Dorsal Brain Research Articles

Neurohormonal and Neuromodulatory Control of Sleep inDrosophila

The fruit fly Drosophila melanogaster has emerged in recent years as a tractable system for studying sleep. The sleep-wake dichotomy represents one of the principal transitions in global brain state, and neurohormones and neuromodulators are well known for their ability to change global brain states. Here, we describe studies of two brain systems that regulate sleep in Drosophila, the neurohormonal epidermal growth factor receptor system and the neuromodulatory dopaminergic system, each of which acts through a discrete anatomical locus in the dorsal brain. Both control systems display considerable mechanistic similarity to those in mammals, suggesting possible functional homologies.

Hedgehog Signaling Promotes Medulloblastoma Survival via BclII

Activation of the Hedgehog (Hh) pathway has been identified in several cancers, including medulloblastoma, but the mechanisms by which this pathway affects tumor survival and growth are incompletely understood. We investigated whether Hedgehog might promote survival of medulloblastoma cells via up-regulation of BclII. We found that mRNA levels of the Hedgehog pathway effector Gli1 were significantly associated with BclII expression in medulloblastoma and that Gli1 and BclII are both present in regions of decreased apoptosis in nodular medulloblastoma. Transient overexpression of Gli1 and Gli2 in medulloblastoma cultures induced a BclII transcriptional reporter and increased BclII protein levels, whereas stable overexpression of Gli1 was associated with increased BclII mRNA. The Hedgehog antagonist cyclopamine blocked expression of the Hh pathway targets PTCH1 and Gli1, lowered BclII levels, and increased apoptosis in DAOY and UW228 medulloblastoma cells. Apoptotic induction caused by cyclopamine could be rescued in part by enforced expression of Gli1 or BclII. Hh pathway blockade also sensitized medulloblastoma to the effects of the proapoptotic agent lovastatin. These data demonstrate that BclII is an important mediator of Hh activity in medulloblastoma and suggest new strategies for combined chemotherapeutic regimens.

Tissue-Specific Splicing of the Herpes Simplex Virus Type 1 Latency-Associated Transcript (LAT) Intron in LAT Transgenic Mice

To study the regulation of herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) expression and processing in the absence of other cis and trans viral functions, a transgenic mouse containing the region encompassing the LAT promoter (LAP1) and the LAT 5' exon through the 2.0-kb intron was created. LAT expression was detectable by reverse transcriptase PCR (RT-PCR) in a number of tissues, including the dorsal root ganglia (DRG), trigeminal ganglia (TG), brain, skin, liver, and kidney. However, when the accumulation of the 2.0-kb LAT intron was analyzed at the cellular level by in situ hybridization, little or no detectable accumulation was observed in the brain, spinal cord, kidney, or foot, although the 2.0-kb LAT intron was detected at high levels (over 90% of neurons) in the DRG and TG. Northern blot analysis detected the stable 2.0-kb LAT intron only in the sensory ganglia. When relative amounts of the spliced and unspliced LAT within the brain, liver, kidney, spinal cord, TG, and DRG were analyzed by real-time RT-PCR, splicing of the 2.0-kb LAT intron was significantly more efficient in the sensory ganglia than in other tissues. Finally, infection of both transgenic mice and nontransgenic littermates with HSV-1 revealed no differences in lytic replication, establishment of latency, or reactivation, suggesting that expression of the LAT transgene in trans has no significant effect on those functions. Taken together, these data indicate that the regulation of expression and processing of LAT RNA within the mouse is highly cell-type specific and occurs in the absence of other viral cis- and trans-acting factors.

Identification of potential target genes for RFX4_v3, a transcription factor critical for brain development

Regulatory factor X4 variant transcript 3 (Rfx4_v3) gene disruption in mice demonstrated that interruption of a single allele (heterozygous, +/-) prevented formation of the subcommissural organ, resulting in congenital hydrocephalus, while interruption of two alleles (homozygous, -/-) caused fatal failure of dorsal midline brain structure formation. To identify potential target genes for RFX4_v3, we used microarray analysis to identify differentially expressed genes in Rfx4_v3-deficient mouse brains at embryonic day 10.5, before gross structural changes were apparent. Of 109 differentially expressed transcripts, 24 were chosen for validation and 22 were confirmed by real-time PCR. Many validated genes encoded critical proteins involved in brain morphogenesis, such as the signaling components in the Wnt, bone morphogenetic protein (BMP) and retinoic acid (RA) pathways. Cx3cl1, a CX3C-type chemokine gene that is highly expressed in brain, was down-regulated in the Rfx4_v3-null mice. Both human and mouse Cx3cl1 proximal promoters contained highly conserved X-boxes, known cis-acting elements for RFX protein binding. Using the Cx3cl1 promoter as an example of a target gene, we demonstrated direct binding of RFX4_v3 to the Cx3cl1 promoter, and trans-acting activity of RFX4_v3 protein to stimulate gene expression. These data suggest that RFX4_v3 may act upstream of critical signaling pathways in the process of brain development.

