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Mouse Molecular Genetics and Stem Cell Research

Heiner Westphal, MD, Head, Section on Mammalian Molecular Genetics
Alexander J. Blood, BS, Postbaccalaureate Fellow
Justin Chen, BS, Postbaccalaureate Fellow
Kevin Francis, PhD, Postdoctoral Fellow
Alexander Grinberg, DVM, Senior Research Assistant
Nicole Khezri, BS, Postbaccalaureate Fellow
Eric J. Lee, DVM, Senior Research Assistant
Ginat Narkis, PhD, Postdoctoral Fellow
Peter O'Halloran, BS, Postbaccalaureate Fellow
William Olson, BS, Postbaccalaureate Fellow
Kayla Y. Perez Ortiz, BS, Postbaccalaureate Fellow
Lisa Williams-Simons, BS, AAS, Senior Research Assistant
Yangu Zhao, PhD, Staff Scientist

A major effort of our group is directed toward the functional analysis of LIM-homeodomain transcription factors encoded by the Lhx gene family and of associated Ldb co-regulators in mouse embryonic development. Current studies are centered on the factors' and co-regulators' involvement in patterning of the nascent forebrain and the limb anlagen. A second project concerns the reprogramming of human somatic cells to an induced pluripotent stem (iPS) cell state. We gained experience in generating iPS cells from human fibroblasts and have set up collaborations aimed at generating iPS cell clones pertaining to a number of patient cohorts currently under study at the NICHD. We expect that the cells and their differentiated derivatives will become valuable tools for probing disease mechanisms and for drug screening.

Roles of LIM-homeodomain factors and Ldb coregulators in forebrain patterning

Using a floxed allele of the obligatory Ldb1 coregulator of Lhx gene function, we extended our analysis of transcriptional controls exerted by LIM-homeodomain factors on the development of a diverse array of structures in the nascent forebrain. Our studies reflect in part a fruitful collaboration with the laboratory of John Rubenstein (1). Nkx2.1-Cre–mediated deletion of Ldb1 in the major ganglionic eminence (MGE) affected development of a number of neuronal precursors derived from this structure. Our study showned that Ldb1 plays an essential role in the formation of several important nuclei in this forebrain region. Some of the Ldb1/Nkx2.1-Cre mutants survive to adulthood because deletion of Ldb1 is restricted to populations of cells derived from the Nkx2.1 lineage. This has provided us with an opportunity to analyze behavioral consequences resulting from a loss of Nkx2.1 lineage–derived neurons in the forebrain. We detected a defect in the nesting behavior of these mutants. Furthermore, a close examination of the mutant hypothalamus showed that Ldb1 plays an essential role in the formation of several important nuclei in this region of the forebrain, including the arcuate nucleus, the ventromedial nucleus (VMH), and the paraventricular nucleus. Nkx2.1-Cre–mediated deletion of Ldb1 resulted in loss of NPY⁺ and POMC⁺ neurons in the arcuate nucleus and disorganization of the VMH. We observed that the Ldb1/Nkx2.1-Cre mutants accumulate more fat, resulting in characteristic distortions of the body shape. This is consistent with earlier reports pointing to a role of the ventral-medial hypothalamus in the regulation of energy balance and metabolism. Several members of the Lhx gene family whose action is mediated by Ldb1 are also expressed in the developing hypothalamus. We are currently analyzing mutants that lack the function of these genes in an effort to determine their contribution to the development of the hypothalamus.

Generating human induced pluripotent stem (iPS) cells as tools for the study and potential treatment of childhood disorders caused by defects in cholesterol metabolism

Our previous efforts toward understanding the mechanisms underlying the reprogramming of a somatic cell to the status of an embryonic stem cell (2) shaped our interest in exploring the use of induced pluripotent stem (iPS) cells for translational research on specific human childhood disorders presently under investigation at NICHD. The discovery of transcription factor–mediated reprogramming of somatic cells to an iPS cell state has created a powerful technological advance toward cell and tissue regeneration and cell-replacement therapy. A prominent goal of iPS technology is the derivation of disease-specific iPS cells, allowing for the study of cell-based disease pathology and the identification of novel drug therapies. Smith-Lemli-Opitz syndrome (SLOS) is a recessive syndrome extensively studied by the laboratory of Forbes Porter at the NICHD. The disorder is caused by a spectrum of mild-to-severe mutations of the 7-dehydrocholesterol reductase (DHCR7) gene. The encoded enzyme catalyses the penultimate step in endogenous cholesterol synthesis. Hence, DHCR7 mutations significantly impair intrinsic cholesterol supply, resulting in multiple malformations and central nervous system dysfunction. DHCR7–mutant mice die soon after birth, limiting the utility of animal models for the study of this disorder. In SLOS patients, cholesterol supplementation can alleviate some symptoms, yet dietary cholesterol fails to cross the blood-brain-barrier. Thus, there is currently no established therapeutic regimen to address behavioral and learning problems in these patients. Neural derivatives produced from SLOS patient–derived iPS cells would represent ideal tools for studying disease pathology and identifying new therapies. We have gained proficiency in generating human iPS cells, verifying their pluripotency and subjecting them to neural differentiation programs. The laboratory uses viral vectors encoding the transcription factors Sox2, Oct-4, and Klf4 to reprogram to the iPS cell state fibroblasts derived from skin biopsies of SLOS patients or healthy individuals. We have been able to generate a number of iPS cell lines from skin fibroblasts of SLOS patients collected by the Porter group. The fibroblasts carry a spectrum of mild to classical to severe DHCR7 mutations. The iPS lines have been thoroughly analyzed for cell-surface marker and pluripotent gene expression, germ layer differentiation, and karyotypic integrity.

Cognitive and behavioral impairments suggest functional deficits in both neural progenitor and neuronal populations of the cerebral cortex of SLOS patients. We are therefore in the process of generating neural progenitors as well as forebrain and dopaminergic neurons from DHCR7–mutant and control iPS lines. Differentiation, progenitor proliferation, synaptic activity, and sterol synthesis will be analyzed in the iPS–derived derivates at various stages of neural differentiation to characterize impairments of sterol metabolism. In support of an ongoing NICHD intramural drug trial, we will also test the effect of the HMG-CoA reductase inhibitor simvastatin on sterol levels in these cells. If successful, this study will advance our understanding of the cellular basis of the SLOS disorder and open novel avenues of drug therapy.

Additional Funding

NIH Director's Challenge Award Program for the study of "Induced pluripotent stem cells for the study of human disorders"

Publications

Flandin P, Zhao Y, Vogt D, Jeong J, Long J, Potter G, Westphal H, Rubenstein JL. Lhx6 and Lhx8 coordinately induce neuronal expression of Shh that controls the generation of interneuron progenitors. Neuron 2011;70:939-950.
Hezroni H, Tzchori I, Davidi A, Mattout A, Biran A, Nissim-Rafinia M, Westphal H, Meshorer E. H3K9 histone acetylation predicts pluripotency and reprogramming capacity of ES cells. Nucleus 2011;2(4):E-pub ahead of print.

Collaborators

Forbes D. Porter, MD, PhD, Clinical Director, NICHD, Bethesda, MD
John L. Rubenstein, MD, PhD, University of California San Francisco, San Francisco, CA

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