title: Mitotic chromosome size scaling in Xenopus.
abstract: As rapid divisions without growth generate progressively smaller cells within an embryo, mitotic chromosomes must also decrease in size to permit their proper segregation, but this scaling phenomenon is poorly understood. We demonstrated previously that nuclear and spindle size scale between egg extracts of the related frog species Xenopus tropicalis and Xenopus laevis, but show here that dimensions of isolated mitotic sperm chromosomes do not differ. This is consistent with the hypothesis that chromosome scaling does not occur in early embryonic development when cell and spindles sizes are large and anaphase B segregates chromosomes long distances. To recapitulate chromosome scaling during development, we combined nuclei isolated from different stage Xenopus laevis embryos with metaphase-arrested egg extracts. Mitotic chromosomes derived from nuclei of cleaving embryos through the blastula stage were similar in size to replicated sperm chromosomes, but decreased in area approximately 50% by the neurula stage, reproducing the trend in size changes observed in fixed embryos. Allowing G2 nuclei to swell in interphase prior to mitotic condensation did not increase mitotic chromosome size, but progression through a full cell cycle in egg extract did, suggesting that epigenetic mechanisms determining chromosome size can be altered during DNA replication. Comparison of different sized mitotic chromosomes assembled in vitro provides a tractable system to elucidate underlying molecular mechanisms.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA, USA.
authors.forename: Esther K
authors.initials: EK
authors.lastname: Kieserman
authors.forename: Rebecca
authors.initials: R
authors.lastname: Heald
mesh_terms: D000818:Animals; D002453:Cell Cycle; D002467:Cell Nucleus / Q000648:ultrastructure; D048429:Cell Size; D020090:Chromosome Segregation / Q000502:physiology; D002875:Chromosomes / Q000502:physiology / Q000648:ultrastructure*; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000648:ultrastructure; D008941:Spindle Apparatus / Q000502:physiology*; D014981:Xenopus / Q000196:embryology; D014982:Xenopus laevis
references.citation: Genes Dev. 2011 Jul 15;25(14):1464-9
references.pmid: 21715560
references.citation: J Cell Biol. 2005 Jun 20;169(6):859-69
references.pmid: 15967810
references.citation: Cell Cycle. 2009 Apr 15;8(8):1115-21
references.pmid: 19282671
references.citation: Science. 2011 Apr 22;332(6028):465-8
references.pmid: 21393511
references.citation: Methods Mol Biol. 2006;322:459-74
references.pmid: 16739744
references.citation: Curr Opin Cell Biol. 2006 Dec;18(6):632-8
references.pmid: 17046228
references.citation: J Cell Biol. 2007 Mar 12;176(6):765-70
references.pmid: 17339377
references.citation: Chromosome Res. 2009;17(2):131-44
references.pmid: 19308696
references.citation: Nat Cell Biol. 2007 Jul;9(7):822-31
references.pmid: 17558394
references.citation: Chromosoma. 1993 Jul;102(7):478-83
references.pmid: 8375216
references.citation: J Cell Biol. 1998 Sep 7;142(5):1159-66
references.pmid: 9732278
references.citation: Anal Biochem. 2004 Jan 1;324(1):39-44
references.pmid: 14654043
references.citation: Methods Cell Biol. 1991;36:581-605
references.pmid: 1839804
references.citation: Proc Natl Acad Sci U S A. 2009 Jan 20;106(3):749-54
references.pmid: 19131518
references.citation: Chromosome Res. 2010 Jun;18(4):431-9
references.pmid: 20390340
references.citation: J Cell Sci. 2006 Dec 15;119(Pt 24):5057-66
references.pmid: 17158911
references.citation: Cell. 1997 Feb 21;88(4):515-20
references.pmid: 9038342
references.citation: J Biol Chem. 2009 Jan 9;284(2):1064-74
references.pmid: 18957438
references.citation: Cell Cycle. 2010 Aug 15;9(16):3243-55
references.pmid: 20703077
references.citation: J Cell Sci. 2007 Apr 1;120(Pt 7):1245-55
references.pmid: 17356064
references.citation: Curr Biol. 2008 Aug 26;18(16):1256-61
references.pmid: 18718761
references.citation: Cell. 2010 Oct 15;143(2):288-98
references.pmid: 20946986
references.citation: Cell Cycle. 2010 Jun 1;9(11):2065-70
references.pmid: 20495382
references.citation: Can J Genet Cytol. 1986 Aug;28(4):536-9
references.pmid: 3530406
references.citation: Cytogenet Genome Res. 2002;98(1):101-7
references.pmid: 12584450
references.citation: Curr Biol. 2010 Jun 8;20(11):1048-52
references.pmid: 20471264