The generation of pluripotent stem cells from an individual patient would enable the large-scale production of the cell types affected by that patient's disease. These cells could in turn be used for disease modeling, drug discovery, and eventually autologous cell replacement therapies. Although recent studies have demonstrated the reprogramming of human fibroblasts to a pluripotent state, it remains unclear whether these induced pluripotent stem (iPS) cells can be produced directly from elderly patients with chronic disease. We have generated iPS cells from an 82-year-old woman diagnosed with a familial form of amyotrophic lateral sclerosis (ALS). These patient-specific iPS cells possess properties of embryonic stem cells and were successfully directed to differentiate into motor neurons, the cell type destroyed in ALS.

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The development of a patterned vasculature is essential for normal organogenesis. We found that signaling by semaphorin 3E (Sema3E) and its receptor plexin-D1 controls endothelial cell positioning and the patterning of the developing vasculature in the mouse. Sema3E is highly expressed in developing somites, where it acts as a repulsive cue for plexin-D1-expressing endothelial cells of adjacent intersomitic vessels. Sema3E-plexin-D1 signaling did not require neuropilins, which were previously presumed to be obligate Sema3 coreceptors. Moreover, genetic ablation of Sema3E or plexin-D1 but not neuropilin-mediated Sema3 signaling disrupted vascular patterning. These findings reveal an unexpected semaphorin signaling pathway and define a mechanism for controlling vascular patterning.

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Although often considered as a group, spinal motor neurons are highly diverse in terms of their morphology, connectivity, and functional properties and differ significantly in their response to disease. Recent studies of motor neuron diversity have clarified developmental mechanisms and provided novel insights into neurodegeneration in amyotrophic lateral sclerosis (ALS). Motor neurons of different classes and subtypes--fast/slow, alpha/gamma--are grouped together into motor pools, each of which innervates a single skeletal muscle. Distinct mechanisms regulate their development. For example, glial cell line-derived neurotrophic factor (GDNF) has effects that are pool-specific on motor neuron connectivity, column-specific on axonal growth, and subtype-specific on survival. In multiple degenerative contexts including ALS, spinal muscular atrophy (SMA), and aging, fast-fatigable (FF) motor units degenerate early, whereas motor neurons innervating slow muscles and those involved in eye movement and pelvic sphincter control are strikingly preserved. Extrinsic and intrinsic mechanisms that confer resistance represent promising therapeutic targets in these currently incurable diseases.

Human embryonic (ESC) and induced pluripotent stem cells (iPSC) present exciting opportunities for studying development and in vitro disease modeling. However, reported variability in iPSC behavior has called their utility into question. We therefore constituted a test set of 16 iPSCs lines from 7 individuals of varying gender and health status, characterized them extensively for pluripotency, and evaluated their ability to terminally differentiate. Using standardized procedures in two independent laboratories, 13 of the iPSC lines gave rise to functional motor neurons with a range of efficiencies similar to ESCs. Although three iPSC lines were resistant to neural differentiation, early neuralization rescued their performance. Therefore, all lines in the test set passed a stringent test of differentiation capacity despite variations in expression of early pluripotency markers, transgenes and karyotype. This novel iPSC/ESC test set is a robust resource for those interested in the basic biology of stem cells and their applications.

Death pathways restricted to specific neuronal classes could potentially allow for precise control of developmental neuronal death and also underlie the selectivity of neuronal loss in neurodegenerative disease. We show that Fas-triggered death of normal embryonic motoneurons requires transcriptional upregulation of neuronal NOS and involves Daxx, ASK1, and p38 together with the classical FADD/caspase-8 cascade. No evidence for involvement of this pathway was found in cells other than motoneurons. Motoneurons from transgenic mice overexpressing ALS-linked SOD1 mutants (G37R, G85R, or G93A) displayed increased susceptibility to activation of this pathway: they were more sensitive to Fas- or NO-triggered cell death but not to trophic deprivation or excitotoxic stimulation. Thus, triggering of a motoneuron-restricted cell death pathway by neighboring cells might contribute to motoneuron loss in ALS.

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