Albumin is ubiquitously expressed in the dolphin body and upregulated by an extracellular albumin shortage

This study demonstrates that hepatocyte-specific albumin is ubiquitously expressed and the protein is produced in both common bottlenose dolphins Tursiops truncatus and striped dolphins Stenella coeruleoalba. Quantitative PCR revealed that albumin precursor mRNA is expressed in all 12 tissues examined, with the highest levels observed in the liver. Next, TA cloning using skin and liver of the two species confirmed that the deduced albumin animo acid sequences in the tissues are 100% identical within each species and slightly different between the species or between tissues in common bottlenose dolphin and cultured cells derived from the same species. In addition, western blot analysis showed positive bands of approximately 66 kDa in all tissues examined, as seen with serum albumin. Immunohistochemistry assays also revealed that albumin protein was distributed in most cells in each tissue. These results suggest that albumin protein, with the same sequence as the serum albumin synthesized in liver, may be ubiquitously expressed in the dolphin body. Furthermore, to clarify the function of albumin, we removed bovine serum albumin from culture medium. This enhanced albumin mRNA expression in the cells. Albumin protein with the specific dolphin sequence then began to be detected in the medium. These data strongly indicate that albumin may be synthesized in many tissue types and extracellularly secreted in the same manner as in the liver. Additionally, albumin expression is likely to be upregulated in the absence of albumin around the cells. Ubiquitous albumin expression may be essential for dolphin peripheral cells, possibly to supply albumin during dive-induced ischemia.