Maternal RNA localization during early development of the axolotl

The asymmetric localization of maternal biomolecules is critical for body plan development. One of the most popular model organisms for early embryogenesis studies is Xenopus laevis but there is a lack of information in other animal species. Here, we compare the early development of two amphibian species – the frog X. laevis and the axolotl Ambystoma mexicanum. This study aimed to identify asymmetrically localized RNAs along the animal-vegetal axis during the early development of A. mexicanum. For that purpose, we performed spatial transcriptome-wide analysis, which revealed dynamic changes along the animal-vegetal axis classified into the following categories: relocalization, de novo synthesis and degradation. Surprisingly, our results showed that many of the vegetally localized genes, which are important for germ cell development, are degraded during early development. Furthermore, we assessed the motif presence in UTRs of degraded mRNAs and revealed the enrichment of several motifs in RNAs of germ cell markers. Our results suggest novel reorganization of the transcriptome during embryogenesis of A. mexicanum to converge to the similar developmental pattern as the X. laevis. To assess the alterations of the transcriptome during embryogenesis, TOMOSeq was utilized on fertilized oocytes, 1-cell, 4-cells, 64-cells and 1000-cells. The experiment was performed using biological triplicates with each sample aligned from animal to vegetal regions and sectioned to produce 5 main sections (A to E) with “A” being the extreme animal region and “E” being the extreme vegetal region. The temporal and spatial changes in the transcriptome were then assessed to identify unique changes during the early stages of embryogenesis.