The amazing and anomalous axolotls as scientific models

Abstract

Ambystoma mexicanum (axolotl) embryos and juveniles have been used as model organisms for developmental and regenerative research for many years. This neotenic aquatic species maintains the unique capability to regenerate most, if not all, of its tissues well into adulthood. With large externally developing embryos, axolotls were one of the original model species for developmental biology. However, increased access to, and use of, organisms with sequenced and annotated genomes, such as Xenopus laevis and tropicalis and Danio rerio, reduced the prevalence of axolotls as models in embryogenesis studies. Recent sequencing of the large axolotl genome opens up new possibilities for defining the recipes that drive the formation and regeneration of tissues like the limbs and spinal cord. However, to decode the large A. mexicanum genome will take a herculean effort, community resources, and the development of novel techniques. Here, we provide an updated axolotl‐staging chart ranging from one‐cell stage to immature adult, paired with a perspective on both historical and current axolotl research that spans from their use in early studies of development to the recent cutting‐edge research, employment of transgenesis, high‐resolution imaging, and study of mechanisms deployed in regeneration.

Developmental staging and future research directions of the model marine tubewormHydroides elegans

“…Despite its utility as a developmental model [12][13][14][15][16][17] , characterizations of the growth and development of Hydroides remains fragmented, and the community has yet to establish a standardized staging scheme that spans the entirety of development. Staging schemes have become a commonplace tool across all major developmental model systems including frog 18 , chick 19 , zebrafish 20 , and sea urchin [21][22][23] , and are fundamental for the development and utility of non-traditional model organisms [24][25][26][27][28] . Staging schemes provide a unified narrative of development under tightly controlled environmental conditions, and offer accuracy and consistency in describing the progression of key developmental events.…”

Salamander models for elucidating mechanisms of developmental biology, evolution, and regeneration: Part two

“…Several articles and reviews also built on scientific understanding of development in salamander models as it relates to animal age, size, and life cycle transitions. A wonderful review article from Adamson et al 12 brings us through the past, present, and future of biological research on the axolotl model. Additionally, two studies using this model leveraged the response of axolotls to exogenous l ‐thyroxine stimulation, whereby the typically aquatic axolotls transition to a metamorphic form.…”