Migration toward pathology is the first critical step in stem cell engagement during regeneration. Neural stem cells (NSCs) migrate through the parenchyma along nonstereotypical routes in a precise directed manner across great distances to injury sites in the CNS, where they might engage niches harboring local transiently expressed reparative signals. The molecular mechanisms for NSC mobilization have not been identified. Because NSCs seem to home similarly to pathologic sites derived from disparate etiologies, we hypothesized that the inflammatory response itself, a characteristic common to all, guides the behavior of potentially reparative cells. As proof of concept, we show that human NSCs migrate in vivo (including from the contralateral hemisphere) toward an infarcted area (a representative CNS injury), where local astrocytes and endothelium up-regulate the inflammatory chemoattractant stromal cell-derived factor 1␣ (SDF-1␣). NSCs express CXC chemokine receptor 4 (CXCR4), the cognate receptor for SDF-1␣. Exposure of SDF-1␣ to quiescent NSCs enhances proliferation, promotes chain migration and transmigration, and activates intracellular molecular pathways mediating engagement. CXCR4 blockade abrogates their pathology-directed chain migration, a developmentally relevant mode of tangential migration that, if recapitulated, could explain homing along nonstereotypical paths. Our data implicate SDF-1␣͞CXCR4, representative of the inflammatory milieu characterizing many pathologies, as a pathway that activates NSC molecular programs during injury and suggest that inflammation may be viewed not simply as playing an adverse role but also as providing stimuli that recruit cells with a regenerative homeostasis-promoting capacity. CXCR4 expression within germinal zones suggests that NSC homing after injury and migration during development may invoke similar mechanisms.human stem cells ͉ homing ͉ chain migration ͉ stroke ͉ hypoxia-ischemia

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Stable clones of neural stem cells (NSCs) have been isolated from the human fetal telencephalon. These self-renewing clones give rise to all fundamental neural lineages in vitro. Following transplantation into germinal zones of the newborn mouse brain they participate in aspects of normal development, including migration along established migratory pathways to disseminated central nervous system regions, differentiation into multiple developmentally and regionally appropriate cell types, and nondisruptive interspersion with host progenitors and their progeny. These human NSCs can be genetically engineered and are capable of expressing foreign transgenes in vivo. Supporting their gene therapy potential, secretory products from NSCs can correct a prototypical genetic metabolic defect in neurons and glia in vitro. The human NSCs can also replace specific deficient neuronal populations. Cryopreservable human NSCs may be propagated by both epigenetic and genetic means that are comparably safe and effective. By analogy to rodent NSCs, these observations may allow the development of NSC transplantation for a range of disorders.

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A new autosomal recessive mouse mutation, Purkinje cell degeneration (ped), is described. Mutants exhibit a moderate ataxia beginning at 3 to 4 weeks of age. The ataxia results from postnatal degeneration of virtually all cerebellar Purkinje cells beginning around 15 to 18 days of age and progressing rapidly over the next 2 weeks. In addition to the cerebellar disease there is slow progressive degeneration in the retina (photoreceptor cells) and olfactory bulb. Also, adult males have abnormal sperm.Because of the uniform, stereotyped, and relatively simple organization of the cerebellar cortex many neuroscientists have chosen to study its functional organization (1), cytology and synaptic architecture (2), or development (3). Since the most obvious functions of the cerebellum involve posture and motor coordination, most mutations will affect behavior and are readily detected. In mice, a number of cerebellar mutants have been described (4) MATERIALS AND METHODSThe pcd mutation occurred in the C57BR/cdJ strain at The Jackson Laboratory. Because of the poor breeding performance of this strain, pcd/pcd females were mated to C3H/ HeJ males and the Fj-animals were intercrossed to produce pcd/pcd F2 females. These females were then crossed back to C57BR/cdJ males and the pcd mutation was maintained thereafter by brother-sister matings. The mutant gene is also being transferred to the C57BL/6J strain. The animals used in this study came from both lines.For histological studies, the mice were fixed by perfusion through the heart with 1% formaldehyde and 1.25% glutaraldehyde in 0.1 M sodium phosphate buffer, pH 7.2. The brains were removed, dehydrated, and embedded in either paraffin or celloidin. Sections were cut at 7 or 20 gm and stained with cresyl violet. In addition, pieces of cerebellum and eyes were postfixed in OS04, dehydrated, embedded in an Epon-Araldite mixture, and sectioned at 1 Am, and the sections were stained with toluidine blue.The various brain regions are designated according to the atlas of Sidman et al. (14). Day of birth is considered day 0.To determine if there was any difference in body weights between mutants and controls, all young in 8 litters were earmarked on day 15

Retinal dystrophies, known in man, dog, mouse, and rat, involve progressive loss of photoreceptor cells with onset during or soon after the developmental period. Functional (electroretinogram), chemical (rhodopsin analyses) and morphological (light and electron microscopy) data obtained in the rat indicated two main processes: (a) overproduction of rhodopsin and an associated abnormal lamellar tissue component, (b) progressive loss of photoreceptor cells. The first abnormality recognized was the appearance of swirling sheets or bundles of extracellular lamellae between normally developing retinal rods and pigment epithelium; membrane thickness and spacing resembled that in normal outer segments. Rhodopsin content reached twice normal values, was present in both rods and extracellular lamellae, and was qualitatively normal, judged by absorption maximum and products of bleaching. Photoreceptors attained virtually adult form and ERG function. Then rod inner segments and nuclei began degenerating; the ERG lost sensitivity and showed selective depression of the a-wave at high luminances. Outer segments and lamellae gradually degenerated and rhodopsin content decreased. No phagocytosis was seen, though pigment cells partially dedifferentiated and many migrated through the outer segment-debris zone toward the retina. Eventually photoreceptor cells and the b-wave of the ERG entirely disappeared. Rats kept in darkness retained electrical activity, rhodopsin content, rod structure, and extracellular lamellae longer than litter mates in light.

Mutations in rod opsin, the visual pigment protein of rod photoreceptors, account for Ϸ15% of all inherited human retinal degenerations. However, the physiological and molecular events underlying the disease process are not well understood. One approach to this question has been to study transgenic mice expressing opsin genes containing defined mutations. A caveat of this approach is that even the overexpression of normal opsin leads to photoreceptor cell degeneration. To overcome the problem, we have reduced or eliminated endogenous rod opsin content by targeted gene disruption. Retinas in mice lacking both opsin alleles initially developed normally, except that rod outer segments failed to form. Within months of birth, photoreceptor cells degenerated completely. Retinas from mice with a single copy of the opsin gene developed normally, and rods elaborated outer segments of normal size but with half the normal complement of rhodopsin. Photoreceptor cells in these retinas also degenerated but did so over a much slower time course. Physiological and biochemical experiments showed that rods from mice with a single opsin gene were Ϸ50% less sensitive to light, had accelerated f lash-response kinetics, and contained Ϸ50% more phosducin than wild-type controls.