Sequence analysis of a fish vitellogenin cDNA with a large phosvitin domain

Vitellogenins (Vtg) are egg-yolk precursor proteins crucial for reproductiv e success in oviparous animals. We have cloned the first complete cichlid V tg cDNA from the tilapia fish, Oreochromis aureus. This cDNA has the larges t phosvitin (PV) domain amongst piscine Vtgs, being comparable to those of lamprey, Xenopus, and chicken. Thus, the size of PV is independent of the e volutionary advancement of a species. The closer interspecific relationship between O. aureus Vtg1 and Fundulus Vt-H than the intraspecific relationsh ip between Fundulus VtgI and II isoforms suggests that teleost ancestors ha d at least two Vtg isoforms. Contrary to the results of previous phylogenet ic inference using Vtgs which indicate that insect lineage is most diverged and nematodes are closer to vertebrate lineage., our results show that nem atodes and hexapods form two monophyletic sister groups. Another arthropod taxon, represented by a malacostracan crustacean, Penaeus japonicus, appear s to be more closely related to the vertebrates than the hexapods. (C) 2001 Elsevier Science B.V. All rights reserved.