tbx-9 is expressed in three different cell types in the embryo, gut, muscle and hypodermis. The earliest embryonic expression was detected in the E lineage gut cell precursors Ea and Ep at the beginning of gastrulation (100 minutes after first cleavage). Expression was seen in the direct descendents of Ea and Ep but was not obvious later in E lineage nuclei.
tbx-9 was subsequently expressed in muscle and hypodermal cells. The expression of
tbx-9 was stronger in dorsal hypodermal nuclei. This is particularly evident in embryos that have been co-stained with LIN-26 and GFP antibodies. Expression could also be seen in dorsal hypodermal nuclei undergoing contralateral migration following cellular intercalation, and in lateral hypodermal cells during dorsal intercalation, although expression in lateral hypodermal cells at this stage was weaker. Expression in lateral hypodermal (seam) cells could also be seen later in embryogenesis until the 1.5-fold stage. No expression was observed in ventral hypodermal cells. The earliest detectable muscle cell expression was seen around the 400-cell stage, when muscle cells were present as two rows on the left and right sides of the embryo.