The mechanism of mimecan transcription induced by glucocorticoid in pituitary corticotroph cells

Blubber proteome response to repeated ACTH administration in a wild marine mammal

While the response to acute stress is adaptive in nature, repeated or chronic stress can impact an animal's fitness by depleting its energy stores and suppressing immune function and reproduction. This can be especially deleterious for species that rely on energy reserves to fuel key life history stages (e.g. reproduction), already experience physiological extremes (e.g. fasting), and/or have undergone significant population declines, such as many marine mammals. However, identifying chronically stressed individuals is difficult due to the practical challenges to sample collection from large aquatic animals and a paucity of information on downstream consequences of the stress response. We previously simulated repeated stress by ACTH administration in a model marine mammal, the northern elephant seal, and showed that changes in blubber gene expression, but not circulating cortisol levels, could distinguish between single and repeated responses to ACTH. Here, we profiled changes in the proteome of the same blubber cell population and identified a set of differentially expressed proteins that included extracellular matrix components, heat shock and mitochondrial proteins, metabolic enzymes, and metabolite transporters. Differentially expressed proteins and genes shared similar functions that suggest that repeated corticosteroid elevation may affect blubber tissue proteostasis, mitochondrial activity, adipogenesis, and metabolism in marine mammals. For marine mammal species from which blubber biopsies, but not blood can be obtained by remote sampling, measurement of abundance of such proteins may serve as a novel method for identifying chronically stressed animals.

Transcriptional dynamics of a conserved gene expression network associated with craniofacial divergence in Arctic charr

Background

Understanding the molecular basis of craniofacial variation can provide insights into key developmental mechanisms of adaptive changes and their role in trophic divergence and speciation. Arctic charr (Salvelinus alpinus) is a polymorphic fish species, and, in Lake Thingvallavatn in Iceland, four sympatric morphs have evolved distinct craniofacial structures. We conducted a gene expression study on candidates from a conserved gene coexpression network, focusing on the development of craniofacial elements in embryos of two contrasting Arctic charr morphotypes (benthic and limnetic).

Results

Four Arctic charr morphs were studied: one limnetic and two benthic morphs from Lake Thingvallavatn and a limnetic reference aquaculture morph. The presence of morphological differences at developmental stages before the onset of feeding was verified by morphometric analysis. Following up on our previous findings that Mmp2 and Sparc were differentially expressed between morphotypes, we identified a network of genes with conserved coexpression across diverse vertebrate species. A comparative expression study of candidates from this network in developing heads of the four Arctic charr morphs verified the coexpression relationship of these genes and revealed distinct transcriptional dynamics strongly correlated with contrasting craniofacial morphologies (benthic versus limnetic). A literature review and Gene Ontology analysis indicated that a significant proportion of the network genes play a role in extracellular matrix organization and skeletogenesis, and motif enrichment analysis of conserved noncoding regions of network candidates predicted a handful of transcription factors, including Ap1 and Ets2, as potential regulators of the gene network. The expression of Ets2 itself was also found to associate with network gene expression. Genes linked to glucocorticoid signalling were also studied, as both Mmp2 and Sparc are responsive to this pathway. Among those, several transcriptional targets and upstream regulators showed differential expression between the contrasting morphotypes. Interestingly, although selected network genes showed overlapping expression patterns in situ and no morph differences, Timp2 expression patterns differed between morphs.

Conclusion

Our comparative study of transcriptional dynamics in divergent craniofacial morphologies of Arctic charr revealed a conserved network of coexpressed genes sharing functional roles in structural morphogenesis. We also implicate transcriptional regulators of the network as targets for future functional studies.

Electronic supplementary material

The online version of this article (doi:10.1186/2041-9139-5-40) contains supplementary material, which is available to authorized users.