Different populations of pig epidermal cells: isolation and lipid composition.

Preparations representing populations of (a) basal and spinous cells, (b) granular cells, and (c) stratum corneum cells were obtained by successive treatments of epidermal slices from pig skin with dilute buffered trypsin solutions. Total lipids accounted for about 8% of the cell dry weight in each of the three populations. Phospholipids, which predominated in the basal and spinous cells, accounted for only 21% of the total lipids in the granular cells and less than 0.1% in the stratum corneum. The latter cells contained more cholesterol (23% of total lipid) than either the granular cells (18%) or the basal and spinous cells (8%). The proportion of ceramide was also much higher in the stratum corneum (17%) and granular cells (9%) than in the basal and spinous cells (1%). The relative amounts of glycosphingolipid (glucosylceramide) and cholesteryl sulfate in the total lipids of stratum corneum cells were less than half those in the granular cells and basal and spinous cells. A novel phospholipid was a major component (26% of total) of the phospholipids from granular cells. The compound, which was partially characterized, contained phosphorus, fatty acids, and glycerol (molar ratio 1:3:2) and appeared to be a neutral derivative of phosphatidic acid.     

Regenerative abnormalities in Notophthalmus viridescens induced by repeated amputations.

The fidelity of the regenerative response in the adult newt, Notophthalmus viridescens, was examined following repeated amputations at the level of the distal one-third of humerus. Three to four months following amputation, all regenerates were scored for gross morphology, reamputated, and stained with methylene blue for skeletal elements. The occurrence of abnormal regeneration with respect both to gross morphology and to skeletal structure was found to increase directly with the number of times the limb stumps were required to initiate dedifferentiation and repair. The initial amputation-regeneration process produced structurally normal replacement limbs in 91% of the cases examined. Reamputations of 4-digit regenerates (3--4 months after the previous transection) resulted in structurally abnormal regenerates in 28% of the cases following two amputations; 50% of the cases following three amputations; 65% of the cases following four amputations; and 81% of the cases following five amputations. The relationships between repeated dedifferentiation, proliferation, and redifferentiation and normal limb development are discussed.