Thymic lymphocyte origin in the newt Pleurodeles waltlii studied by embryonic grafts between diploid and tetraploid embryos.

Thymic lymphocytes origin in the newt Pleurodeles waltlii was studied by embryonic grafts of the gill area between diploid and tetraploid embryos. By this way, either cell size or chromosome number are used as markers. Heterotopic transplantation of the gill area to the ventral region of a host embryo is followed by differentiation of gills and gill-associated structures including thymus. Analysis of cell size and chromosome number shows that in Pleurodeles, thymocytes do not differentiate in situ but originate from blood-borne stem cells that migrate into the thymus anlage.