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Fig. 7. Conditional ablation of Pitx2 in mesoderm-derived cells reveals
an autonomous role for Pitx2 in branchiomeric muscle development.
Pitx2 deletion in mesoderm using the Mesp1cre and
Pitx2flox alleles. (A,B) Lineage tracing
indicates a reduction in the number of LacZ-marked Pitx2
mutant descendents in the masseter muscle (outlined, arrow).
(C,D) Myogenin expression (arrow) is greatly reduced in the
Pitx2 mutant compared with control. Sections through the masseter
muscle of control (E,F) and Mesp1cre; Pitx2
n/f mutant (G,H) indicate a muscle deficiency in the
Pitx2 conditional mutant (arrows). (I-L) Myosin immunostaining with
the MF20 antibody in 14.5 control (I,J) and Pitx2
conditional null mutant (K,L) to mark branchiomeric muscle in
control and show deficiency in mutant (arrows). Note that in the mutant (L)
there is residual subcutaneous muscle that shows myosin reactivity
(arrowhead). e, eye; mc, Meckel's cartilage; md, mandible; mx, maxilla.