be inappropriate for transplantation strategies.

Notch signaling in chondrogenesis

The different stages of cartilage development are well described but no transcription factor capable of specifically inducing differentiation to articular cartilage has been identified and little is known about the molecular mechanisms regulating cartilage development. Notch signaling is an evolutionarily conserved pathway taking part in many developmental and cell type specification processes. It has been demonstrated that markers for Notch signaling are differentially expressed during cartilage development and there is evidence for their functional role during this process. Notch signaling has further been implicated in osteoarthritis and Notch1 has been suggested as a marker for chondrogenic progenitor cells. This review summarizes the current knowledge on the role of the Notch signaling pathway in cartilage development and osteoarthritis.

Identification and subclassification of new Atoh1 derived cell populations during mouse spinal cord development

At spinal levels, sensory information pertaining to body positioning (proprioception) is relayed to the cerebellum by the spinocerebellar tracts (SCTs). In the past we revealed the basic helix-loop-helix transcription factor Atoh1 (Math1) to be important for establishing Dorsal Progenitor 1 (DP1) commissural interneurons, which comprise a subset of proprioceptive interneurons. Given there exists multiple subdivisions of the SCT we asked whether Atoh1 may also play a role in specifying other cell types in the spinal cord. Here, we reveal the generation of at least three DP1 derived interneuron populations that reside at spatially restricted positions along the rostral-caudal axis. Each of these cell populations expresses distinct markers and anatomically coincides with the cell bodies of the various subdivisions of the SCT. In addition, we found that as development proceeds (e.g. by E13.5) Atoh1 expression becomes apparent in the dorsal midline in the region of the roof plate (RP). Interestingly, we find that cells derived from Atoh1 expressing RP progenitors express SSEA-1, and in the absence of Atoh1 these progenitors become SOX9 positive. Altogether we reveal the existence of multiple Atoh1 dependent cell types in the spinal cord, and uncover a novel progenitor domain that arises late in development.

Transcriptional cascade from Math1 to Mbh1 and Mbh2 is required for cerebellar granule cell differentiation

Cerebellar granule cells (CGCs) are the most abundant neuronal type in the mammalian brain, and their differentiation is regulated by the basic helix-loop-helix gene, Math1. However, little is known about downstream genes of Math1 and their functions in the cerebellum. To investigate them, we have here established an electroporation-based in vivo gene transfer method in the developing mouse cerebellum. Misexpression of Math1 ectopically induced expression of Bar-class homeobox genes, Mbh1 and Mbh2, which are expressed by CGCs. Conversely, their expression was repressed in CGCs by knockdown of Math1. These findings, taken together with chromatin immunoprecipitation assays, suggest that Math1 directly regulates the Mbh genes in CGCs. Furthermore, a dominant-negative form of the Mbh proteins disrupted proper formation of the external granule layer and differentiation of CGCs, whereas misexpression of the Mbh genes ectopically induced expression of a CGC marker in nonneuronal cells, indicating that the Mbh proteins are required for the differentiation of CGCs.

Mash1 is required for neuroendocrine cell development in the glandular stomach

In the epithelium of the developing glandular stomach, neuroendocrine cells differentiate from common progenitors, but the mechanism of how these cells are specified remains to be determined. Here, we show that the basic helix-loop-helix (bHLH) gene, mammalian achaete-scute homologue 1 (Mash1), is highly expressed in the glandular stomach epithelium. In Mash1-null mice, almost all gastric neuroendocrine cells are missing, whereas development of non-neuroendocrine cells is not significantly affected. The bHLH gene Neurogenin3 (Ngn3), which is known to regulate formation of subsets of gastric neuroendocrine cells (gastrin-, glucagon- and somatostatin-producing cells), is expressed normally in the Mash1-null stomach. Thus, Ngn3 alone is not sufficient but Mash1 is additionally required for the differentiation of these neuroendocrine cells. Taken together, these results indicate that formation of gastrin-, glucagon- and somatostatin-producing cells depends on both Mash1 and Ngn3, while that of other neuroendocrine cells depends on Mash1 alone, suggesting that combinations of bHLH genes may contribute to cell type diversity.

Cerebellar development and disease

The molecular control of cell-type specification within the developing cerebellum as well as the genetic causes of the most common human developmental cerebellar disorders have long remained mysterious. Recent genetic lineage and loss-of-function data from mice have revealed unique and nonoverlapping anatomical origins for GABAergic neurons from ventricular zone precursors and glutamatergic cell from rhombic lip precursors, mirroring distinct origins for these neurotransmitter-specific cell types in the cerebral cortex. Mouse studies elucidating the role of Ptf1a as a cerebellar ventricular zone GABerigic fate switch were actually preceded by the recognition that PTF1A mutations in humans cause cerebellar agenesis, a birth defect of the human cerebellum. Indeed, several genes for congenital human cerebellar malformations have recently been identified, including genes causing Joubert syndrome, Dandy-Walker malformation, and pontocerebellar hypoplasia. These studies have pointed to surprisingly complex roles for transcriptional regulation, mitochondrial function, and neuronal cilia in patterning, homeostasis, and cell proliferation during cerebellar development. Together, mouse and human studies are synergistically advancing our understanding of the developmental mechanisms that generate the uniquely complex mature cerebellum.

Post-transcriptional down-regulation of Atoh1/Math1 by bone morphogenic proteins suppresses medulloblastoma development

Bone morphogenic proteins 2 and 4 (BMP2 and BMP4) inhibit proliferation and induce differentiation of cerebellar granule neuron progenitors (GNPs) and primary GNP-like medulloblastoma (MB) cells. This occurs through rapid proteasome-mediated degradation of Math1 (Atoh1), a transcription factor expressed in proliferating GNPs. Ectopic expression of Atoh1, but not of Sonic hedgehog (Shh)-regulated Gli1 or Mycn, cancels these BMP-mediated effects and restores Shh-dependent proliferation of GNPs and MB cells in vitro and in vivo. Genes regulating the BMP signaling pathway are down-regulated in mouse MBs. Thus, BMPs are potent inhibitors of MB and should be considered as novel therapeutic agents.

Proteasomal degradation of Atoh1 by aberrant Wnt signaling maintains the undifferentiated state of colon cancer

Atoh1 plays a crucial role in intestinal cell differentiation. We have demonstrated that its human homolog Hath1 protein is targeted by the Wnt-GSK3 axis, resulting in the proteasomal degradation in human colon cancer. However, the contribution of Hath1 degradation to the undifferentiated state of colon cancer remains unknown. In this study, we demonstrated that both constitutive expression of mutant Hath1 and stabilization of Hath1 protein by a GSK3 inhibitor in colon cancer cells increased the expression of MUC2 known as a representative function of differentiated goblet cells. This means that Hath1 protein degradation may be required for maintaining the undifferentiated state of colon cancers, and that GSK3 inhibitors have potential for use in cancer therapy.

