Faculty Bibliography

In October 2013, the International Combined Orthopaedic Research Societies (ICORS; https://urldefense.proofpoint.com/v2/url?u=http-3A__i- 2Dcors.org&d=DQIBAg&c=j5oPpO0eBH1iio48DtsedbOBGmuw5jHLjgvtN2r4ehE&r=KRXeNoRy5_8lkSwAJ G5vjS1yT0aFSItfe494dmkdSVs&m=Q128C029R6hKpAWrbdSw1X1eyRa_A15Le8lQ5N7b464&s=WM_- 4Atc-eAEEnVXWhP05NYU50wYQsZ1AXGjxxkozSw&e= ) was founded with inaugural member organisations from the previous Combined Orthopaedic Research Society, which had sponsored combined meetings for more than 2 decades. The ICORS is dedicated to the stimulation of orthopaedic and musculoskeletal research in fields such as biomedical engineering, biology, chemistry, and veterinary and human clinical research. The ICORS seeks to facilitate communication with member organisations to enhance international research collaborations and to promote the development of new international orthopaedic and musculoskeletal research organisations. Through new categories of membership, the ICORS represents the broadest coalition of orthopaedic research organisations globally.

One of the most remarkable chromatin remodelling processes occurs during spermiogenesis, the post-meiotic phase of sperm development during which histones are replaced with sperm-specific protamines to repackage the genome into the highly compact chromatin structure of mature sperm. Here we identify Chromodomain helicase DNA binding protein 5 (Chd5) as a master regulator of the histone-to-protamine chromatin remodelling process. Chd5 deficiency leads to defective sperm chromatin compaction and male infertility in mice, mirroring the observation of low CHD5 expression in testes of infertile men. Chd5 orchestrates a cascade of molecular events required for histone removal and replacement, including histone 4 (H4) hyperacetylation, histone variant expression, nucleosome eviction and DNA damage repair. Chd5 deficiency also perturbs expression of transition proteins (Tnp1/Tnp2) and protamines (Prm1/2). These findings define Chd5 as a multi-faceted mediator of histone-to-protamine replacement and depict the cascade of molecular events underlying this process of extensive chromatin remodelling.

Ectopic expression of defined sets of transcription factors in somatic cells enables them to adopt the qualities of pluripotency. Mouse embryonic fibroblasts (MEFs) are the classic target cell used to elucidate the core principles of nuclear reprogramming. However, their phenotypic and functional heterogeneity represents a major hurdle for mechanistic studies aimed at defining the molecular nature of cellular plasticity. We show that reducing the complexity of MEFs by flow cytometry allows the isolation of discrete cell subpopulations that can be efficiently reprogrammed to pluripotency with fewer genes. Using these FACS-sorted cells, we performed a systematic side-by-side analysis of the reprogramming efficiency with different two- and three-factor combinations of Oct4, Sox2 and Klf4. We show that introduction of exogenous Oct4 with either Sox2 or Klf4 does not directly convert MEFs to a pluripotent state. Instead, each combination of factors disrupts the normal cellular homeostasis and establishes transient states characterized by the concurrent expression of mixed lineage markers. These cells convert into induced pluripotent stem cells in a stochastic fashion. Our data suggest that there is a partial functional redundancy between Sox2 and Klf4 in the disruption of cellular homeostasis and activation of regulatory networks that define pluripotency.

The generation of induced pluripotent stem cells (iPSCs) often results in aberrant epigenetic silencing of the imprinted Dlk1-Dio3 gene cluster, compromising the ability to generate entirely iPSC-derived adult mice ('all-iPSC mice'). Here, we show that reprogramming in the presence of ascorbic acid attenuates hypermethylation of Dlk1-Dio3 by enabling a chromatin configuration that interferes with binding of the de novo DNA methyltransferase Dnmt3a. This approach allowed us to generate all-iPSC mice from mature B cells, which have until now failed to support the development of exclusively iPSC-derived postnatal animals. Our data show that transcription factor-mediated reprogramming can endow a defined, terminally differentiated cell type with a developmental potential equivalent to that of embryonic stem cells. More generally, these findings indicate that culture conditions during cellular reprogramming can strongly influence the epigenetic and biological properties of the resultant iPSCs.

Somatic reprogramming induced by defined transcription factors is a low-efficiency process that is enhanced by p53 deficiency. So far, p21 is the only p53 target shown to contribute to p53 repression of iPSC (induced pluripotent stem cell) generation, indicating that additional p53 targets may regulate this process. Here, we demonstrate that miR-34 microRNAs (miRNAs), particularly miR-34a, exhibit p53-dependent induction during reprogramming. Mir34a deficiency in mice significantly increased reprogramming efficiency and kinetics, with miR-34a and p21 cooperatively regulating somatic reprogramming downstream of p53. Unlike p53 deficiency, which enhances reprogramming at the expense of iPSC pluripotency, genetic ablation of Mir34a promoted iPSC generation without compromising self-renewal or differentiation. Suppression of reprogramming by miR-34a was due, at least in part, to repression of pluripotency genes, including Nanog, Sox2 and Mycn (also known as N-Myc). This post-transcriptional gene repression by miR-34a also regulated iPSC differentiation kinetics. miR-34b and c similarly repressed reprogramming; and all three miR-34 miRNAs acted cooperatively in this process. Taken together, our findings identified miR-34 miRNAs as p53 targets that play an essential role in restraining somatic reprogramming.

A key obstacle to understanding neural circuits in the cerebral cortex is that of unraveling the diversity of GABAergic interneurons. This diversity poses general questions for neural circuit analysis: how are these interneuron cell types generated and assembled into stereotyped local circuits and how do they differentially contribute to circuit operations that underlie cortical functions ranging from perception to cognition? Using genetic engineering in mice, we have generated and characterized approximately 20 Cre and inducible CreER knockin driver lines that reliably target major classes and lineages of GABAergic neurons. More select populations are captured by intersection of Cre and Flp drivers. Genetic targeting allows reliable identification, monitoring, and manipulation of cortical GABAergic neurons, thereby enabling a systematic and comprehensive analysis from cell fate specification, migration, and connectivity, to their functions in network dynamics and behavior. As such, this approach will accelerate the study of GABAergic circuits throughout the mammalian brain

RNA interference is a powerful tool for studying gene function, however, the reproducible generation of RNAi transgenic mice remains a significant limitation. By combining optimized fluorescence-coupled miR30-based shRNAs with high efficiency ES cell targeting, we developed a fast, scalable pipeline for the production of shRNA transgenic mice. Using this system, we generated eight tet-regulated shRNA transgenic lines targeting Firefly and Renilla luciferases, Oct4 and tumor suppressors p53, p16(INK4a), p19(ARF) and APC and demonstrate potent gene silencing and GFP-tracked knockdown in a broad range of tissues in vivo. Further, using an shRNA targeting APC, we illustrate how this approach can identify predicted phenotypes and also unknown functions for a well-studied gene. In addition, through regulated gene silencing we validate APC/Wnt and p19(ARF) as potential therapeutic targets in T cell acute lymphoblastic leukemia/lymphoma and lung adenocarcinoma, respectively. This system provides a cost-effective and scalable platform for the production of RNAi transgenic mice targeting any mammalian gene. PAPERCLIP: