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Epithelial differentiation in the fetal rat colon. I. Plasma membrane phosphatase activities
Insights
During fetal rat colon development, new phosphatases appear and segregate to specific membrane domains as the epithelium transforms from stratified to simple columnar. This ensures distinct luminal and basolateral functions during this critical remodeling process.
Area of Science:
- Developmental Biology
- Cell Biology
- Gastrointestinal Physiology
Background:
- The fetal rat colon undergoes significant epithelial remodeling during late gestation.
- Understanding the molecular changes during this transformation is crucial for comprehending colon development.
Purpose of the Study:
- To investigate the appearance and localization of plasma membrane phosphatases during fetal rat colon epithelial remodeling.
- To determine if these enzymatic activities segregate to specific membrane domains during the transition from stratified to simple columnar epithelium.
Main Methods:
- Utilized cytochemical analysis on fetal rat colon tissue slices (16-22 days gestation).
- Employed freeze-fracture electron microscopy to examine membrane structures.
- Performed biochemical analysis of cytochemical media to confirm enzyme activity.
Main Results:
- Two distinct phosphatase activities (pH 9.0 and pH 8.0) emerged at 18 days gestation.
- The pH 9.0 phosphatase localized primarily to luminal membranes, while the pH 8.0 phosphatase was mainly on nonluminal membranes.
- These activities were segregated to specific membrane domains even when the epithelium was still stratified and remained so during its conversion to simple columnar.
Conclusions:
- Plasma membrane phosphatase activities appear and become spatially segregated during fetal colon epithelial development.
- This segregation is established early and maintained throughout the remodeling process, suggesting functional specialization of membrane domains.
Abstract:
During the last week of gestation of the fetal rat, the epithelium of the colon is rapidly remodeled. At 16 days a primitive stratified epithelium surrounds a small central lumen. Over the next 3 days, the main lumen extends narrow clefts down to the basal cell layer and small secondary lumina appear within the stratified epithelium between these clefts. At 19 and 20 days, secondary lumina enlarge but remain discrete; an infusion of cationic ferritin into the main lumen does not enter secondary lumina. During the 2 days prior to birth (21-22), the secondary lumina join the main lumen as superficial cells are sloughed, and the epithelium becomes simple columnar. Freeze-fracture replicas indicate that luminal and nonluminal membrane domains of epithelial cell plasma membranes are separated by continuous tight junctions throughout the conversion process. Cytochemical analysis of tissue slices from 16- to 22-day fetal colon demonstrated the appearance and segregation of two phosphatases on apical and basolateral membrane domains during epithelial conversion. Cysteine-sensitive pH 9.0 (alkaline) phosphatase activity was first detected along the luminal membranes of cells bordering both primary and secondary lumina at 18 days gestation and increased to a maximum at 20-21 days; weaker activity was present on basolateral membranes. Phosphatase activity at pH 8.0 also appeared at 18 days and increased thereafter, but was localized primarily on nonluminal membranes. At pH 8.0, reaction product appeared on both inner and outer sides of the membrane, and was only partially abolished by omission of K+ or addition of ouabain; thus the reaction may be only partially due to K+-dependent ATPase activity. Biochemical analysis of the cytochemical media confirmed the appearance of phosphatase activities at 18 days. Thus, plasma membrane phosphatase activities appear while the epithelium is still stratified, but are segregated to luminal and nonluminal membrane domains at the onset of activity. Segregation is maintained throughout the process of conversion of a simple columnar epithelium.