Press Releases
Apr. 20, 2010

Genome analyses unveiling the evolution toward female and male

— Discovery of the female-limited “HIBOTAN” genes in the origin of the femaleness —
Presenters
  • Hisayoshi Nozaki (Dept. of Biological Science, Graduate School of Science, Univ. of Tokyo)
  • Ichiro Nishii (Nara Women’s University)
  • Takashi Hamaji (Dept. of Biological Science, Graduate School of Science, Univ. of Tokyo)
  • Patrick Ferris (The Salk Institute, U.S.A.; formerly Graduate School of Science, Univ. of Tokyo)
  • James Umen (The Salk Institute, U.S.A)

Abstract

How femaleness and maleness evolved from the primitive isogamous organisms (with equal-sized gametes) has been unclear based on the gene and genome information. Here we determined the genome sequence of the mating locus (MT) of the sexually dimorphic multicellular green alga Volvox carteri that exhibits the production of eggs and sperm. The Volvox MT shows 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 identified five new female-limited “HIBOTAN” genes and ten male-limited genes (including “OTOKOGI” gene) from the MT of V. carteri. These suggest that origins of femaleness and maleness are principally affected by the evolution of the MT that has undergone a remarkable expansion, gain of new male- and female-limited genes and divergence of genes shared by both female and male. Our finding of the female-limited “HIBOTAN” genes is remarkable in considering that female is not a direct descendant of the basic isogametic mating type.

Paper information

Ferris, P., B. J.S.C. Olson, P. L. De Hoff, S. Douglass, D. C. Diaz-Cano, S. Prochnik, S. Geng, R. Rai, J. Grimwood, J. Schmutz, I. Nishii, T. Hamaji, H. Nozaki, M. Pellegrini and J. G. Umen (2010). Evolution of an expanded sex-determining locus in Volvox. Science Vol. 328. no. 5976, pp. 351-354, DOI: 10.1126/science.1186222.

Figure 1

Fig 1: Asexual colony of multicellular green alga Volvox carteri, containing 16 daughter colonies. Note gonidia (large reproductive cells) already differentiated within each daughter colony. Photo by Ichiro Nishii.

Figure 2

Fig 2: Sexual rproduction of the multicellular green alga Volvox carteri. Female colonies and male colonies with sperm packets develop in female and male strains, respectively when sexually induced. A. Sperm packet attaching to female colony cotaning many eggs. B. Sperm packet (arrow) dissociating into indovidual sperm that penetrate female colony. C. Sperm. Photos by Hosayoshi Nozaki

Figure 3

Fig 3: Schematic representation of evolution of the colonial volvocalean algae from the unicellular Chlamydomonas-like ancestor. Note that differentiation of small somatic cells and evolutiion from isogamy to oogamy occurred in relation to the increase in colony cell number. Based on our recent phylogenetic analyses of morphological and mltigene sequence data (e.g. Nozaki et al. 2000, Mol. Phylog. Evol.).

Figure 4

Fig 4: Diagram of evolution of oogamy from isogamy and sex-determiming loci in the volvocalean algae. Based on the present data and Nozaki et al. (2006, Curr. Biol.).