Fundulus heteroclitus vitellogenin: The deduced primary structure of a piscine precursor to noncrystalline, liquid-phase yolk protein

Abstract

We have cloned and sequenced a cDNA encoding a vitellogenin (Vtg) from the mummichog, Fundulus heteroclitus, an estuarine teleost. We constructed a liver cDNA library against RNA from estrogen-treated male mummichogs. Five overlapping cDNA clones totalling 5,197 bp were isolated through a combination of degenerate oligonucleotide probing of the library and PCR. The cDNA sequence contains a 5,112 bp open reading frame. The predicted primary structure of the deduced 1,704-amino-acid protein is 30-40% identical to other documented chordate Vtgs, establishing this Vtg as a member of the ancient Vtg gene family. Of the previously reported chordate Vtg sequences (Xenopus laevis, Gallus domesticus, Ichthyomyzon unicuspis, and Acipenser transmontanus), all four act as precursor proteins to a yolk which is eventually rendered insoluble under physiological conditions, either as crystalline platelets or as noncrystalline granules. The yolk of F. heteroclitus, on the other hand, remains in a soluble state throughout oocyte growth. The putative F. heteroclitus Vtg contains a polyserine region with a relative serine composition that is 10-20% higher than that observed for the other Vtgs. The trinucleotide repeats encoding the characteristic polyserine tracts of the phosvitin region follow a previously reported trend: TCX codons on the 5' end and AGY codons toward the 3' end. Whether the difference in Vtg primary structure between F. heteroclitus and that of other chordates is responsible for the differences in yolk structure remains to be elucidated. As the first complete teleost Vtg to be reported, these data will aid in designing nucleotide and immunological probes for detecting Vtg as a reproductive status indicator in F. heteroclitus and other piscine species.

Extensive Sequence Conservation Among Insect, Nematode, and Vertebrate Vitellogenins Reveals Ancient Common Ancestry

“…Complete and partial Vg deduced amino acid sequences were obtained from the GenBank database and published papers: boll weevil, Anthonomus grandis (M72980; Trewitt et al 1992); chicken, Gallus gallus (M18060; van het Schip et al 1987); frog, Xenopus laevis (Y00354; Gerber-Huber et al 1987); gypsy moth, Lymantria dispar (L28097; Hiremath et al 1994); lamprey, Ichthyomyzon unicuspus (M88749; Sharrock et al 1992); nematode, Caenorhabditis elegans (X56121 and X56213; Spieth et al 1985Spieth et al , 1991; mummichog, Fundulus heteroclitus (U07055; LaFleur et al 1995); sawfly, Athalia rosae (Kageyama et al 1994); silkworm moth, Bombyx mori (D13160; Yano et al 1994a); white sturgeon, Acipenser transmontanus (U00455; Bidwell and Carlson 1995); and yellow fever mosquito, Aedes aegypti (U02548; Chen et al 1994).…”

“…Our alignment evinces a lack of homology among insect polyserine tracts and the vertebrate phosvitin domain, another point of uncertainty since the surprising discovery of the former in mosquito Vg (Chen et al 1994;LaFleur et al 1995). In addition, we present phylogenetic analyses suggesting the evolutionary relationships of insect, nematode, and vertebrate Vgs to one another as well as to related serum proteins from mammals (apolipoprotein B-100 and von Willebrand factor).…”

Vitellogenesis and choriogenesis in fishes

“…Recently, several Vtg gene transcripts were discovered in the African clawed frog (VtgA1, A2, B1, B2) [74,75] and chicken (Vtg I, II, III) [76,77], along with fish species such as mummichog [78,79], barfin flounder [64], haddock Melanogrammus aeglefinus, a species of cod [80], tilapia Oreochromis aureus [81] and sheepshead minnow Cyprinodon variegatus, an estuarine-species of pupfish [82]. Among fishes, a gene encoding a special form of Vtg lacking the Pv region (phosvitinless Vtg, Pv-less Vtg) was first discovered in zebrafish Danio rerio [83].…”

Sensitivities of mRNA Expression of Vitellogenin, Choriogenin and Estrogen Receptor by Estrogenic Chemicals in Medaka, Oryzias latipes.

“…For the sequence analysis of vitellogenin (VTG) cDNA, amplification of cDNA specific for the VTG gene from the estrogen-treated medaka was performed using degenerated primers based on the published VTG sequences of other fish species; rainbow trout 13) and mummichog. 14) Amplified cDNA products were separated on 1.0% agarose gel by electrophoresis, and the cDNA fragments were cut out from the agarose gel and cloned into pGEM-T easy vector (Promega, Madison, WI, U.S.A.). Then the cDNA clones were applied to the automatic DNA sequencer (ABI3700, Applied Biosystems, Foster City, CA, U.S.A.).…”