Genetic evaluation of the serotonergic system in chronic fatigue syndrome

Chronic fatigue syndrome (CFS) is a debilitating disorder of unknown etiology with no known lesions, diagnostic markers or therapeutic intervention. The pathophysiology of CFS remains elusive, although abnormalities in the central nervous system (CNS) have been implicated, particularly hyperactivity of the serotonergic (5-hydroxytryptamine; 5-HT) system and hypoactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Since alterations in 5-HT signaling can lead to physiologic and behavioral changes, a genetic evaluation of the 5-HT system was undertaken to identify serotonergic markers associated with CFS and potential mechanisms for CNS abnormality. A total of 77 polymorphisms in genes related to serotonin synthesis (TPH2), signaling (HTR1A, HTR1E, HTR2A, HTR2B, HTR2C, HTR3A, HTR3B, HTR4, HTR5A, HTR6, and HTR7), transport (SLC6A4), and catabolism (MAOA) were examined in 137 clinically evaluated subjects (40 CFS, 55 with insufficient fatigue, and 42 non-fatigued, NF, controls) derived from a population-based CFS surveillance study in Wichita, Kansas. Of the polymorphisms examined, three markers (-1438G/A, C102T, and rs1923884) all located in the 5-HT receptor subtype HTR2A were associated with CFS when compared to NF controls. Additionally, consistent associations were observed between HTR2A variants and quantitative measures of disability and fatigue in all subjects. The most compelling of these associations was with the A allele of -1438G/A (rs6311) which is suggested to have increased promoter activity in functional studies. Further, in silico analysis revealed that the -1438 A allele creates a consensus binding site for Th1/E47, a transcription factor implicated in the development of the nervous system. Electrophoretic mobility shift assay supports allele-specific binding of E47 to the A allele but not the G allele at this locus. These data indicate that sequence variation in HTR2A, potentially resulting in its enhanced activity, may be involved in the pathophysiology of CFS.

The derivatives of the Wnt3a lineage in the central nervous system

The dorsal midline of the vertebrate neural tube is a source of signals that direct cell fate specification and proliferation. Using genetic fate mapping in the mouse and a previously generated Wnt3aCre line, we report here that genetically labeled cells of the Wnt3a lineage migrate widely from the dorsal midline into the dorsal half of the adult brain and spinal cord, contributing to diverse structures in the diencephalon, midbrain, and brainstem and extensively populating the rostral spinal cord. Conspicuously, many of these structures are linked in specific functional networks. Wnt3a lineage cells populate nuclei of the central auditory system from the medulla to thalamus, and the trigeminal sensory system from the cervical spinal cord to the midbrain. Our findings reveal the rich contributions of the Wnt3a lineage to a variety of brain structures and show that functionally integrated nuclei can share a molecular identity, provided by transient gene expression early in their development.

Conserved regulation of Math5 and Math1 revealed by Math5-GFP transgenes

Retinal ganglion cell genesis requires the proneural bHLH transcription factor Math5 (Atoh7), but little is known about the regulatory elements that control its expression. Here, we investigate Math5 gene regulation using transgenic mice. These mice express GFP in the prenatal retina, live-labeling RGC axon migration and innervation of the brain. Unexpectedly, these Math5-GFP transgenes are also found in Math1 expression domains throughout the nervous system, intriguing since Math5 and Math1 normally exhibit nonoverlapping expression. Furthermore, Math5-GFP and Math1 are regulated similarly, by both Pax6 and Math1 itself, in the lower rhombic lip and dorsal spinal cord. We also show that Pax6 binds to particular Math5 and Math1 regulatory sequences in vitro. Together these data suggest that these atonal semi-orthologues may share conserved regulatory elements that are normally silent in the Math5 gene.

Basic helix-loop-helix gene Hes6 delineates the sensory hair cell lineage in the inner ear

The basic helix-loop-helix (bHLH) gene Hes6 is known to promote neural differentiation in vitro. Here, we report the expression and functional studies of Hes6 in the inner ear. The expression of Hes6 appears to be parallel to that of Math1 (also known as Atoh1), a bHLH gene necessary and sufficient for hair cell differentiation. Hes6 is expressed initially in the presumptive hair cell precursors in the cochlea. Subsequently, the expression of Hes6 is restricted to morphologically differentiated hair cells. Similarly, the expression of Hes6 in the vestibule is in the hair cell lineage. Hes6 is dispensable for hair cell differentiation, and its expression in inner ear hair cells is abolished in the Math1-null animals. Furthermore, the introduction of Hes6 into the cochlea in vitro is not sufficient to promote sensory or neuronal differentiation. Therefore, Hes6 is downstream of Math1 and its expression in the inner ear delineates the sensory lineage. However, the role of Hes6 in the inner ear remains elusive.

Origin of climbing fiber neurons and their developmental dependence on Ptf1a

Climbing fiber (CF) neurons in the inferior olivary nucleus (ION) extend their axons to Purkinje cells, playing a crucial role in regulating cerebellar function. However, little is known about their precise place of birth and developmental molecular machinery. Here, we describe the origin of the CF neuron lineage and the involvement of Ptf1a (pancreatic transcription factor 1a) in CF neuron development. Ptf1a protein was found to be expressed in a discrete dorsolateral region of the embryonic caudal hindbrain neuroepithelium. Because expression of Ptf1a is not overlapping other transcription factors such as Math1 (mouse atonal homolog 1) and Neurogenin1, which are suggested to define domains within caudal hindbrain neuroepithelium (Landsberg et al., 2005), we named the neuroepithelial region the Ptf1a domain. Analysis of mice that express beta-galactosidase from the Ptf1a locus revealed that CF neurons are derived from the Ptf1a domain. In contrast, retrograde labeling of precerebellar neurons indicated that mossy fiber neurons are not derived from Ptf1a-expressing progenitors. We could observe a detailed migratory path of CF neurons from the Ptf1a domain to the ION during embryogenesis. In Ptf1a null mutants, putative immature CF neurons produced from this domain were unable to migrate or differentiate appropriately, resulting in a failure of ION formation. Apoptotic cells were observed in the mutant hindbrain. Furthermore, the fate of some cells in the Ptf1a lineage were changed to mossy fiber neurons in Ptf1a null mutants. These findings clarify the precise origin of CF neurons and suggest that Ptf1a controls their fate, survival, differentiation, and migration during development.

Developmental expression and differentiation-related neuron-specific splicing of metastasis suppressor 1 (Mtss1) in normal and transformed cerebellar cells

Background

Mtss1 encodes an actin-binding protein, dysregulated in a variety of tumors, that interacts with sonic hedgehog/Gli signaling in epidermal cells. Given the prime importance of this pathway for cerebellar development and tumorigenesis, we assessed expression of Mtss1 in the developing murine cerebellum and human medulloblastoma specimens.

