1. Division of Neuroscience, Children's Hospital, and
2. Department of Neurology and Program in Neuroscience, Harvard Medical School, Enders 350, 320 Longwood Avenue, Boston, Massachusetts 02115 USA
3. Present address: Center for Molecular Medicine and Therapeutics, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia V5Z 4H4 , Canada.

Correspondence to: Jeffrey D. Macklis Correspondence and requests for materials should be addressed to J.D.M. (e-mail: Email: macklis@hub.tch.harvard.edu).

Abstract

Neurogenesis normally only occurs in limited areas of the adult mammalian brain—the hippocampus¹, olfactory bulb^{2, 3, 4} and epithelium⁵, and at low levels in some regions of macaque cortex⁶. Here we show that endogenous neural precursors can be induced in situ to differentiate into mature neurons, in regions of adult mammalian neocortex that do not normally undergo any neurogenesis. This differentiation occurs in a layer- and region-specific manner, and the neurons can re-form appropriate corticothalamic connections. We induced synchronous apoptotic degeneration^{7, 8} of corticothalamic neurons in layer VI of anterior cortex of adult mice and examined the fates of dividing cells within cortex, using markers for DNA replication (5-bromodeoxyuridine; BrdU) and progressive neuronal differentiation. Newly made, BrdU-positive cells expressed NeuN, a mature neuronal marker, in regions of cortex undergoing targeted neuronal death and survived for at least 28 weeks. Subsets of BrdU+ precursors expressed Doublecortin, a protein found exclusively in migrating neurons^{9, 10}, and Hu, an early neuronal marker^{11, 12}. Retrograde labelling from thalamus demonstrated that BrdU+ neurons can form long-distance corticothalamic connections. Our results indicate that neuronal replacement therapies for neurodegenerative disease and CNS injury may be possible through manipulation of endogenous neural precursors in situ.

1. Division of Neuroscience, Children's Hospital, and
2. Department of Neurology and Program in Neuroscience, Harvard Medical School, Enders 350, 320 Longwood Avenue, Boston, Massachusetts 02115 USA
3. Present address: Center for Molecular Medicine and Therapeutics, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia V5Z 4H4 , Canada.

Correspondence to: Jeffrey D. Macklis Correspondence and requests for materials should be addressed to J.D.M. (e-mail: Email: macklis@hub.tch.harvard.edu).