DrosophilaCLOCK Is Constitutively Expressed in Circadian Oscillator and Non-Oscillator Cells

CLOCK (CLK) is a core component of the transcriptional feedback loops that comprise the circadian timekeeping mechanism in Drosophila. As a heterodimer with CYCLE (CYC), CLK binds E-boxes to activate the transcription of rhythmically expressed genes within and downstream of the circadian clock, but this activation unexpectedly occurs at times when CLK is at its lowest levels on Western blots. Recent studies demonstrate that CLK also regulates nonrhythmic gene expression and behaviors. Despite the critical roles CLK plays within and outside the circadian clock, its spatial expression pattern has not been characterized. Using a newly developed CLK antibody, the authors show that CLK is coexpressed with PERIOD (PER) in canonical oscillator cells throughout the head and body. In contrast to PER, however, the levels of CLK immunoreactivity do not cycle in intensity, CLK is detected primarily in the nucleus throughout the circadian cycle, and CLK is expressed in non-oscillator cells within the lateral and dorsal brain, including Kenyon cells, which mediate various forms of learning and memory. These results indicate that constitutive levels of nuclear CLK regulate rhythmic transcription in circadian oscillator cells and suggest that CLK contributes to other behavioral processes by regulating gene expression in non-oscillator cells.

Conventional MRI and MR spectroscopy in nonclassical mitochondrial disease: report of three patients with mitochondrial DNA deletion

The objectives were to present magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) findings in three patients with deletion on mitochondrial DNA (mtDNA) and nonclassical mitochondrial disorders (NCMD), correlating these findings with the percentage of deleted mtDNA. Our study confirms the high prevalence of white matter (WM), basal ganglia, and posterior fossa lesions in NCMD, ranging from mild to severe involvement. The subcortical WM, caudate, thalamus, globus pallidus, and dorsal brain stem were more frequently affected. A lactate peak was the most frequent finding at the MRS. We found a correlation between the percentage of mtDNA deletion and degree of MRS abnormalities. Our findings showed that MRS is a useful investigational tool in patients with NCMD. Supplementary studies are necessary to elucidate the correlation of quantitative mtDNA deletion and neuroimaging phenotype.

Growth Hormone Deficiency and Memory Functioning in Adults Visualized by Functional Magnetic Resonance Imaging

Cognitive functioning, especially memory performance, is known to be impaired in patients with childhood-onset growth hormone deficiency (CO-GHD), and growth hormone substitution has been found to counteract this memory impairment. Neuropsychological and functional magnetic resonance imagining (fMRI) data acquired during a working memory task in 13 childhood-onset GH-deficient patients were compared with 13 age, sex and education level matched healthy controls. Results demonstrated that there is no difference in the quality of the performance in the working memory task between GH-deficient patients and control subjects. However, memory speed was found to be subnormal in patients. Concerning mood, patients reported more complaints of fatigue, and less vigor. Imaging data showed that patients had increased activity in dorsolateral/ventrolateral prefrontal cortex, anterior cingulate cortex, parietal cortex, supplementary motor and motor cortex, as well as in the thalamus and precuneus area. Increasing task load was also associated with an increase in brain activity in similar areas in patients compared to control subjects. In conclusion, this fMRI study shows that GH-deficient patients have a subnormal memory speed, but no impaired quality of memory performance, which may be due to compensatory recruitment of dorsal prefrontal brain regions. These findings indicate that the GH-IGF-1 axis contributes to prefrontal functioning in patients with CO-GHD.

