Using Atlantic cod (Gadus morhua) as a model organism, the aim of this report was to delineate whether teleostean eggshell
zona radiata
proteins have their origin, i.e., site of synthesis, in gonadal or somatic tissues.
Estradiol-17 beta was administered intraperitoneally to one-year-old cod (Gadus morhua) with either undeveloped gonads or with differentiated gonads. By immunoblotting procedures
estradiol-dependent
protein induction was investigated using specific rabbit
antisera directed against cod
eggshell proteins and brown trout
vitellogenin. No immunological cross-reactions were observed between the two
antisera, and
eggshell proteins and
vitellogenin were detected in blood plasma and somatic tissues only in
estradiol-treated cod. Three plasma-components were immunoreactive to antiserum directed against
eggshell proteins, and these
proteins possessed molecular weights of 78, 54 and 47 kDa, identical to the molecular weights of the cod eggshell alpha, beta and gamma
zona radiata-
proteins. These three immunoreactive plasma-components were observed after administration of
estradiol-17 beta to both sexes, also in males having reached spermiation, and in juveniles of either sex without developed gonads. The data are interpreted to signify that cod eggshell
zona radiata-
proteins originate in an extra-ovarian tissue and are transported in the blood for deposition in the ovaries. We propose that oogenesis involves
estradiol-17 beta regulation of both eggshell
zona radiata-
proteins and
vitellogenin synthesis.