Modulation of warm-temperature-acclimation-associated 65-kDa protein genes (Wap65-1 and Wap65-2) in mud loach (Misgurnus mizolepis, Cypriniformes) liver in response to different stimulatory treatments

Two paralogous isoform cDNAs of warm-temperature-acclimation-associated 65-kDa protein (Wap65-1 and Wap65-2) were isolated from the cypriniform species, mud loach (Misgurnus mizolepis), and characterized. The deduced amino acid sequences of the two mud loach Wap65 isoforms (mlWap65-1 and mlWap65-2) share moderate levels of sequence homology with their corresponding orthologues from teleosts and with human hemopexin, a possible mammalian homologue. Both isoforms display conserved features, including essential motifs and/or residues that are important for the protein structure of hemopexin. In overall, mlWap65-2 is more homologous to human hemopexin than is mlWap65-1. Both mud loach Wap65 transcripts are predominantly expressed in liver, although the transcripts are ubiquitously detectable in most tissues with variable basal expression. Both mlWap65 isoforms are differentially regulated during embryonic development, and the changes in transcript levels during embryogenesis are greater for mlWap65-2 than for mlWap65-1. The transcription of the mlWap65 genes is differentially modulated by various stimuli, including thermal changes, immune challenge (lipopolysaccharide injection or bacterial infection), and heavy metal exposure (cadmium, copper, or nickel). The isoform mlWap65-1 is more responsive to warm temperature treatments than mlWap65-2, whereas mlWap65-2 is much more strongly stimulated by immune and heavy metal challenges than is mlWap65-1. Taken together, the results of this study suggest that mud loach Wap65 isoforms are potentially involved in multiple cellular pathways and that the two mud loach Wap65 isoforms undergo functional partitioning or subfunctionalization.