Exploring Complex Phenotypes: Information Storage in the Planarian Flatworm
Development, carcinogenesis, and regeneration all hinge on an organisms ability to store and distribute information regarding developmental history, current and “target” morphologies, or environmental context. Understanding how organisms induce, orchestrate, and terminate regenerative processes, how patterning decisions are extrapolated during development, and how environment informs phenotype, will be vital for furthering biomedical research and therapy development. To interrogate complex phenotypes in planarian, I have undertaken two projects. The first investigates physiological adaptation in response to an environmental insult, and the second explores the encoding of shape morphology within a bioelectric context. In response to dilute (1mM) concentrations of barium chloride (BaCl2), a potassium channel blocker, planarian degenerate their anterior tissues, and, when left to regenerate in the barium chloride solution, regenerate heads that are insensitive to the toxic environmental conditions. Investigating this phenomenon could lead to a deeper understanding of differential drug responses, phenotypic accommodation in the face of environmental challenge, and plasticity of morphology in the absence of trauma. Transient blockage of gap junction channels with octanol (8-OH) leads to the regeneration of worms that have head shapes that are different from the original worm, and morphologically similar to other species of planarian. Wild type D. dorotacephala planaria display a very pointed head shape, with two elongated oracles at the plane of the eyes. 8-OH treated fragments regenerate both head and tail correctly, but in many cases, head shape is drastically altered. Fragments subjected to the same treatment scheme regenerate entirely rounded heads (like the planarian S. mediterranea), heads with thick necks and cat-like oracles (like the planarian P. felina), or heads that are very triangular (like the planarian D. japonica). The alteration of morphology by a pharmacological approach, without any change in the genome, is an entirely novel addition to the study of morphogenesis, which has thus far been dominated by molecular approaches. By disturbing bioelectric signaling mechanisms at work during regenerative processes, we can induce changes that are far more elaborate than a binary loss of primary axis polarity. These findings bring us closer to understanding the means by which organisms organize into “target” morphology.