title: Avian IgY is selectively incorporated into the egg yolks of oocytes by discriminating Fc amino acid residues located on the Cυ3/Cυ4 interface.
abstract: In avian species, maternal IgY is selectively incorporated into the egg yolks of maturing oocytes, but the relevance of receptor-mediated uptake is unclear. Here we investigated the critical amino acid residues of IgY required for egg yolk transport by conducting mutational analyses of selected residues located along the Cυ3 and Cυ4 domains of chicken IgY. Recombinant wild-type IgY-Fc (WT) and its mutants were synthesized, and their uptakes into the egg yolks of quail were determined. Among the 17 amino acid residues located on the Cυ3/Cυ4 interface, the substitution of Y363 at the Cυ3 domain to alanine abolished the IgY-Fc uptake into egg yolks. The comprehensive substitution of Y363 with other amino acids revealed that the residue at 363 needs to be allocated with aromatic amino acids to maintain the high transport ability. The deglycosylation of the N-linked carbohydrate chain by substituting N407 at the Cυ3 domain with alanine also caused a marked reduction of IgY-Fc uptake. The microscopic detection of the injected WT and Y363A mutant in ovarian follicles showed that the WT was concentrically accumulated in yolk granules, whereas the Y363A mutant was hardly accumulated in yolk granules, but it had infiltrated into the granulosa cell layer, suggesting that a major hurdle disturbing the infiltration of the Y363A mutant lies on the inside of the granulosa cell layer. The identification of important amino acid residues required for efficient IgY transport enhances our understanding of the molecular mechanisms underlying IgY transport through a specific IgY receptor in ovarian follicles.
authors.affiliation: Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan. atsushi@agr.nagoya-u.ac.jp
authors.forename: Atsushi
authors.initials: A
authors.lastname: Murai
authors.forename: Rie
authors.initials: R
authors.lastname: Murota
authors.forename: Kasumi
authors.initials: K
authors.lastname: Doi
authors.forename: Toshinori
authors.initials: T
authors.lastname: Yoshida
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Aoyama
authors.forename: Misato
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Horio
mesh_terms: D000818:Animals; D003370:Coturnix / Q000276:immunology; D004530:Egg Yolk / Q000276:immunology*; D005260:Female; D007141:Immunoglobulin Fc Fragments / Q000276:immunology* / Q000378:metabolism; D007136:Immunoglobulins / Q000235:genetics / Q000276:immunology*; D009865:Oocytes / Q000276:immunology*; D011961:Receptors, Fc / Q000378:metabolism; D011994:Recombinant Proteins / Q000276:immunology
chemical_list: C016512:IgY; D007141:Immunoglobulin Fc Fragments; D007136:Immunoglobulins; D011961:Receptors, Fc; D011994:Recombinant Proteins