Fig. 4: Expression profile of the ACE2 and TMPRSS2 proteins in the taste circumvallate papilla.

Immunohistochemical investigations on the taste buds for SARS-CoV-2 entry sites in circumvallate papillae. a, b Here, the gustducin marker protein (GUST; in red) allows the localization of the gustatory sensory cells. a Large view of GUST+ sensory cells of the circumvallate papilla (CV). b Enlarged view of ((a), dashed rectangle), showing expression of ACE2 (in pink) in the apical keratinocytes and in the microvilli of the chemosensory cells forming the taste pores, which are in direct contact with the oral cavity. A zoom in view of the microvilli of a taste pore is shown. c Co-expression profile of TMPRSS2 (in red) and ACE2 in the taste pores (highlighted with a zoom in view). d Control experiment (Ctrl neg) illustrating the absence of fluorescent background expression. Colocalization between red and pink signals is highlighted in light gray (a–d). Nuclei are counterstained with Dapi (DAPI, in blue). Representative protein expression profiles were obtained from heterozygous OMP-GFP mice of 6 (a, b), 5 (c), and 7 months old (d). Scale bars are 50 μm (a), 10 μm (b–d).