Species differences in the expression of multiple tyrosine hydroxylase protein isoforms

In subprimates, a single form of tyrosine hydroxylase (TH) is expressed, whereas two TH protein isoforms have been identified in monkeys and four isoforms have been demonstrated in humans. In order to establish the evolutionary pattern/emergence of these multiple TH isoforms, adrenal medullae from different mammalian species were analyzed by blot immunolabeling using pan-specific TH antibodies and antibodies specific to each of the four human TH isoforms. The expression of multiple TH isoforms was primate specific and restricted to anthropoids: only a single TH isoform was detected in adrenal medullae from several subprimate and prosimian species (six species from four families), while two TH isoforms were found in all of the anthropoid species studied. The presence of four TH isoforms could only be demonstrated in human specimens. Contrary to previous suggestions, only one TH protein isoform was found in rats and only four TH protein isoforms were found in humans.