Results

During development, Mtss1 is transiently expressed in granule cells, from the time point they cease to proliferate to their synaptic integration. It is also expressed by granule cell precursor-derived medulloblastomas. In the adult CNS, Mtss1 is found exclusively in cerebellar Purkinje cells. Neuronal differentiation is accompanied by a switch in Mtss1 splicing. Whereas immature granule cells express a Mtss1 variant observed also in peripheral tissues and comprising exon 12, this exon is replaced by a CNS-specific exon, 12a, in more mature granule cells and in adult Purkinje cells. Bioinformatic analysis of Mtss1 suggests that differential exon usage may affect interaction with Fyn and Src, two tyrosine kinases previously recognized as critical for cerebellar cell migration and histogenesis. Further, this approach led to the identification of two evolutionary conserved nuclear localization sequences. These overlap with the actin filament binding site of Mtss1, and one also harbors a potential PKA and PKC phosphorylation site.

Conclusion

Both the pattern of expression and splicing of Mtss1 is developmentally regulated in the murine cerebellum. These findings are discussed with a view on the potential role of Mtss1 for cytoskeletal dynamics in developing and mature cerebellar neurons.

The E-protein Tcf4 interacts with Math1 to regulate differentiation of a specific subset of neuronal progenitors

Proneural factors represent <10 transcriptional regulators required for specifying all of the different neurons of the mammalian nervous system. The mechanisms by which such a small number of factors creates this diversity are still unknown. We propose that proteins interacting with proneural factors confer such specificity. To test this hypothesis we isolated proteins that interact with Math1, a proneural transcription factor essential for the establishment of a neural progenitor population (rhombic lip) that gives rise to multiple hindbrain structures and identified the E-protein Tcf4. Interestingly, haploinsufficiency of TCF4 causes the Pitt-Hopkins mental retardation syndrome, underscoring the important role for this protein in neural development. To investigate the functional relevance of the Math1/Tcf4 interaction in vivo, we studied Tcf4(-/-) mice and found that they have disrupted pontine nucleus development. Surprisingly, this selective deficit occurs without affecting other rhombic lip-derived nuclei, despite expression of Math1 and Tcf4 throughout the rhombic lip. Importantly, deletion of any of the other E-protein-encoding genes does not have detectable effects on Math1-dependent neurons, suggesting a specialized role for Tcf4 in distinct neural progenitors. Our findings provide the first in vivo evidence for an exclusive function of dimers formed between a proneural basic helix-loop-helix factor and a specific E-protein, offering insight about the mechanisms underlying transcriptional programs that regulate development of the mammalian nervous system.

Localization, characterization and function of pituitary adenylate cyclase-activating polypeptide during brain development

Neural development is controlled by region-specific factors that regulate cell proliferation, migration and differentiation. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that exerts a wide range of effects on different cell types in the brain as early as the fetal stage. Here we review current knowledge concerning several aspects of PACAP expression in embryonic and neonatal neural tissue: (i) the distribution of PACAP and PACAP receptors mRNA in the developing brain; (ii) the characteristic generation of neurons, astrocytes and oligodendrocytes in brain areas where the PACAP receptor is expressed and (iii) the role of PACAP as a regulator of neural development, inducing differentiation and proliferation in association with other trophic factors or signal transduction molecules.

Antagonism between Notch and bone morphogenetic protein receptor signaling regulates neurogenesis in the cerebellar rhombic lip

Background

During the embryonic development of the cerebellum, neurons are produced from progenitor cells located along a ventricular zone within dorsal rhombomere 1 that extends caudally to the roof plate of the fourth ventricle. The apposition of the caudal neuroepithelium and roof plate results in a unique inductive region termed the cerebellar rhombic lip, which gives rise to granule cell precursors and other glutamatergic neuronal lineages. Recently, we and others have shown that, at early embryonic stages prior to the emergence of granule cell precursors (E12), waves of neurogenesis in the cerebellar rhombic lip produce specific hindbrain nuclei followed by deep cerebellar neurons. How the induction of rhombic lip-derived neurons from cerebellar progenitors is regulated during this phase of cerebellar development to produce these temporally discrete neuronal populations while maintaining a progenitor pool for subsequent neurogenesis is not known.

Results

Employing both gain- and loss-of-function methods, we find that Notch1 signaling in the cerebellar primordium regulates the responsiveness of progenitor cells to bone morphogenetic proteins (BMPs) secreted from the roof plate that stimulate the production of rhombic lip-derived neurons. In the absence of Notch1, cerebellar progenitors are depleted during the early production of hindbrain neurons, resulting in a severe decrease in the deep cerebellar nuclei that are normally born subsequently. Mechanistically, we demonstrate that Notch1 activity prevents the induction of Math1 by antagonizing the BMP receptor-signaling pathway at the level of Msx2 expression.

Conclusion

Our results provide a mechanism by which a balance between neural induction and maintenance of neural progenitors is achieved in the rhombic lip throughout embryonic development.

Flow cytometric analysis of mouse neurospheres based on the expression level of RANDAM-2

RANDAM-2, a type-I transmembrane antigen constitutively expressed on the neuronal cell lineage during mouse neurogenesis, shows the highest expression level between embryonic day 8.5 (E8.5) and E10.5. As the period well overlaps with the proliferating stages of neural stem cells (NSCs), it is conceivable that NSCs are efficiently separable based on the expression level of RANDAM-2. In this paper, we show that NSCs can be efficiently enriched as RANDAM-2(high+) cells by fluorescence-activated cell sorting. Many cells in the RANDAM-2(high+) cells had the characteristics of the self-renewal capability and potential for multilineage differentiation into neural cells. In contrast, almost all of the RANDAM-2(low+/-) cells exhibited not only the extremely low self-renewability but the differentiation capability restricted to neurons. These two subpopulations also differed from each other in terms of the expression level of molecules associated with neural differentiation. These findings demonstrate that RANDAM-2 can be regarded as a useful marker for enrichment of NSCs.

Math1 target genes are enriched with evolutionarily conserved clustered E-box binding sites

The basic helix-loop-helix (bHLH) transcription factor Math1 and its orthologs are fundamental for proper development of various neuronal subpopulations, such as cerebellar granule cells, D1 interneurons in the spinal cord, and inner ear hair cells. Although crucial for neurogenesis, the mechanisms by which Math1 specifically recognizes its direct targets are not fully understood. To search for direct and indirect target genes and signaling pathways controlled by Math1, we analyzed the effect of Math1 knockout on the expression profile of multiple genes in the embryonic cerebellum. Eighteen differentially expressed transcripts were identified and found to belong to a few developmentally-related functional groups, such as transcriptional regulation, proliferation, organogenesis, signal transduction, and apoptosis. Importantly, genomic analysis of E-box motifs has identified a significant enrichment and clustering of MATH1-binding E-boxes only in a subset of differentially expressed genes (Nr2f6, Hras1, and Hes5) in both mouse and man. Moreover, Math1 was shown by chromatin immunoprecipitation (ChIP) to bind, and by a luciferase reporter assay to activate transcription, of an upstream genomic fragment of Nr2f6. Taken together, we propose that when putative direct targets of Math1 are being selected for detailed studies on DNA microarray hybridization, the enrichment and clustering of binding E-boxes in multiple species may be helpful criteria. Our findings may be useful to the study of other bHLH transcription factors, many of which control the development of the nervous system.

