Use of planaria for evaluation of complex mixture toxicity.
Dugesia dorotocephala with several tumor-like growths.
The goal of this research is to develop an invertebrate model for
evaluating the potential of extracts from complex environmental matrices
(derived from known locations of toxicity) for their potential to induce solid
tumors in planaria. Planaria are
flatworms (Platyhelminthes) that were once widely used for toxicity testing but
were largely abandoned as molecular
biology tools became more important in toxicology. Before their decline in
popularity, there were a handful of scattered reports that these simple
animals, unlike other invertebrates, were capable of forming solid tumors when
exposed to human carcinogens. This unusual characteristic is presumably related to their well-known exaggerated
capability of regeneration which in turn is associated with an abundance of stem
cells distributed throughout their somatic tissues. In the mid 1980s, the planaria model of
tumorigenesis was definitively described by researchers at Colorado State
University in a pair of publications in the Journal of Experimental Zoology
(Neoplastic Transformation in the Planarian: I. Carcinogenesis and
Histopathology. 1986 F. Hall, M. Morita
and J. Best. J. Exp. Zool. 240:211-227 and Neoplastic Transformation in the
Planarian: II. Ultrastructure and Malignant Reticuloma. 1986 F. Hall, M. Morita and J. Best. J. Exp.
Zool. 240:229-244.). This work was
followed by that of Dr. David Schaeffer at the University of Illinois School of
Veterinary Medicine. Recently, planaria have returned to the forefront of
biological research due to the discovery of a diploid species (Schmidtea
mediterranea) that
has both sexual and asexual strains and a wide range of molecular tools have
been developed for this species including the mapping of the its genome. Development of an invertebrate assay for
tumorigenesis could provide alternatives to much more costly and time-consuming
rodent models as well as facilitate the identification of genotoxic components
of complex mixtures through bioassay-driven fractionation studies.