Molecular cloning of natriuretic peptides from the heart of reptiles: loss of ANP in diapsid reptiles and birds.

Atrial natriuretic peptide (ANP) and B-type NP (BNP) are hormones involved in homeostatic control of body fluid and cardiovascular regulation. Both ANP and BNP have been cloned from the heart of mammals, amphibians, and teleost fishes, while an additional cardiac peptide, ventricular NP, has been found in selected species of teleost fish. However, in chicken, BNP is the primary cardiac peptide identified thus far. In contrast, the types of NP/s present in the reptilian heart are unknown, representing a considerable gap in our understanding of NP evolution. In the present study, we cloned and sequenced a BNP cDNA from the atria of representative species of reptile, including crocodile, lizard, snake, and tortoise. In addition, we cloned BNP from the pigeon atria. The reptilian and pigeon BNP cDNAs had ATTTA repeats in the 3' untranslated region, as observed in all vertebrate BNP mRNAs. A high sequence homology was evident when comparing reptile and pigeon preproBNP with the previously identified chicken preproBNP. In particular, the predicted mature BNP-29 was identical between crocodile, tortoise, and chicken, with pigeon having a single amino acid substitution; lizard and snake BNP had seven and nine substitutions, respectively. Furthermore, an ANP cDNA could only be cloned from the tortoise atria. Since ANP was not isolated from the heart of any non-chelonian reptile and appears to be absent in birds, we propose that the ANP gene has been lost after branching of the turtles in the amniote line. This data provides new avenues for research on NP function in reptiles.