Histogenesis of Newt Blastema

¹ Loyola University School of Dentistry, Chicago, Illinois

Two large groups of adult Triturus viridescens viridescens were treated by amputation of the right forelimb at the distal of the radius and ulna. In Group I, tritiated thymidine was intraperitoneally administered 1 hour before sacrifice of the animals as follows: every 2 hours through 24 hours and daily through 16 days. In the Group II, the tritiated thymidine was administered to all animals 6 days after amputation and sacrificed at 24-hour intervals, thereafter, through 16 days.

Autoradiograms were prepared using liquid emulsion and an exposure time of 3 days. The autoradiograms were stained with hematoxylin and eosin; also, methyl green pyronine stain for ribose nucleic acid was used. In Group I, labeling of cells with tritiated thymidine began at 72 hours. The periosteum, perichondrium, Schwann cells, and perivascular interstitial cells were labeled cells were found free in the inflammatory exudate. At 6 days the increase in the number of labeled cells in the subepithelial region of the regenerating limb suggested the earliest organized blastema.

In Group II, the same cells were labeled as in Group I. There appeared to be increases in labeled cells in all such areas through 16 days. This was a function of mitotic activity of the labeled-cell population.

The RNA was localized as granules in the cells of the periosteum and perichondrium, Schwann cells, perivascular interstitial cells, and blastema cells. Muscle cells showed no granular cytoplasm when stained for RNA.

The most active cells showing labeling and proliferation were the perivascular interstitial cells between muscle fibers. Such perivascular cells and the Schwann cells contributed to the early establishment of the regenerate blastema.