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H. MOSER, I. HADJI-AZIMI AND S. SLATKINE 



tion of kidney cells derived from premetamorphotic tadpoles of Xenopus yields 

 more constant results than the explantation of adult cells. 



The formation of the kidney-cell monolayer cultures is not the resuit of cell 

 migration from the tissue fragments and the cell clumps but due mainly to active 

 cell prolifération, which is indicated by numerous mitosis, especially in young 

 cultures. Kidney-cell monolayer cultures are composed predominantly of poly- 

 gonal shaped epithelioid cells (see figure la); in certain areas of thèse cultures, 

 however, colonies of elongated fibroblast-like cells can be detected (see figure lb). 



Primary kidney cell cultures of Xenopus laevis maintained in our growth 

 média TCM-A1 and TCM-A2 remain diploid. As can be seen from figure 2a, 

 b, c, cells which have been cultured for 10 days in TCM-A1 and are undergoing 

 mitosis exhibit the normal-diploid chromosome complément of Xenopus laevis 

 (2N = 36). 



Attempts to subculture kidney-cell monolayer cultures derived from adult 

 Xenopus source material have completely failed so far. This behaviour is not sur- 

 prising at ail as also, according to our expérience, normal-diploid kidney cells 

 of adult vertebrates have a very limited capacity for cell division in vitro and 

 possibly also in vivo. 



PLANCHES I AND II 



Fig. 1 a and b 



Monolayer culture of adult Xenopus laevis (Daudin) kidney cells grown in TCM-A1 for 10 days 

 at room température: a) epithelioid cells (magnification, 380 X); b) colony of fibroblast-like 

 cells (magnification, 390 X). Fixed (Bouin) and stained (Hematoxylin-eosin). 



Fig. 2a and b 



Chromosome complément of kidney cells of premetamorphotic tadpoles of Xenopus laevis 

 (Daudin) cultivated in vitro in TCM-A1 for 7 days at 25° C: a) prophase chromosomes (magni- 

 fication, 7625 X); b) metaphase chromosomes (magnification 8125 X). 



Fig. 5 



Living primary-explant culture derived from whole advanced Xenopus laevis embryos (stages 

 35 to 40), grown in TCM-A2 for 3 months at room température: Sheets of epithelioid cells; 



magnification, 312 X. 



Fig. 6 



Primary-explant culture derived from whole advanced embryos of Xenopus laevis (stages 37 to 40, 

 grown for 3 weeks at room température in TCM-A2: Sheet of fibrocyte-like cells. Magnification 

 160 X. Fixed (Bouin) and stained (Hematoxylin-eosin). 



Fig. la 



Primary-explant culture derived from whole young Xenopus laevis tadpoles (stages 42 to 45), 

 grown at room température in TCM-A2: a) colony of differentiating melanoblasts (culture 

 2 weeks old), magnification, 160 X. 



Fig. 8 



Primary-explant culture derived from whole advanced embryos of Xenopus laevis (stages 37 to 40), 

 grown for 3 weeks at room température in TCM-A2: Giant transparent cells of unknown origin 

 and function. Magnification, 320 X. Fixed (Bouin) and stained (Hematoxylin-eosin). 



