the data demonstrate that ( a ) ggt expression followed a program of activity and localization changes that correlated with the progressive emergence of developmental stages and ( b ) ggt activity in developing tissues derived either from epithelium ( enamel-producing cells and hair follicle cells ) or from mesenchyme ( intervertebral disc cells ) was localized only in mitotically quiescent cellular layers or regions associated with the production of specialized tissue products ;
C0014609
epithelium
C0018496
hair