Flatworm asexual multiplication implicates stem cells and regeneration

Abstract

The phenomenon of asexual multiplication is rare in the animal kingdom, but it occurs in all main flatworm taxa. In the present paper, we review data regarding the presence of different forms of asexual multiplication in flatworms and argue that the presence of a population of totipotent or pluripotent stem cells, "neoblasts", is a primitive feature of decisive importance for the developing potential of flatworms. Next we present information on the role of stem cells in fission, head regeneration, and pharynx regeneration of planarians. Furthermore, the tracing of neoblasts in lower flatworms and cestodes is presented, and the results indicating heterogeneity of the neoblast pool are discussed. Finally, the mode by which the neoblasts are stimulated to divide, migrate, and differentiate and the nature of the interactions are discussed. We focus on (i) biogenic amines and neuropeptides, (ii) the role of neuropeptides in the early stage of regeneration, (iii) the evidence for the influences of growth factors and nitric oxide, and (iv) the influence of weak electromagnetic fields. We discuss the pattern in which a gradient system of morphogens and (or) a hierarchical system of inductions is expressed in development.

Hepatic infestation of Echinococcus multilocularis with extension to regional lymph nodes

“…[11] and Mehlhorn et al [13] described filamentous solid cell columns protruding from the germinal layer of the metacestode into adjacent host tissue and assumed that detachment of cells from these structures and their subsequent distribution via the circulation (lymphogenous and/or hematogenous) may play a role in formation of 'metastasis'. A hallmark of flatworms is the regenerative capacity which has been attributed to a population of totipotent stem cells called germinal cells in case of obligatory parasitic groups like E. multilocularis and these cells are regarded to be the only cell type that is mitotically active and, in E. multilocularis, germinal cells are thought to contribute crucially to metacestode growth via fusion with the tegument as well as to metastasis during chronic infection [11,[13][14][15]. Furthermore, evidence has been obtained that post-oncospherical development and differentiation to the metacestode stage in cestodes originates from mitotically active germinal cells that are present in the oncosphere [15].…”

Demography and feeding behavior of Stenostomum leucops (Dugés, 1828)

“…Most studies on flat worms are aimed at regeneration (Reddien and Alvarado, 2004;Cebrià and Newmark, 2005;Bely and Sikes, 2010), senescence (Martinez and Levinton, 1992;Mouton et al, 2009) and stem cells subjects (Reuter and Kreshchenko, 2004). Most turbellarians have neoblasts (Newmark and Alvarado, 2000) which allow them to be good models for this type of research.…”

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

“…Platyhelminthes are, with few exceptions, hermaphroditic (Hyman 1951 ). However, asexual reproduction by fi ssion occurs in some catenulids and macrostomids, and it is quite common among triclads (Hyman 1951 ;Reuter and Kreshchenko 2004 ). As expected, regenerative abilities are less pronounced in taxa containing species with sexual reproduction than in taxa that reproduce asexually, as regeneration is absolutely required for survival of the mother animal during asexual reproduction .…”

“…Some species, such as Microstomum lineare , combine sexual and asexual modes of reproduction. In these fl atworms, a good regenerative capacity is seen during the asexual stage of their life cycle, but this capacity is reduced with the appearance of sexuality (Reuter and Kreshchenko 2004 ).…”

“…Despite this lack of external signs and organ differentiation before fi ssioning, some molecular changes have been described in animals committed to asexual reproduction (Bueno et al 2002 ). Architomy is common in triclads, whereas paratomy is often found in several species of catenulids and macrostomids (Reuter and Kreshchenko 2004 ). After architomic fi ssioning, the tiny body piece that is produced must regenerate a new organism.…”