Size regulation of dorsal root ganglia (DRG) in developing axolotls with a deficiency or oversupply of neural crest material
Final Report Abstract
How animals adjust the size of their organs is a fundamental, enduring question in biology. Here we manipulate the amount of neural crest (NC) precursors for the dorsal root ganglia (DRG) in axolotl. We produce embryos with an under- or over-supply of premigratory NC in order to find out if DRG can regulate their sizes. Axolotl embryos are perfectly suitable for this research. They are optimal for microsurgical manipulations and tissue repair and, in contrast to most other vertebrates, possess a single neural crest string on top of the neural tube whose cells can migrate to either side of the embryo. We show that size compensation of dorsal root ganglia in axolotl occurs in 2 cm juveniles (upreglation) after undersupply of NC and in 5 cm juveniles (downregulation) after oversupply of NC. The size of DRG seems to be regulated via local mechanisms at the DRG site and not via systemic repair such as adaptations of premigratory NC, although ipsi- and contralateral NC migration occurs. Compensatory size increase is controlled mainly via cell division of a DRG precursor pool rather than by DRG neurons or glial cells. Compensatory size decrease is regulated by apoptosis and reduction of proliferation of DRG cells. Our results show that in the model system of the axolotl mechanisms for adjusting tissue sizes occur long after embryonic development is over. This may help to explain principles for regulating cell growth and homeostasis.
