A transcriptomic scan for potential candidate genes involved in osmoregulation in an obligate freshwater palaemonid prawn (Macrobrachium australiense)

Abstract

BackgroundUnderstanding the genomic basis of osmoregulation (candidate genes and/or molecular mechanisms controlling the phenotype) addresses one of the fundamental questions in evolutionary ecology. Species distributions and adaptive radiations are thought to be controlled by environmental salinity levels, and efficient osmoregulatory (ionic balance) ability is the main mechanism to overcome the problems related to environmental salinity gradients.MethodsTo better understand how osmoregulatory performance in freshwater (FW) crustaceans allow individuals to acclimate and adapt to raised salinity conditions, here we (i), reviewed the literature on genes that have been identified to be associated with osmoregulation in FW crustaceans, and (ii), performed a transcriptomic analysis using cDNA libraries developed from mRNA isolated from three important osmoregulatory tissues (gill, antennal gland, hepatopancreas) and total mRNA from post larvae taken from the freshwater prawn, Macrobrachium australiense using Illumina deep sequencing technology. This species was targeted because it can complete its life cycle totally in freshwater but, like many Macrobrachium sp., can also tolerate brackish water conditions and hence should have genes associated with tolerance of both FW and saline conditions.ResultsWe obtained between 55.4 and 65.2 million Illumina read pairs from four cDNA libraries. Overall, paired end sequences assembled into a total of 125,196 non-redundant contigs (≥200 bp) with an N50 length of 2,282 bp and an average contig length of 968 bp. Transcriptomic analysis of M. australiense identified 32 different gene families that were potentially involved with osmoregulatory capacity. A total of 32,597 transcripts were specified with gene ontology (GO) terms identified on the basis of GO categories. Abundance estimation of expressed genes based on TPM (transcript per million) ≥20 showed 1625 transcripts commonly expressed in all four libraries. Among the top 10 genes expressed in four tissue libraries associated with osmoregulation, arginine kinase and Na+/K+- ATPase showed the highest transcript copy number with 7098 and 660, respectively in gill which is considered to be the most important organ involved in osmoregulation.DiscussionThe current study provides the first broad transcriptome from M. australiense using next generation sequencing and identifies potential candidate genes involved in salinity tolerance and osmoregulation that can provide a foundation for investigating osmoregulatory capacity in a wide variety of freshwater crustaceans.

Characterization and expression profiles of aquaporins (AQPs) 1a and 3a in mud loach Misgurnus mizolepis after experimental challenges

“…In freshwater prawn Macrobrachium rosenbergii, change in salinity has showed a direct or indirect effect on the respiratory metabolism, mortality, growth, and even immune response later (Cheng and Chen 2000;Moshtaghi et al 2016). To date, extensive studies have been conducted on a number of fish species to investigate tissuespecific functional roles of AQPs under different salinity environments (Cutler and Cramb 2000;Watanabe et al 2005;Giffard-Mena et al 2007;Kim et al 2010;Choi et al 2013).…”

Understanding the molecular basis of adaptation to freshwater environments by prawns in the genus Macrobrachium

“…Invasion of freshwater can involve a multiplicity of complex adaptive responses including physiological, biochemical, mechanical, molecular and diverse environmental (phenotypic) traits (Wray, 2013;Moshtaghi et al, 2016). It is presumed that adaptations are a response to specific environmental conditions and are propagated by evolutionary forces.…”

“…Thus, prolonged however, crustacean osmoregulation predominantly involves ion balance via active uptake or secretion, as well as maintaining composition and concentration of hemolymph and urine (Barman et al, 2012;McNamara and Faria, 2012). It has been observed that freshwater crustaceans typically expend more energy for osmoregulation compared with comparable marine or brackish water species (Moshtaghi et al, 2016). Therefore, external salinity is one of the most important abiotic factors that can influence natural distributions, abundance, general physiology and wellbeing of aquatic crustaceans.…”

“…Alkaline phosphatase (AP), Carbonic anhydrase (CA), Na + /K + -ATPase (NKA) and V-ATPase (VAT) (Tsai and Lin, 2007;Ali et al, 2015;Moshtaghi et al, 2016). Branchiostegites are also known as osmoregulatory structures in larvae, epipodites contain typical ionocytes with numerous mitochondria and elevated levels of NKA activity, while the antennal gland is associated with regulation of body fluid volume, concentration of organic solutes and bivalent ions and Na + Cl -reabsorption (Pongsomboon et al, 2009).…”

“…Several studies have identified specific genes involved in osmoregulation in crustacean species that include NKA, NKCC, VTA, CA and Cystic fibrosis transmembrane regulator (CFTR) (Pongsomboon et al, 2009;Faleiros et al, 2010;Havird et al, 2013). Functional roles of these genes are known to be: NKA establishes an electromechanical gradient across the gill cell membrane; NKCC transports ions into gill cells from the blood or the environment depending on salinity level; VTA pumps protons to influence HCO 3 -and Cl -exchange, and Na + uptake; CA produces H + and HCO 3 -that are needed to drive Na + and Cl -exchange; and CFTR is the Cl -channel regulator for osmoregulation in crustaceans (Singer et al, 1998;Hwang and Lee, 2007;Moshtaghi et al, 2016 (Foster et al, 2010;Havird et al, 2013;Scott and Brix, 2013). While the genes identified above provide a starting point, there is a notable dearth of information regarding osmotic and ionic regulation in decapods, in particular, from a comparative evolutionary phylogenetic history perspective.…”