If the neotenic Mexican axolotl, Ambystoma mexicanum is given thyroid hormone or TSH.
Answers
The axolotl is unusual in that it doesn't undergo a metamorphosis and develop lungs. Instead, axolotls hatch from eggs into a juvenile form that grows to become its adult form. Axolotls keep their gills and permanently reside in the water.Apr 2, 2019
Common Names: Axolotl, Mexican salamander, Mexican walking fish
Scientific Name: Ambystoma mexicanum
Conservation Status: Critically Endangered
The Mexican axolotl (Ambystoma mexicanum) is an ... and the role of thyroid hormone in development and evolution. ... Given the importance of thyroid hormone feedback on HPT axis ...The Mexican axolotl (Ambystoma mexicanum) is an important model organism in biomedical research. Much current attention is focused on the axolotl's amazing ability to regenerate tissues and whole organs after injury. However, not forgotten is the axolotl's equally amazing ability to thwart aspects of tissue maturation and retain juvenile morphology into the adult phase of life. Unlike close tiger salamander relatives that undergo a thyroid hormone regulated metamorphosis, the axolotl does not typically undergo a metamorphosis. Instead, the axolotl exhibits a paedomorphic mode of development that enables a completely aquatic life cycle. The evolution of paedomorphosis allowed axolotls to exploit relatively permanent habitats in Mexico, and preadapted axolotls for domestication and laboratory study. In this perspective, we first introduce the axolotl and the various meanings of paedomorphosis, and then stress the need to move beyond endocrinology-guided approaches to understand the axolotl's hypothyroid state. With the recent completion of the axolotl genome assembly and established methods to manipulate gene functions, the axolotl is poised to provide new insights about paedomorphosis and the role of thyroid hormone in development and evolution.Mexican axolotls (Ambystoma mexicanum) have been studied in laboratories throughout the world for over two-hundred years (1). Beginning in the early nineteenth century, French expeditions to Mexico brought preserved adult specimens back to Paris for examination by curators at the Jardin des Plantes. Esteemed zoologist Georges Cuvier originally classified these specimens as larvae of an unknown species (Paedomorphosis is a somewhat confusing term because it has been used to explain variation at evolutionary, ecological, and genetic levels of inquiry.Endocrinology of Paedomorphosis
Over the last century, axolotl paedomorphosis has been the subject of a number of physiological studies. We refer readers to two relatively recent reviews of the literature pertaining to the endocrinology of axolotl paedomorphosis (7, 19). Our goal here is to briefly review salient features of axolotl hypothyroidism to provide context for identifying mechanisms that may regulate metamorphic timing and expression of paedomorphosis.
Genetics of Paedomorphosis
As was introduced above, genetic studies are beginning to resolve the location of genetic factors within the axolotl genome that regulate metamorphic timing and expression of paedomorphosis. Primarily, axolotls have been crossed to metamorphic tiger salamanders to segregate alleles that affect paedomorph expression and metamorphic timing, however we highlight a study (17) that crossed the axolotl to a paedomorphic relative to identify genetic factors associated with T4 sensitivity. In that study, second generation A. mexicanum/A. andersoni paedomorphic hybrids were created and administered 50 mM T4 at the time
Conclusion
Although the Mexican axolotl has been studied for over 150 years, the mechanism associated with its unique paedomorphic mode of development remains unknown. Endocrinology studies have established the importance of thyroid hormone in regulating amphibian metamorphosis