Transcriptomic Plasticity of the Core Hypothalamic Osmoregulatory Control Centre of the Arabian Dromedary Camel

Abstract

To live and thrive in arid environments places enormous evolutionary pressure on processes of water conservation. These are epitomised by the numerous adaptations manifested in those mammals, such as the dromedary camel (Camelus dromedarius), that thrive in the scorching heat of the Arabian deserts. At the level of the kidney, the dromedary produces low volumes of highly concentrated urine, more so when water is scarce, to conserve body water. Two hormones, arginine vasopressin (AVP) and oxytocin (OXT), both produced in the supraoptic nucleus (SON), the core hypothalamic osmoregulatory control centre, are vital for this adaptive process. Studies on rats have shown that the rat SON transcriptome undergoes dramatic function-related plasticity during water deprivation, but the mechanisms that enable the camel SON to cope with osmotic stress remained unknown. Thus, to investigate the central control of water homeostasis in the camel, RNAseq transcriptome studies were performed on the SON under control (water ad libitum, n=5), dehydrated (DH: dehydration for 20 days, n=5) and rehydrated (RH: dehydration followed by water ad libitum for three days, n=5) conditions. The multiplex fluorescence in situ hybridization (RNAscope) was first used to build three dimensional models of the camel SON based on the expression of the AVP and OXT mRNAs in order to facilitate sampling. The transcriptomes of the SON under control and DH conditions were then compared and identified genes that change in expression due to hyperosmotic stress. The expression of these genes were quantified by qRT-PCR under control, DH and RH conditions. By comparing the camel and rat datasets, common elements of the DH transcriptomic response network have been identified, as well as elements that appear to be unique to the dromedary camel and that may be essential for adaptations necessary for life in the desert