ENTEROCYTE EXPRESSION OF CALBINDIN, CALBINDIN MESSENGER-RNA AND CALCIUM-TRANSPORT INCREASES IN JEJUNAL TISSUE DURING ONSET OF EGG-PRODUCTION IN THE FOWL (GALLUS-DOMESTICUS)

1. Quantitative measurements of calbindin mRNA, calbindin protein and calcium uptake have been made in sectioned intestinal villi to determi ne the location and cellular characteristics of their expression in im mature, point of lay and laying chickens. 2. Trace amounts of calbindi n mRNA were detected by in situ hybridization in enterocytes located a round the crypt-villus junction in jejunal tissue taken from immature and point of lay chickens. Large amounts of calbindin mRNA were detect ed in upper crypt and all villus enterocytes in tissue taken from layi ng chickens. Maximal levels of calbindin mRNA occurred in the basal th ird of the villus in laying chickens. 3. No calbindin was detected imm unocytochemically in tissue taken from immature and point of lay chick ens. Large amounts of calbindin were expressed in tissue taken from la ying chickens. Maximal expression of calbindin in this case occurred i n villus tip enterocytes. 4. Rapid uptake of calcium by tissue taken f rom laying chickens was twice that found in immature and point of lay birds. Calcium uptake in tissue taken from laying hens was also shown by quantitative autoradiography to take place maximally in villus tip enterocytes. 5. Regulation of calbindin gene expression and the cellul ar characteristics of calcium transport in laying chickens are discuss ed in terms of an adaptive response taking place in birds undergoing a daily loss of egg shell calcium.