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Table 3.

Glandular phenotypes of Fgf8 domain-specific mutants: sectioned specimens at E18.5

GenotypeNormal thymusEctopic thymusHypoplastic thymusNormal parathyroid glands*Ectopic parathyroid glandsHypoplastic parathyroid glandsAbsent parathyroid glands
AP/+ or +/N (n=40) 38 (95%) 2 (5%) 76 (100%) 3 (4%) 1 (1%) 
AP/N (n=15) 15 (100%) 30 (100%) 
AP/N; AP2α-ICre (n=24) 22 (92%) 2 (8%) 44 (92%) 2 (4%) 2 (4%) 
AP/N; hoxa3-ICre (n=33) 10 (31%) 17 (51%) 13(41%) 20 (32%) 31 (48%) 38 (58%) 18 (28%)§ 
P value Ap2α versus hoxa3 mutants 0.05 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 
GenotypeNormal thymusEctopic thymusHypoplastic thymusNormal parathyroid glands*Ectopic parathyroid glandsHypoplastic parathyroid glandsAbsent parathyroid glands
AP/+ or +/N (n=40) 38 (95%) 2 (5%) 76 (100%) 3 (4%) 1 (1%) 
AP/N (n=15) 15 (100%) 30 (100%) 
AP/N; AP2α-ICre (n=24) 22 (92%) 2 (8%) 44 (92%) 2 (4%) 2 (4%) 
AP/N; hoxa3-ICre (n=33) 10 (31%) 17 (51%) 13(41%) 20 (32%) 31 (48%) 38 (58%) 18 (28%)§ 
P value Ap2α versus hoxa3 mutants 0.05 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 

These data indicate that the pharyngeal endodermal domain of FGF8 has a required separable role in thymic and parathyroid morphogenesis, and that the ectodermal domain does not contribute to these processes.

*

Note individual glands were scored

Eight animals had isolated ectopic lobes; nine had ectopic lobes in combination with hypoplasia of one or both lobes. Sixty-eight percent had markedly abnormal migration and/or hypoplasia of thymic tissue

Five animals had isolated hypoplastic lobes; nine had hypoplastic lobes in combination with ectopy of one or both lobes

§

67% were abnormal overall. Ten animals had bilaterally normal parathyroids;seven had unilateral defects and 15 had bilateral defects. As parathyroids may be found embedded in, posterior-lateral to, or anterior-lateral to the thyroids in normal animals at this age, ectopy was scored only if a gland was estimated to be less than 50% the size of a normal gland

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