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The importance of combinatorial gene expression in early Mammalian thalamic patterning and thalamocortical axonal guidance.

Price DJ, Clegg J, Duocastella XO, Willshaw D, Pratt T - Front Neurosci (2012)

Bottom Line: Mechanisms include guidance by previously generated guidepost cells, such as those in the subpallium that maintain thalamic axonal order and direction, and axons such as those of reciprocal projections from intermediate structures or from the cortex itself back toward the thalamus.We show how thalamocortical pathfinding involves numerous guidance cues operating at a series of steps along their route.We stress the importance of the combinatorial actions of multiple genes for the development of the numerous specific identities and functions of cells in this exquisitely complex system and their orderly innervation of the cortex.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Physiology, University of Edinburgh Edinburgh, UK.

ABSTRACT
The thalamus is essential for sensory perception. In mammals, work on the mouse has taught us most of what we know about how it develops and connects to the cortex. The mature thalamus of all mammalian species comprises numerous anatomically distinct collections of neurons called nuclei that differ in function, connectivity, and molecular constitution. At the time of its initial appearance as a distinct structure following neural tube closure, the thalamus is already patterned by the regional expression of numerous regulatory genes. This patterning, which lays down the blueprint for later development of thalamic nuclei, predates the development of thalamocortical projections. In this review we apply novel analytical methods to gene expression data available in the Allen Developing Mouse Brain Atlas to highlight the complex organized molecular heterogeneity already present among cells in the thalamus from the earliest stages at which it contains differentiating neurons. This early patterning is likely to invest in axons growing from different parts of the thalamus the ability to navigate in an ordered way to their appropriate area in the cerebral cortex. We review the mechanisms and cues that thalamic axons use, encounter, and interpret to attain the cortex. Mechanisms include guidance by previously generated guidepost cells, such as those in the subpallium that maintain thalamic axonal order and direction, and axons such as those of reciprocal projections from intermediate structures or from the cortex itself back toward the thalamus. We show how thalamocortical pathfinding involves numerous guidance cues operating at a series of steps along their route. We stress the importance of the combinatorial actions of multiple genes for the development of the numerous specific identities and functions of cells in this exquisitely complex system and their orderly innervation of the cortex.

No MeSH data available.


Measuring cell density in the thalamus. (A) E13.5 coronal thalamic sections counterstained with the DNA stain Feulgen-HP yellow from ADMBA. There is substantial variation in cell density in different parts of the thalamus, for example cell density is very high in the proliferative ventricular zone (VZ) adjacent to the thalamic midline (M, dashed line). Boxed areas indicate areas of high, medium, and low density examined further in (B). (B) Top panels show raw image examples of low, medium, and high cell densities taken from thalamic areas indicated in (A). Bottom panels show manual annotation of these data where the operator identifies nuclei by eye and marks each one with a black dot.
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Figure 4: Measuring cell density in the thalamus. (A) E13.5 coronal thalamic sections counterstained with the DNA stain Feulgen-HP yellow from ADMBA. There is substantial variation in cell density in different parts of the thalamus, for example cell density is very high in the proliferative ventricular zone (VZ) adjacent to the thalamic midline (M, dashed line). Boxed areas indicate areas of high, medium, and low density examined further in (B). (B) Top panels show raw image examples of low, medium, and high cell densities taken from thalamic areas indicated in (A). Bottom panels show manual annotation of these data where the operator identifies nuclei by eye and marks each one with a black dot.

Mentions: Serial sections were downloaded from E13.5 embryos. Within the thalamus, cell densities varied from low to high (Figure 4) and cells could be counted manually in such areas (Figure 4B), but this was very time-consuming and so an automatic method was devised. The method was based on the use of Hessian matrices to describe mathematically local morphological features across an image, such as the curvatures of edges (Sato et al., 1998). In the ADMBA, counterstained nuclei have edges that are clear enough to allow the application of this approach. The calculation of the eigenvalues of the Hessian matrices and their subsequent classification allows the identification of round or oval shapes that correspond to cells. Data from this automated approach were compared with data obtained manually. For each image, the distance was calculated between each point allocated manually to a cell nucleus and its nearest neighbor among points allocated automatically, and where the distance was less than the radius of a nucleus (5 μm) it was designated as a hit. This method gave hit rates of 90%, indicating excellent correlation between the automatic and manual methods, and so the former was used to measure density across all E13.5 coronal sections through the entire thalamus. The surface of each section was divided into tiles (20 μm × 20 μm) using a grid and cell density was measured in each tile.


