Response of optic gland pathways to thermal stress in the reproductive phase of female Octopus maya

The octopus optic glands are the source of multiple signalling molecules that control the transitions through different physiological stages, such as maturation, ageing and death. This study focused on the role of the optic glands during the reproductive phase of Octopus maya, investigating the molecular mechanisms that prevent reproduction at elevated temperatures. RNA sequencing was used to analyse and compare optic gland transcriptomic profiles of female O. maya before, during and after egg-laying under optimal and thermal stress (elevated temperature) conditions. Each stage showed well-defined transcriptomic patterns, and all were strongly affected by thermal stress. At optimal temperature, the optic glands contribute importantly to regulating the energetic balance, as suggested by the expression of genes that modulate the metabolic rate, arterial blood pressure and the management of ATP sources in response to food deprivation. At elevated temperatures, the optic glands of mated females (before egg-laying) showed upregulation of genes encoding neuropeptides (FMRF-amide, APGW-amide, PRQFV-amide, FCAP, buccalin and myomodulin) and the dopamine beta-hydroxylase gene. During egg-laying at elevated temperatures, the neuropeptide receptor capaR and the sex peptide receptor were upregulated whereas homologs of fetuin-B and oviduct-specific glycoprotein genes, crucial for fertilization, were downregulated. These changes in optic gland gene expression in O. maya may be the basis for the high-temperature inhibition of egg-laying, previously observed from this octopus species. Furthermore, after egg-laying, during egg incubation thermal stress affected the expression of genes involved in steroid and thyroid hormone biosynthesis and in inflammatory and apoptotic pathways.