title: Vertically- and horizontally-transmitted memories - the fading boundaries between regeneration and inheritance in planaria.
abstract: The Weismann barrier postulates that genetic information passes only from the germline to the soma and not in reverse, thus providing an obstacle to the inheritance of acquired traits. Certain organisms such as planaria - flatworms that can reproduce through asymmetric fission - avoid the limitations of this barrier, thus blurring the distinction between the processes of inheritance and development. In this paper, we re-evaluate canonical ideas about the interaction between developmental, genetic and evolutionary processes through the lens of planaria. Biased distribution of epigenetic effects in asymmetrically produced parts of a regenerating organism could increase variation and therefore affect the species' evolution. The maintenance and fixing of somatic experiences, encoded via stable biochemical or physiological states, may contribute to evolutionary processes in the absence of classically defined generations. We discuss different mechanisms that could induce asymmetry between the two organisms that eventually develop from the regenerating parts, including one particularly fascinating source - the potential capacity of the brain to produce long-lasting epigenetic changes.
authors: Department of Neurobiology, Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel neuhofmo@gmail.com michael.levin@tufts.edu odedrechavi@gmail.com.
authors: Moran
authors: M
authors: Neuhof
authors: Allen Discovery Center, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155, USA neuhofmo@gmail.com michael.levin@tufts.edu odedrechavi@gmail.com.
authors: Michael
authors: M
authors: Levin
authors: Department of Neurobiology, Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel Allen Discovery Center, Tufts University, 200 Boston Avenue, Suite 4600, Medford, MA 02155, USA Sagol School of Neuroscience, Tel Aviv University, Tel Aviv 69978, Israel neuhofmo@gmail.com michael.levin@tufts.edu odedrechavi@gmail.com.
authors: Oded
authors: O
authors: Rechavi
keywords: Chromatin; Epigenetics; Evolution; Generations; Inheritance; Memory; Planaria; Regeneration; Small RNAs; Transgenerational