Flatworm stem cells and the germ line: Developmental and evolutionary implications of macvasa expression in Macrostomum lignano

Abstract

We have isolated and identified the vasa homologue macvasa, expressed in testes, ovaries, eggs and somatic stem cells of the flatworm Macrostomum lignano. Molecular tools such as in situ hybridization and RNA interference were developed for M. lignano to study gene expression and function. Macvasa expression was followed during postembryonic development, regeneration and in starvation experiments. We were able to follow gonad formation in juveniles and the reformation of gonads from stem cells after amputation by in situ hybridization and a specific Macvasa antibody. Expression of macvasa in the germ cells was highly affected by feeding conditions and correlated with the decrease and regrowth of the gonads. RNA interference showed specific down-regulation of macvasa mRNA and protein. The absence of Macvasa did not influence gonad formation and stem cell proliferation. Our results corroborate the exclusive nature of the flatworm stem cell system but challenge the concept of a solely postembryonic specification of the germ line in Platyhelminthes. We address the transition of somatic stem cells to germ cells and speculate on Macrostomum as a system to unravel the mechanisms of preformation or epigenesis in the evolution of germ line specification from somatic stem cells.

Characterization of the piRNA pathway during development of the sea anemone Nematostella vectensis

“…These genes are also expressed in broad regions at early stages of development in multiple species across animal phylogeny including flatworms, mollusks, annelids and arthropods and involvement of these factors in embryogenesis has been proposed. 38,[43][44][45][46][47][48][49][50] The highly similar expression domains of Nematostella piwi and vasa homologs (Fig. 3) are in line with their clustering in the nCounter analysis (Fig.…”

Molecular and Sub-Cellular Gametogenic Machinery of Stem and Germline Cells Across Metazoa

“…Only one of these homologues was expressed in neoblasts (Shibata et al 1999). Flatworm vasa homologue of Macrostomum lignano was expressed in germ and stem cells (Pfister et al, 2008). Planarian homologues of piwi and pumilio genes were found specifically expressed in a neoblasts (Rossi et al, 2007) and the expression pattern of Piwi protein in planaria Schmidtea mediterranea coincides with the neoblasts (Reddien et al, 2005).…”

“…The chromatoid bodies in planarian neoblasts and germ cells are found near the nuclear envelope, in close proximity to mitochondria as well (Coward, 1974;Hori, 1982;Isaeva et al, 2005;Shibata et al, 1999). Nuage-like structures morphologically different from planarian chromatoid bodies were found in the flatworm Macrostomum lignano (Pfister et al, 2008). The chromatoid bodies in planarian neoblasts decrease in number and size during differentiation of somatic cells from neoblasts and disappear in completely differentiated cells, while in oogenic cells the chromatoid bodies were found during the entire life cycle (Hori, 1982;Shibata et al, 1999).…”

“…Planarian (Plathyhelminthes) neoblasts can differentiate into germ and somatic cells and express vasa, piwi, nanos, pumilio, bruno, tudor homologues (Agata et al, 2006;Pfister et al, 2008;Reddien et al, 2005;Rossi et al, 2007;Shibata et al, 1999Shibata et al, , 2010Solana et al, 2009). In Dugesia japonica two vasa homologues are expressed in the germ cells of the adult gonads.…”

Germ Cell Specification: The Evolution of a Recipe to Make Germ Cells

“…Germ plasm components are believed to act in stem cells to convey longevity and totipotency, similar to the magic substances ambrosia/amrit in Greek or Hindu mythology, which kept the gods immortal. Many components of germ plasm, like Vasa, are also present in multipotent stem cells latworms [29]. Nanos is present in stem cells involved in regeneration in planarians [30].…”