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, 328 (5976), 351-4

Evolution of an Expanded Sex-Determining Locus in Volvox

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Evolution of an Expanded Sex-Determining Locus in Volvox

Patrick Ferris et al. Science.

Erratum in

  • Science. 2010 Sep 17;329(5998):1467

Abstract

Although dimorphic sexes have evolved repeatedly in multicellular eukaryotes, their origins are unknown. The mating locus (MT) of the sexually dimorphic multicellular green alga Volvox carteri specifies the production of eggs and sperm and has undergone a remarkable expansion and divergence relative to MT from Chlamydomonas reinhardtii, which is a closely related unicellular species that has equal-sized gametes. Transcriptome analysis revealed a rewired gametic expression program for Volvox MT genes relative to Chlamydomonas and identified multiple gender-specific and sex-regulated transcripts. The retinoblastoma tumor suppressor homolog MAT3 is a Volvox MT gene that displays sexually regulated alternative splicing and evidence of gender-specific selection, both of which are indicative of cooption into the sexual cycle. Thus, sex-determining loci affect the evolution of both sex-related and non-sex-related genes.

Figures

Figure 1
Figure 1
Expansion of Volvox MT and sex-regulated gene expression. (A) Schematic of Chlamydomonas mating locus with rearranged domains in light blue or pink. MT+ limited genes are shaded red if unique or orange if they have an autosomal copy. MT− limited genes are shaded blue. Flanking and shared genes are shaded black and gray respectively. Synteny is indicated by gray shading. (B) Schematic of Volvox MT scaled as in (A). Boxed genes were used for mapping. The broken segment represents a transposon repeat region containing copies of VPS53. (C) Expression heat maps of Volvox MT genes. Left panel, female/male expression ratio; middle panel, total expression; right panel, sexual induction (Sex) or repression (Veg). Diagonal hatch, insufficient data.
Figure 2
Figure 2
Divergence of MT genes. (A,B) dN and dS for shared Volvox (A) or Chlamydomonas (B) genes within MT (orange shading) or flanking MT. Asterisks mark saturated dS values. (C,D) Maximum likelihood phylogenies for PRP4 (C) and MT gene PRX1 (D). Red/blue signify female/male strains and clades.
Figure 3
Figure 3
Gender-specific divergence and splicing of MAT3. Schematic of MAT3 from Chlamydomonas (top), Volvox female (middle) and Volvox male (bottom). Volvox exons are numbered.

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