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Extensive networks of TMPase positive basal lysosomes are present in fetal rat gastric epithelium before overt
1Department of Histology and Embryology, University of São Paulo, Brazil.
Insights
During fetal development, rat gastric epithelium transforms, revealing basal granules containing trimetaphosphatase (TMPase) activity. This enzyme
Area of Science:
- Developmental Biology
- Cell Biology
- Gastroenterology
Background:
- The rat gastric epithelium undergoes significant morphological changes during intrauterine development.
- Early differentiation involves the appearance of basal granules in undifferentiated epithelial cells.
Purpose of the Study:
- To investigate the biochemical nature of basal granules in the developing rat gastric epithelium.
- To characterize the enzyme activities present in these structures using cytochemistry.
Main Methods:
- Enzyme cytochemistry was employed to detect acid phosphatase and trimetaphosphatase (TMPase) activities.
- Ultrastructural analysis was performed on fetal rat gastric epithelium at 17-19 days of gestation.
Main Results:
- Acid phosphatase activity was localized to typical lysosomes near the Golgi apparatus.
- Strong trimetaphosphatase (TMPase) activity was observed in basal granules and tubular structures at 17-18 fetal days.
- At 19 fetal days, TMPase-positive basal structures diminished, with new lateral tubular and vesicular structures appearing.
Conclusions:
- Trimetaphosphatase (TMPase) activity is associated with specific basal granules and tubular structures in the early fetal rat gastric epithelium.
- The presence of coated pits and vesicles suggests a role for these TMPase-positive structures in endocytosis and receptor internalization prior to overt epithelial differentiation.
Abstract:
The rat gastric epithelium of 17 to 19 days of intrauterine life changes from a pseudostratified epithelium to a simple columnar epithelium. From a flat epithelium at 17-18 days, groups of epithelial cells begin to invaginate towards a cellularly rich mesenchyma and foveolae appear at 19 fetal days. Ultrastructural differentiation of the first cells of gastric glands occurs at 19 days. The ultrastructure of the undifferentiated cells at 17-18 fetal days shows extensive distribution of granules in the basal cytoplasm, near the basal lamina. To investigate the nature of these structures, enzyme cytochemistry was carried out. Acid phosphatase and trimetaphosphatase activities were demonstrated cytochemically in the gastric epithelium of the fetal rat. Whereas acid phosphatase positive lysosomes were observed mainly in typical round lysosomes, near the Golgi, a strong positive reaction for trimetaphosphatase, at 17 and 18 fetal days, was present in granules and tubular structures located in the basal cytoplasm. This reaction was coincident with the observed basal granules. At 19 days, the number of basal TMPase positive lysosomes was diminished, but other lateral tubular and vesicular positive structures were seen. The presence of coated pits in the basal membrane and microtubules and coated vesicles between tubular lysosomes, at 17-18 days, just before overt differentiation, reinforces the possibility of the association of this kind of lysosome with endosomes and the internalization of receptors.