Cellular dynamics underlying regeneration of appropriate segment number during axolotl tail regeneration

Abstract

BackgroundSalamanders regenerate their tails after amputation anywhere along their length. How the system faithfully reconstitutes the original number of segments and length is not yet known.MethodsTo gain quantitative insight into how the system regenerates the appropriate length, we amputated tails at 4 or 16 myotomes post-cloaca and measured blastema size, cell cycle kinetics via cumulative Bromodeoxyuridine (BrdU) incorporation and the method of Nowakowski, and myotome differentiation rate.ResultsIn early stages until day 15, blastema cells were all proliferative and divided at the same rate at both amputation levels. A larger blastema was formed in 4th versus 16th myotome amputations indicating a larger founding population. Myotome differentiation started at the same timepoint in the 4th and 16 th level blastemas. The rate of myotome formation was more rapid in 4th myotome blastemas so that by day 21 the residual blastema from the two amputation levels achieved equivalent size. At that time point, only a fraction of blastema cells remain in cycle, with the 4th myotome blastema harboring double the number of cycling cells as the 16th myotome blastema allowing it to grow faster and further reconstitute the larger number of missing myotomes.ConclusionsThese data suggest that there are two separable phases of blastema growth. The first is level-independent, with cells displaying unrestrained proliferation. In the second phase, the level-specific growth is revealed, where differing fractions of cells remain in the cell cycle over time.

Longitudinal 16S rRNA data derived from limb regenerative tissue samples of axolotl Ambystoma mexicanum

“…Of these amphibians, Mexican axolotl ( Ambystoma mexicanum ), a critically endangered species 1 , is one of the few adult animals capable of complete and functional regeneration of missing body parts throughout its life 2 . Axolotl can regenerate their extremities including limbs 3 , tail 4 , brain 5 , spinal cord 6 and internal organs 7 during larval and adult stages. Despite growing publicly available resources for cellular and molecular research on axolotl regeneration 8,9 (e.g.…”

The constrained architecture of mammalian Hox gene clusters

“…Of note, the only known exception thus far is the axolotl, where the HoxA cluster spans more than 1 Mb, mostly due to the high density of repeated elements (24). Interestingly, this neotenic animal develops at a speed globally 3 to 4 times slower than vertebrates, including other amphibians (25,26).…”

Tail regeneration and other phenomena of wound healing and tissue restoration in lizards

“…Multi-tissue tail, including spinal cord Blastema-mediated cell proliferation, axonogenesis, angiogenesis, chondrogenesis, myogenesis Egar and Singer, 1972;Iten and Bryant, 1976;O'Hara et al, 1992;Schnapp et al, 2005;Vincent et al, 2015 Possibly most species Adult and juvenile Multi-tissue limbs, including muscle and skeleton Blastema-mediated cell proliferation, axonogenesis, angiogenesis, chondrogenesis, myogenesis Scadding, 1977;Gardiner and Bryant, 2007;Kragl et al, 2009;Garza-Garcia et al, 2010 Axolotl (Ambystoma mexicanum) Adult and juvenile Heart (ventricle) De-differentiation, organ-wide and blastema-mediated cell proliferation, myogenesis, angiogenesis Flink, 2002;Vargas-Gonzalez et al, 2005;Cano-Martínez et al, 2010 Eastern spotted newt (Notopthalmus viridescens) Adult Heart (ventricle) De-differentiation, organ-wide and blastema-mediated cell proliferation, myogenesis, angiogenesis Laube et al, 2006;Witman et al, 2011;Mercer et al, 2013 Axolotl (Ambystoma mexicanum)…”