Head sensory organs ofDactylopodola baltica (Macrodasyida, Gastrotricha): A combination of transmission electron microscopical and immunocytochemical techniques

The anterior and posterior head sensory organs of Dactylopodola baltica (Macrodasyida, Gastrotricha) were investigated by transmission electron microscopy (TEM). In addition, whole individuals were labeled with phalloidin to mark F-actin and with anti-alpha-tubulin antibodies to mark microtubuli and studied with confocal laser scanning microscopy. Immunocytochemistry reveals that the large number of ciliary processes in the anterior head sensory organ contain F-actin; no signal could be detected for alpha-tubulin. Labeling with anti-alpha-tubulin antibodies revealed that the anterior and posterior head sensory organs are innervated by a common stem of nerves from the lateral nerve cords just anterior of the dorsal brain commissure. TEM studies showed that the anterior head sensory organ is composed of one sheath cell and one sensory cell with a single branching cilium that possesses a basal inflated part and regularly arranged ciliary processes. Each ciliary process contains one central microtubule. The posterior head sensory organ consists of at least one pigmented sheath cell and several probably monociliary sensory cells. Each cilium branches into irregularly arranged ciliary processes. These characters are assumed to belong to the ground pattern of the Gastrotricha.

GW274150, a novel and highly selective inhibitor of the inducible isoform of nitric oxide synthase (iNOS), shows analgesic effects in rat models of inflammatory and neuropathic pain

Nitric oxide (NO), synthesised by different isoforms of nitric oxide synthase (NOS), has been linked with the development and maintenance of nociception. We studied the role of the inducible isoform, iNOS, in two different rat pain models with an inflammatory component. iNOS was immunohistochemically detected locally in the paw 6 h after Freund's Complete Adjuvant (FCA) injection, showing a plateau at 24–72 h and falling slowly in the following weeks. This correlated with the late phase of the hypersensitivity to pain revealed in the behavioural tests. A highly selective iNOS inhibitor GW274150 (1–30 mg/kg orally, 24 h after FCA) suppressed the accumulation of nitrite in the inflamed paw indicating substantial iNOS inhibition. At the same time it partially reversed FCA-induced hypersensitivity to pain and edema in a dose-dependent manner. After Chronic Constriction Injury (CCI) surgery to the sciatic nerve, iNOS presence was only detected locally in the region of the nerve (inflammatory cells). GW274150 (3–30 mg/kg orally, 21 days after surgery) also reversed significantly the CCI-associated hypersensitivity to pain. No iNOS was detectable in dorsal root ganglia, spinal cord or brain in either model. This study demonstrates a role for peripherally-expressed iNOS in pain conditions with an inflammatory component and the potential value of iNOS inhibitors in such conditions.

A G Protein-Coupled Receptor, groom-of-PDF, Is Required for PDF Neuron Action in Circadian Behavior

The neuropeptide Pigment-Dispersing Factor (PDF) plays a critical role in mediating circadian control of behavior in Drosophila. Here we identify mutants (groom-of-PDF; gop) that display phase-advanced evening activity and poor free-running rhythmicity, phenocopying pdf mutants. In gop mutants, a spontaneous retrotransposon disrupts a coding exon of a G protein-coupled receptor, CG13758. Disruption of the receptor is accompanied by phase-advanced oscillations of the core clock protein PERIOD. Moreover, effects on circadian timing induced by perturbation of PDF neurons require gop. Yet PDF oscillations themselves remain robust in gop mutants, suggesting that GOP acts downstream of PDF. gop is expressed most strongly in the dorsal brain in regions that lie in proximity to PDF-containing nerve terminals. Taken together, these studies implicate GOP as a PDF receptor in Drosophila.

Hypertension and Exercise Training Differentially Affect Oxytocin and Oxytocin Receptor Expression in the Brain

We have previously shown that exercise training activates nucleus tractus solitarii (NTS) oxytocinergic projections, resulting in blunted exercise tachycardia. The objective of this study was to determine the effects of hypertension and training on oxytocin (OT) and OT receptor expression in the hypothalamic paraventricular nucleus (PVN) and projection areas (dorsal brain stem [DBS]). Male, normotensive, Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were trained (55% maximal exercise capacity, 3 months) or kept sedentary, and pressure was measured weekly. DBS sections were processed for immunohistochemistry (polyclonal guinea pig anti-OT) or in situ hybridization for OT and OT receptor (35S-oligonucleotide probes). Other groups of rats had brains removed and frozen to isolate the DBS and PVN; samples were processed for OT and OT receptor cDNA reverse transcription-polymerase chain reaction amplification with beta-actin as the housekeeping gene. Training was equally effective in improving running distance in both groups, with pressure reduction only in SHR (-10%, P<0.05). In trained WKY, baseline bradycardia (P<0.05) occurred simultaneously with increased NTS OT immunostaining and mRNA expression (+3.5-fold), without any change in OT receptor mRNA expression. PVN OT mRNA and DBS OT receptor mRNA expressions were significantly lower in SHR versus WKY (-39% and -56%, respectively). Training did not alter DBS OT receptor density in the SHR group but increased OT mRNA in both PVN and DBS areas (+78% and +45%, respectively). Our results show a marked hypertension-induced reduction in OT receptor mRNA expression, not altered by training. In contrast, training increased OT mRNA expression in sedentary and hypertensive rats, which may facilitate training-induced cardiac performance.

