The Pttr-33::gfp reporter was found to be expressed in six cells residing in the head of L1 larvae. Two of the labelled cells were located next to the first pharyngeal bulb and four were situated halfway between the mouth and the first pharyngeal bulb. All six cells form protrusions towards the mouth of the larva. The cells were labelled as early as in the embryonic pretzel stage. Comparison with the cell atlas of C. elegans and a GFP reporter under the control of the
grl-27 arcade cell-specific promoter revealed that these cells represent most likely the posterior arcade cells, which are located between external epidermis and anterior pharynx. In addition, in L1 stage larvae,
ttr-33 expression was observed in the pharynx and in several unidentified cells immediately posterior to the second pharyngeal bulb. In older animals, the Pttr-33::GFP transcriptional reporter highlights head cells next to and anterior of the first pharyngeal bulb, as well as the pharynx and the hypodermis.