Analysis of TBX18 expression in chick embryos.

T-box genes encode transcription factors that control the development of diverse tissues and organs in vertebrate embryos. Here, we report the expression of the TBX18 gene during chick development. TBX18 expression is found in anterior halves of prospective and definitive somites as well as in the unsegmented cranial region of the paraxial mesoderm. Expression levels are high in the presomitic mesoderm but decrease in newly formed somites. This is in contrast to the mouse where uniform expression has been reported in the paraxial mesoderm. TBX18 expression is also prominent in the proepicardial serosa and in the epicardium of the heart. Other sites of expression include the genital ridge and the developing limb buds.