Miller Andrew L.

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Miller
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Andrew L.
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  • Article
    Expression and reconstitution of the bioluminescent Ca2+ reporter aequorin in human embryonic stem cells, and exploration of the presence of functional IP3 and ryanodine receptors during the early stages of their differentiation into cardiomyocytes
    (Springer, 2016-07-19) Chan, Harvey Y. S. ; Cheung, Man Chun ; Gao, Yi ; Miller, Andrew L. ; Webb, Sarah E.
    In order to develop a novel method of visualizing possible Ca2+ signaling during the early differentiation of hESCs into cardiomyocytes and avoid some of the inherent problems associated with using fluorescent reporters, we expressed the bioluminescent Ca2+ reporter, apo-aequorin, in HES2 cells and then reconstituted active holo-aequorin by incubation with f-coelenterazine. The temporal nature of the Ca2+ signals generated by the holo-f-aequorin-expressing HES2 cells during the earliest stages of differentiation into cardiomyocytes was then investigated. Our data show that no endogenous Ca2+ transients (generated by release from intracellular stores) were detected in 1–12-day-old cardiospheres but transients were generated in cardiospheres following stimulation with KCl or CaCl2, indicating that holo-f-aequorin was functional in these cells. Furthermore, following the addition of exogenous ATP, an inositol trisphosphate receptor (IP3R) agonist, small Ca2+ transients were generated from day 1 onward. That ATP was inducing Ca2+ release from functional IP3Rs was demonstrated by treatment with 2-APB, a known IP3R antagonist. In contrast, following treatment with caffeine, a ryanodine receptor (RyR) agonist, a minimal Ca2+ response was observed at day 8 of differentiation only. Thus, our data indicate that unlike RyRs, IP3Rs are present and continually functional at these early stages of cardiomyocyte differentiation.
  • Article
    Morphometric analysis of human embryonic stem cell-derived ventricular cardiomyocytes : determining the maturation state of a population by quantifying parameters in individual cells
    (Hindawi Publishing Corp, 2015-07) Chan, Harvey Y. S. ; Keung, Wendy ; Li, Ronald A. ; Miller, Andrew L. ; Webb, Sarah E.
    Quantitative methods were established to determine the level of maturation of human embryonic stem cell-derived ventricular cardiomyocytes (hESC-vCMs) that were treated with different metabolic stimulants (i.e., isoproterenol and oleic acid) during early differentiation. Cells were double-immunolabeled with α-actinin and COX IV antibodies, to label the myofibrils and mitochondria, respectively, after which images were acquired via confocal microscopy. In order to determine the extent of differentiation, image analysis protocols were then used to quantify cell shape and area, as well as the degree of myofibrillar organization and intercalation of mitochondria between the myofibrils within the cells. We demonstrated that oleic acid or isoproterenol alone, or a combination of the two, induced a more elongated hESC-vCM phenotype than the untreated controls. In addition, cells treated with isoproterenol alone exhibited a similar level of myofibrillar organization as the controls, but those treated with oleic acid with/without isoproterenol exhibited a more organized (parallel) orientation of myofibrils. The combined isoproterenol/oleic acid treatment also resulted in enhanced intercalation of mitochondria between the myofibrils. We suggest that these quantitative morphometric methods might serve as simple and effective tools that can be utilized in the determination of the level of structural maturation of hESC-vCMs.
  • Preprint
    Molecular insights into the coding region determinant-binding protein-RNA interaction through site-directed mutagenesis in the heterogeneous nuclear ribonucleoprotein-K-homology domains
    ( 2014-11) Barnes, Mark ; van Rensburg, Gerrit ; Li, Wai-Ming ; Mehmood, Kashif ; Mackedenski, Sebastian ; Chan, Ching-Man ; King, Dustin T. ; Miller, Andrew L. ; Lee, Chow H.
    The ability of its four heterogeneous nuclear ribonucleoprotein-K-homology (KH) domains to physically associate with oncogenic mRNAs is a major criterion for the function of Coding Region Determinant-Binding Protein (CRD-BP). However, the particular RNA binding role of each of the KH domains remains largely unresolved. Here, we mutated the first glycine to an aspartate in the universally conserved Glycine-X-X-Glycine (GXXG) motif of the KH domain as an approach to investigate their role. Our results show that mutation of a single GXXG motif generally had no effect on binding but the mutation in any two KH domains, with the exception of the combination of KH3 and KH4 domains, completely abrogated RNA-binding in vitro and significantly retarded granule formation in zebrafish embryos, suggesting that any combination of at least two KH domains cooperate in tandem to bind RNA efficiently. Interestingly, we found that any single point mutation in one of the four KH domains significantly impacted CRD-BP binding to mRNAs in HeLa cells, suggesting that the dynamics of CRD-BP-mRNA interaction vary over time in vivo. Furthermore, our results suggest that different mRNAs bind preferentially to distinct CRD-BP KH domains. The novel insights revealed in this study have important implications on the understanding of the oncogenic mechanism of CRD-BP a well as in the future design of inhibitors against CRDBP function.