Equine zona pellucida and capsule: Some physicochemical and antigenic properties

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Abstract
The capsule which surrounds the pre‐attachment equine embryo has been compared with the zona pellucida (zp) that it replaces, as well as with the rabbit blastocyst coverings, by means of physicochemical and immunological methods. Trypsin solution at pH varying between 7.5 and 9.0 completely solubilized the capsule, as did Na borohydride. However, solutions of pH 2.0 or 12.0, urea, high temperature (65°C, 60 min or 80°C, 30 min), mercaptoethanol and dithiothreitol were able to solubilize the zp but not the capsule at the concentrations used. Indirect immunofluorescence on cryostat sections and whole mounts of fresh or frozen‐thawed material showed that 1) common antigens are shared by equine, porcine and bovine zp; 2) day 7 to day 15.5 capsule reacted with anti‐capsule‐serum but not with anti‐zp‐serum except for a few patches on the surface of the capsule; 3) anti‐capsule‐serum, but not anti‐zp‐serum, reacted with the capsular material recovered along with a broken day 27.5 conceptus; 4) anti‐capsule‐serum does not react with rabbit blastocyst coverings; 5) anti‐capsule antibodies can be absorbed from the anti‐capsule‐serum by uterine proteins from either pregnant or non‐pregnant mares; and 6) the capsule does not contain mouse laminin‐like material.