Visual spatial and visual pattern working memory: Neuropsychological evidence for a differential role of left and right dorsal visual brain

According to neurophysiological, neuroimaging, and behavioural evidence, visual working memory (WM) can be separated into a “what” and a “where” component, reflecting the duality of visual processing. Whereas a wealth of empirical data suggests a right-sided fronto-parietal network critical for the maintenance of spatial information, the cortical structures underlying maintenance of object information have remained controversial. Although visual object processing depends on ventral, inferior temporal areas, recent neuroimaging results suggest that maintenance of visual object information involves a left-sided or bilateral fronto-parietal network. The aim of the present study is to further clarify the role of the left and right parietal lobes for pattern and spatial visual WM. Seven patients with left-sided, seven with right-sided parietal brain injury, and two age-matched healthy control groups performed a delayed-matching-to-sample task using either pattern (shape) or spatial (location) information or both. In addition, eight patients with left-sided injury sparing parietal areas were tested to further examine the specific role of the left parietal cortex in pattern WM. Left parietal injury resulted in pattern WM impairment, only, while right parietal injury was associated with pattern and spatial WM deficits. Non-parietal injury was not associated with comparable deficits. These results suggest that visual spatial WM depends critically on right parietal areas; in contrast, pattern WM depends on both, left and right parietal areas.

Disorder-Specific Neuroanatomical Correlates of Attentional Bias in Obsessive-compulsive Disorder, Panic Disorder, and Hypochondriasis

Attentional bias to disease-relevant emotional cues is considered to be pathogenetically relevant in anxiety disorders. To investigate functional neural correlates and disease specificity of attentional bias across different anxiety disorders. A cognitive and emotional Stroop task, consisting of congruent and incongruent color words, obsessive-compulsive disorder (OCD)-related and panic-related negative words, and neutral words, was used in 3 patient groups and a control group during functional magnetic resonance imaging. Academic outpatient department for anxiety disorders. Medication-free patients with OCD (n = 16), panic disorder (PD) (n = 15), and hypochondriasis (n = 13) and 19 controls. Voxel-wise analyses of cerebral blood flow changes for contrasts of interest (incongruent vs congruent color words, OCD-related vs neutral words, and panic-related vs neutral words) within and between groups. During incongruent vs congruent color naming, all patient groups recruited additional posterior brain regions relative to controls, but performance was impaired only in OCD. In OCD, color naming OCD-related, but not PD-related, words correlated with increased activation of frontal-striatal and temporal regions, although performance was unimpaired. In contrast, in PD, increased frontal-striatal involvement was found during color naming both OCD-related and panic-related words. In PD, color naming panic-related words was slowed and correlated with increased activation of the right amygdala and hippocampus. Patients with hypochondriasis showed a similar activation pattern to patients with PD. Our results support the hypothesis of increased distractibility for irrelevant information in patients with OCD, PD, and hypochondriasis associated with frontal-striatal and limbic involvement compared with controls. Although patients with OCD did not display an attentional bias in behavior relative to controls, there was a clear, specific neural response during color naming OCD-related words, involving mainly ventral brain regions. In contrast, generalized emotional interference effects were found in PD and hypochondriasis, involving ventral and widespread dorsal brain regions, reflecting not only unconscious emotional stimulus processing but also increased cognitive elaboration.

