The long-term goals of the proposed experiments are both to elucidate molecular-genetic controls over the neuron subtype-specific development of corticospinal motor neurons (CSMN) (and related neocortical projection neurons), and to potentially enable future approaches to repair of degenerating or injured CSMN. CSMN are both developmentally prototypical for all neocortical projection neurons, and clinically important as the brain neurons that degenerate in amyotrophic lateral sclerosis / motor neuron disease (ALS/MND) and whose axonal injury is central to loss of motor function in spinal cord injury. Proposed experiments will deeply investigate function of the centrally important CSMN/subcerebral-specific transcription factor CTIP2 (COUP-TF interacting protein 2) and its paralog CTIP1 in development of CSMN and related neurons in murine neocortex. Ctip2 has increasingly emerged as both a critical regulator of development and connectivity of CSMN, and as a common target for regulation (largely repression) by multiple projection neuron subtype differentiation pathways. Ctip2 is known from other organ systems to be involved in developmental lineage specification decisions. Within the neocortex, CTIP2 is specifically expressed by CSMN and related subcerebral projection neurons, and is necessary for outgrowth, fasciculation, and targeting of CSMN axons. While Ctip2 has emerged as centrally important for CSMN development, most aspects of its function remain unknown. Substantial preliminary data support these aims. Previous work from this laboratory identified Ctip2 as a critical CSMN molecular control, and demonstrated that CSMN axons in Ctip2-/- mice are misrouted before penetrating the internal capsule (IC), defasciculate in the IC, and fail to project to the spinal cord (SC). Because CTIP2 also controls differentiation of striatal medium-sized spiny neurons (MSN), which surround CSMN axons in the IC, the hypothesis is suggested that some defects in Ctip2-/- CSMN connectivity to SC might result from dysregulation of axon growth and guidance controls in Ctip2-/- MSN. Mice lacking Ctip2 only in neocortex (Emx1-Cre;Ctip2fl/fl) reveal that a subset of CSMN enter and fasciculate in the IC, and some even reach the SC. Other preliminary studies find that the Ctip2 paralog Ctip1 interacts cross-repressively with Ctip2 to control deep-layer projection neuron development, and that Ctip1 additionally regulates areal organization. Proposed experiments will:
(Aims 1, 2) delineate CSMN-autonomous and non-CSMN-autonomous roles of Ctip2 in CSMN axon growth and fasciculation;
(Aims 3, 4) investigate a newly-identified genetically cross- repressive interaction between Ctip2 and its paralog Ctip1 in CSMN development, as well as independent roles of Ctip1 in areal organization and development of other deep-layer projection neurons. Experiments beyond this proposal could identify genes regulated directly or indirectly by Ctip2 in CSMN. These studies will elucidate mechanisms by which Ctip2, a central regulator of CSMN differentiation, acts alone and with other genes to instruct the precision of development of this developmentally prototypical, clinically important neuron type.
/ Relevance Degenerative and traumatic neurological disorders are the source of great personal suffering and disability, and they account for a huge public health financial and social burden;these include neurodegenerative diseases involving cerebral cortex long-connection nerve cells termed corticospinal motor neurons (CSMN), such as ALS / Lou Gehrig's disease, primary lateral sclerosis (PLS), hereditary spastic paraplegia (HSP), and Huntington's disease (HD);and traumatic spinal cord injury (SCI). A gene and molecule called Ctip2 has increasingly emerged as both a critical control over development and function of CSMN, and as a key regulatory hub for central pathways controlling brain development and function more generally, but most aspects of its function remain unknown. Building on recent work identifying molecular controls over these cerebral cortex-to-spinal cord brain neurons'growth and function, this project will pursue state-of-the-art investigation of how Ctip2 regulates the growth, health, and correct function of this important neuron type in mice, toward new approaches for the treatment of injured or degenerating neurons in the cerebral cortex, the highest region of the brain, that connect to the spinal cord and are central to human ALS, SCI, HSP, PLS.
|Wuttke, Thomas V; Markopoulos, Foivos; Padmanabhan, Hari et al. (2018) Developmentally primed cortical neurons maintain fidelity of differentiation and establish appropriate functional connectivity after transplantation. Nat Neurosci 21:517-529|
|Rodriguez-Muela, Natalia; Litterman, Nadia K; Norabuena, Erika M et al. (2017) Single-Cell Analysis of SMN Reveals Its Broader Role in Neuromuscular Disease. Cell Rep 18:1484-1498|
|Itoh, Yasuhiro; Poulopoulos, Alexandros; Macklis, Jeffrey D (2017) Unfolding the Folding Problem of the Cerebral Cortex: Movin' and Groovin'. Dev Cell 41:332-334|
|Fame, Ryann M; Dehay, Colette; Kennedy, Henry et al. (2017) Subtype-Specific Genes that Characterize Subpopulations of Callosal Projection Neurons in Mouse Identify Molecularly Homologous Populations in Macaque Cortex. Cereb Cortex 27:1817-1830|
|Chen, Zhongbo; Lin, Kuang; Macklis, Jeffrey D et al. (2017) Proposed association between the hexanucleotide repeat of C9orf72 and opposability index of the thumb. Amyotroph Lateral Scler Frontotemporal Degener 18:175-181|
|Frangeul, Laura; Kehayas, Vassilis; Sanchez-Mut, Jose V et al. (2017) Input-dependent regulation of excitability controls dendritic maturation in somatosensory thalamocortical neurons. Nat Commun 8:2015|
|Sances, Samuel; Bruijn, Lucie I; Chandran, Siddharthan et al. (2016) Modeling ALS with motor neurons derived from human induced pluripotent stem cells. Nat Neurosci 19:542-53|
|Woodworth, Mollie B; Greig, Luciano C; Liu, Kevin X et al. (2016) Ctip1 Regulates the Balance between Specification of Distinct Projection Neuron Subtypes in Deep Cortical Layers. Cell Rep 15:999-1012|
|Fame, Ryann M; MacDonald, Jessica L; Dunwoodie, Sally L et al. (2016) Cited2 Regulates Neocortical Layer II/III Generation and Somatosensory Callosal Projection Neuron Development and Connectivity. J Neurosci 36:6403-19|
|Greig, Luciano C; Woodworth, Mollie B; Greppi, Chloé et al. (2016) Ctip1 Controls Acquisition of Sensory Area Identity and Establishment of Sensory Input Fields in the Developing Neocortex. Neuron 90:261-77|
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