Analysis of embryonic development in the unsequenced axolotl: waves of transcriptional upheaval and stability
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ABSTRACT:
ORGANISM(S): Ambystoma mexicanum
PROVIDER: GSE78034 | GEO | 2016/07/12
SECONDARY ACCESSION(S): PRJNA312389
REPOSITORIES: GEO
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Project description:The axolotl (Ambystoma mexicanum) has long been the subject of biological research, primarily owing to its outstanding regenerative capabilities. However, the gene expression programs governing its embryonic development are particularly underexplored, especially when compared to other amphibian model species. Therefore, we performed whole transcriptome polyA+ RNA sequencing experiments on 17 stages of embryonic development. As the axolotl genome is unsequenced and its gene annotation is incomplete, we built de novo transcriptome assemblies for each stage and garnered functional annotation by comparing expressed contigs with known genes in other organisms. In evaluating the number of differentially expressed genes over time, we identify three waves of substantial transcriptome upheaval each followed by a period of relative transcriptome stability. The first wave of upheaval is between the one and two cell stage. We show that the number of differentially expressed genes per unit time is higher between the one and two cell stage than it is across the mid-blastula transition (MBT), the period of zygotic genome activation. We use total RNA sequencing to demonstrate that the vast majority of genes with increasing polyA+ signal between the one and two cell stage result from polyadenylation rather than de novo transcription. The first stable phase begins after the two cell stage and continues until the mid-blastula transition, corresponding with the pre-MBT phase of transcriptional quiescence in amphibian development. Following this is a peak of differential gene expression corresponding with the activation of the zygotic genome and a phase of transcriptomic stability from stages 9-11. We observe a third wave of transcriptomic change between stages 11 and 14, followed by a final stable period. The last two stable phases have not been documented in amphibians previously and correspond to times of major morphogenic change in the axolotl embryo: gastrulation and neurulation. These results yield new insights into global gene expression during early stages of amphibian embryogenesis and will help to further develop the axolotl as a model species for developmental and regenerative biology.
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Project description:The ability to taste is critical for animal nutrition and toxin deterrence. The majority of research on taste bud development and regeneration is in mice, where taste buds are located within specialized papillae on the tongue. However, taste buds in fish and amphibians, such as axolotls (Ambystoma mexicanum), are not housed in papillae, rather they are within the pharyngeal epithelium. This simplified tissue level organization, along with the ability of cultured oropharyngeal explants from early embryos to produce taste buds on the same time-line as embryos, make the axolotl an excellent model to identify molecules specifically involved in taste bud cell differentiation. In this study, we performed de novo transcriptomic analysis on RNA sequences from three different stages of oropharyngeal explants: stages 37/38, 39, and 41. RNA-seq data from 17 total samples representing these stages were pooled to generate de novo assemblie(s) of the transcriptome using a Trinity pipeline. Raw reads and the assembly were uploaded to Mendeley (doi:10.17632/tvxh3jm83m.1). From 27.9Gb of raw sequences, we identified 21,244 transcripts. To our knowledge, this study provides the first published assembly of axolotl oropharyngeal endoderm explants. This RNA-seq data and transcriptome assembly provide information on genes expressed in the oropharyngeal endoderm and will be valuable in the identification of taste bud development genes.
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