PROLIFERATIVE CAPACITY OF EMBRYONIC CHICK NOTOCHORD - A COMPARISON BETWEEN PCNA POSITIVITY VERSUS H-3 THYMIDINE INCORPORATION

The proliferation rate of the embryonic chick notochord is measured du ring its functional period. Chick embryos of 4 different age groups re spectively, 3.5, 4.5, 5.5 and 6.5 days of development, are selected. T o measure proliferation activity in the notochords, two different meth ods are used. 1. Notochords are immunostained for proliferating cell n uclear antigen (PCNA). 2. After in vivo incorporation of H-3-thymidine (H-3-TdR), DNA synthesis is visualized by autoradiography. After embe dding in paraffin, 5 mu m sections are cut and stained with PC10 monoc lonal antibody and avidine biotin peroxidase complex (ABC) technique. Corresponding chick embryos of the same age groups are injected in ovo with H-3-thymidine. After fixation 2 mu m sections are made and expos ed for autoradiography. Results obtained by PCNA and autoradiography l abelling techniques for the evaluation of the proliferative capacity a re different. Both however show a regression of the proliferative acti vity. The regression of the number of cells that went through S-phase, as shown by autoradiography, is lower than that of PCNA positive cell s. So, a number of notochordal cells stops in G1 phase. Our results mo reover, indicate that the proliferating activity of the notochord of c hick embryos is higher at young developmental stages than at later sta ges.