Experimentally induced metamorphosis in highly regenerative axolotl (ambystoma mexicanum) under constant diet restructures microbiota

Abstract

Axolotl (Ambystoma mexicanum) is a critically endangered salamander species and a model organism for regenerative and developmental biology. Despite life-long neoteny in nature and in captive-bred colonies, metamorphosis of these animals can be experimentally induced by administering Thyroid hormones (THs). However, microbiological consequences of this experimental procedure, such as host microbiota response, remain largely unknown. Here, we systematically compared host bacterial microbiota associated with skin, stomach, gut tissues and fecal samples, between neotenic and metamorphic axolotls based on 16S rRNA gene sequences. Our results show that distinct bacterial communities inhabit individual organs of axolotl and undergo substantial restructuring through metamorphosis. Skin microbiota among others, shifted sharply, as highlighted by a major transition from Firmicutes-enriched to Proteobacteria-enriched relative abundance and precipitously decreased diversity. Fecal microbiota of neotenic and metamorphic axolotl shared relatively higher similarity, suggesting that diet continues to shape microbiota despite fundamental transformations in the host digestive organs. We also reproduced the previous finding on reduction in regenerative capacity in limbs of axolotl following metamorphosis, highlighting the need to investigate whether shifts in microbiota is causally linked to regenerative capacity of axolotl. The initial results on axolotl microbiota provide novel insights into microbiological aspects of axolotl metamorphosis and will establish a baseline for future in-depth studies.

Comparison of Gene Expression During Early Phases of Limb Regeneration Between Regeneration-permissive Neotenic and Regeneration-deficient Metamorphic Axolotl

“…For a better understanding of such morphological changes in axolotl, a comprehensive histological atlas of the morphological alterations taking place within tissues and organs throughout metamorphosis has been described (Demircan et al 2016) . In addition to morphological and histological changes, metamorphosis of axolotl brings about a sharp reduction in regeneration rate, and leads to carpal and digit malformations (Monaghan et al 2014;Demircan et al 2018). Obtained results from axolotl are well aligned with the previous studies on Xenopus laevis which demonstrate dramatic restriction in regenerative capacity with metamorphosis (Mescher and Neff 2006;Godwin and Rosenthal 2014) .Furthermore, studies on regenerationdeficient animal models suggest that there is a correlation between cellular changes during ontogenic development and progressive loss of regenerative ability (Seifert et al 2012;Lee-Liu et al 2018) .…”

“…While animals such as zebrafish, lizards, and urodeles are able to regenerate some of their extremities even after reaching adulthood, frogs and mammals lose this ability prior to metamorphosis (Seifert et al 2012) or during post embryonic development. Although neotenic axolotls have an exceptional regenerative capacity, previous studies (Demircan et al 2018(Demircan et al , 2019 have shown defective and infidel limb regeneration of axolotl after metamorphosis. Since findings of published studies underlined an apparent delay in phases of regeneration for metamorphic animals, in this study we aimed to reveal the gene expression pattern at early phases of regeneration (day0,1,4 and 7) for both neotenic and metamorphic axolotls at the protein level.…”

“…No. T2376) as described in (Demircan et al 2018). Briefly, T4 solution was prepared by dissolving L-thyroxine in Holtfreter's solution equivalent to 50 nM final concentration.…”

“…Until very recently (Nowoshilow et al 2018), obtaining a reference genome for axolotl has been a great challenge due to insufficient read-length, highly repetitive composition of DNA and incompetent methodologies for genome assembly. Recent efforts to elucidate microbial diversity of Axolotl during metamorphosis (Demircan et al 2018) and limb regeneration (Demircan et al 2019) has expanded the reference datasets. But still, much of the established knowledge on axolotl limb regeneration has relied on and is mostly still contingent upon, microarray such as (Knapp et al 2013;Voss et al 2015) and high-throughput technologies including transcriptomics (e.g.…”

Integrative Analysis of Axolotl Gene Expression Data From Regenerative and Wound Healing Limb Tissues

“…It's been suggested that, unlike the amniote vertebrate, the successive regenerative capacity of axolotls may be driven by a weak inflammatory response due to their simpler adaptive immune system [1,10]. In response to experimental induction of metamorphosis via thyroid hormone administration, diminished regenerative power of axolotls is observed for some body parts such as appendages [11,12], while such regenerative potential seems to be unobstructed for other parts of the body [1,13].…”