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DNA damage in sea stars

In contrast to most vertebrates, some invertebrates, such as the sea star Asterias rubens, undergo regeneration of lost body parts. Some sea star species can regrow the rest of their bodies from a single arm, while others need at least part of the central disc to be attached to the arm.  The regeneration of a sea star’s arm, depending on species, can take several months or years.

The current thinking in the field of Asterias rubens regeneration suggests that differentiated cells are the main source for regenerating arms in sea stars, but there is little information regarding the origin and identity of these cells.

The aim of this study was to define the sources of cells taking part in regenerative processes.  This required the researchers to look at a variety of organs within the sea star, and investigate a range of biological markers, including DNA damage (tested by the comet assay). 

The researchers believed that cells contributing to the new arm likely originate from progenitors, rather than differentiated cells. The biological markers for proliferating cells and parameters indicating cell ageing which were measured in this investigation included: levels of DNA damage, pigment, and lipofuscin contents as well as telomere length and telomerase activity. 

The comet assay was used to detect single- and double-stranded DNA damage in nuclei from coelomic epithelia cells in regenerating and intact arms of the same sea star.  SYBR Gold was used to stain DNA and the comets were visualized and scored using a fluorescence microscope equipped with a CCD camera and the image analysis program Comet Assay IV from Perceptive Instruments.  For each sample, 100–150 comets were scored. Median and mean relative tail intensity, collected using the Comet Assay Spreadsheet Generator (Perceptive Instruments) were used to represent the DNA damage level of the populations in each sample

The comet assay data, together with data from the other biological parameters tested, showed that several organs, which were distant to the regenerating arm, responded by proliferation.  This is the first study showing that cells of mixed origin may be recruited to aid regeneration from distant sources in a sea star.   Data on growth rate during arm regeneration further indicated that regeneration is at the expense of whole animal growth.

Case study based on:
Possibility of Mixed Progenitor Cells in Sea Star Arm Regeneration J. Exp. Zool., 314B: 457–468. Hernroth, B., Farahani, F., Brunborg, G., Dupont, S., Dejmek, A. and Nilsson Sköld, H. (2010),

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