Exercise Training Differentially Affects Intrinsic Excitability of Autonomic and Neuroendocrine Neurons in the Hypothalamic Paraventricular Nucleus

Oxytocinergic and vasopressinergic brain stem projections have been shown to play an important role in mediating cardiovascular adjustments during exercise training (ET). The aim of the present work was to determine whether the intrinsic excitability of hypothalamic neurons giving rise to brain stem peptidergic projections is altered as a consequence of ET. Whole cell patch-clamp recordings were obtained from nucleus of the solitarii tract (NTS)-projecting paraventricular nucleus of the hypothalamus (PVN) neurons and from supraoptic nucleus (SON) and PVN magnocellular cells (MNCs), in hypothalamic slices obtained from sedentary (S) and ET rats. Our results indicate that intrinsic excitability of PVN neurons that innervate the NTS (PVN-NTS) is enhanced by ET, resulting in a more efficient input-output function (increase number of evoked actions potentials, steeper frequency/current relationships and slower decaying frequency/time relationships). Changes in input-output function were accompanied by smaller hyperpolarizing afterpotentials (HAPs) and afterhyperpolarizing potentials (AHPs), during and after trains of spikes, respectively. On the other hand, a decreased efficacy in the input-output function was observed in SON/PVN MNCs during ET. Altogether, our results indicate that ET differentially affects the intrinsic excitability of autonomic and neurosecretory SON and PVN neurons. Increased excitability in PVN-NTS neurons may contribute to enhanced release of OT and VP peptides in the dorsal brain stem, and cardiovascular fine-tuning during exercise training.

Brain as a paradigm of organ growth: Hedgehog–Gli signaling in neural stem cells and brain tumors

The Hedgehog-Gli (Hh-Gli) signaling pathway is essential for numerous events during the development of many animal cell types and organs. In particular, it controls neural cell precursor proliferation in dorsal brain structures and regulates the number of neural stem cells in distinct embryonic, perinatal, and adult niches, such as the developing neocortex, the subventricular zone of the lateral ventricle of the forebrain, and the hippocampus. We have proposed that Hh-Gli signaling regulates dorsal brain growth during ontogeny and that its differential regulation underlays evolutionary change in the morphology (size and shape) of dorsal brain structures. It is also critically involved in sporadic brain tumorigenesis--as well as several other human cancer--suggesting that tumors derive from stem cells or progenitors maintaining an inappropriate active Hh-Gli pathway. Importantly, we and others have demonstrated that human sporadic tumors from the brain and other organs require sustained HH-GLI signaling for sustained growth and survival. Modulating HH-GLI signaling thus represents a novel rational avenue to treat, on one hand, brain degeneration and injury by inducing controlled HH-GLI-mediated regeneration and growth, and on the other hand, to combat cancer by blocking its abnormal activity in tumor cells.

The Functional Organization of Auditory Working Memory as Revealed by fMRI

Spatial and nonspatial auditory tasks preferentially recruit dorsal and ventral brain areas, respectively. However, the extent to which these auditory differences reflect specific aspects of mental processing has not been directly studied. In the present functional magnetic resonance imaging experiment, participants encoded and maintained either the location or the identity of a sound for a delay period of several seconds and then subsequently compared that information with a second sound. Relative to sound localization, sound identification was associated with greater hemodynamic activity in the left rostral superior temporal gyrus. In contrast, localizing sounds recruited greater activity in the parietal cortex, posterior temporal lobe, and superior frontal sulcus. The identification differences were most prominent during the early stage of the trial, whereas the location differences were most evident during the late (i.e., comparison) stage. Accordingly, our results suggest that auditory spatial and identity dissociations as revealed by functional imaging may be dependent to some degree on the type of processing being carried out. In addition, dorsolateral prefrontal and lateral superior parietal areas showed greater activity during the comparison as opposed to the earlier stage of the trial, regardless of the type of auditory task, consistent with results from visual working memory studies.

Signaling cascade coordinating growth of dorsal and ventral tissues of the vertebrate brain, with special reference to the involvement of Sonic hedgehog signaling

The vertebrate brain is a complex and highly organized structure with numerous neurons and glial cells. During development, undifferentiated progenitor cells proliferate from neural stem/precursor cells and gradually restrict their fates according to their environment. Differentiated cells are arranged precisely to accomplish their function and to maintain integrity as a whole brain. In this respect, cells must receive signals to know where and when they determine their fates. Secreted and membrane molecules convey the information between cells. The secreted glycoprotein Sonic hedgehog (Shh) is one of such signaling molecules. Sonic hedgehog is widely known to specify ventral neuronal types according to the concentration of Shh, whereas differentiation of dorsal neurons is largely independent of Shh. However, in the diencephalon and midbrain, dorsal parts are also affected in Shh-mutant embryos. Detailed analysis demonstrated that Shh signaling indirectly regulates the growth of the dorsal tissue in these regions. One of the fibroblast growth factor (FGF) members, namely FGF15, has been reported to be downstream to Shh signaling in the mouse embryonic brain. Luciferase assays and transgenic analysis revealed that the Fgf15 gene is a direct target of Shh. Downregulation of Tcf4 and upregulation of Bmp4 in Shh mutants suggest that Wnt and BMP signals from the dorsal midline are also involved in the dorsal brain phenotype. These data suggest the coordinating role of the Shh-FGF15-Wnt/BMP signaling cascade between the ventral and dorsal parts of the brain.