Reciprocal targeting of Hath1 and beta-catenin by Wnt glycogen synthase kinase 3beta in human colon cancer

BACKGROUND & AIMS

The transcription factor Hath1 plays a crucial role in the differentiation program of the human gut epithelium. The present study was conducted to investigate the molecular mechanism of Hath1 expression and its close association with beta-catenin/glycogen synthase kinase 3beta (GSK3beta) under the Wnt pathway in human colonocytes.

METHODS

Tissue distribution of Hath1 messenger RNA in human tissues was examined by Northern blot. Stability of Hath1 protein was analyzed by expression of FLAG-tagged Hath1 in human cell lines. Targeting of Hath1 protein by GSK3beta was determined by specific inhibition of GSK-3beta function. Expression of Hath1 protein in colorectal cancers was examined by immunohistochemistry.

RESULTS

Hath1 messenger RNA expression was confined to the lower gastrointestinal tract in human adult tissues. In colon cancer cells, although Hath1 messenger RNA was also detected, Hath1 protein was positively degradated by proteasome-mediated proteolysis. Surprisingly, the GSK3beta-dependent protein degradation was switched between Hath1 and beta-catenin by Wnt signaling, leading to the dramatic alteration of cell status between proliferation and differentiation, respectively. Hath1 protein was detected exclusively in normal colon tissues but not in cancer tissues, where nuclear-localized beta-catenin was present.

CONCLUSIONS

The present study suggests a novel function of the canonical Wnt signaling in human colon cancer cells, regulating cell proliferation and differentiation by GSK3beta-mediated, reciprocal degradation of beta-catenin or Hath1, respectively, which further emphasizes the importance of aberrant Wnt signaling in colonocyte transformation.

Retrograde infection of precerebellar nuclei neurons by injection of a recombinant adenovirus into the cerebellar cortex of normal and reeler mice

The reeler mouse is an autosomal recessive mutant mouse caused by mutation of the reelin gene and characterized by cerebellar ataxia. To determine whether the distribution pattern of precerebellar nuclei neurons in the brainstem of the reeler mouse changes, we injected a small volume of a replication-defective recombinant adenovirus carrying E. coli beta-galactosidase (lacZ) into the cerebellar cortex of normal and reeler mice. Five days later, the mice were transcardially perfused by a fixative solution. X-gal staining of coronal or sagittal sections of the brainstem revealed that many origins for reticulocerebellar, cuneocerebellar, trigeminocerebellar, and pontocerebellar projections were retrogradely labeled, but only a few olivocerebellar neurons were labeled. Retrogradely labeled neurons in the lateral reticular nucleus tended to locate more laterally and be more condensed into a small compartment in the reeler compared with their normal counterparts. Retrogradely labeled neurons in the external cuneate nucleus were more dorsally shifted in the reeler mice compared with their normal counterparts. We could not find any differences between the normal and reeler mice in the distribution patterns of their trigeminocerebellar projection neurons. Retrogradely labeled pontocerebellar neurons in the basilar pons of the reeler mouse were reduced in number compared with their normal counterparts in addition to being more ventrally and laterally shifted. These findings strongly suggest that the migration of some precerebellar nuclei neurons from the rhombic lip to their final loci may be obstructed in the reeler mice.

HATH1 Expression in Mucinous Cancers of the Colorectum and Related Lesions

PURPOSE

Mucinous cancers and signet ring carcinomas are distinct classes of colon cancers characterized by their production of copious quantities of intestinal goblet cell mucin, MUC2. Deletion of transcription factor HATH1 ablates the biogenesis of goblet cells in developing mouse intestine, and forced expression of HATH1 results in elevated expression of MUC2 in colon cancer cells. The aim of this study was to assess the possible role of HATH1 in the development of mucinous cancers and signet ring carcinomas.

EXPERIMENTAL DESIGN

Immunohistochemistry and confocal microscopy was used to examine HATH1 expression and subcellular distribution in normal colon and small intestine, mucinous cancers, signet ring carcinomas, and nonmucinous cancers and in precursor lesions, including hyperplastic polyps, serrated adenomas, tubular adenomas, and villous adenomas. We also analyzed the transactivation of MUC2 promoter/reporter constructs by a HATH1 expression vector.

RESULTS

HATH1 expression transactivated MUC2 promoter/reporter constructs, an activity that was significantly inhibited by mutation of putative HATH1-binding sites. HATH1 was expressed in the nuclei of goblet cells and in the cytoplasm and nuclei of enteroendocrine cells of the colon. In the small intestine, only cytoplasmic expression of HATH1 in enteroendocrine cells was detected. HATH1 was found to be strongly expressed in the nuclei of hyperplastic polyps, serrated adenomas, villous adenomas, mucinous cancers, and signet ring carcinomas but repressed in nonmucinous cancers and tubular adenomas.

CONCLUSIONS

This study confirms the importance of HATH1 for the development of intestinal secretory cells. The results further suggest that HATH1 is an important factor in the up-regulation of MUC2 expression that occurs in mucinous cancers and signet ring carcinomas. In addition, the expression of HATH1 in hyperplastic polyps, serrated adenomas, and villous adenomas lends support to the hypothesis that these neoplasms are frequent precursors in mucinous cancer and signet ring carcinoma development.

The intestine-specific homeobox gene Cdx2 induces expression of the basic helix-loop-helix transcription factor Math1

The basic helix-loop-helix transcription factor Math1, which is transiently expressed in proliferating neural precursors in multiple domains of the developing nervous system, is also related to the cell fate decision of enteroendocrine, goblet, and Paneth cells in the intestine. On the other hand, the transcription factor Cdx2, which is normally confined to intestinal epithelial cells, is related to the differentiation of these cells. Therefore, we investigated the relationship between Math1 and Cdx2 in intestinal epithelial cells. The Math1 and Cdx2 expressions in normal intestinal mucosa and intestinal metaplastic mucosa from mouse and human stomachs, as well as an intestinal crypt-derived cell line, were analyzed by immunohistochemistry, reverse transcription-polymerase chain reaction and Northern blotting, and Math1 enhancer element was analyzed by luciferase reporter assays. Math1-positive epithelial cells co-expressing Cdx2 were found in normal intestinal mucosa from humans and mice. Furthermore, Math1-producing epithelial cells that showed positive immunostaining for Cdx2 were also observed in intestinal metaplastic mucosa from human and Cdx2 transgenic mouse stomachs, although they were not detected in normal gastric mucosa of humans and mice. Expression of Cdx2 stimulated endogenous Math1 mRNA expression in the intestinal crypt-derived cell line IEC-6, corroborating observations in Cdx2-expressing intestinal metaplastic mucosa. Furthermore, expression of Cdx2 in IEC-6 cells conferred the ability to express a Math1 reporter gene containing a Math1 enhancer. Based on these results, we hypothesize that Cdx2 is involved in activating Math1 expression in intestinal epithelial cells.

