Embryonic development of the mouse mutant pupoid foetus (pf/pf).

The pupoid foetus mutation in the mouse is a recessive lethal mutation causing death of homozygous (pf/pf) embryos immediately after birth. From 11.3 days gestation onwards, these embryos are characterised externally by the development of a tail twist, followed by apparent stunting of the limbs and tail (when compared with the development of these structures in normal embryos), lack of digits, distortion of facial features, and possession of a smooth, mottled skin. Embryos ranging in age from 11.3 days gestation to full term have been examined using light microscopy and scanning and transmission electron microscopy. The skeletal structure and internal organs of the embryo are normal, but abnormalities occur in the external epidermis, the dermis, and the peripheral sensory nerves. Development of the palate and the eyes are affected by the behaviour of these tissues. The epidermis undergoes hypertrophy and fails to differentiate, and, on the basis of morphological criteria and theoretical considerations, it is suggested that the pf gene is activated in the epidermis during the keratinization pathway, preventing differentiation and altering the cell surface characteristics of the cells. Other abnormalities are explained in terms of interactions with the epidermis. This mutant is compared with other similar mutants.