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Developmental regulation of alpha-fetoprotein expression in intestinal epithelial cells of transgenic mice
L A Cirillo1, J A Emerson, J Vacher
1Department of Biology, Carleton College, Northfield, Minnesota 55057, USA.
Insights
A repressor element in the alpha-fetoprotein (AFP) gene controls its expression in the adult mouse intestine. Removing this element increases AFP expression in goblet cells, but not enterocytes.
Area of Science:
- Molecular Biology
- Developmental Biology
- Genetics
Background:
- Alpha-fetoprotein (AFP) gene expression in the fetal mouse small intestine decreases significantly after birth.
- Persistent AFP transcription in adults is limited to a small subset of enteroendocrine cells (<1%).
Purpose of the Study:
- To investigate the role of a specific repressor element (-838 to -250 bp) in regulating AFP gene expression in the adult mouse intestine.
- To determine how deletion of this repressor element affects AFP minigene expression patterns in transgenic mice.
Main Methods:
- Utilized transgenic mouse models containing AFP minigene constructs with and without the identified repressor element.
- Analyzed AFP minigene RNA expression patterns in various intestinal epithelial cell types (enteroendocrine, goblet, enterocytes) of adult and neonatal mice.
Main Results:
- Deletion of the AFP repressor element led to a tenfold increase in minigene expression in adult mouse intestines, expanding to ~10% of epithelial cells.
- The increased expression included goblet cells and enteroendocrine cells, but not enterocytes, indicating the repressor is active in goblet cells.
- AFP minigene expression in enterocytes decreased in neonates, suggesting a separate regulatory mechanism or loss of positive factors.
Conclusions:
- The identified AFP repressor element specifically functions in goblet cells to suppress gene transcription.
- Regulation of AFP expression in enterocytes likely involves distinct cis-acting elements or differential expression of transcription factors.
Abstract:
The alpha-fetoprotein (AFP) gene is transcribed in most epithelial cells lining the fetal mouse small intestine, but transcription persists in only a subset of enteroendocrine cells representing less than 1% of the total intestinal epithelial cells in the adult. The decrease in AFP expression after birth is mediated in part by a repressor element lying between -838 and -250 bp of the AFP gene. Deletion of this element from AFP minigene constructs results in high-level minigene expression in the intestines of adult transgenic mice. Although high levels of AFP minigene RNA are expressed, the fetal pattern of expression is not maintained upon deletion of the repressor element. Instead, the number of cells in which the minigene is expressed increases from less than 1% to approximately 10% of the epithelial cells in the adult small intestine, and includes the majority of the goblet cells in addition to the enteroendocrine cells. In contrast, the pattern of AFP minigene expression in the enterocytes is unaffected by deletion of the repressor element and continues to decrease in the neonate. These studies indicate that the identified AFP repressor is active specifically in goblet cells. The decrease in AFP expression in the enterocytes may be mediated by a separate cis-acting element that is contained in the AFP minigene construct. Alternatively, it is possible that mature enterocytes lack some of the positive factors required for initiation and maintenance of minigene transcription in the absence of the identified negative element.