Hedgehog signaling regulation of postnatal tongue and taste organ morphogenesis - Abstract The tongue has a major developmental trajectory during suckling and weaning periods as they adapt for changes in feeding patterns and movement for speech. This growth encompasses numerous and extreme changes, including increases in anterior tongue taste organ fungiform papilla (FP) taste cell number and size, conical keratinization of non-taste filiform papillae (FILIFP), thickening of stroma and biochemical changes in muscles. However, knowledge gaps remain regarding the molecular mechanisms orchestrating this growth in different anatomical compartments of the postnatal tongue. Hedgehog (HH) signaling is vital for embryonic tongue development and taste organ maintenance in adults, but its role in postnatal tongue is not clearly elucidated. We have strikingly discovered that it extends beyond FP in the early postnatal tongue, specifically within FILIFP, suggesting a potential role for HH signaling in FILIFP maturation. To challenge the current paradigm, we will identify HH pathway components and HH-regulated target genes in early postnatal FILIFP epithelium using RNA and DNA sequencing tools (Aim 1a). We will then describe how HH signaling and its candidate FILIFP-specific target genes contribute to postnatal FILIFP maturation and function by using an epithelium-specific genetic mouse model to inhibit the pathway (Aim 1b). Further, HH receptors CDON, GAS1 and PTCH1, despite their known relevance in other postnatal tissues, remain uninvestigated in the postnatal tongue. We observe that their expression is largely non-overlapping in FP and FILIFP epithelium, stroma or lingual muscles during the first postnatal week. Importantly, their expression patterns shift in coordination with tongue and taste organ maturation by postnatal day 21. We hypothesize that the distinct spatiotemporal expression of HH receptors in the early postnatal tongue differentially regulates morphogenesis in different anatomical compartments and restricts their function in late postnatal stages to maintaining taste organs. Therefore, our second aim will employ epithelium-, stroma- or muscle-specific conditional loss-of-function approaches for Cdon, Gas1 or Ptch1 to elucidate their functions in feeding and taste. We will describe the individual contributions of Cdon, Gas1 or Ptch1 to the growth of FP and FILIFP (Aim 2a), stroma (Aim 2b) and muscle (Aim 2c) across early and late postnatal stages. Our goals are to unveil the role of HH signaling and its essential cell surface receptors in the postnatal development of the lingual epithelium, stroma and muscles, and to elucidate the functional consequences of HH pathway/receptor inhibition on the juvenile feeding and taste system. These findings will provide a molecular understanding of tongue maturation after birth across different anatomical compartments, laying the groundwork for improved diagnostic and treatment strategies for pediatric tongue-related abnormalities.
