ABSTRACT
Both X-irradiation and certain genetic mutations can produce loss of vibrissae in mice.
The aim of this investigation was to determine whether disruption occurred at the same point in development and in the same manner.
Histological investigation was made of vibrissae during early stages of development.
It was found that two periods of epigenetic crisis exist in vibrissa develop-ment, one at the time of site determination and the other at the time of follicle-papilla interaction when development has just been initiated.
Irradiation damage acts by disrupting this follicle-papilla interaction. If the contact is broken in the very early stage, the vibrissa will degenerate. If irradia-tion acts a little later, when the cells are less sensitive, the contact is not broken, and the vibrissa follicle cells will recover from the damage and continue to develop.
In one mutation studied, the same interaction was destroyed because there was a genetic abnormality in the papilla. This produced the same ultimate effect as did irradiation.
In other cases, the mutation acted on the first crisis, affecting the site determination. Here, although the apparent effect was the same as in irradiation, the mechanism differed.
