developmental stage:First detected at embryonic week 8 in individual 'converted' simple epithelial cells of the developing intestinal mucosa. In later fetal stages , synthesis extends over most goblet cells and a variable number of villus enterocytes. In the developing gastric and intestinal mucosa , expressed in all enterocytes and goblet cells as well as certain 'low-differentiated' columnar cells , whereas the neuroendocrine and Paneth cells are negative. ,Function:Plays a significant role in maintaining keratin filament organization in intestinal epithelia. When phosphorylated , plays a role in the secretion of mucin in the small intestine. ,miscellaneous:There are two types of cytoskeletal and microfibrillar keratin: I (acidic; 40-55 kDa) and II (neutral to basic; 56-70 kDa) . ,PTM:Hyperphosphorylation at Ser-13 occurs during the early stages of apoptosis but becomes less prominent during the later stages. Phosphorylation at Ser-13 also increases in response to stress brought on by cell injury. ,PTM:Proteolytically cleaved by caspases during apoptosis. Cleavage occurs at Asp-228. ,similarity:Belongs to the intermediate filament family. ,subunit:Heterotetramer of two type I and two type II keratins. Associates with KRT8. ,tissue specificity:Expressed predominantly in the intestinal epithelium. Expressed in luminal cells of colonic mucosa. Also expressed in the Merkel cells of keratinized oral mucosa; specifically at the tips of some rete ridges of the gingival mucosa , in the basal layer of the palatal mucosa and in the taste buds of lingual mucosa. ,
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