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Transcriptomic analysis of the developing neocortex of the Australian marsupial fat-tailed dunnart (Sminthopsis crassicaudata)

ABSTRACT: The six-layered neocortex is exclusively present in mammals and mediates sensory-motor and higher-order functions. Key differences in this structure and its connections exist between the main mammalian groups: eutherians and marsupials, however, the molecular changes that underlie these known morphological differences remain unknown. This question is particularly difficult to address because small and transient changes in gene expression during development may be crucial to brain formation, which would not be detectable in adult transcriptomic analyses. To address this question of the developmental origin of changes in the evolution of the mammalian neocortex, we performed transcriptomic analysis on the marsupial fat-tailed dunnart (Sminthopsis crassicaudata) at postnatal ages P12 and P20 corresponding to the generation of infragranular (layers 5/6) and supragranular (layers 2/3) neurons, respectively. We assembled a de novo transcriptome of the neocortex of fat-tailed dunnarts using RNA-seq data from all samples, then differential gene expression analysis performed across the two ages. Additional cross-species analysis was performed against existing mouse neocortical datasets in the NCBI Sequence Read Archive at equivalent developmental ages embryonic (E) day 12.5 (SRR1509162, SRR1509163, SRR1509164) and E16 (SRR5755669, SRR5755670, SRR5755671, SRR5755672). We identified 12,632 protein-coding transcripts orthologous to mouse RNA reference sequences (Refseq) in the dunnart neocortical transciptome. The results also revealed divergences in gene sets known to be enriched in different neuronal populations, revealing a more advanced stage of maturation in the marsupial neocortex at the period of infragranular birth compared to the eutherian mouse.

ORGANISM(S): Sminthopsis crassicaudata

PROVIDER: GSE161274 | GEO | 2022/01/17

REPOSITORIES: GEO

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Project description:Production of milk is a key characteristic of mammals, but the features of lactation vary greatly between monotreme, marsupial and eutherian mammals. Marsupials have a short gestation followed by a long lactation period, and the milk constituents vary greatly across lactation to meet the changing needs of the developing young. Marsupials are born immunologically naïve and rely on their mother’s milk for immunological protection. The koala is an iconic Australian species and many are increasingly threatened by disease. Here we use a mammary transcriptome, two milk proteomes and the koala genome to comprehensively characterise the protein components of the milk of the koala, with a key focus on the immune constituents during early and late lactation. We have characterised the most abundant peptides present in milk, examined key differences between early and late lactation, and determined differences between the koala and other marsupial species. The most abundant proteins were well characterised mammalian and marsupial-specific milk proteins including β-lactoglobulin, lactotransferrin, caseins and early lactation protein. We have generated a list of 851 immune compounds identified in the mammary transcriptome and examined a range of immune proteins that were highly abundant in the milk proteomes. These include immunoglobulins, complement components and immune receptors. A host of antimicrobial peptides were identified including cathelicidins, lysozyme, WAP four-disulfide core domain protein 2, Mucin-1 and Peptidoglycan recognition protein. We discovered that the previously described marsupial milk protein Very Early Lactation Protein is an ortholog of the eutherian gene Glycam1 (PP3) and likely has an antimicrobial role in milk. We also identified highly abundant koala endogenous retrovirus sequences in the mammary and milk transcriptome and proteomes, identifying a potential route for retroviral transmission from mother to young. Identifying and characterising the immune components of milk is key to understanding how marsupial young are protected throughout lactation and the novel immune compounds identified may have applications in clinical research.

Dataset Information

Transcriptomic analysis of the developing neocortex of the Australian marsupial fat-tailed dunnart (Sminthopsis crassicaudata)

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