The planarian nanos-like gene Smednos is expressed in germline and eye precursor cells during development and regeneration
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Planarians are highly regenerative organisms with the ability to remake all their cell types, including the germ cells. The germ cells have been suggested to arise from totipotent neoblasts through epigenetic mechanisms. Nanos is a zinc-finger protein with a widely conserved role in the maintenance of germ cell identity. In this work, we describe the expression of a planarian nanos-like gene Smednos in two kinds of precursor cells namely, primordial germ cells and eye precursor cells, during both development and regeneration of the planarian Schmidtea mediterranea. In sexual planarians, Smednos is expressed in presumptive male primordial germ cells of embryos from stage 8 of embryogenesis and throughout development of the male gonads and in the female primordial germ cells of the ovary. Thus, upon hatching, juvenile planarians do possess primordial germ cells. In the asexual strain, Smednos is expressed in presumptive male and female primordial germ cells. During regeneration, Smednos expression is maintained in the primordial germ cells, and new clusters of Smednos-positive cells appear in the regenerated tissue. Remarkably, during the final stages of development (stage 8 of embryogenesis) and during regeneration of the planarian eye, Smednos is expressed in cells surrounding the differentiating eye cells, possibly corresponding to eye precursor cells. Our results suggest that similar genetic mechanisms might be used to control the differentiation of precursor cells during development and regeneration in planarians.
KeywordsPlanarian nanos Germ cells Eye Development Regeneration
We would like to thank Dr. S González-Crespo for nanos primers, J González-Linares for initial PCRs with degenerate primers, Dr. H Orii for providing anti-VC-1, Dr. M Riutort for phylogenetic analysis, Dr. J Fernández and J Solana for advices on in situ hybridization on paraffin sections, Dr. R Romero and Dr. J Baguñà for discussions about planarian germ cells, Dr. F Cebrià for critical reading of the manuscript, and Dr. I. Patten for advice on English style in a version of the manuscript. This work was supported by grants BMC2002-03992 and BFU2005-00422 from the Ministerio de Educación y Ciencia, Spain, and grant 2005SGR00769 from AGAUR (Generalitat de Catalunya, Spain). M.H-T received an FPU fellowship from the Ministerio de Educación y Ciencia.
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