The unique stem cell system of the immortal larva of the human parasite Echinococcus multilocularis

Abstract

BackgroundIt is believed that in tapeworms a separate population of undifferentiated cells, the germinative cells, is the only source of cell proliferation throughout the life cycle (similar to the neoblasts of free living flatworms). In Echinococcus multilocularis, the metacestode larval stage has a unique development, growing continuously like a mass of vesicles that infiltrate the tissues of the intermediate host, generating multiple protoscoleces by asexual budding. This unique proliferation potential indicates the existence of stem cells that are totipotent and have the ability for extensive self-renewal.ResultsWe show that only the germinative cells proliferate in the larval vesicles and in primary cell cultures that undergo complete vesicle regeneration, by using a combination of morphological criteria and by developing molecular markers of differentiated cell types. The germinative cells are homogeneous in morphology but heterogeneous at the molecular level, since only sub-populations express homologs of the post-transcriptional regulators nanos and argonaute. Important differences are observed between the expression patterns of selected neoblast marker genes of other flatworms and the E. multilocularis germinative cells, including widespread expression in E. multilocularis of some genes that are neoblast-specific in planarians. Hydroxyurea treatment results in the depletion of germinative cells in larval vesicles, and after recovery following hydroxyurea treatment, surviving proliferating cells grow as patches that suggest extensive self-renewal potential for individual germinative cells.ConclusionsIn E. multilocularis metacestodes, the germinative cells are the only proliferating cells, presumably driving the continuous growth of the larval vesicles. However, the existence of sub-populations of the germinative cells is strongly supported by our data. Although the germinative cells are very similar to the neoblasts of other flatworms in function and in undifferentiated morphology, their unique gene expression pattern and the evolutionary loss of conserved stem cells regulators suggest that important differences in their physiology exist, which could be related to the unique biology of E. multilocularis larvae.

Echinococcus as a model system: biology and epidemiology

“…These provided a 173 means to maintain the parasite virtually indefinitely in vivo by 174 serial passage (e.g., Thompson, 1976;Whitfield and Evans, 1983; 175 Kamiya et al, 1985 (Smyth and Davies, 1974a (reviewed in Smyth and Davies, 1974a;Howell and Smyth, 194 1995 (Smyth and Davies, 1975;Smyth, 1979;197 (Smyth, 1982;Smyth and 208 Davies, 1974a;Thompson, 1988, 2012;Lymbery 209 et al, 1989;Howell and Smyth, 1995 (Esch and Smyth, 1976;Osuna-Carrillo and Mascaró-Lazcano, 214 1982), as well as Mesocestoides corti (Barrett et al, 1982; 215 Thompson et al, 1982 Echinococcus (Smyth, 1969 Thompson, 1995 andParkinson et al, 2012) 262 but how they fit together in a control network has yet to be deter- (2014) (Howell and Smyth, 1995). metacestode (Smyth, 1969;Gustafsson, 1976;Thompson et al, 290 1990; Thompson, 1995;Koziol et al, 2014). The undifferentiated (Gustafsson, 1976;Galindo et al, 2003).…”

“…The undifferentiated (Gustafsson, 1976;Galindo et al, 2003). They have considerable 299 proliferative potential Mehlhorn et al, 1983; 300 Galindo et al, 2003;Martínez et al, 2005), and are the only prolif-301 erating cells in Echinococcus (Koziol et al, 2014). This is particularly neous morphogenesis (Smyth, 1969 (Smyth, 1964;Smyth et al, 1969;Thompson et al, 1979; 340 Thompson and Eckert, 1983;Fig.…”

Regeneration and Growth as Modes of Adult Development: The Platyhelminthes as a Case Study

“…In cestodes, systems have been developed for the short-term culture of neoblast populations from asexually multiplying larval stages (Brehm 2010 ). Despite some similarities, the germinative cells do not contain chromatoid bodies and they do not express vasa and piwi gene orthologs, suggesting fundamental differences between these and other neoblast cell populations Koziol et al 2014 ). In Taenia solium , there is a germinative region posterior to the apex of the scolex, the neck, in which stem cells proliferate continuously, differentiate into all cell types, and migrate to the tegument (Merchant et al 1997 ).…”

Radiotherapy of osseous echinococcosis: where is the evidence?

“…26 In vitro studies on E. granulosus protoscoleces showed that radiation with up to 300 Gy did not affect their infectivity for hamsters or puppies. 27 However, doses of 300-600 Gy reduced the infectivity of protoscoleces and stunted the consecutive development of the metacestode in mice.…”