Stem cell proliferation during in vitro development of the model cestode Mesocestoides corti from larva to adult worm

Uriel Koziol,Estela Castillo,Mónica Marín,Alejandra Kun,María F Domínguez

doi:10.1186/1742-9994-7-22

Abstract

BackgroundIn free-living flatworms somatic differentiated cells do not divide, and a separate population of stem cells (called neoblasts) is responsible for cell proliferation and renewal. In cestodes, there is evidence that similar mechanisms of cell renewal exist.ResultsIn this work, we have characterized proliferative cells during the development of the model cestode Mesocestoides corti from larva (tetrathyridium) to young segmented worm. This was done by two complementary strategies with congruent results: characterizing cells in S phase and their progeny by incorporation of 5-bromo-2'-deoxyuridine, and characterizing cells in M phase by arresting mitotic cells with colchicine and studying their morphology and distribution. Proliferative cells are localized only in the inner parenchyma, particularly in close proximity to the inner muscle layer, but not in the cortical parenchyma nor in the sub-tegumental tissue. After proliferation some of these cells migrate to the outer regions were they differentiate. In the larvae, proliferative cells are more abundant in the anterior regions (scolex and neck), and their number diminishes in an antero-posterior way. During the development of adult segments periodic accumulation of proliferative cells are observed, including a central mass of cells that constitutes the genital primordium, which grows at least in part due to in situ proliferation. In later segments, the inner cells of genital primordia cease to proliferate and adopt a compact distribution, and proliferative cells are also found in the testes primordia.ConclusionsProliferative cells have a characteristic localization and morphology throughout development from larva to adult of Mesocestoides corti, which is similar, and probably evolutionary conserved, to that described in other model cestodes. The characteristics of proliferative cells suggest that these consist of undifferentiated stem cells.

Highlights

In free-living flatworms somatic differentiated cells do not divide, and a separate population of stem cells is responsible for cell proliferation and renewal
Description of early proglottid formation in M. corti Strobilar development of M. corti has been described both in vivo and in vitro [25,26,34], but the first stages of development of the genital primordia have not been characterized in detail
Experimental amputation of the scolex and apical massif followed by BrdU labeling further confirms this suggestion, since it demonstrates that proliferating cells from the medullary parenchyma of the body can be the source of cells in the sub-tegumental region

Summary

Introduction

In free-living flatworms somatic differentiated cells do not divide, and a separate population of stem cells (called neoblasts) is responsible for cell proliferation and renewal. In the parasitic clade Neodermata, which includes the well known classes Cestoda, Monogenea and Trematoda, there is evidence that similar mechanisms of cell renewal exist [2] This has been studied mostly in cestodes, in which the functional equivalents of neoblasts are usually referred to as germinative cells. Germinative cells in the plerocercoid larva and adult of D. dendriticum and other Diphyllobothrium species are absent in the outer regions of the cortical parenchyma and sub-tegumental tissue, and are localized mainly in the inner regions of cortical parenchyma and in the medullary parenchyma. They are especially abundant in close proximity to the inner muscle layer. Ultrastructural studies demonstrate the abundance of free ribosomes and the absence or paucity of endoplasmic reticulum and Golgi apparatus [9,18]

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