A threshold requirement for Gbx2 levels in hindbrain development

Gbx2 is a homeobox gene that plays a crucial role in positioning the mid/hindbrain organizer (isthmus), which regulates midbrain and cerebellar development primarily through the secreted factor FGF8. In Gbx2 null homozygotes, rhombomeres (r) 1-3 fail to develop and the isthmic expression of Fgf8 is reduced and disorganized. These mutants fail to form a cerebellum, as it is derived from r1. Here, we analyze mice homozygous for a Gbx2 hypomorphic allele (Gbx2(neo)). Quantitative RT-PCR and RNA in situ analyses indicate that the presence of a neo-resistance cassette impairs normal Gbx2 splicing thus reducing wild-type Gbx2 mRNA levels to 6-10% of normal levels in all domains and stages examined. In Gbx2 hypomorphic mutants, gene marker and neuronal patterning analyses indicate that reduced Gbx2 expression is sufficient to support the development of r3 but not r2. The posterior region of r1, from which the lateral cerebellum develops, is unaffected in these mutants. However, the anterior region of r1 is converted to an isthmus-like tissue. Hence, instead of expressing r1 markers, this region displays robust expression of Fgf8 and Fgf17, as well as the downstream FGF targets Spry1 and Spry4. Additionally, we demonstrate that the cell division regulator cyclin D2 is downregulated, and that cellular proliferation is reduced in both the normal isthmus and in the mutant anterior r1. As a result of this transformation, the cerebellar midline fails to form. Thus, our studies demonstrate different threshold requirements for the level of Gbx2 gene product in different regions of the hindbrain.

Persistent and high levels of Hes1 expression regulate boundary formation in the developing central nervous system

The developing central nervous system is partitioned into compartments by boundary cells, which have different properties than compartment cells, such as forming neuron-free zones, proliferating more slowly and acting as organizing centers. We now report that in mice the bHLH factor Hes1 is persistently expressed at high levels by boundary cells but at variable levels by non-boundary cells. Expression levels of Hes1 display an inverse correlation to those of the proneural bHLH factor Mash1, suggesting that downregulation of Hes1 leads to upregulation of Mash1 in non-boundary regions,whereas persistent and high Hes1 expression constitutively represses Mash1 in boundary regions. In agreement with this notion, in the absence of Hes1 and its related genes Hes3 and Hes5, proneural bHLH genes are ectopically expressed in boundaries, resulting in ectopic neurogenesis and disruption of the organizing centers. Conversely, persistent Hes1 expression in neural progenitors prepared from compartment regions blocks neurogenesis and reduces cell proliferation rates. These results indicate that the mode of Hes1 expression is different between boundary and non-boundary cells, and that persistent and high levels of Hes1 expression constitutively repress proneural bHLH gene expression and reduce cell proliferation rates,thereby forming boundaries that act as the organizing centers.

Notch1 signaling influences v2 interneuron and motor neuron development in the spinal cord

The Notch signaling pathway plays a variety of roles in cell fate decisions during development. Previous studies have shown that reduced Notch signaling results in premature differentiation of neural progenitor cells, while increased Notch activities promote apoptotic death of neural progenitor cells in the developing brain. Whether Notch signaling is involved in the specification of neuronal subtypes is unclear. Here we examine the role of Notch1 in the development of neuronal subtypes in the spinal cord using conditional knockout (cKO) mice lacking Notch1 specifically in neural progenitor cells. Notch1 inactivation results in accelerated neuronal differentiation in the ventral spinal cord and gradual disappearance of the ventral central canal. These changes are accompanied by reduced expression of Hes1 and Hes5 and increased expression of Mash1 and Neurogenin 1 and 2. Using markers (Nkx2.2, Nkx6.1, Olig2, Pax6 and Dbx1) for one or multiple progenitor cell types, we found reductions of all subtypes of progenitor cells in the ventral spinal cord of Notch1 cKO mice. Similarly, using markers (Islet1/2, Lim3, Sim1, Chox10, En1 and Evx1/2) specific for motor neurons and distinct classes of interneurons, we found increases in the number of V0-2 interneurons in the ventral spinal cord of Notch1 cKO mice. Specifically, the number of Lim3+/Chox10+ V2 interneurons is markedly increased while the number of Lim3+/Islet+motor neurons is decreased in the Notch1 cKO spinal cord, suggesting that V2 interneurons are generated at the expense of motor neurons in the absence of Notch1. These results provide support for a role of Notch1 in neuronal subtype specification in the ventral spinal cord.

Genetic analyses demonstrate that bone morphogenetic protein signaling is required for embryonic cerebellar development

The cerebellum has been a useful model for studying many aspects of neural development because of its relatively simple cytoarchitecture and developmental program. Yet, the genetic mechanisms underlying early differentiation and patterning of the cerebellum are still poorly characterized. Cell expression studies and culture experiments have suggested the importance of bone morphogenetic proteins (BMPs) in development of specific populations of cerebellar neurons. Here, we examined mice with targeted mutations in the BMP type I receptor genes Bmpr1a and Bmpr1b, to genetically test the hypothesis that BMPs play an inductive role in the embryogenesis of cerebellar granule cells. In Bmpr1a;Bmpr1b double knock-out mice, severe cerebellar patterning defects are observed resulting in smaller cerebella that are devoid of foliation. In mutants containing either single BMP receptor gene mutation alone, cerebellar histogenesis appears normal, thereby demonstrating functional redundancy of type I BMP receptors during cerebellar development. Loss of BMP signaling in double mutant animals leads to a dramatic reduction in the number of cerebellar granule cells and ectopic location of many of those that remain. Molecular markers of granule cell specification, including Math1 and Zic1, are drastically downregulated. In addition, Purkinje cells are disorganized and ectopically located, but they appear to be correctly specified. Consistent with the interpretation that granule cells alone are affected, phosphorylated Smad1/5/8 is immunolocalized predominantly to granule cell precursors and not appreciably detected in Purkinje cell precursors. This study demonstrates that BMP signaling plays a crucial role in the specification of granule cells during cerebellar development.

Hath1 up-regulates gastric mucin gene expression in gastric cells

The Notch signaling pathway is known to mediate the differentiation and fate specification of cells in embryonic stage and adult tissues. Several tumors exhibit aberrant expression of Notch signaling component genes, such as Notch1/2/3 and Hath1. In this study, we investigated the mRNA expression of seven Notch-related genes, Notch1/2/3, Hes1/2/3, and Hath1, and then compared it with the expression of gastric mucin genes, MUC5AC and MUC6, in eight gastric cancer (GC) cell lines. Notch1/2/3 and Hes1 were expressed in most GC cell lines as well as normal gastric mucosae, while Hes2/3 were expressed in neither these cell lines nor the normal stomach. As for Hath1, five GC cell lines exhibited undetectable levels, while normal gastric mucosa expressed Hath1. The expression patterns of Hath1 and MUC6 were closely related in most GC cell lines. Many MUC5AC-positive cases also tended to show Hath1 expression. Over-expression of Math1, a mouse Hath1 homolog, in the GC cells strongly enhanced both the MUC6 and MUC5AC mRNA levels. Moreover, knockdown of Hath1 by means of RNA interference significantly decreased the expression of both mucin genes. These data indicate that Hath1 is one of the transcriptional regulators for MUC6 and MUC5AC in GC cells. It is also possible that loss of Hath1 expression may play a role in gastric carcinogenesis.

