DNA ligase changes and cell population in thymus of corticosteroid-treated chick embryo

Two successive forms of DNA ligases normally occur successively in the chicken and chick embryo thymus, a 8.2 S, before hatching and a 6.2 S, after hatching. The disappearance of the 8.2 S and the appearance of the 6.2 S together with its increased activity can be observed earlier under the effect of corticosteroids (dexamethasone (DMSO) and hydrocortisone). The biochemical, histological and cell sorting observations are consistent with the presence of the heavy enzyme in large (7.5 μm) thymocytes and the light enzyme in smaller (5 μm) T-antigen possessing cells. These results are discussed on the basis of the effect of steroids on thymocyte maturation and with regard to cell migration within the lymphoid system.