Publications by authors named "Evan M Smoak"

9 Publications

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Centromere inheritance through the germline.

Chromosoma 2017 Oct 8;126(5):595-604. Epub 2017 Aug 8.

Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, PA, 19104, USA.

The centromere directs chromosome segregation and genetic inheritance but is not itself heritable in a canonical, DNA-based manner. In most species, centromeres are epigenetically defined by the presence of a histone H3 variant centromere protein A (CENP-A), independent of underlying DNA sequence. Therefore, centromere inheritance depends on maintaining the CENP-A nucleosome mark across generations. Experiments in cycling somatic cells have led to a model in which centromere identity is maintained by a cell cycle-coupled CENP-A chromatin assembly pathway. However, the processes of animal gametogenesis pose unique challenges to centromere inheritance because of the extended cell cycle arrest and the massive genome reorganization in the female and male germline, respectively. Here, we review our current understanding of germline centromere inheritance and highlight outstanding questions.
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http://dx.doi.org/10.1007/s00412-017-0640-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5693723PMC
October 2017

Identification and characterization of Aurora kinase B and C variants associated with maternal aneuploidy.

Mol Hum Reprod 2017 06;23(6):406-416

Department of Genetics, Rutgers, The State University of New Jersey, 145 Bevier Rd. Piscataway, NJ 08854, USA.

Study Question: Are single nucleotide variants (SNVs) in Aurora kinases B and C (AURKB, AURKC) associated with risk of aneuploid conception?

Summary Answer: Two SNVs were found in patients with extreme aneuploid concepti rates with respect to their age; one variant, AURKC p.I79V, is benign, while another, AURKB p.L39P, is a potential gain-of-function mutant with increased efficiency in promoting chromosome alignment.

What Is Known Already: Maternal age does not always predict aneuploidy risk, and rare gene variants can be drivers of disease. The AURKB and AURKC regulate chromosome segregation, and are associated with reproductive impairments in mouse and human.

Study Design, Size, Duration: An extreme phenotype sample selection scheme was performed for variant discovery. Ninety-six DNA samples were from young patients with higher than average embryonic aneuploidy rates and an additional 96 DNA samples were from older patients with lower than average aneuploidy rates.

Participants/materials, Setting, Methods: Using the192 DNA samples, the coding regions of AURKB and AURKC were sequenced using next generation sequencing. To assess biological significance, we expressed complementary RNA encoding the human variants in mouse oocytes. Assays such as determining subcellular localization and assessing catalytic activity were performed to determine alterations in protein function during meiosis.

Main Results And The Role Of Chance: Ten SNVs were identified using three independent variant-calling methods. Two of the SNVs (AURKB p.L39P and AURKC p.I79V) were non-synonymous and identified by at least two variant-identification methods. The variant encoding AURKC p.I79V, identified in a young woman with a higher than average rate of aneuploid embryos, showed wild-type localization pattern and catalytic activity. On the other hand, the variant encoding AURKB p.L39P, identified in an older woman with lower than average rates of aneuploid embryos, increased the protein's ability to regulate alignment of chromosomes at the metaphase plate. These experiments were repeated three independent times using 2-3 mice for each trial.

Large Scale Data: N/A.

Limitations, Reasons For Caution: Biological significance of the human variants was assessed in an in vitro mouse oocyte model where the variants are over-expressed. Therefore, the human protein may not function identically to the mouse homolog, or the same in mouse oocytes as in human oocytes. Furthermore, supraphysiological expression levels may not accurately reflect endogenous activity. Moreover, the evaluated variants were identified in one patient each, and no trial linking the SNV to pregnancy outcomes was conducted. Finally, the patient aneuploidy rates were established by performing comprehensive chromosome screening in blastocysts, and because of the link between female gamete aneuploidy giving rise to aneuploid embryos, we evaluate the role of the variants in Meiosis I. However, it is possible that the chromosome segregation mistake arose during Meiosis II or in mitosis in the preimplantation embryo. Their implications in human female meiosis and aneuploidy risk remain to be determined.

Wider Implications Of The Findings: The data provide evidence that gene variants exist in reproductively younger or advanced aged women that are predictive of the risk of producing aneuploid concepti in humans. Furthermore, a single amino acid in the N-terminus of AURKB is a gain-of-function mutant that could be protective of euploidy.

Study Funding/competing Interests: This work was supported by a Research Grant from the American Society of Reproductive Medicine and support from the Charles and Johanna Busch Memorial Fund at Rutgers, the State University of NJ to K.S. and the Foundation for Embryonic Competence, Inc to N.T. The authors declare no conflicts of interest.
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http://dx.doi.org/10.1093/molehr/gax018DOI Listing
June 2017

Long-Term Retention of CENP-A Nucleosomes in Mammalian Oocytes Underpins Transgenerational Inheritance of Centromere Identity.

