Induced Preincubation Aging of the Avian Egg and Subsequent Development of the Embryo, as Revealed by the DNA, RNA, and Protein Level of Its Spleen

The phenomenon of splenomegaly was utilized to examine the effect of preincubation storage of chicken and turkey eggs on the capacity of the host spleen to respond to a specific growth stimulus. The preincubation treatment consisted of holding fertile eggs at 13° and 85% relative humidity: chicken eggs, 0, 7, 14, and 21 days and turkey eggs, 0, 7, and 14 days. The eggs were then incubated at 37° and 65% relative humidity: chicken eggs for 10–11 days and turkey eggs for 14 days before receiving a chorioallantoic graft of splenic tissue from mature White Leghorn male donors. Suitable nongrafted controls were maintained. After 8 additional days of incubation, the surviving embryos in both the experimental (grafted) and control groups provided data on the following parameters: weight of the embryo, weight of the embryo spleen, mitotic index of the latter organ as well as its DNA, RNA, and protein content. Grafting resulted in a marked enlargement of the host embryo spleen. Storing eggs before incubation, regardless of the subsequent treatment of embryos (i) depressed the weight of the whole embryo and of its spleen, (ii) decreased the frequency of mitotic rate in the spleen, and (iii) reduced the protein content of the target organ both in absolute and relative terms. The storage treatment had no discernible effect on the DNA and RNA content of the host spleen. The grafting procedure, however, induced a highly significant increase in the number of dividing cells in the host embryo spleen. It was concluded that graft-induced stimulation of the host spleen could not overcome its basically depressed growth rate when the host was an embryo from a stored (“aged”) eggs.