Expression of vasa(vas)-related genes in germline cells and totipotent somatic stem cells of planarians

Planarians are known for their strong regenerative ability. This ability ha s been considered to reside in the totipotent somatic stem cell called the "neoblast." Neoblasts contain a unique cytoplasmic structure called the "ch romatoid body," which has similar characteristics to the germline granules of germline cells of other animals. The chromatoid bodies decrease in numbe r and size during cytodifferentiation and disappear in completely different iated cells during regeneration. However, germ cells maintain the chromatoi d body during their differentiation from neoblasts. These observations sugg est that the chromatoid body is concerned with the totipotency of cells. To understand the molecular nature of the chromatoid body in the neoblast, we focused on vasa (vas)-related genes, since VAS and VAS-related proteins ar e known to be components of the germline granules in Drosophila and Caenorh abditis elegans. By PCR, two vas-related genes (Dugesia japonica vasa-like gene, DjvlgA and DjvlgB) were isolated, and they were shown to be expressed in germ cells. Interestingly, DjvlgA was also expressed in a number of som atic cells in the mesenchymal space. In regenerating planarians, accumulati on of DivlgA-expressing cells was observed in both the blastema and the bla stema-proximal region. In X-ray-irradiated planarians, which had lost regen erative capacity, the number of DjvlgA-expressing cells decreased drastical ly. These results suggest that the product of DivlgA may be a component of the chromatoid body and may be involved in the totipotency of the neoblast. (C) 1999 Academic Press.