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Dev Dyn
2007 Sep 01;2369:2475-84. doi: 10.1002/dvdy.21244.
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Transient early embryonic expression of Nkx2-5 mutations linked to congenital heart defects in human causes heart defects in Xenopus laevis.
Bartlett HL
,
Sutherland L
,
Kolker SJ
,
Welp C
,
Tajchman U
,
Desmarais V
,
Weeks DL
.
???displayArticle.abstract??? Nkx2-5 is a homeobox containing transcription factor that is conserved and expressed in organisms that form hearts. Fruit flies lacking the gene (tinman) fail to form a dorsal vessel, mice that are homozygous null for Nkx2-5 form small, deformed hearts, and several human cardiac defects have been linked to dominant mutations in the Nkx2-5 gene. The Xenopus homologs (XNkx2-5) of two truncated forms of Nkx2-5 that have been identified in humans with congenital heart defects were used in the studies reported here. mRNAs encoding these mutations were injected into single cell Xenopus embryos, and heart development was monitored. Our results indicate that the introduction of truncated XNkx2-5 variants leads to three principle developmental defects. The atrial septum and the valve of the atrioventricular canal were both abnormal. In addition, video microscopic timing of heart contraction indicated that embryos injected with either mutant form of XNkx2-5 have conduction defects.
Figure 2. Atrial septum morphology at embryonic stage 46. The images are of 20 compiled confocal sections taken at 8-micron intervals. Embryos were fixed in Dent's fixative and used for whole-mount immunostaining. The primary antibody used was anti-cardiac troponin T (CT3) monoclonal antibody followed by incubation with anti-mouse Alexa 568 conjugate. Arrowheads point to the atrial septum and the atrioventricular canal is marked with an asterisk. A–D: A normal septum seen in a heart from a water injected control (A), a normal septum seen in a heart from an embryo injected with the XNkx2-5 full length mRNA (B), thin septum seen in a heart from an embryo injected with XNkx2-5 His156ter (C), and a frayed and deviated septum seen in the heart of an embryo injected with XNkx2-5 Gln185ter (D). E,F: Histological sections of hearts from a buffer-injected embryo (E) or an embryo injected with the XNkx2-5 His156ter mRNA (F) allow an alternative comparison of normal and frayed septum. In panels E and F, atrial nuclei were pseudocolored red using Adobe Photoshop to provide a clear view of septal structure.Download figure to PowerPoint
Figure 3. Altered morphology of the atrioventricular canal in embryos injected with XNkx2-5 encoding truncated protein. Embryos were fixed in Dent's fixative and used for whole-mount immunostaining using JB3 (anti-fibrillin) antibody followed by a Cy5 secondary antibody and viewed using a confocal microscope. Images show the atrioventricular canal viewed from the atrial side of the valve and include arrowheads to denote the anterior and posterior leaflets of the atrioventricular valve. A: Non-injected embryo. B: XNkx2-5 FL-injected embryo. C: XNkx2-5 His156ter-injected embryo. D: XNkx2-5 Gln185ter-injected embryo. Note the dysplastic appearance and poor coaptation of the valve leaflets in the embryos injected with mutant XNkx2-5 (C,D).Download figure to PowerPoint
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