The first report on circulating microRNAs at Pre- and Post-metamorphic stages of axolotls.

MicroRNAs (miRNAs) are endogenously coded small RNAs, implicated in post-transcriptional gene regulation by targeting messenger RNAs (mRNAs). Circulating miRNAs are cell-free molecules, found in body fluids, such as blood and saliva, and emerged recently as potential diagnostic biomarkers. Functions of circulating miRNAs and their roles in target tissues have been extensively investigated in mammals, and the reports on circulating miRNAs in non-mammalian clades are largely missing. Salamanders display remarkable regenerative potential, and the Mexican axolotl (Ambystoma mexicanum), a critically endangered aquatic salamander, has emerged as a powerful model organism in regeneration and developmental studies. This study aimed to explore the circulating miRNA signature in axolotl blood plasma. Small RNA sequencing on plasma samples revealed 16 differentially expressed (DE) circulating miRNAs between neotenic and metamorphic stages out of identified 164 conserved miRNAs. Bioinformatics predictions provided functional annotation of detected miRNAs for both stages and enrichment of DE miRNAs in cancer-related and developmental pathways was notable. Comparison with previous reports on axolotl miRNAs unraveled common and unique members of the axolotl circulating miRNome. Overall, this work provides novel insights into non-mammalian aspects of circulating miRNA biology and expands the multi-omics toolkit for this versatile model organism.

Detailed tail proteomic analysis of axolotl (Ambystoma mexicanum) using an mRNA-seq reference database.

Salamander axolotl has been emerging as an important model for stem cell research due to its powerful regenerative capacity. Several advantages, such as the high capability of advanced tissue, organ, and appendages regeneration, promote axolotl as an ideal model system to extend our current understanding on the mechanisms of regeneration. Acknowledging the common molecular pathways between amphibians and mammals, there is a great potential to translate the messages from axolotl research to mammalian studies. However, the utilization of axolotl is hindered due to the lack of reference databases of genomic, transcriptomic, and proteomic data. Here, we introduce the proteome analysis of the axolotl tail section searched against an mRNA-seq database. We translated axolotl mRNA sequences to protein sequences and annotated these to process the LC-MS/MS data and identified 1001 nonredundant proteins. Functional classification of identified proteins was performed by gene ontology searches. The presence of some of the identified proteins was validated by in situ antibody labeling. Furthermore, we have analyzed the proteome expressional changes postamputation at three time points to evaluate the underlying mechanisms of the regeneration process. Taken together, this work expands the proteomics data of axolotl to contribute to its establishment as a fully utilized model.