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Machado-Joseph disease (MJD; also called spinocerebellar ataxia type 3) is a dominantly inherited late-onset neurodegenerative disorder caused by expansion of polyglutamine (polyQ)-encoding CAG repeats in the MJD1 gene (also known [...]

Reprogramming somatic cells to pluripotency can be achieved by forced expression of a defined set of factors (1,2). Several methods have been developed for generating human iPS cells, such as [...], The mechanisms underlying the low efficiency of reprogramming somatic cells into induced pluripotent stem (iPS) cells are poorly understood. There is a clear need to study whether the reprogramming process itself compromises genomic integrity and, through this, the efficiency of iPS cell establishment. Using a high-resolution single nucleotide polymorphism array, we compared copy number variations (CNVs) of different passages of human iPS cells with their fibroblast cell origins and with human embryonic stem (ES) cells. Here we show that significantly more CNVs are present in early-passage human iPS cells than intermediate passage human iPS cells, fibroblasts or human ES cells. Most CNVs are formed de novo and generate genetic mosaicism in early-passage human iPS cells. Most of these novel CNVs rendered the affected cells at a selective disadvantage. Remarkably, expansion of human iPS cells in culture selects rapidly against mutated cells, driving the lines towards a genetic state resembling human ES cells.

An intriguing question in human embryonic stem cell (hESC) biology is whether these pluripotent cells can give rise to stably expandable somatic stem cells, which are still amenable to extrinsic fate instruction. Here, we present a pure population of long-term self-renewing rosette-type hESC-derived neural stem cells (It-hESNSCs), which exhibit extensive self-renewal, clonogenicity, and stable neurogenesis. Although It-hESNSCs show a restricted expression of regional transcription factors, they retain responsiveness to instructive cues promoting the induction of distinct subpopulations, such as ventral midbrain and spinal cord fates. Using It-hESNSCs as a donor source for neural transplantation, we provide direct evidence that hESC-derived neurons can establish synaptic connectivity with the mammalian nervous system. Combining long-term stability, maintenance of rosette-properties and phenotypic plasticity, It-hESNSCs may serve as useful tool to study mechanisms of human NSC self-renewal, lineage segregation, and functional in vivo integration. human embryonic stem cells | neural differentiation | regionalization | synapse formation

It was, until now, not entirely clear how the nervous system attains its cellular phenotypic diversity and wired complexity during development. Here we describe how environmental interactions alone can modify the development of neurogenic precursor cells. Upon evaluating distinct growth-permissive substrates in an embryonic stem cell-neurogenesis assay, we found that laminin, fibronectin, and gelatin instruct neural fate and alter the functional specification of neurons when applied at distinct stages of development. Changes in phenotypic, electrophysiological, and molecular characteristics could resemble cellular events and interactions in the early embryonic brain and may explain why these extracellular matrix components transiently demarcate certain developing brain structures. cell culture | extracellular matrix | fibronectin | laminin | sonic hedgehog

Neuronal induction by retinoic acid (RA) is commonly used in embryonic stem (ES) cell differentiation. Two recent papers show that this paradigm induces a population of neurogenic precursors with properties of radial glia. Upon differentiation, RA-treated cells give rise to a defined and developmentally restricted neuronal lineage. This role of RA in cell fate specification provides new perspectives for studying the radial glia--neuron transition and for generating homogenous populations of neurons from ES cells.

During embryogenesis, pluripotent stem cells segregate into daughter lineages of progressively restricted developmental potential. In vitro, this process has been mimicked by the controlled differentiation of embryonic stem cells into neural precursors. To explore the developmental potential of these cell-culture-derived precursors in vivo, we have implanted them into the ventricles of embryonic rats. The transplanted cells formed intraventricular neuroepithelial structures and migrated in large numbers into the brain tissue. Embryonic-stem-cell-derived neurons, astrocytes, and oligodendrocytes incorporated into telencephalic, diencephalic, and mesencephalic regions and assumed phenotypes indistinguishable from neighboring host cells. These observations indicate that entirely in vitro-generated neural precursors are able to respond to environmental signals guiding cell migration and differentiation and have the potential to reconstitute neuronal and glial lineages in the central nervous system.

A study shows that stem cells can be used to generate self-organizing three-dimensional tissues that mimic the developing human brain. These tissues provide a tool for modelling neurodevelopmental disorders. Pluripotent [...]

Reports on the functional integration of embryonic stem (ES) cell-derived neurons in hippocampal slice cultures. Incorporation of ES cell-derived neurons (ESN) into hippocampal slice cultures; Intrinsic properties of incorporated ESN; Development of synaptic input onto ESN with time in culture.