Analysis on Nkx2.1 expression in the embryonic foregut endoderm during cephalocaudal folding process

Introduction: Schematically, embryonic folding and segmental ventrodorsal juxtapositioning theory assert that primitive foregut has different dorsal and ventral parts due to cephalocaudal folding in the fields of trilaminar embryonic plate. However, it is unclear whether all segments of primitive gut endoderm is formed from the ventral and dorsal components due to cephalocaudal folding or there is any segments only from dorsal component due to embryonic lateral folding. To solve this puzzle, we observed the expression pattern of Nkx2.1, a determinant of dorsoventral pattern in the early foregut formation. We wanted to know whether Nkx2.1 can be a marker of cephalocaudal folding-derived ventral foregut. Methods: Sprague-Dawley rat’s embryo ED 9.5–11 (n = 12) were fixed with 10% neutral formalin buffer, embedded in paraffin, serially sectioned (5 _m) and were immunohistochemically stainned against Nkx2.1 antibody. Results: Nkx2.1 expression in the ventral foregut were first seen in embryos ED 11. The expression showed a specific pattern, as it was seen in the area of primordium thyroid at the level of the first pharyngeal arch, and at the heart level from atrioventricular canal to the distal of venous sinuses. The lateral border of Nkx2.1 expression was indecisive. Conclusion: During cephalocaudal folding, Nkx2.1 expressed in the foregut endoderm in a specific pattern instead of in the entire length of the gut. It was not expressed at the lower border of the cephalocaudal folding too. Therefore, Nkx2.1 cannot be used as a marker for the cephalocaudal folding-derived ventral foregut.