Curr Biol 2016 04 31;26(8):1110-6. Epub 2016 Mar 31.

Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Graduate Program in Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address:

Centromeres control genetic inheritance by directing chromosome segregation but are not genetically encoded themselves. Rather, centromeres are defined by nucleosomes containing CENP-A, a histone H3 variant [1]. In cycling somatic cells, centromere identity is maintained by an established cell-cycle-coupled CENP-A chromatin assembly pathway, but how centromeres are inherited through the mammalian female germline is unclear because of the long (months to decades) prophase I arrest. Here we show that mouse oocytes retain the pool of CENP-A nucleosomes assembled before birth, and that this pool is sufficient for centromere function, fertility, and genome transmission to embryos. Indeed, oocytes lack any measurable CENP-A nucleosome assembly through the entire fertile lifespan of the female (>1 year). Thus, the remarkable stability of CENP-A nucleosomes confers transgenerational centromere identity in mammals.
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http://dx.doi.org/10.1016/j.cub.2016.02.061DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4846481PMC
April 2016

Chromosomes. CENP-C reshapes and stabilizes CENP-A nucleosomes at the centromere.

Science 2015 May;348(6235):699-703

Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Graduate Program in Cell and Molecular Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Graduate Program in Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.

Inheritance of each chromosome depends upon its centromere. A histone H3 variant, centromere protein A (CENP-A), is essential for epigenetically marking centromere location. We find that CENP-A is quantitatively retained at the centromere upon which it is initially assembled. CENP-C binds to CENP-A nucleosomes and is a prime candidate to stabilize centromeric chromatin. Using purified components, we find that CENP-C reshapes the octameric histone core of CENP-A nucleosomes, rigidifies both surface and internal nucleosome structure, and modulates terminal DNA to match the loose wrap that is found on native CENP-A nucleosomes at functional human centromeres. Thus, CENP-C affects nucleosome shape and dynamics in a manner analogous to allosteric regulation of enzymes. CENP-C depletion leads to rapid removal of CENP-A from centromeres, indicating their collaboration in maintaining centromere identity.
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http://dx.doi.org/10.1126/science.1259308DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4610723PMC
May 2015

Feedback control in sensing chromosome biorientation by the Aurora B kinase.

Curr Biol 2011 Jul 30;21(13):1158-65. Epub 2011 Jun 30.

Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6059, USA.

Maintenance of genome stability during cell division depends on establishing correct attachments between chromosomes and spindle microtubules. Correct, bioriented attachments are stabilized, whereas incorrect attachments are selectively destabilized. This process relies largely on increased phosphorylation of kinetochore substrates of Aurora B kinase at misaligned versus aligned kinetochores. Current models explain this differential phosphorylation by spatial changes in the position of substrates relative to a constant pool of kinase at the inner centromere. However, these models are based on studies in aneuploid cells. We show that normal diploid cells have a more robust error-correction machinery. Aurora B is enriched at misaligned centromeres in these cells, and the dynamic range of Aurora B substrate phosphorylation at misaligned versus aligned kinetochores is increased. These findings indicate that in addition to Aurora B regulating kinetochore-microtubule binding, the kinetochore also controls Aurora B recruitment to the inner centromere. We show that this recruitment depends on both activity of Plk1, a kinetochore-localized kinase, and activity of Aurora B itself. Our results suggest a feedback mechanism in which Aurora B both regulates and is regulated by chromosome attachment to the spindle, which amplifies the differential phosphorylation of kinetochore substrates and increases the efficiency of error correction.
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http://dx.doi.org/10.1016/j.cub.2011.06.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3156581PMC
July 2011

Interactions of amyloid Aβ(1-42) peptide with self-assembled peptide nanospheres.

J Pept Sci 2011 Jan 2;17(1):14-23. Epub 2010 Sep 2.

Department of Chemistry, Fordham University, 441 East Fordham Road, Bronx, NY 10458, USA.

In this work we have probed the interactions of the amyloid Aβ(1-42) peptide with self-assembled nanospheres. The nanospheres were formed by self-assembly of a newly developed bolaamphiphile bis(N-alpha-amido-methionine)-1,8 octane dicarboxylate under aqueous conditions. It was found that the interactions of the Aβ(1-42) peptide with the nanospheres were concentration as well as pH dependent and the peptide largely adopts a random coil structure upon interacting with the nanospheres. Further, upon incorporation with the nanospheres, we observed a relative diminution in the aggregation of Aβ(1-42) at low concentrations of Aβ(1-42). The interactions between the nanospheres and the Aβ(1-42) peptide were investigated by atomic force microscopy, transmission electron microscopy, circular dichroism, FTIR and fluorescence spectroscopy, and the degree of fibrillation in the presence and absence of nanospheres was monitored by the Thioflavine T assay. We believe that the outcome from this work will help further elucidate the binding properties of Aβ peptide as well as designing nanostructures as templates for further investigating the nucleation and fibrillation process of Aβ-like peptides.
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http://dx.doi.org/10.1002/psc.1284DOI Listing
January 2011

Interactions of zeatin with gold ions and biomimetic formation of gold complexes and nanoparticles.

