The stem‐cell zone of the small intestinal epithelium. V. Evidence for controls over orientation of boundaries between the stem‐cell zone, proliferative zone, and the maturation zone

Abstract

We studied, in mouse jejunum, the possibility that coordinate systems related to crypt axis or muscularis mucosae have an influence over the orientation of the boundaries between three crypt compartments: the stem‐cell, the proliferative, and the maturation zones. Segments of jejunum, from male Swiss albino mice injected with ³H‐thymidine 1 hour before death, were collected, embedded in Epon, and 1‐μm‐thick serial sections were prepared and radioautographed. Similar material was also obtained from an experimental preparation in which the anti‐mesenteric border of a short segment of jejunum was involuted surgically, thus creating a fold similar to the plicae circulares in the human intestine. The crypts lining the sides and top of the folds were greatly tilted, relative to the muscularis mucosae 2 weeks after surgery. The angle formed between the crypt axis and the plane of the muscularis mucosae (Θ) was measured. This was related to the angle formed between the crypt axis and the ³H‐thymidine‐labeled leading edge (β), and that between the crypt axis and the upper boundary of the Paneth‐cell distribution (α). The angle α indicates the orientation of the boundary between the stem‐cell and proliferative zones, while β indicates the orientation of the boundary between the proliferative and maturation zones. We found that β remained perpendicular to the crypt axis for all degrees of crypt tilt (Θ). In contrast, α did not remain perpendicular to the crypt axis over all degrees of crypt tilt. When crypts were tilted by more than 30°, α reoriented and was found to be parallel to the plane of the muscularis mucosae. However, in crypts tilted less than 30°, α remained perpendicular to the crypt axis. We concluded that there are probably two coordinate systems that provide information to the crypt epithelium. The first is a coordinate system related to crypt axis that influences the orientation of the boundary between the proliferative and maturation zones and the second is related to muscularis mucosae an influences the orientation of the boundary between the stem‐cell and proliferative zones. The latter has a threshold of about 30°, which probably represents the range of peristalsis‐induced crypt tilt.