The midbrain of sauropsides shares a common subdivision pattern defined by embryonic radial glia

Delgado, Ana C.; Alonso, Antonia; Damas, Carmen; Trujillo, Carmen M.a

doi:10.1016/j.brainresbull.2005.05.013

Cited by 4 publications

(3 citation statements)

References 23 publications

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“…Another interesting question is whether parakeets reduced only the tectum or also some adjacent components of the midbrain (Delgado et al,2005). Our observation that the diencephalon/tegmentum is slightly smaller in parakeets than age‐matched quail (Fig.…”

Section: Discussionmentioning

confidence: 99%

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Developmental origins of species differences in telencephalon and tectum size: Morphometric comparisons between a parakeet (Melopsittacus undulatus) and a quail (Colinus virgianus)

Striedter

Charvet

2008

J of Comparative Neurology

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Parrots, including parakeets, evolved significantly larger brains than other birds, relative to their body size, and they possess a proportionately larger telencephalon. For example, the telencephalon occupies approximately 68% of the brain in parakeets but only 52% in bobwhite quail. The present study was designed to determine when and how this difference in brain region proportions arises during development. To that end, we present volumetric data on the major brain regions in parakeets and bobwhite quail at several stages of embryogenesis, at hatching and, for the parakeets, 1 week after hatching. We also report on the proportional sizes of each region's proliferative and postproliferative zones. One major finding is that parakeets develop a proportionately larger telencephalon relatively late in development and that this late increase correlates with a delay in telencephalic neurogenesis. The most prominent aspect of this delayed telencephalic development is a tremendous expansion of the proliferative subventricular zone in the telencephalon of late embryonic and posthatching parakeets. The second major finding is that the tectum is much smaller in parakeets than in quail at all developmental stages examined, suggesting that the tectum's reduced size is due to an evolutionary change in how much tissue was allocated to become tectum at the time of brain regionalization. Collectively these findings indicate that evolutionary changes in brain region proportions are caused not by a single type of change but by several distinct developmental mechanisms, including changes in brain regionalization and neurogenesis timing.

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Section: Discussionmentioning

confidence: 99%

“…Our definition of the tectum corresponds to what others have called the optic or dorsal tectum (Delgado et al,2005). It excludes the torus semicircularis and the tectal gray, which we here group with the diencephalon and tegmentum.…”

Section: Methodsmentioning

confidence: 99%

Developmental origins of species differences in telencephalon and tectum size: Morphometric comparisons between a parakeet (Melopsittacus undulatus) and a quail (Colinus virgianus)

Striedter

Charvet

2008

J of Comparative Neurology

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“…Brain regions were delineated and volumes estimated using the Cavalieri method, as described previously (7). As defined here, the telencephalon includes the evaginated hemispheres and midline telencephalic structures; the tectum corresponds to what others have called the optic or dorsal tectum (45). Telencephalon and tectum volumes for the ED12 embryos were normalized by comparing them to the rest of the brain, including diencephalon, pretectum, tegmentum, torus semicircularis, and hindbrain (but excluding tectum or telencephalon, respectively).…”

Section: Methodsmentioning

confidence: 99%

Expansion, folding, and abnormal lamination of the chick optic tectum after intraventricular injections of FGF2

McGowan

Alaama

Freise

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Comparative research has shown that evolutionary increases in brain region volumes often involve delays in neurogenesis. However, little is known about the influence of such changes on subsequent development. To get at this question, we injected FGF2-which delays cell cycle exit in mammalian neocortex-into the cerebral ventricles of chicks at embryonic day (ED) 4. This manipulation alters the development of the optic tectum dramatically. By ED7, the tectum of FGF2-treated birds is abnormally thin and has a reduced postmitotic layer, consistent with a delay in neurogenesis. FGF2 treatment also increases tectal volume and ventricular surface area, disturbs tectal lamination, and creates small discontinuities in the pia mater overlying the tectum. On ED12, the tectum is still larger in FGF2-treated embryos than in controls. However, lateral portions of the FGF2-treated tectum now exhibit volcano-like laminar disturbances that coincide with holes in the pia, and the caudomedial tectum exhibits prominent folds. To explain these observations, we propose that the tangential expansion of the ventricular surface in FGF2-treated tecta outpaces the expansion of the pial surface, creating abnormal mechanical stresses. Two alternative means of alleviating these stresses are tectal foliation and the formation of pial holes. The latter probably alter signaling gradients required for normal cell migration and may generate abnormal patterns of cerebrospinal fluid flow; both abnormalities would generate disturbances in tectal lamination. Overall, our findings suggest that evolutionary expansion of sheet-like, laminated brain regions requires a concomitant expansion of the pia mater.brain evolution | evolutionary developmental biology | proliferation | meninges | cortical folding E volutionary increases in brain region volumes are common (1).For example, the neocortex is disproportionately enlarged in primates relative to other mammals, and the telencephalon is disproportionately enlarged in parrots and songbirds relative to other birds (1-4). Recent work in evolutionary developmental neurobiology has shown that these evolutionary increases in brain region volumes are often caused by delays in cell cycle exit of neuronal precursors (5, 6). Among birds, for example, parrots and songbirds exhibit delayed telencephalic neurogenesis relative to chicken-like birds (7-9). Among mammals, cell cycle exit in the neocortex is similarly delayed in primates, which have a disproportionately enlarged neocortex (5, 10-12).Unfortunately, the downstream effects of delayed cell cycle exit on subsequent developmental processes and adult morphology remain poorly understood. One way to fill this gap in our knowledge is to experimentally recreate the key species differences in the laboratory by means of carefully selected developmental manipulations. A good example of this phenocopy approach was the creation of transgenic mice with a constitutively active form of β-catenin that prolongs proliferation, increases neocortical volume, and generates cortica...

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The rostral and caudal boundaries of the diencephalon

Trujillo

Alonso

Delgado

et al. 2005

Brain Research Reviews

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The midbrain of sauropsides shares a common subdivision pattern defined by embryonic radial glia

Cited by 4 publications

References 23 publications

Developmental origins of species differences in telencephalon and tectum size: Morphometric comparisons between a parakeet (Melopsittacus undulatus) and a quail (Colinus virgianus)

Developmental origins of species differences in telencephalon and tectum size: Morphometric comparisons between a parakeet (Melopsittacus undulatus) and a quail (Colinus virgianus)

Expansion, folding, and abnormal lamination of the chick optic tectum after intraventricular injections of FGF2

The rostral and caudal boundaries of the diencephalon

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