An ultrastructural study of early development of vibrissae in normal and X-irradiated embry mice

Abstract

(1) Embryo mice have been subjected to irradiation dosages which will cause subsequent failure of vibrissa follicle development. The fine structure of the regions of skin which bear vibrissae has then been examined and compared with the same structure in non-irradiated animals. (2) At 10 days of development, prior to vibrissa initiation, the epidermis of facial skin consists of two layers of cells which are very loosely connected, rather disorganized, and have few cell inclusions. (3) Subsequent development in non-follicular areas includes not only cell multiplication but also an increase in cell surface contact in organization of the cell layers and in the number of various inclusions. (4) The elaboration of vibrissa rudiments is characterized by an accelerated rate and a much greater degree of these changes. There is particularly close cell contact across the basement membrane between the epidermal and dermal layers. (5) The basement membrane is shown to consist of three layers. The median one is wide, light, and non-granular. The upper and lower layers are composed of lines of organized granules each several layers deep. These granules are in close association with the RNA-containing granules (ribosomes) of the epidermal and dermal cells. (6) X-irradiation disrupts the membrane organization within the cells. It also alters the arrangement of the cellular granules and finally causes the disintegration of some of them. This effect is more violent and widespread in the vibrissa rudiments than in the non-follicular regions. (7) After X-irradiation the normal linear arrangement of the basement membrane breaks down. This also proceeds further in the vibrissa than in the unspecialized areas. (8) These results are interpreted to show that X-irradiation halts development of vibrissae because, by disrupting the normal cell contacts and granular organization, it prevents the action of an induction system which functions by the transport of vital substances by "infection" of particles through the granular layers.