The Tbx6 (T-box 6) gene belongs to a family of transcription factors involved in development and is crucial to specification of the posterior paraxial mesoderm and the extraembryonic allantois. Tbx6 alleles are associated with human spondylocostal dysostosis and scoliosis. These knock-out mice contain a human HIST1H2BB-EYFP fusion in frame with exon 1 and replacing exon 2 and part of exon 3. The region represents a portion of the T-box, a DNA binding domain. EYFP expression recapitulates Tbx6 expression. Homozygous embryos develop heterotaxia characterized by abnormal heart looping and randomized embryo turning. In addition, nodal cilia appears shortened, and thickened with terminal knobs and abnormal cilia motility is observed throughout the node, particularly in the pit of the node. Loss of asymmetric calcium signaling occurs at the periphery of the node. Somites develop ectopic neural tubes. Homozygous embryos die by E9.5 due to vascular hematomas. Heterozygotes are viable and fertile with minor skeletal abnormalities in the tail tip. These mice may be useful for studying left/right axis determination.

This knock-out/knock-in EYFP reporter allele of Tbx6 (T-box 6) uses an EYFP fusion to delete exons 2 and part of 3, resulting in embryonic lethality by E9.5. Homozygous embryos develop randomized left/right axis patterning and altered morphology and motility in nodal cilia. These mice may be useful for studying left/right axis determination.

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