Palestrante
Descrição
The homeothermy endothermy feature observed in avian reptiles and mammals might be one of the most important events during vertebrate evolution. The increase of body temperature arouse some genomes changes such as an increase in gene GC content, genome fragmentation into isochores and intron lengthening.(1) The study of introns in several organisms shows a bimodal distribution of length where one of those modes is around a minimal size that is species-specific. Introns that have sizes near this mode are named minimal introns.(2) In fact, in the genome of vertebrates, minimal introns are still present but do not show lengthening in response to temperature increase. In this study, we explored how those minimal introns were influenced by temperature changes through vertebrate evolution. Analysing the GC content of introns in human, we observed that minimal introns are divided into two defined populations of low and high GC% with peaks around 30% and 70% respectively. Long introns, on the other hand, do not show the same bimodal distribution, but a single GC% peak near the overall GC content of the genome. The same analysis was conducted for different vertebrates and showed that organisms displaying low temperatures have the majority of minimal introns in the low GC% population and that increase in body temperature shifts minimal introns into the high GC% population. Indeed, the population of high GC% minimal introns surpasses those of low GC% in mammals and birds. We speculate that minimal introns segregation might be a response to temperature increment. In order to check this hypothesis, we analysed minimal introns from genes enriched in the human testicles where the temperature is around 2 to 5 degrees Celcius below body temperature.(3) We noticed that the proportion of low GC% minimal introns population in testicles increases in relation to the analysis of the entire body. This appears to point out that the shift in GC content is connected to the temperature in which the transcription of the gene occurs. Interesting, the population of genes containing low GC% minimal introns in human is enriched by genes associated with cell cycle, DNA repair and mRNA splicing. Another intriguing observation caused by the bimodal distribution of the GC content of minimal introns is the scarce frequency of introns of intermediate GC content (around 40%). This may suggest that transcription or mRNA processing of these genes must be somehow affected. To better explored this observation, we calculated the percentage of intron retention (PIR) from RNA-Seq data. In this analysis, we noticed greater PIR values for those minimal introns of intermediate content. We speculate that the transition from low to high GC content may be limited by deleterious effects of a high level of intron retention in the intermediate state. In this manner, we hypothesize that some of the minimal introns population that retained low GC content might represent genes associated with essential processes for which production of miss-processed transcripts could impair proper cellular function.
Referências
1 AMIT, M. et al. Differential GC content between exons and introns establishes distinct strategies of splice-site recognition. Cell Reports, v.1, n.5, p.543-556, 2012
2 YU, J. et al. Minimal introns are not “junk. Genome Research, v.12, n.8, p.1185-1189, 2002.
3 MIEUSSET, R.; BUJAN,L. Testicular heating and its possible contributions to male infertility: a review. International Journal of Andrology, v.18, n.4, p. 169-184,1995.
| Subárea | Biofísica |
|---|---|
| Apresentação do trabalho acadêmico para o público geral | Sim |
