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Evolution of IESs and scrambling in the actin I gene in hypotrichous ciliates

D J Hogan1, E A Hewitt, K E Orr

  • 1Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-034, USA.

Proceedings of the National Academy of Sciences of the United States of America
|December 14, 2001
PubMed

Insights

Internal eliminated segments (IESs) interrupt genes in ciliates, dividing them into macronuclear destined segments (MDSs). Gene evolution involves IES addition and scrambling, increasing structural complexity over time.

Area of Science:

  • Molecular Biology
  • Evolutionary Genetics
  • Ciliate Genomics

Background:

  • Hypotrichous ciliates possess germ-line micronuclear genes interrupted by internal eliminated segments (IESs).
  • These IESs divide genes into macronuclear destined segments (MDSs) that are processed after cell mating.
  • The micronuclear actin I gene exhibits variations in MDS order due to evolutionary recombination.

Purpose of the Study:

  • To investigate the evolutionary mechanisms driving the structural complexity of micronuclear actin I genes in hypotrichous ciliates.
  • To elucidate the roles of IES addition and MDS scrambling in gene evolution.

Main Methods:

  • Phylogenetic analysis using rDNA sequences to establish relationships among eight hypotrichous species.
  • Comparative analysis of micronuclear actin I gene structures across different species.

Main Results:

  • Early diverging species show IES addition without MDS scrambling in the actin I gene.
  • Later diverging species exhibit both IES addition and MDS scrambling, leading to increased gene complexity.
  • IES insertions occurred progressively, with additional insertions in more recently evolved species.

Conclusions:

  • The evolution of micronuclear actin I genes in hypotrichs is a progressive process involving IES insertions and MDS scrambling.
  • This stepwise addition and recombination of IESs results in genes of increasing structural complexity over evolutionary time.

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