Nonproliferation in dermal condensations of mouse vibrissae and pelage hairs

The early development of mouse embryo vibrissae and pelage hairs has been investigated by labeling with nucleic acid precursors and by organ culture procedures. As soon as dermal condensations form in either hair type, condensation cells fail to incorporate H 3-thymidine or show mitoses, although such cells continue to bind H 3-uridine into ribonuclease-sensitive material. Condensation cells remain relatively quiescent mitotically during hair peg downgrowth and few adjacent (labeled) dermal cells migrate into the condensation mass. These observations, in conjunction with earlier work, demonstrate remarkable similarities between hairs and feathers in terms of nonproliferation at times when significant tissue interactions are thought to be occurring.