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. 2020 Feb 14;30(2):300–313. doi: 10.1089/thy.2019.0366

FIG. 4. .

FIG. 4. 

Total knockout of TRs reduces the rate of natural metamorphic progression and causes tadpoles lethality at the climax of metamorphosis. (A) Representative photos of tadpoles for three TRβ genotypes at the stage of forelimb emergence (stage 58). Adult TRα (−/−)TRβ (+/−) animals were mated, and the resulting tadpoles were euthanized when their forelimbs broke through the membrane-enclosure, photographed, and genotyped to identify the three genotypes [(a) TRα (−/−)TRβ (+/+), (b) TRα (−/−)TRβ (+/−), and (c) TRα (−/−)TRβ (−/−)]. Lowercase letters indicate the same tadpole with two different views: dorsal view (upper) and a higher magnification from the dorsal side for the head (lower: a′–c′). Scale bars: 5 mm. (B) TRDKO tadpoles have shorter body length at the onset of metamorphic climax (stage 58). The body length of individual tadpoles at stage 58 as identified in (A) was measured and plotted with the mean, marked as a line, and SE. The asterisks (*) indicate a significant difference for the three genotypes (p < 0.01). (C) TRDKO tadpoles have delayed onset of metamorphic climax (stage 58). The age of individual tadpoles at stage 58 as identified in (A) was recorded and plotted with the mean, marked as a line, and SE. The asterisks (*) indicate a significant difference for the three genotypes (p < 0.01). (D) TRDKO tadpoles have a reduced rate of metamorphic progression at the climax stages. The time in days for the tadpoles as identified in (A) to go from stage 58 to stage 61 [as judged by the length of NO and BO. At stage 61, NO = BO (Fig. 6A)] was recorded and plotted with the mean, marked as a line, and SE. The asterisks (*) indicate a significant difference for the three genotypes (p < 0.01). (E) TRDKO leads to lethality at metamorphic climax. The tadpoles as identified in (A) were allowed to develop from stage 58 or stage 62, or when they died and were then genotyped. The survival rate for each of the three genotypes, TRα (−/−)TRβ (+/+) (n = 17), TRα (−/−)TRβ (+/−) (n = 21), and TRα (−/−)TRβ (−/−) (n = 15), was determined and plotted. Note that no double knockout tadpoles developed to stage 62. BO, bulbus olfactorius; NO, nervus olfactorius.