The integration of CGE-derived interneurons into the developing cortex: challenging the temporal matching hypothesis
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1
New York University School of Medicine, Smilow Neuroscience Program and the Department of Cell Biology, United States
Cortical interneurons are derived from two prominent developmental structures, the MGE (medial ganglionic eminence) and the CGE (caudal ganglionic eminence). Birthdating (Anderson et al., 2002) studies indicate that cortical pyramidal neurons and interneurons are both born in an inside out fashion. Similarly, genetic fate mapping studies of the MGE (Miyoshi et al., 2007) suggest that MGE-derived interneurons are born in this manner. Given that the primary neuronal target of cortical interneurons are the pyramidal cells, a temporal matching hypothesis has been proposed, where the connectivity between these neuronal classes is simply based on their coincident birthdates. Following this scenerio, one would imagine that early born pyramidal neurons are innervated by early born interneuron populations, while late born pyramidal neurons are targeted by the late born cortical interneuronal cohort. Recently we have developed a novel approach for genetically fate mapping the CGE-derived cortical interneuron population. This study has revealed two unforeseen aspects concerning the CGE-derived cortical interneuron populations. First, we have found that CGE-derived progenitors gives rise to a much larger proportion of the cortical interneuron population than previously anticipated. Previous estimates by our group and others have suggested that only 15% of all cortical interneurons are derived from the CGE. Our present study suggests that this is a gross underestimate, arising from the observation that CGE-progenitors produce a large proportion of cortical interneurons at late developmental time points (around E16.5). Taking into account the CGE-derived late born cohort, we now believe that upwards 40% of all cortical interneurons arise from the CGE. Second, unlike the MGE where different subtypes of cortical interneurons are born at different developmental times, the CGE produces all classes of interneurons in equal percentages at all developmental timepoints. As regardless of birthdate, CGE-derived cortical interneurons target the superficial layers of cortex (layers 2-3), this realization suggests that CGE-derived interneurons rather than innervating aged match cortical pyramidal neurons, preferentially innervate superficial populations regardless of their birthdate. These studies provide strong evidence against the temporal matching hypothesis.
Conference:
INMED Satellite Conference of SFN - Neuroscience 2009, Multiple Facets of GABA in Brain Development, Chicago, United States, 16 Oct - 16 Oct, 2009.
Presentation Type:
Oral Presentation
Topic:
Abstracts
Citation:
Miyoshi
G,
Hjerling-Leffler
J,
Sousa
V,
Butt
S and
Fishell
G
(2009). The integration of CGE-derived interneurons into the developing cortex: challenging the temporal matching hypothesis.
Conference Abstract:
INMED Satellite Conference of SFN - Neuroscience 2009, Multiple Facets of GABA in Brain Development.
doi: 10.3389/conf.neuro.03.2009.13.004
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Received:
23 Jul 2009;
Published Online:
23 Jul 2009.
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Correspondence:
Gord Fishell, New York University School of Medicine, Smilow Neuroscience Program and the Department of Cell Biology, New York, United States, gordon_fishell@hms.harvard.edu