HerrickLab

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HerrickLab
Jon Seger Kevin Williams Tom
Doak David Witherspoon

• I. Understanding de novo telomere formation in
  Oxytricha macronuclear development by analyses of
  cis-acting sequences
• II. Developmental transcription of transposons of
  Oxytricha trifallax old data in the light of
  ciliate RNAi phenomena

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Oxytricha trifallax SEM

• A ciliated protozoan.
• All ciliates are covered with cilia.
• in this hypotrichous ciliate, bundles of cilia
  are used to walk on the substrate, in fresh water.

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DAPI-stained vegetative cell

• All ciliates also havea specialized gene
  expression organelle, the macronucleus MAC.
• We study
• development of the somatic macronucleus
• from a copy of the germline micronucleus Mi
• after sexual conjugation.
• Cilia, and this nuclear dimorphismthe two major
  taxonomic characters that define the clade,
  ciliates

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Baldauf tree
Baldauf et al. 2000. Science 290972.
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Re Baldauf tree

• Ciliates diverged from other eukaryotes maybe
  1.1-1.2 BYA.

• Features in common between ciliates and us are
  especially rich to study in ciliates, because
  shared features have been conserved and are
  probably important.
• We will consider ciliate developmental chromosome
  breakage and de novo telomere formation.
• This process occurs massively during
  macronuclear development.
• Telomeres end bodies cap the ends of
  eukaryotic chromosomes and make them inert.
• The failure of telomere function appears to be
  basic to metazoan cell senescence and oncogenic
  initiation.

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Nuclear dimorphismRelationship between nuclei

• Clonal proliferation by binary fission

• Conjugation
• Meiosis 2N gt 1N
• Gametic nuclei exchange
• Zygosis 2N1N2N
• Replace old MAC with new MAC
• Destroy old MAC
• Duplicate zygotic 2N nucleus
• One copy is new MIC
• Edit other copy gtnew MAC
• New MAC gt mRNAs
• MAC development takes 3 days. A rich program.

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Macronuclear developmentfrom a mitotic sister of
the new MIC

• Macronuclear development
• from a mitotic sister of the new MIC

Polytene chromatids

• Telomeres
• 40,000,000/MAC
• Rich biochem source of
• telomere DNA
• telomere proteins
• First studied in Oxytricha Tetrahymena
• Created de novo in a few hours, by telomerase
• Exconjugants a rich source
• Large RiboNucleoProtein
• A reverse transcriptase protein
• Carries its own RNA template
• Polymerizes GT-rich repeats onto 3OH ends

Chromatid breakageandconcertedde novo
telomere formation
20,000 genes

• Replication leaves 5termini
• Recessed
• 5 phosphorylated important for TAS mapping

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Conjugation and Macronuclear Development
MIC
MAC
Cell Pairing
Meiosis and Nuclear Exchange
Nuclear Fusion and Duplication of the Zygotic
Nucleus
Macronuclear Development and Nuclear Degeneration
Polytenization
Chromatid breakage
De novo telomere formation
Modified from Larry Klobutcher Carolyn
Jahn Ann. Review Microbiology, 2002
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4 TAS regions of the 81 MAC locus
Four Telomere Addition Site regions of the 81 MAC
family locus
CR-L
CR-R

• Model for generation of family by alternative
  processing of polytene chromatids.

• Three chromosomes, comprised from three
  segments
• Each segment carries a protein coding gene.
• All chromosomes share a common region (CR).
• MAC III CRtelomeres
• MACs I II
• have arms appended to their CRs.
• have two genes each gene-sized NOT!

• Complete cutting of all chromatids at the arm
  ends

• but incomplete cutting at the CR borders,

• de novo telomere formation on MAC ends,

• generates MACs IIIs, IIs, Is

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