Type 1 keratin (Probable). Maintains postnatal tongue mucosal cell homeostasis and tissue organization in response to mechanical stress, potentially via regulation of the G1/S phase cyclins CCNE1 and CCNE2 (PubMed:32758484). Heterotetramer of two type I and two type II keratins. Expressed in tongue epithelia (at protein level) (PubMed:1695590). Expressed in upper suprabasal layers of the corneal epithelium (at protein level) (PubMed:26758872). Expressed in the oral mucosa, including the palate, dorsal tongue, ventral tongue, and the floor of the mouth at 17.5 dpc (PubMed:32758484). Expressed in basal cells and differentiated keratinocytes at the ventral surface and the oral interpapillary cell column on the dorsal surface of the tongue at birth (PubMed:32758484). Ubiquitously expressed in basal cells and differentiated keratinocytes on the ventral tongue epithelium, however expression was limited to the cells in the interpapillary region and keratinized layer on the dorsal tongue at postnatal day 20 (P20) (PubMed:32758484). Also expressed in the buccal mucosa and esophagus at P20 (PubMed:32758484). O-glycosylated; glycans consist of single N-acetylglucosamine residues. Knockout mice maintain a normal body weight and developmental phenotype (PubMed:32758484). Tongue histological abnormalities are evident at P20 including the loss of two lingual vessel branches at the ventral side of the tongue which appears white and wrinkled, especially on the ventral surface at three weeks of age (PubMed:32758484). Loss of column-like basal cell organization and increase in nuclear atypia and vacuolization in both the basal and suprabasal layers of the tongue (PubMed:32758484). Loss of keratohyalin granules, abnormal presence of cuboidal cells in the suprabasal layers and loss of organization of the outermost keratin layer leading to a foamy appearance (PubMed:32758484). Increase in intracellular gaps, however desmosomes still formed but were found broken and intermediate filaments running from the desmosomes to the cytoplasm were missing or reduced (PubMed:32758484). Cytoplasmic vacuolization is evident in all cell layers and large lipid droplets are found in granular cells in the tongue epithelia (PubMed:32758484). Severe abnormalities in buccal mucosa and esophagus including thickened epithelium, immature suprabasal cells, loss of keratohyalin granules and a disorganized keratin layer at P20 (PubMed:32758484). Disrupted proliferation and differentiation in tongue epithelial cells at P20, as indicated by disordered expression of the transcription factor Tp63/P63, the basal progenitor cell marker Krt5, and the differentiated epithelial cell marker Loricrin (PubMed:32758484). Increase in proliferating cells in the upper layers of the tongue epithelium at P20 (PubMed:32758484). Normal tongue morphology, structural architecture and epithelial cell proliferation at birth (PubMed:32758484). Differential expression of 125 genes in the tongue at P0, enriched in keratinization, proinflammatory responses, stress-activated protein kinase signaling and threonine/lipid metabolic processes (PubMed:32758484). Differential expression of 2907 genes in the ventral tongue at P20 involved in a range of processes, however primarily in cell cycle regulatory pathways (PubMed:32758484). Increase in the expression of CCNE1 and CCNE2 in response to in vitro mechanical stress of the tongue (PubMed:32758484). There are two types of cytoskeletal and microfibrillar keratin: I (acidic; 40-55 kDa) and II (neutral to basic; 56-70 kDa). Belongs to the intermediate filament family.