title: A comparative study of vitellogenesis in Echinodermata: Lessons from the sea star.
abstract: The provision of yolk precursor proteins to the oviparous egg is crucial for normal embryo development. In Echinodermata, a transferrin-like yolk component termed major yolk protein (MYP) is a major precursor protein in Echinoidea and Holothuroidea. In contrast, in Asteroidea a single vitellogenin (Vtg) was recently identified, but its role as primary yolk protein remains unclear. To resolve the apparent MYP-Vtg dichotomy in sea stars and to understand the dynamics of candidate yolk protein gene expression during the reproductive cycle, we investigated the molecular structures of sea star Vtg and MYP and quantified their transcript levels during oogenesis. By combining protein sequencing of the predominant proteins in ovulated eggs of Patiriella regularis with ovarian transcriptome sequencing and molecular cloning, we characterized two cDNAs encoding two bona fide Vtgs (PrVtg1 and PrVtg2) and a partial cDNA encoding MYP (PrMYP). PrMYP mRNA was found in low abundance in growing oocytes, possibly as maternal transcripts for translation after ovulation. In contrast, PrVtg transcripts, whose levels varied during the reproductive cycle, were not found in developing oocytes - rather, they were detected in ovarian follicle cells and pyloric caeca, indicating an extra-oocytic origin. Vtg accumulating in oocytes was stored in the form of cleaved products, which constituted the most abundant yolk polypeptides in ovulated sea star eggs; their levels decreased during early embryonic and larval development. Together, these traits are the hallmarks of a classical yolk protein - and hence, we contend that Vtg, and not MYP, is the main yolk protein in asteroids.
authors.affiliation: Department of Zoology, University of Otago, 340 Great King Street, Dunedin 9016, New Zealand. Electronic address: khalid.abdallah@otago.ac.nz.
authors.forename: Khalid M
authors.initials: KM
authors.lastname: Alqaisi
authors.affiliation: Department of Marine Science, University of Otago, 310 Castle Street, Dunedin 9016, New Zealand.
authors.forename: Miles D
authors.initials: MD
authors.lastname: Lamare
authors.affiliation: Department of Anatomy, University of Otago, 270 Great King Street, Dunedin 9016, New Zealand.
authors.forename: Dave R
authors.initials: DR
authors.lastname: Grattan
authors.affiliation: Department of Zoology, University of Otago, 340 Great King Street, Dunedin 9016, New Zealand.
authors.forename: Erin L
authors.initials: EL
authors.lastname: Damsteegt
authors.affiliation: Department of Medical Biochemistry, Medical University of Vienna, Max F. Perutz Laboratories, Dr. Bohr Gasse 9, 1030 Vienna, Austria.
authors.forename: Wolfgang J
authors.initials: WJ
authors.lastname: Schneider
authors.affiliation: Department of Zoology, University of Otago, 340 Great King Street, Dunedin 9016, New Zealand.
authors.forename: P Mark
authors.initials: PM
authors.lastname: Lokman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004527:Egg Proteins / Q000235:genetics* / Q000378:metabolism; D004625:Embryo, Nonmammalian; D005260:Female; D015870:Gene Expression; D009865:Oocytes / Q000502:physiology; D010053:Ovary / Q000502:physiology; D010802:Phylogeny; D012616:Sea Cucumbers / Q000235:genetics; D012617:Sea Urchins / Q000235:genetics; D013215:Starfish / Q000196:embryology / Q000235:genetics*; D014819:Vitellogenins / Q000235:genetics* / Q000378:metabolism
chemical_list: D004527:Egg Proteins; D014819:Vitellogenins
keywords: Asteroids; Echinoderms; Major yolk protein; Vitellogenesis; Vitellogenin