title: Changes in major proteins in the embryonic capsule during immobilization (fixation) of the conceptus in the third week of pregnancy in the mare.
abstract: During the third week of pregnancy, the equine conceptus is enclosed within a capsule, the glycan composition of which changes at around day 16 (ovulation = day 0) when the conceptus becomes immobilized (fixed) in the uterine lumen. Our objective was to characterize the process of fixation by identifying changes in major capsule-associated proteins. Individual equine conceptuses (n = 55) were collected transcervically by uterine lavage between days 13.5 and 26.5. Major proteins extracted from capsules were compared with those in fluids from the uterus and yolk sac by SDS-PAGE. Until day 14, a major capsule-associated protein that migrated at approximately 10 kDa was identified by N-terminal sequencing as equine beta2 microglobulin (beta2M). During fixation, beta2M in the capsule underwent limited proteolysis to an approximately 8 kDa form lacking nine amino acids from the N terminus, and was subsequently degraded. Expression of beta2M mRNA was detected in the yolk-sac wall tissues and endometrium between days 13.5 and 17.5. During this period, beta2M in the capsule was evidently not part of a complex with major histocompatibility complex class 1 heavy alpha chain bands because these were undetectable in the capsule and uterine lavage. Uterocalin (p19) was detected in uterine lavage and capsule throughout fixation, but in yolk-sac fluid only before fixation. These studies indicate that intact beta2M is a major protein associated with the embryonic capsule before fixation, after which it undergoes limited proteolysis to a truncated approximately 8 kDa form that remains in the capsule after the conceptus is immobilized.
authors.affiliation: Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.
authors.forename: B A
authors.initials: BA
authors.lastname: Quinn
authors.forename: M A
authors.initials: MA
authors.lastname: Hayes
authors.forename: R O
authors.initials: RO
authors.lastname: Waelchli
authors.forename: M W
authors.initials: MW
authors.lastname: Kennedy
authors.forename: K J
authors.initials: KJ
authors.lastname: Betteridge
mesh_terms: D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D010064:Embryo Implantation / Q000502:physiology*; D004622:Embryo, Mammalian / Q000378:metabolism*; D005260:Female; D015870:Gene Expression; D005865:Gestational Age; D006023:Glycoproteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000378:metabolism; D006736:Horses / Q000378:metabolism*; D015151:Immunoblotting; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014598:Uteroglobin / Q000032:analysis / Q000378:metabolism; D014599:Uterus / Q000737:chemistry / Q000378:metabolism; D015017:Yolk Sac / Q000737:chemistry / Q000378:metabolism; D001613:beta 2-Microglobulin / Q000032:analysis / Q000378:metabolism
chemical_list: D006023:Glycoproteins; D015395:Histocompatibility Antigens Class I; C099187:MHC class I-related chain A; D012333:RNA, Messenger; D001613:beta 2-Microglobulin; D014598:Uteroglobin