Colloids Surf B Biointerfaces 2010 Jul 25;78(2):250-8. Epub 2010 Mar 25.

Department of Chemistry, Fordham University, 441, East Fordham Road, Bronx, NY 10458, USA.

We report here a simple one-pot synthesis for the preparation of gold nanoparticles biomimetically using zeatin nanostructures. Zeatin, a plant phytohormone was self-assembled into nanospheres. Those nanospheres transformed into nanoribbons over a period of time upon formation of zeatin-gold (III) complexes in the presence of hydrogen tetrachloroaurate. Further, upon heating, gold nanoparticles were formed due to mineralization in the presence of zeatin nanofibers. The effect of pH on the self-assembly of zeatin and the formation of gold nanoparticles, was investigated. We also compared the preparation of gold nanoparticles in the presence of zeatin nanoribbons, using a known reducing agent such as hydrazine, which resulted in loss of morphology control and alignment of the gold nanoparticles. Thus zeatin nanoribbons act as templates which allow for size as well as alignment control for the gold nanoparticles. The materials obtained were analyzed using FTIR, absorbance spectroscopy as well as by transmission electron microscopy, EDX, SEM and AFM. The method involved here is a mild, green-synthetic process, which could be used for facile preparation of morphology controlled gold nanoparticles and may open up new avenues for device fabrications for a wide range of applications, particularly in optoelectronics and sensors.
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http://dx.doi.org/10.1016/j.colsurfb.2010.03.010DOI Listing
July 2010

Self-assembled nanofibers from leucine derived amphiphiles as nanoreactors for growth of ZnO nanoparticles.

Chem Commun (Camb) 2010 Mar 12;46(10):1757-9. Epub 2010 Jan 12.

Department of Chemistry, Fordham University, 441 East Fordham Road, Bronx, New York, USA.

We report a new method for the green synthesis of ZnO nanoparticles. A new leucine-based diamine amphiphile was synthesized and self-assembled, which in the presence of Zn(2+) ions assembled into nanofibers, that efficiently formed ZnO nanoparticles upon heating in the presence of Zn(CH(3)COO)(2). Further, these ZnO nanoparticles functioned as efficient photocatalysts.
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http://dx.doi.org/10.1039/b921254jDOI Listing
March 2010

Self-assembly of gibberellic amide assemblies and their applications in the growth and fabrication of ordered gold nanoparticles.

Nanotechnology 2010 Jan 3;21(2):025603. Epub 2009 Dec 3.

Department of Chemistry, Fordham University, Bronx, NY 10458, USA.

Gibberellins are a group of naturally occurring diterpenoid based phytohormones that play a vital role in plant growth and development. In this work, we have studied the self-assembly of gibberellic acid, a phytohormone, which belongs to the family of gibberellins, and designed amide derivatives of gibberellic acid (GA(3)) for the facile, green synthesis of gold nanoparticles. It was found that the derivatives self-assembled into nanofibers and nanoribbons in aqueous solutions at varying pH. Further, upon incubation with tetrachloroaurate, the self-assembled GA(3)-amide derivatives efficiently nucleated and formed gold nanoparticles when heated to 60 degrees C. Energy dispersive x-ray spectroscopy, transmission electron microscopy and scanning electron microscopy analyses revealed that uniform coatings of gold nanoparticles in the 10-20 nm range were obtained at low pH on the nanowire surfaces without the assistance of additional reducing agents. This simple method for the development of morphology controlled gold nanoparticles using a plant hormone derivative opens doors for a new class of plant biomaterials which can efficiently yield gold nanoparticles in an environmentally friendly manner. The gold encrusted nanowires formed using biomimetic methods may lead on to the formation of conductive nanowires, which may be useful for a wide range of applications such as in optoelectronics and sensors. Further, the spontaneous formation of highly organized nanostructures obtained from plant phytohormone derivatives such as gibberellic acid is of particular interest as it might help in further understanding the supramolecular assembly mechanism of more highly organized biological structures.
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http://dx.doi.org/10.1088/0957-4484/21/2/025603DOI Listing
January 2010
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