Cloning of a neonatal calcium atpase isoform (SERCA 1B) from extraocular muscle of adult blue marlin (Makaira nigricans)

Complete cDNAs for the fast-twitch Ca2+-ATPase isoform (SERCA 1) were clone d and sequenced from blue martin (Makaira nigricans) extraocular muscle (EO M). Complete cDNAs for SERCA 1 were also cloned from fast-twitch skeletal m uscle of the same species. The two sequences are identical over the coding region except for the last five codons on the carboxyl end; EOM SERCA 1 cDN A codes for 996 amino acids and the fast-twitch cDNAs code for 991 aa. Phyl ogenetic analysis revealed that EOM SERCA 1 clusters with an isoform of Ca2 +-ATPase normally expressed in early development of mammals (SERCA 1B). Thi s is the first report of SERCA 1B in an adult vertebrate. RNA hybridization assays indicate that 1B expression is limited to extraocular muscles. Beca use EOM gives rise to the thermogenic heater organ in martin, we investigat ed whether SERCA 1B may play a role in heat generation, or if 1B expression is common in EOM among vertebrates. Chicken also expresses SERCA 1B in EOM , but rat expresses SERCA 1A; because SERCA 1B is not specific to heater ti ssue we conclude it is unlikely that it plays a specific role in intracellu lar heat production. Comparative sequence analysis does-reveal, however, se veral sites that may be the source of functional differences between fish a nd mammalian SERCAs. (C) 2000 Elsevier Science Inc. All rights reserved.