Multilocus isozyme systems in African lungfish, Protopterus annectens:: distribution, differential expression and variation in dipnoans

Distribution of ADH, ALP, FBALD, GAPDH, G3PDH, G6PDH, GPI, LDH, MDH, PGM, and SOD was identified in retina, heart, muscle, liver, kidney, gills, brain, gut, lung and ovary of the African lungfish. Data are compared with patterns previously described in dipnoans and other vertebrates. The number of loci expressed for all enzymes was found to be similar to those of diploid Actinopterygii. Differences in the number of loci expressed in Amphibia. were found for ALP, sG3PDH, GPI, LDH, MDH and SOD. Differences in tissue distribution were noted in ALP due to the absence of an intestinal-specific form typical of teleostean fish, amphibians, reptiles and birds, and in GPI and MDH, due to the tissue expression, as in primitive fish. There were also differences in LDH, where a third locus (LDH-C*) was expressed in the gills of Protopterus annectens and not in the retina or liver tissues, as in teleosts. LDH-A(4) was most common in all the tissues. Major differences were noted in the tissue patterns of protein expression in the three dipnoans compared. As expected, the least divergence was found between the two species belonging to the same family (Lepidosirenidae). The highest index of divergence was observed between Neoceratodus forsteri and Lepidosiren paradoxa, belonging to the families Ceratontidae and Lepidosirenidae, respectively. The divergence is revealed by changes at the enzyme and morphological levels. These results suggest that P. annectens occupies an interesting systematic position, its biochemical characteristics distinguishing it from N. forsteri, L. paradoxa, the advanced fish and amphibians. (C) 2002 Elsevier Science Inc. All rights reserved.