The importance of combinatorial gene expression in early Mammalian thalamic patterning and thalamocortical axonal guidance.

Price DJ, Clegg J, Duocastella XO, Willshaw D, Pratt T - Front Neurosci (2012)

Measuring cell density in the thalamus. (A) E13.5 coronal thalamic sections counterstained with the DNA stain Feulgen-HP yellow from ADMBA. There is substantial variation in cell density in different parts of the thalamus, for example cell density is very high in the proliferative ventricular zone (VZ) adjacent to the thalamic midline (M, dashed line). Boxed areas indicate areas of high, medium, and low density examined further in (B). (B) Top panels show raw image examples of low, medium, and high cell densities taken from thalamic areas indicated in (A). Bottom panels show manual annotation of these data where the operator identifies nuclei by eye and marks each one with a black dot.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3304307&req=5

Figure 4: Measuring cell density in the thalamus. (A) E13.5 coronal thalamic sections counterstained with the DNA stain Feulgen-HP yellow from ADMBA. There is substantial variation in cell density in different parts of the thalamus, for example cell density is very high in the proliferative ventricular zone (VZ) adjacent to the thalamic midline (M, dashed line). Boxed areas indicate areas of high, medium, and low density examined further in (B). (B) Top panels show raw image examples of low, medium, and high cell densities taken from thalamic areas indicated in (A). Bottom panels show manual annotation of these data where the operator identifies nuclei by eye and marks each one with a black dot.
Mentions: Serial sections were downloaded from E13.5 embryos. Within the thalamus, cell densities varied from low to high (Figure 4) and cells could be counted manually in such areas (Figure 4B), but this was very time-consuming and so an automatic method was devised. The method was based on the use of Hessian matrices to describe mathematically local morphological features across an image, such as the curvatures of edges (Sato et al., 1998). In the ADMBA, counterstained nuclei have edges that are clear enough to allow the application of this approach. The calculation of the eigenvalues of the Hessian matrices and their subsequent classification allows the identification of round or oval shapes that correspond to cells. Data from this automated approach were compared with data obtained manually. For each image, the distance was calculated between each point allocated manually to a cell nucleus and its nearest neighbor among points allocated automatically, and where the distance was less than the radius of a nucleus (5 μm) it was designated as a hit. This method gave hit rates of 90%, indicating excellent correlation between the automatic and manual methods, and so the former was used to measure density across all E13.5 coronal sections through the entire thalamus. The surface of each section was divided into tiles (20 μm × 20 μm) using a grid and cell density was measured in each tile.

Bottom Line: Mechanisms include guidance by previously generated guidepost cells, such as those in the subpallium that maintain thalamic axonal order and direction, and axons such as those of reciprocal projections from intermediate structures or from the cortex itself back toward the thalamus.We show how thalamocortical pathfinding involves numerous guidance cues operating at a series of steps along their route.We stress the importance of the combinatorial actions of multiple genes for the development of the numerous specific identities and functions of cells in this exquisitely complex system and their orderly innervation of the cortex.

View Article: PubMed Central - PubMed

Affiliation: Centre for Integrative Physiology, University of Edinburgh Edinburgh, UK.

ABSTRACT
The thalamus is essential for sensory perception. In mammals, work on the mouse has taught us most of what we know about how it develops and connects to the cortex. The mature thalamus of all mammalian species comprises numerous anatomically distinct collections of neurons called nuclei that differ in function, connectivity, and molecular constitution. At the time of its initial appearance as a distinct structure following neural tube closure, the thalamus is already patterned by the regional expression of numerous regulatory genes. This patterning, which lays down the blueprint for later development of thalamic nuclei, predates the development of thalamocortical projections. In this review we apply novel analytical methods to gene expression data available in the Allen Developing Mouse Brain Atlas to highlight the complex organized molecular heterogeneity already present among cells in the thalamus from the earliest stages at which it contains differentiating neurons. This early patterning is likely to invest in axons growing from different parts of the thalamus the ability to navigate in an ordered way to their appropriate area in the cerebral cortex. We review the mechanisms and cues that thalamic axons use, encounter, and interpret to attain the cortex. Mechanisms include guidance by previously generated guidepost cells, such as those in the subpallium that maintain thalamic axonal order and direction, and axons such as those of reciprocal projections from intermediate structures or from the cortex itself back toward the thalamus. We show how thalamocortical pathfinding involves numerous guidance cues operating at a series of steps along their route. We stress the importance of the combinatorial actions of multiple genes for the development of the numerous specific identities and functions of cells in this exquisitely complex system and their orderly innervation of the cortex.

No MeSH data available.