Dorsally derived netrin 1 provides an inhibitory cue and elaborates the`waiting period' for primary sensory axons in the developing spinal cord

Dorsal root ganglion (DRG) neurons extend axons to specific targets in the gray matter of the spinal cord. During development, DRG axons grow into the dorsolateral margin of the spinal cord and projection into the dorsal mantle layer occurs after a `waiting period' of a few days. Netrin 1 is a long-range diffusible factor expressed in the ventral midline of the developing neural tube, and has chemoattractive and chemorepulsive effects on growing axons. Netrin 1 is also expressed in the dorsal spinal cord. However, the roles of dorsally derived netrin 1 remain totally unknown. Here, we show that dorsal netrin 1 controls the correct guidance of primary sensory axons. During the waiting period, netrin 1 is transiently expressed or upregulated in the dorsal spinal cord, and the absence of netrin 1 results in the aberrant projection of sensory axons, including both cutaneous and proprioceptive afferents, into the dorsal mantle layer. Netrin 1 derived from the dorsal spinal cord, but not the floor plate, is involved in the correct projection of DRG axons. Furthermore,netrin 1 suppresses axon outgrowth from DRG in vitro. Unc5crcm mutant shows abnormal invasion of DRG axons as observed in netrin 1 mutants. These results are the first direct evidence that netrin 1 in the dorsal spinal cord acts as an inhibitory cue for primary sensory axons and is a crucial signal for the formation of sensory afferent neural networks.

Generation of cerebellar neuron precursors from embryonic stem cells

Here, we report in vitro generation of Math1+ cerebellar granule cell precursors and Purkinje cells from ES cells by using soluble patterning signals. When neural progenitors induced from ES cells in a serum-free suspension culture are subsequently treated with BMP4 and Wnt3a, a significant proportion of these neural cells become Math1+. The induced Math1+ cells are mitotically active and express markers characteristic of granule cell precursors (Pax6, Zic1, and Zipro1). After purification by FACS and coculture with postnatal cerebellar neurons, ES cell-derived Math1+ cells exhibit typical features of neurons of the external granule cell layer, including extensive motility and a T-shaped morphology. Interestingly, differentiation of L7+/Calbindin-D28K+ neurons (characteristic of Purkinje cells) is induced under similar culture conditions but exhibits a higher degree of enhancement by Fgf8 rather than by Wnt3a. This is the first report of in vitro recapitulation of early differentiation of cerebellar neurons by using the ES cell system.

Smaller inner ear sensory epithelia in Neurog 1 null mice are related to earlier hair cell cycle exit

We investigated whether co-expression of Neurog 1 and Atoh 1 in common neurosensory precursors could explain the loss of hair cells in Neurog 1 null mice. Analysis of terminal mitosis, using BrdU, supports previous findings regarding timing of exit from cell cycle. Specifically, we show that cell cycle exit occurs in spiral sensory neurons in a base-to-apex progression followed by cell cycle exit of hair cells in the organ of Corti in an apex-to-base progression, with some overlap of cell cycle exit in the apex for both hair cells and spiral sensory neurons. Hair cells in Neurog 1 null mice show cell cycle exit in an apex-to-base progression about 1-2 days earlier. Atoh 1 is expressed in an apex-to-base progression rather then a base-to-apex progression as in wildtype littermates. We tested the possible expression of Atoh1 in neurosensory precursors using two Atoh 1-Cre lines. We show Atoh 1-Cre mediated beta-galactosidase expression in delaminating sensory neuron precursors as well as undifferentiated epithelial cells at E11 and E12.5. PCR analysis shows expression of Atoh 1 in the otocyst as early as E10.5, prior to any histology-based detection techniques. Combined, these data suggest that low levels of Atoh 1 exist much earlier in precursors of hair cells and sensory neurons, possibly including neurosensory precursors. Analysis of Atoh 1-Cre expression in E18.5 embryos and P31 mice reveal beta-galactosidase stain in all hair cells but also in vestibular and cochlear sensory neurons and some supporting cells. A similar expression of Atoh 1-LacZ exists in postnatal and adult vestibular and cochlear sensory neurons, and Atoh 1 expression in vestibular sensory neurons is confirmed with RT-PCR. We propose that the absence of NEUROG 1 protein leads to loss of sensory neuron formation through a phenotypic switch of cycling neurosensory precursors from sensory neuron to hair cell fate. Neurog 1 null mice show a truncation of clonal expansion of hair cell precursors through temporally altered terminal mitosis, thereby resulting in smaller sensory epithelia.

Short-term lineage analysis of dorsally derived Olig3 cells in the developing spinal cord

We examined the migration and differentiation of cells expressing Olig3, a basic helix-loop-helix transcriptional factor, in the developing spinal cord. Distribution of Olig3 lineage cells was demonstrated with in situ hybridization and X-gal staining in an Olig3-lacZ knock-in mouse. Olig3-positive cells first appeared in the dorsal spinal cord, except for the roof plate. Some of the dorsal Olig3 lineage cells co-expressed Islet1/2, Math1, or Brn3a, markers for dorsal interneuron. LacZ-positive cells were observed in the ventral-most part of the E10.5 spinal cord, suggesting that some dorsal Olig3 lineage cells migrate into the ventral-most part by E10.5. Ventral-ward migration of dorsal cells and contribution to commissural interneurons were substantiated by electroporation of EGFP expression plasmid in the dorsal spinal cord of chick embryo. Dorsal midline cells were also LacZ-positive during development. These findings suggest that dorsal Olig3 cells contribute to dorsal midline cells and commissural interneurons at intermediate and ventral levels.

Differential transcription ofBarhl1homeobox gene in restricted functional domains of the central nervous system suggests a role in brain patterning

The mouse Barhl1 homeogene, member of the BarH subfamily, play a crucial role in the cerebellum development and its human ortholog BARHL1 has been proposed as a positional and functional candidate gene for the Joubert syndrome, a form of cerebellar ataxia. The Barhl1 expression has been demonstrated to be induced by the transcription factor Math1 involved in BMP responses. We isolated the mouse Barhl1 by screening of a cDNA library with the Xenopus Xvent-2, member of the BarH subfamily, which acts in the BMP4 pathway during embryonic patterning and neural plate differentiation. We studied the detailed Barhl1 expression pattern and showed its transcription in spatio-temporally and functionally restricted domains of the developing central nervous system (CNS). Using our new optical microscopy technology, we compare the transcript steady state level and cell density in the Barhl1-expressing regions. We found that Barhl1 was transcribed in superior and inferior colliculi in the dorsal mesencephalon at a relatively low transcriptional level. In the diencephalon, Barhl1 was found higher expressed first within the basal plate and later in the mammillary region. In the cerebellum, Barhl1 showed the highest transcriptional level restricted to the anterior and posterior rhombic lips giving rise to the external and internal cerebellar granular cells and to the deep nuclei. In the spinal cord, Barhl1 showed similar expression level than in the cerebellum and is delimited to a subset of dorsal interneurons. Therefore, our results indicated that Barhl1 homeodomain gene is exclusively transcribed in restricted CNS domain at differential transcription levels which suggest a highly regulated transcriptional mechanism. In addition, these regional and cellular specificities indicated that Barhl1 may be involved in the differentiation of the specific subsets of neuronal progenitors.

