Abstract
BackgroundThe multiplicity or loss of the vitellogenin (vtg) gene family in vertebrates has been argued to have broad implications for the mode of reproduction (placental or non-placental), cleavage pattern (meroblastic or holoblastic) and character of the egg (pelagic or benthic). Earlier proposals for the existence of three forms of vertebrate vtgs present conflicting models for their origin and subsequent duplication.ResultsBy integrating phylogenetics of novel vtg transcripts from old and modern teleosts with syntenic analyses of all available genomic variants of non-metatherian vertebrates we identify the gene orthologies between the Sarcopterygii (tetrapod branch) and Actinopterygii (fish branch). We argue that the vertebrate vtg gene cluster originated in proto-chromosome m, but that vtg genes have subsequently duplicated and rearranged following whole genome duplications. Sequencing of a novel fourth vtg transcript in labrid species, and the presence of duplicated paralogs in certain model organisms supports the notion that lineage-specific gene duplications frequently occur in teleosts. The data show that the vtg gene cluster is more conserved between acanthomorph teleosts and tetrapods, than in ostariophysan teleosts such as the zebrafish. The differential expression of the labrid vtg genes are further consistent with the notion that neofunctionalized Aa-type vtgs are important determinants of the pelagic or benthic character of the eggs in acanthomorph teleosts.ConclusionThe vertebrate vtg gene cluster existed prior to the separation of Sarcopterygii from Actinopterygii >450 million years ago, a period associated with the second round of whole genome duplication. The presence of higher copy numbers in a more highly expressed subcluster is particularly prevalent in teleosts. The differential expression and latent neofunctionalization of vtg genes in acanthomorph teleosts is an adaptive feature associated with oocyte hydration and spawning in the marine environment.
Highlights
The multiplicity or loss of the vitellogenin gene family in vertebrates has been argued to have broad implications for the mode of reproduction, cleavage pattern and character of the egg
Babin [7] has provided a syntenic map of vertebrate vtg genes, which shows that the three forms of vtg are encoded in a vtg gene cluster (VGC) in non-eutherian vertebrates
The deduced amino acid sequences of the full-length rock cook and cuckoo wrasse Vtgs revealed that the VtgAa and VtgAb products are complete pentapartite type proteins (NH2-LvH-PvLvL-β'-CT-COO-) while VtgC belongs to the phosvitinless class of Vtg (NH2-LvH-LvL-COO-) [25]
Summary
The multiplicity or loss of the vitellogenin (vtg) gene family in vertebrates has been argued to have broad implications for the mode of reproduction (placental or non-placental), cleavage pattern (meroblastic or holoblastic) and character of the egg (pelagic or benthic). The major products of the vitellogenin (vtg) genes that encode yolk proteins have been considered to be simple precursors of the energy reserve of vertebrate eggs, but the latest studies have demonstrated several non-nutritional roles for Vtg [1,2]. We identified vtgC as an ancestral gene, and argued that the dual vtgAa/vtgAb system, first noted by La Fleur et al [5] was derived from a single form, the A-type vtg In this model, the separation of the vtgC- and vtgA-type genes occurred following the second round (R2) of whole genome duplication (WGD). VtgA duplicated and formed paragolous vtgAa and vtgAb genes in acanthomorph teleosts This phylogenetic model has been corroborated by other investigators [6]. A major goal of the present study was to integrate the statistical, biochemical and physical models of vtg gene evolution in vertebrates
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
