Abstract
Cetacea is a clade well-adapted to the aquatic lifestyle, with diverse adaptations and physiological responses, as well as a robust antioxidant defense system. Serious injuries caused by boats and fishing nets are common in bottlenose dolphins (Tursiops truncatus); however, these animals do not show signs of serious infections. Evidence suggests an adaptive response to tissue damage and associated infections in cetaceans. Heme oxygenase (HO) is a cytoprotective protein that participates in the anti-inflammatory response. HO catalyzes the first step in the oxidative degradation of the heme group. Various stimuli, including inflammatory mediators, regulate the inducible HO-1 isoform. This study aims to characterize HO-1 of the bottlenose dolphin in silico and compare its structure to the terrestrial mammal protein. Upstream HO-1 sequence of the bottlenose dolphin was obtained from NCBI and Ensemble databases, and the gene structure was determined using bioinformatics tools. Five exons and four introns were identified, and proximal regulatory elements were detected in the upstream region. The presence of 10 α-helices, three 310 helices, the heme group lodged between the proximal and distal helices, and a histidine-25 in the proximal helix serving as a ligand to the heme group were inferred for T. truncatus. Amino acid sequence alignment suggests HO-1 is a conserved protein. The HO-1 “fingerprint” and histidine-25 appear to be fully conserved among all species analyzed. Evidence of positive selection within an α-helix configuration without changes in protein configuration and evidence of purifying selection were found, indicating evolutionary conservation of the coding sequence structure.
Highlights
Many reports suggest that mammals returned to the water in separate lineages and times
A motif occurrence is only given when the p-value is less than 0.0001. To verify if these motifs harbor binding for the transcriptional factors identified in this study, a search for candidate cis-regulatory elements of Heme oxygenase (HO)-1 was conducted from the ENCODE portal2 in the human genome assembly GRCh38
Proximal regulatory elements were detected in the upstream region (Figure 1), including the following transcriptional factors, activating protein 2 (AP-2), nuclear factor kappalight-chain-enhancer of activated B cells (NF-κB), heat shock factor 1 (HSF1), signal transducers, and transcription activators (STAT1:STAT2), as well as nuclear factor erythroid 2 (NF-E2) and CCCTC-binding factor (CTCF), a multifunctional transcription factor
Summary
Many reports suggest that mammals returned to the water in separate lineages and times. Cetaceans returned to the ocean approximately 53–56 million years ago (Thewissen et al, 2007). This transition from a terrestrial to an aquatic lifestyle poses different challenges, including but not limited to the change of pathogens and their pathogenresponse proteins and the oxygen source (since they must dive to obtain prey or any food source). Evidence of selective pressures can be found in distinct cetacean genes like the toll-like receptor (TLR) 4 (a recognition receptor of pathogen-associated molecular patterns which mediates the innate immune system), hemoglobin, (alpha and beta) myoglobin and endothelin (Tian et al, 2016), suggesting an adaptive evolution to the aquatic lifestyle (Shen et al, 2012). Antioxidants and other proteins (e.g., glutathione peroxidase 2 and haptoglobin) showed amino-acid changes in cetaceans (Yim et al, 2014)
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