A novel role for the choroid plexus in BMP-mediated inhibition of differentiation of cerebellar neural progenitors

Cerebellar granule cells, the most abundant neurons in the mammalian brain, arise in the rhombic lip located at the roof of the brain's fourth ventricle. Bordering the rhombic lip is the choroid plexus, a non-neuronal structure, composed of blood vessels enveloped by epithelial cells. Here, we show a striking decrease in neural differentiation of rhombic lip-derived cells, which failed to extend neuritic processes and attenuate Math1 promoter activity, when co-cultured with choroid plexus cells. Moreover, a blocking antibody against BMP7, a morphogenetic protein expressed in the choroid plexus, blocked the inhibitory effect of the choroid plexus, whereas purified BMP7 mimicked this effect, demonstrating causal involvement of BMP. On the other hand, the BMP antagonist NBL1 promoted neurogenesis in rhombic lip cultures from Math1 null mice displaying arrested differentiation. Our data indicate that besides its secretory and barrier functions, the choroid plexus has a novel role in attenuating the differentiation of adjacent neural progenitors.

Gfi1 functions downstream of Math1 to control intestinal secretory cell subtype allocation and differentiation

Gfi1 is a transcriptional repressor implicated in lymphomagenesis, neutropenia, and hematopoietic development, as well as ear and lung development. Here, we demonstrate that Gfi1 functions downstream of Math1 in intestinal secretory lineage differentiation. Gfi1(-/-) mice lack Paneth cells, have fewer goblet cells, and supernumerary enteroendocrine cells. Gfi1(-/-) mice show gene expression changes consistent with this altered cell allocation. These data suggest that Gfi1 functions to select goblet/Paneth versus enteroendocrine progenitors. We propose a model of intestinal cell fate choice in which beta-catenin and Cdx function upstream of Math1, and lineage-specific genes such as Ngn3 act downstream of Gfi1.

Suppression of Stat3 promotes neurogenesis in cultured neural stem cells

To investigate the effects of signal transducer and activator of transcription 3 (Stat3) on neural stem cell fate, stem cells were inoculated with an adenovirus vector expressing dominant negative form of Stat3 (Stat3F). One day later, a promoter assay revealed significant reduction of the transcriptional level in the transfected cells. Three days later, Western blot analysis and immunocytochemical analysis revealed that the protein level of microtubule-associated protein (MAP)2 and the number of MAP2-positive cells were increased significantly in the transfected cells whereas the protein level of glial fibrillary acidic protein (GFAP) and the number of GFAP-positive cells were decreased significantly. In addition, mRNA levels of Notch family members (Notch1, 2, and 3) and of inhibitory basic helix-loop-helix (bHLH) factors (Hes5, Id2, and Id3) were significantly downregulated at 3 days after viral inoculation with Stat3F; however, mRNA levels of bHLH determination factors (Math1 and Neurogenin3) and bHLH differentiation factors (NeuroD1 and NeuroD2) were significantly upregulated. These data indicated that suppression of Stat3 directly induced neurogenesis and inhibited astrogliogenesis in neural stem cells.

A Role for Hath1, a bHLH Transcription Factor, in Colon Adenocarcinoma

A significant reduction or loss of goblet cells is often observed in clinical samples of colon adenocarcinomas, which is the predominant form of colon carcinoma. Mice lacking Math1, a bHLH transcription factor downstream of the Notch signaling pathway, demonstrates that Math1 is necessary for cell fate determination of the intestinal secretory cells, including goblet cells. Examination of Hath1, the human orthologue of Math1, expression in multiple colon tumor samples and colon cancer cell lines reveals a dramatic decrease in Hath1 expression in colon tumor samples and colon cancer cell lines. Hath1 expression in the HT29 colon cancer cell line can significantly inhibit its proliferation and anchorage-independent growth both in vitro and in vivo. At the molecular level, Hath1 may regulate the expression of MUC2, a mucin secreted by goblet cells, and Hath1 may also be a novel factor normally repressed as a consequence of activation of the Wnt signaling pathway, which has been clearly implicated in colon tumorigenesis.

Ptf1a, a bHLH transcriptional gene, defines GABAergic neuronal fates in cerebellum

The molecular machinery governing glutamatergic-GABAergic neuronal subtype specification is unclear. Here we describe a cerebellar mutant, cerebelless, which lacks the entire cerebellar cortex in adults. The primary defect of the mutant brains was a specific inhibition of GABAergic neuron production from the cerebellar ventricular zone (VZ), resulting in secondary and complete loss of external germinal layer, pontine, and olivary nuclei during development. We identified the responsible gene, Ptf1a, whose expression was lost in the cerebellar VZ but was maintained in the pancreas in cerebelless. Lineage tracing revealed that two types of neural precursors exist in the cerebellar VZ: Ptf1a-expressing and -nonexpressing precursors, which generate GABAergic and glutamatergic neurons, respectively. Introduction of Ptf1a into glutamatergic neuron precursors in the dorsal telencephalon generated GABAergic neurons with representative morphological and migratory features. Our results suggest that Ptf1a is involved in driving neural precursors to differentiate into GABAergic neurons in the cerebellum.

Math1 Expression Redefines the Rhombic Lip Derivatives and Reveals Novel Lineages within the Brainstem and Cerebellum

The rhombic lip (RL) is an embryonic proliferative neuroepithelium that generates several groups of hindbrain neurons. However, the precise boundaries and derivatives of the RL have never been genetically identified. We use beta-galactosidase expressed from the Math1 locus in Math1-heterozygous and Math1-null mice to track RL-derived cells and to evaluate their developmental requirements for Math1. We uncover a Math1-dependent rostral rhombic-lip migratory stream (RLS) that generates some neurons of the parabrachial, lateral lemniscal, and deep cerebellar nuclei, in addition to cerebellar granule neurons. A more caudal Math1-dependent cochlear extramural stream (CES) generates the ventral cochlear nucleus and cochlear granule neurons. Similarly, mossy-fiber precerebellar nuclei require Math1, whereas the inferior olive and locus coeruleus do not. We propose that Math1 expression delimits the extent of the rhombic lip and is required for the generation of the hindbrain superficial migratory streams, all of which contribute neurons to the proprioceptive/vestibular/auditory sensory network.

