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Arcuate plan of chick midbrain development.

ABSTRACT: In spinal cord and hindbrain development, neurons are generated as longitudinal cell columns aligned with the ventral and dorsal midlines. For rostral brain, however, the fundamental structure of early neuronal patterning remains poorly understood. We report here that, in the chick embryo, the ventral midbrain is remarkably regular in its cellular and molecular organization; it is arranged as a reiterative series of arcuate territories arrayed bilateral to the ventral midline. In the mantle layer of the ventral midbrain, an arcuate series of neuronal cell columns (midbrain arcs) is demonstrated by acetylcholinesterase histochemistry and gene expression for class III beta-tubulin, homeodomain transcription factors, and neurotransmitter synthetic enzymes. In the ventricular layer of midbrain progenitor cells, WNT and NOTCH ligand gene expression displays arcuate periodicities that form a tight three-dimensional registration with the arcs of the underlying mantle layer. Ventral midbrain arcuate patterning is even macroscopically visible, forming ridges along the ventricular surface. These observations establish that a single plan of arcuate organization governs the morphogenesis and cell-type specification of the ventral midbrain. Arcs are not restricted to the midbrain tegmentum but extend through the subthalamic tegmentum of the forebrain. Thus, the chick rostral brain, which is classically divided into midbrain and forebrain, can also be partitioned into the following: (1) a neuraxial region of arcs and (2) an anterodorsal cap that includes midbrain tectum and nonsubthalamic forebrain. We show that this partition of brain tissue is supported by the expression patterns of homologs of Drosophila gap genes.

SUBMITTER: Sanders TA

PROVIDER: S-EPMC6758408 | biostudies-literature | 2002 Dec

REPOSITORIES: biostudies-literature

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Arcuate plan of chick midbrain development.

Sanders Timothy A TA Lumsden Andrew A Ragsdale Clifton W CW

The Journal of neuroscience : the official journal of the Society for Neuroscience 20021201 24

In spinal cord and hindbrain development, neurons are generated as longitudinal cell columns aligned with the ventral and dorsal midlines. For rostral brain, however, the fundamental structure of early neuronal patterning remains poorly understood. We report here that, in the chick embryo, the ventral midbrain is remarkably regular in its cellular and molecular organization; it is arranged as a reiterative series of arcuate territories arrayed bilateral to the ventral midline. In the mantle laye ...[more]

PMID: 12486167

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Project description:BackgroundDuring the development of the central nervous system (CNS), patterning processes along the dorsoventral (DV) axis of the neural tube generate different neuronal subtypes. As development progresses these neurons are arranged into functional units with varying cytoarchitecture, such as laminae or nuclei for efficient relaying of information. Early in development ventral and dorsal regions are similar in size and structure. Different proliferation rates and cell migration patterns are likely to result in the formation of laminae or nuclei, eventually. However, the underlying molecular mechanisms that establish these different structural arrangements are not well understood.We undertook a differential display polymerase chain reaction (DD-PCR) screen to identify genes with distinct expression patterns between dorsal and ventral regions of the chick midbrain in order to identify genes which regulate the sculpturing of such divergent neuronal organisation. We focused on the DV axis of the early chick midbrain since mesencephalic alar plate and basal plate develop into laminae and nuclei, respectively.ResultsWe identified 53 differentially expressed bands in our initial screen. Twenty-six of these could be assigned to specific genes and we could unambiguously show the differential expression of five of the isolated cDNAs in vivo by in situ mRNA expression analysis. Additionally, we verified differential levels of expression of a selected number of genes by using reverse transcriptase (RT) PCR method with gene-specific primers.One of these genes, QR1, has been previously cloned and we present here a detailed study of its early developmental time course and pattern of expression providing some insights into its possible function. Our phylogenetic analysis of QR1 shows that it is the chick orthologue of Sparc-like 1/Hevin/Mast9 gene in mice, rats, dogs and humans, a protein involved in cell adhesion.ConclusionThis study reveals some possible networks, which might be involved in directing the difference in neuronal specification and cytoarchitecture observed in the brain.

Project description:Serotonin (5-hydroxytryptamine, 5-HT) is a phylogenetically conserved modulator of numerous aspects of neural functions. Serotonergic neurons in the dorsal and median raphe nucleus provide ascending innervation to the entire forebrain and midbrain. Another important neural modulatory system exists in the midbrain, the dopaminergic system, which is associated to reward processing and motivation control. Dopaminergic neurons are distributed and clustered in the brain, classically designated as groups A8-A16. Among them, groups A8-A10 associated with reward processing and motivation control are located in the midbrain and projected to the forebrain. Recently, midbrain dopaminergic neurons were shown to be innervated by serotonergic neurons and modulated by 5-HT, with the crosstalk between serotonergic and dopaminergic systems attracting increased attention. In birds, previous studies revealed that midbrain dopaminergic neurons are located in the A8-A10 homologous clusters. However, the detailed distribution of dopaminergic neurons and the crosstalk between serotonergic and dopaminergic systems in the bird are poorly understood. To improve the understanding of the regulation of the dopaminergic by the serotonergic system, we performed in situ hybridization in the chick brainstem. We prepared RNA probes for chick orthologues of dopaminergic neuron-related genes; tyrosine hydroxylase (TH) and dopa decarboxylase (DDC), noradrenaline related genes; noradrenaline transporter (NAT) and dopamine beta-hydroxylase (DBH), and serotonin receptor genes; 5-HTR1A, 5-HTR1B, 5-HTR1D, 5-HTR1E, 5-HTR1F, 5-HTR2A, 5-HTR2B, 5-HTR2C, 5-HTR3A, 5-HTR4, 5-HTR5A, and 5-HTR7. We confirmed that the expression of tyrosine hydroxylase (TH) and NAT was well matched in all chick dopaminergic nuclei examined. This supported that the compensation of the function of dopamine transporter (DAT) by NAT is a general property of avian dopaminergic neurons. Furthermore, we showed that 5-HTR1A and 5-HTR1B were expressed in midbrain dopaminergic nuclei, suggesting the serotonergic regulation of the dopaminergic system via these receptors in chicks. Our findings will help us understand the interactions between the dopaminergic and serotonergic systems in birds at the molecular level.

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Arcuate plan of chick midbrain development.

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Arcuate plan of chick midbrain development.

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