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Fig. 6. Tbx5 misexpression leads to changes in cardiac proliferation
and morphology. The overall morphology of stage 40 (A) uninjected
embryos or (B,C) embryos injected with increasing amounts of
Tbx5 RNA, as indicated. Arrows denote the location of the heart.
(D-G) Whole-mount in-situ hybridization showing expression of (D,E)
Nkx2.5 and (F,G) myosin light chain (MLC) in (D,F) uninjected stage
37 embryos and (E,G) stage-matched embryos injected with 1 ng of Tbx5
RNA. (H) Tbx5 misexpression leads to an increase in the
cardiac mitotic index at stage 37. Mitotic index was calculated as the
percentage of cardiac cells labeled with pH3. The data represents the mean of
at least three different embryos. Error bars denote the standard deviation,
and * denotes a statistically significant difference between
Tbx5-injected and control embryos (at P<0.05). (I)
Mitotic index for sections of the neural tube corresponding to the same
position as the heart along the anterior-posterior axis. The data represents
the mean mitotic index of four different embryos per condition, with four
sections analyzed per embryo. Error bars denote the standard deviation.
(J) Tbx5 misexpression leads to an alteration in the timing
and order of the cardiac differentiation program. RT-PCR analysis of the
expression of Nkx2.5 as well as heart-specific isoforms of MHC,
troponin and tropomyosin, and skeletal-muscle-specific genes, MyoD and muscle
actin, throughout early and mid-gestation stages of development in control
(`C') or Tbx5-injected (`T') stage-matched embryos. All samples are
derived from a single batch of eggs and identical results were achieved in at
least two independent sets of experiments for each marker. EF1-alpha was used
as a control for all RT-PCR reactions.
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