Math1 Is Expressed in Temporally Discrete Pools of Cerebellar Rhombic-Lip Neural Progenitors

We have utilized an in vivo-inducible genetic-fate-mapping strategy to permanently label cohorts of Math1-positive cells and their progeny that arise in the rhombic lip of the cerebellar primordium during embryogenesis. At stages prior to E12.5, with the exception of the deep cerebellar nuclei, we find that Math1 cells migrate out of the cerebellar primordium into the rostral hindbrain to populate specific nuclei that include cholinergic neurons of the mesopontine tegmental system. Moreover, analysis of Math1-null embryos shows that this gene is required for the formation of some of these nuclei. Around E12.5, granule cell precursors begin to be labeled: first, ones that give rise to granule cells that predominantly populate the anterior lobes of the adult cerebellum and later, those that populate progressing more caudally lobes until labeling of all granule cell precursors is complete by E17. Thus, we demonstrate that the cerebellar rhombic lip gives rise to multiple cell types within rhombomere 1.

Zac1 is expressed in progenitor/stem cells of the neuroectoderm and mesoderm during embryogenesis: differential phenotype of the Zac1-expressing cells during development

Zac1, a new zinc-finger protein that regulates both apoptosis and cell cycle arrest, is abundantly expressed in many neuroepithelia during early brain development. In the present work, we study the expression of Zac1 during early embryogenesis and we determine the cellular phenotype of the Zac1-expressing cells throughout development. Our results show that Zac1 is expressed in the progenitor/stem cells of several tissues (nervous system, skeleton, and skeletal muscle), because they colocalize with several progenitor/stem markers (Nestin, glial fibrillary acidic protein, FORSE-1, proliferating cell nuclear antigen, and bromodeoxyuridine). In postnatal development, Zac1 is expressed in all phases of the life cycle of the chondrocytes (from proliferation to apoptosis), in some limbic gamma-aminobutyric acid-ergic neuronal subpopulations, and during developmental myofibers. Therefore, the intense expression of Zac1 in the progenitor/stem cells of different cellular lineages during the proliferative cycle, before differentiation into postmitotic cells, suggests that Zac1 plays an important role in the control of cell fate during neurogenesis, chondrogenesis, and myogenesis.

Evolution of striated muscle: Jellyfish and the origin of triploblasty

The larval and polyp stages of extant Cnidaria are bi-layered with an absence of mesoderm and its differentiation products. This anatomy originally prompted the diploblast classification of the cnidarian phylum. The medusa stage, or jellyfish, however, has a more complex anatomy characterized by a swimming bell with a well-developed striated muscle layer. Based on developmental histology of the hydrozoan medusa this muscle derives from the entocodon, a mesoderm-like third cell layer established at the onset of medusa formation. According to recent molecular studies cnidarian homologs to bilaterian mesoderm and myogenic regulators are expressed in the larval and polyp stages as well as in the entocodon and derived striated muscle. Moreover striated and smooth muscle cells may have evolved directly and independently from non-muscle cells as indicated by phylogenetic analysis of myosin heavy chain genes (MHC class II). To accommodate all evidences we propose that striated muscle-based locomotion coevolved with the nervous and digestive systems in a basic metazoan Bauplan from which the ancestors of the Ctenophora (comb jellyfish), Cnidaria (jellyfish and polyps), as well as the Bilateria are derived. We argue for a motile tri-layered cnidarian ancestor and a monophyletic descent of striated muscle in Cnidaria and Bilateria. As a consequence, diploblasty evolved secondarily in cnidarian larvae and polyps.

Commissural neuron identity is specified by a homeodomain protein, Mbh1,that is directly downstream of Math1

Proneural basic helix-loop-helix (bHLH) proteins are key regulators of neurogenesis. However, downstream target genes of the bHLH proteins remain poorly defined. Mbh1 confers commissural neuron identity in the spinal cord. Enhancer analysis using transgenic mice revealed that Mbh1 expression required an E-box 3′ of the Mbh1 gene. Mbh1 expression was lost in Math1 knockout mice, whereas misexpression of Math1 induced ectopic expression of Mbh1. Moreover, Math1 bound the Mbh1 enhancer containing the E-box in vivo and activated gene expression. Generation of commissural neurons by Math1 was inhibited by a dominant negative form of Mbh1. These findings indicate that Mbh1 is necessary and sufficient for the specification of commissural neurons,as a direct downstream target of Math1.

Hes1-deficient mice show precocious differentiation of Paneth cells in the small intestine

We have previously shown that Hes1 is expressed both in putative epithelial stem cells just above Paneth cells and in the crypt base columnar cells between Paneth cells, while Hes1 is completely absent in Paneth cells. This study was undertaken to clarify the role of Hes1 in Paneth cell differentiation, using Hes1-knockout (KO) newborn (P0) mice. Electron microscopy revealed premature appearance of distinct cells containing cytoplasmic granules in the intervillous region in Hes1-KO P0 mice, whereas those cells were absent in wild-type (WT) P0 mice. In Hes1-KO P0 mice, the gene expressions of cryptdins, exclusively present in Paneth cells, were all enhanced compared with WT P0 mice. Immunohistochemistry demonstrated increased number of both lysozyme-positive and cryptdin-4-positive cells in the small intestinal epithelium of Hes1-KO P0 mice as compared to WT P0 mice. Thus, Hes1 appears to have an inhibitory role in Paneth cell differentiation in the small intestine.

Morphogenetic and cellular movements that shape the mouse cerebellum; insights from genetic fate mapping

We used the cerebellum as a model to study the morphogenetic and cellular processes underlying the formation of elaborate brain structures from a simple neural tube, using an inducible genetic fate mapping approach in mouse. We demonstrate how a 90 degrees rotation between embryonic days 9 and 12 converts the rostral-caudal axis of dorsal rhombomere 1 into the medial-lateral axis of the wing-like bilateral cerebellar primordium. With the appropriate use of promoters, we marked specific medial-lateral domains of the cerebellar primordium and derived a positional fate map of the murine cerebellum. We show that the adult medial cerebellum is produced by expansion, rather than fusion, of the thin medial primordium. Furthermore, ventricular-derived cells maintain their original medial-lateral coordinates into the adult, whereas rhombic lip-derived granule cells undergo lateral to medial posterior transverse migrations during foliation. Thus, we show that progressive changes in the axes of the cerebellum underlie its genesis.

PHR1, a PH domain-containing protein expressed in primary sensory neurons

Previously, we identified PHR1 as an abundantly expressed gene in photoreceptors and showed that it encodes four isoforms, each with N-terminal pleckstrin homology (PH) and C-terminal transmembrane domains. To better understand PHR1 function and expression, we made a Phr1 null mouse by inserting a beta-galactosidase/neor cassette into exon 3. In addition to photoreceptors, we found abundant expression of specific Phr1 splice forms in olfactory receptor neurons and vestibular and cochlear hair cells. We also found Phr1 expression in cells with a possible sensory function, including peripheral retinal ganglion cells, cochlear interdental cells, and neurons of the circumventricular organ. Despite this discrete expression in known and putative sensory neurons, mice lacking PHR1 do not have overt sensory deficits.