Skip to main content

Home > Section on Mammalian Molecular Genetics

Mouse Molecular Genetics and Stem Cell Research

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

This final report summarizes our research efforts during the last year of my tenure as an NIH researcher. On this occasion, I would like to thank the NIH for the generous support I have received during the past four decades of active research in the field of mammalian molecular genetics. I will retire at the end of September 2012, and I thank the NICHD for granting me emeritus status at that time. This will allow me to remain involved in experimental efforts that are briefly outlined further below.

A long-term effort of our group has been directed toward the analysis of LIM-homeodomain transcription factors encoded by the Lhx gene family. The factors act in conjunction with their associated Ldb co-regulators to carry out important and indispensable functions during the development of the mouse embryo. Our most recent studies dealt with their involvement in patterning 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 were able to generate several iPS cell lines from fibroblasts of an NICHD patient cohort of children diagnosed with Smith-Lemli-Opitz Syndrome (SLOS). The SLOS iPS cell lines will serve as tools in subsequent experiments aimed at studying gene defects underlying the neurological deficiencies observed in these patients, establishing drug screening protocols, and developing novel avenues of therapy.

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

Our previous published studies revealed important roles of the two closely related LIM-homeodomain factors Lhx6 and Lhx8 in the development of cortical interneurons that derive from the medial ganglionic eminence (MGE) in the ventral telencephalon. In collab­oration with John Rubenstein's laboratory, we discovered that co-expression of Lhx6 and Lhx8 is required for induction of the Sonic Hedgehog (SHH) signaling molecule in the MGE. Targeted conditional inactivation of Shh in MGE neurons revealed that Shh, in turn, controls Nkx2.1, Lhx6, and Lhx8 and regulates the specification and survival of interneurons emanating from the MGE. We utilized a floxed allele of the obligatory Ldb1 coregulator of Lhx gene function to extend our analysis to transcriptional controls exerted by additional LIM-homeodomain factors on the development of a diverse array of structures in the nascent forebrain. Nkx2.1-Cre–mediated deletion of Ldb1 in the MGE affected development of several distinct neuronal populations. The phenotype of Ldb1/Nkx2.1-Cre mutants allowed us to conclude that Ldb1 plays an essential role in the formation of several nuclei in the hypothala­mus, including the arcuate nucleus, the ventromedial hypothalamus (VMH), and the paraventricular nucleus. We noted a loss of NPY+ and POMC+ neurons in the arcuate nucleus and a disorganization of the VMH. Islet-1 stands out as a member the LIM-homeodomain gene family that is co-expressed with Ldb1 in the developing hypothalamus, notably in the developing arcuate and VMH nuclei. To determine the function of Islet-1 in hypothalamus development, we generated Islet-1 conditional mutants by crossing the Islet-1 floxed mouse to the Nkx2.1-Cre line. Our analysis of the Islet-1/Nkx2.1-Cre mutant revealed that the Islet-1 gene is essential for controlling the differentiation of the NPY+ and POMC+ neurons in the arcuate nucleus. Consistent with the central role of this nucleus in the regulation of energy balance, the Islet-1/Nkx2.1-Cre mutant showed phenotypes of obesity and impaired glucose metabolism.

Human induced pluripotent stem (iPS) cells for the study of Smith-Lemli-Opitz Syndrome (SLOS)

Supported by a Director's Challenge Award Program, our laboratory was able to establish the premises for generating human induced pluripotent stem (iPS) cells from fibroblasts transduced by the transcription factors Sox2, Oct4, and Klf4. Extensive marker analysis identified our reprogrammed cells as iPS cells whose embryonic stem cell–like properties remain stable after multiple rounds of in vitro propagation. The derivation of iPS cells provides a platform for patient-specific in vitro disease modeling, drug screening, and ultimately regenerative therapies. We generated a host of iPS cell lines from children diagnosed with SLOS, a rare recessive childhood disorder caused by mutations in the DHCR7 gene. The gene encodes 7-dehydrocholesterol reductase, an enzyme that catalyzes the final step in cholesterol synthesis. Reduced function of the enzyme results in the accumulation of dehydrocholesterols and impairment of endogenous cholesterol synthesis. SLOS patients are being treated by Forbes Porter. We noted that SLOS iPS cells undergo spontaneous neural differentiation under the cholesterol-free conditions that we use to maintain control iPS cell lines in their pluripotent state. This observation is of preeminent importance for subse­quent experiments aimed at studying gene defects underlying the neurological deficiencies observed in these patients, establishing drug screening protocols, and developing novel avenues of therapy.

Additional Funding

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

Publications

  • Fossat N, Jones V, Khoo PL, Bogani D, Hardy A, Steiner K, Mukhopadhyay M , Westphal H, Nolan PM, Arkell R, Tam PPL. Stringent requirement of a proper level of canonical WNT signalling activity for head formation in mouse embryo. Development 2011;138:667-676.
  • Li L, Jothi R, Cui K, Lee JY, Cohen T, Gorivodsky M, Tzchori I, Zhao Y, Hayes SM, Bresnick EH, Zhao K, Westphal H, Love PE. Nuclear adaptor Ldb1 regulates a transcriptional program essential for the maintenance of hematopoietic stem cells. Nat Immunol 2011;12:129-136.
  • 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.
  • Narkis G, Tzchori I, Cohen T, Holtz A, Wier E, Westphal H. Isl1 and Ldb co-regulators of transcription are essential early determinants of mouse limb development. Dev Dyn 2012;241:787-791.

Collaborators

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

Top of Page