Limits...
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.


Pioneer neurons and axons in the developing thalamocortical tract. As thalamic axons (red) grow they are thought to be guided by the axons of neurons in the reticular nucleus of the prethalamus (black) the site of the future internal capsule (gray). It has been suggested that these two populations of axons guide thalamocortical axons through the diencephalon and into the ventral telencephalon. Within the primitive internal capsule another population of cells project axons in the opposite direction, into the cortex (green). These axons are thought to guide descending corticothalamic axons (blue) into the ventral telencephalon across the pallial–subpallial boundary. Recent evidence suggests that for thalamic axons (red) to grow from subpallium to cortex they require guidance by cortical efferents (blue).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3304307&req=5

Figure 10: Pioneer neurons and axons in the developing thalamocortical tract. As thalamic axons (red) grow they are thought to be guided by the axons of neurons in the reticular nucleus of the prethalamus (black) the site of the future internal capsule (gray). It has been suggested that these two populations of axons guide thalamocortical axons through the diencephalon and into the ventral telencephalon. Within the primitive internal capsule another population of cells project axons in the opposite direction, into the cortex (green). These axons are thought to guide descending corticothalamic axons (blue) into the ventral telencephalon across the pallial–subpallial boundary. Recent evidence suggests that for thalamic axons (red) to grow from subpallium to cortex they require guidance by cortical efferents (blue).

Mentions: In the developing mouse thalamocortical system, it has been proposed that populations of guidepost cells are present along the route taken by thalamocortical axons and that these cells act as intermediate targets for thalamocortical axons or corticothalamic axons. These cells act in a different manner to those found in the grasshopper limb bud in that they extend axons, and it is thought that these axons then act as a scaffold to guide the later thalamocortical and corticothalamic axons. Axon tracing studies have identified populations of cells in two main locations that are proposed to act as guideposts (Figure 10).


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)

Pioneer neurons and axons in the developing thalamocortical tract. As thalamic axons (red) grow they are thought to be guided by the axons of neurons in the reticular nucleus of the prethalamus (black) the site of the future internal capsule (gray). It has been suggested that these two populations of axons guide thalamocortical axons through the diencephalon and into the ventral telencephalon. Within the primitive internal capsule another population of cells project axons in the opposite direction, into the cortex (green). These axons are thought to guide descending corticothalamic axons (blue) into the ventral telencephalon across the pallial–subpallial boundary. Recent evidence suggests that for thalamic axons (red) to grow from subpallium to cortex they require guidance by cortical efferents (blue).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 10: Pioneer neurons and axons in the developing thalamocortical tract. As thalamic axons (red) grow they are thought to be guided by the axons of neurons in the reticular nucleus of the prethalamus (black) the site of the future internal capsule (gray). It has been suggested that these two populations of axons guide thalamocortical axons through the diencephalon and into the ventral telencephalon. Within the primitive internal capsule another population of cells project axons in the opposite direction, into the cortex (green). These axons are thought to guide descending corticothalamic axons (blue) into the ventral telencephalon across the pallial–subpallial boundary. Recent evidence suggests that for thalamic axons (red) to grow from subpallium to cortex they require guidance by cortical efferents (blue).
Mentions: In the developing mouse thalamocortical system, it has been proposed that populations of guidepost cells are present along the route taken by thalamocortical axons and that these cells act as intermediate targets for thalamocortical axons or corticothalamic axons. These cells act in a different manner to those found in the grasshopper limb bud in that they extend axons, and it is thought that these axons then act as a scaffold to guide the later thalamocortical and corticothalamic axons. Axon tracing studies have identified populations of cells in two main locations that are proposed to act as guideposts (Figure 10).

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.