The simple yet powerful technique of induced pluripotency may eventually supply a wide range of differentiated cells for cell therapy and drug development. However, making the appropriate cells via induced pluripotent stem cells (iPSCs) requires reprogramming of somatic cells and subsequent redifferentiation. Given how arduous and lengthy this process can be, we sought to determine whether it might be possible to convert somatic cells into lineagespecific stem/progenitor cells of another germ layer in one step, bypassing the intermediate pluripotent stage. Here we show that transient induction of the four reprogramming factors (Oct4, Sox2, Klf4, and c-Myc) can efficiently transdifferentiate fibroblasts into functional neural stem/progenitor cells (NPCs) with appropriate signaling inputs. Compared with induced neurons (or iN cells, which are directly converted from fibroblasts), transdifferentiated NPCs have the distinct advantage of being expandable in vitro and retaining the ability to give rise to multiple neuronal subtypes and glial cells. Our results provide a unique paradigm for iPSC-factorbased reprogramming by demonstrating that it can be readily modified to serve as a general platform for transdifferentiation.A lthough successful transdifferentiation from one cell type to another by overexpressing lineage-specific genes in vivo (1, 2) and in vitro (3, 4) has been reported, until recently these methods were only effective for fate switching within the major lineages, i.e., ectoderm, mesoderm, and endoderm. However, the generation of iN cells (5) using neural-specific transcription factors has established that interlineage transdifferentiation is also possible in vitro. These transdifferentiation schemes entail overexpression of different sets of lineage-specific transcription factors. A more recent example reported single-factor transdifferentiation of fibroblasts into blood precursors using long-term ectopic expression of OCT4 (6); through extensive binding to the regulatory regions of key hematopoietic genes, OCT4 also appears to be participating in regulating hematopoietic programs acting as a lineage-specific transcription factor in this context. An important aspect of this study is the ability to generate a mitotically active progenitor population that can be further differentiated into a variety of blood cells-a critical feat that has yet to be accomplished in transdifferentiation to neural and endoderm lineages.In an effort to devise a more general transdifferentiation strategy that might give rise to a broad array of unrelated cell typesincluding lineage-specific precursors-we attempted to direct conventional four iPSC-factor-based reprogramming (7, 8) toward alternative outcomes. Specifically, studies indicating that iPSCs are generated in a sequential and stochastic manner (9-11) led us to hypothesize that we might be able to manipulate cells at an early and epigenetically highly unstable state induced by the reprogramming factors. Different conditions could potentially give rise to a multitude ...

The slow kinetics and low efficiency of reprogramming methods to generate human induced pluripotent stem cells (iPSCs) impose major limitations on their utility in biomedical applications. Here we describe a chemical approach that dramatically improves (>200 fold) the efficiency of iPSC generation from human fibroblasts, within seven days of treatment. This will provide a basis for developing safer, more efficient, non-viral methods for reprogramming human somatic cells.

SUMMARY Human induced pluripotent stem cells (hiPSCs) have been generated by reprogramming a number of different somatic cell types using a variety of approaches. In addition, direct reprogramming of mature cells from one lineage to another has emerged recently as an alternative strategy for generating cell types of interest. Here we show that a combination of a microRNA (miR-124) and two transcription factors (MYT1L and BRN2) is sufficient to directly reprogram postnatal and adult human primary dermal fibroblasts (mesoderm) to functional neurons (ectoderm) under precisely defined conditions. These human induced neurons (hiNs) exhibit typical neuronal morphology and marker gene expression, fire action potentials, and produce functional synapses between each other. Our findings have major implications for cell-replacement strategies in neurodegenerative diseases, disease modeling, and neural developmental studies.

The neurotransmitter GABA activates heteropentameric GABA A receptors, which are composed mostly of ␣, ␤, and ␥2 subunits. Regulated membrane trafficking and subcellular targeting of GABA A receptors is important for determining the efficacy of GABAergic inhibitory function. Of special interest is the ␥2 subunit, which is mostly dispensable for assembly and membrane insertion of functional receptors but essential for accumulation of GABA A receptors at synapses. In a search for novel receptor trafficking proteins, we have used the SOS-recruitment system and isolated a Golgi-specific DHHC zinc finger protein (GODZ) as a novel ␥2 subunit-interacting protein.GODZ is a member of the superfamily of DHHC cysteine-rich domain (DHHC-CRD) polytopic membrane proteins shown recently in yeast to represent palmitoyltransferases. GODZ mRNA is found in many tissues; however, in brain the protein is detected in neurons only and highly concentrated and asymmetrically distributed in the Golgi complex. GODZ interacts with a cysteine-rich 14-amino acid domain conserved specifically in the large cytoplasmic loop of ␥1-3 subunits but not in other GABA A receptor subunits. Coexpression of GODZ and GABA A receptors in heterologous cells results in palmitoylation of the ␥2 subunit in a cytoplasmic loop domain-dependent manner. Neuronal GABA A receptors are similarly palmitoylated. Thus, GODZ-mediated palmitoylation represents a novel posttranslational modification that is selective for ␥ subunit-containing GABA A receptor subtypes, a mechanism that is likely to be important for regulated trafficking of these receptors in the secretory pathway.

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