The neuronal ceroid lipofuscinosis Cln8 gene expression is developmentally regulated in mouse brain and up-regulated in the hippocampal kindling model of epilepsy

BackgroundThe neuronal ceroid lipofuscinoses (NCLs) are a group of inherited neurodegenerative disorders characterized by accumulation of autofluorescent material in many tissues, especially in neurons. Mutations in the CLN8 gene, encoding an endoplasmic reticulum (ER) transmembrane protein of unknown function, underlie NCL phenotypes in humans and mice. The human phenotype is characterized by epilepsy, progressive psychomotor deterioration and visual loss, while motor neuron degeneration (mnd) mice with a Cln8 mutation show progressive motor neuron dysfunction and retinal degeneration.ResultsWe investigated spatial and temporal expression of Cln8 messenger ribonucleic acid (mRNA) using in situ hybridization, reverse transcriptase polymerase chain reaction (RT-PCR) and northern blotting. Cln8 is ubiquitously expressed at low levels in embryonic and adult tissues. In prenatal embryos Cln8 is most prominently expressed in the developing gastrointestinal tract, dorsal root ganglia (DRG) and brain. In postnatal brain the highest expression is in the cortex and hippocampus. Expression of Cln8 mRNA in the central nervous system (CNS) was also analyzed in the hippocampal electrical kindling model of epilepsy, in which Cln8 expression was rapidly up-regulated in hippocampal pyramidal and granular neurons.ConclusionExpression of Cln8 in the developing and mature brain suggests roles for Cln8 in maturation, differentiation and supporting the survival of different neuronal populations. The relevance of Cln8 up-regulation in hippocampal neurons of kindled mice should be further explored.

Sonic hedgehog controls stem cell behavior in the postnatal and adult brain

Sonic hedgehog (Shh) signaling controls many aspects of ontogeny, orchestrating congruent growth and patterning. During brain development, Shh regulates early ventral patterning while later on it is critical for the regulation of precursor proliferation in the dorsal brain, namely in the neocortex, tectum and cerebellum. We have recently shown that Shh also controls the behavior of cells with stem cell properties in the mouse embryonic neocortex, and additional studies have implicated it in the control of cell proliferation in the adult ventral forebrain and in the hippocampus. However, it remains unclear whether it regulates adult stem cell lineages in an equivalent manner. Similarly, it is not known which cells respond to Shh signaling in stem cell niches. Here we demonstrate that Shh is required for cell proliferation in the mouse forebrain's subventricular zone (SVZ) stem cell niche and for the production of new olfactory interneurons in vivo. We identify two populations of Gli1+ Shh signaling responding cells: GFAP+ SVZ stem cells and GFAP- precursors. Consistently, we show that Shh regulates the self-renewal of neurosphere-forming stem cells and that it modulates proliferation of SVZ lineages by acting as a mitogen in cooperation with epidermal growth factor (EGF). Together, our data demonstrate a critical and conserved role of Shh signaling in the regulation of stem cell lineages in the adult mammalian brain, highlight the subventricular stem cell astrocytes and their more abundant derived precursors as in vivo targets of Shh signaling, and demonstrate the requirement for Shh signaling in postnatal and adult neurogenesis.

Expression of thymosin beta4 during chick development.

We cloned the chick homologue of Homo sapiens thymosin beta4, encoding a G-actin sequestering factor which plays an important role in angiogenesis, cell motility and tumorigenesis. The thymosin beta4 gene is highly conserved between chick and human. Its expression was analyzed during different stages of development. At early stages thymosin beta4 is expressed in the mesoderm and endoderm and in Hensen's node. Later, thymosin beta4 transcripts are found in the head mesenchyme, somites, dorsal root ganglia, neural tube, brain, blood vessels and feather buds. The pattern of thymosin beta4 expression in blood vessels indicates a function mainly in development of the blood circulatory system which closely parallels findings in vitro. The observed expression pattern shows a high similarity to expression data published for mice, mainly in the heart and in the nervous system. Important new aspects are the early onset of expression, the expression in the mesoderm preceding heart formation and the involvement in feather development.