Regulation of intestinal brush border microvillus length during development by the G- to F-actin ratio.
We examined ultrastructural changes in developing chicken intestinal microvilli and correlated these with changes in the G- to F-actin ratio and the amount of actin per milligram cell protein. Three discrete morphological and temporal changes occur during late microvillus morphogenesis: an increase in microvillus number associated with microvilli becoming hexagonally packed on the cell surface; an increase in core actin filament number; and an increase in the length of microvilli. Dramatic rises in the amount of cell actin occur at the time of the first two morphological changes. Changes in the G- to F-actin ratio suggest that increases in the level of monomeric actin drive the elongation phase of microvillus growth since immediately prior to growth the G- to F-actin ratio shifts from its embryonic and adult 3:7 ratio to a 1:1. Our results also indicate, but do not prove, that an increase in the amount of G-actin precedes the rise in level of F-actin and growth of microvilli by 1 day, implying that an increase in the content of G-actin stimulates actin polymerization. Our findings also suggest that the G- to F-actin ratio and their absolute amounts, perhaps in combination with cytoskeletal protein turnover and/or the pool size of actin binding proteins, plays a role in restricting the mature constant length of microvilli.
D000199:Actins / Q000032:analysis*; D000818:Animals; D002352:Carrier Proteins / Q000032:analysis; D002642:Chick Embryo; D002645:Chickens; D003598:Cytoskeletal Proteins / Q000032:analysis; D018260:Gelsolin; D007422:Intestines / Q000254:growth & development / Q000648:ultrastructure*; D008840:Microfilament Proteins; D008855:Microscopy, Electron, Scanning; D008871:Microvilli / Q000648:ultrastructure; D009024:Morphogenesis; D013997:Time Factors
D000199:Actins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D018260:Gelsolin; D008840:Microfilament Proteins; C016953:brevin