# Transcriptomic Responses of the Heart and Brain to Anoxia in the Western Painted Turtle

## TL;DR

This study explores how the heart and brain of western painted turtles respond at the gene level to anoxia, revealing patterns that help them survive without oxygen for long periods.

## Contribution

The paper provides new insights into the transcriptomic mechanisms enabling anoxia tolerance in turtles, focusing on gene expression patterns in the heart and brain.

## Key findings

- The ventricle showed a significant decrease in total RNA content compared to the telencephalon under anoxia.
- Most genes affected by anoxia were immediate early genes and transcription factors, suggesting a role in metabolic and transcriptional arrest.
- Gene expression changes in the telencephalon correlated with predicted metabolic costs, favoring shorter genes with fewer exons.

## Abstract

Painted turtles are the most anoxia-tolerant tetrapods known, capable of surviving without oxygen for more than four months at 3°C and 30 hours at 20°C. To investigate the transcriptomic basis of this ability, we used RNA-seq to quantify mRNA expression in the painted turtle ventricle and telencephalon after 24 hours of anoxia at 19°C. Reads were obtained from 22,174 different genes, 13,236 of which were compared statistically between treatments for each tissue. Total tissue RNA contents decreased by 16% in telencephalon and 53% in ventricle. The telencephalon and ventricle showed ≥ 2x expression (increased expression) in 19 and 23 genes, respectively, while only four genes in ventricle showed ≤ 0.5x changes (decreased expression). When treatment effects were compared between anoxic and normoxic conditions in the two tissue types, 31 genes were increased (≥ 2x change) and 2 were decreased (≤ 0.5x change). Most of the effected genes were immediate early genes and transcription factors that regulate cellular growth and development; changes that would seem to promote transcriptional, translational, and metabolic arrest. No genes related to ion channels, synaptic transmission, cardiac contractility or excitation-contraction coupling changed. The generalized expression pattern in telencephalon and across tissues, but not in ventricle, correlated with the predicted metabolic cost of transcription, with the shortest genes and those with the fewest exons showing the largest increases in expression.