Topographic distribution pattern of morphologically different G cells in the murine antral mucosa

Abstract

Gastrin-secreting enteroendocrine cells (G cells) in the antrum play an important role in the regulation of gastric secretion, gastric motility and mucosal cell proliferation. Recently we have uncovered the existence of two subpopulations of G cells with pivotally different morphology and a distinct localization in the antral invaginations; the functional implications of the different G cell types are still elusive. In this study a transgenic mouse line in which EGFP is expressed under the control of a gastrin promoter was used to elucidate the distribution pattern of the two G cell types throughout the different regions of the antrum. The results of immunohistochemical analyses revealed that G cells were not equally distributed along the anterior/posterior axis of the antrum. The "typical" pyramidal- or roundish-shaped G cells, which are located in the basal region of the antral invaginations, were more abundant in the proximal antrum bordering the corpus region but less frequent in the distal antrum bordering the pylorus. In contrast, the "atypical" G cells, which are located in the upper part of the antral invaginations and have a spindle-like contour with long processes, were evenly distributed along the anterior/posterior axis. This characteristic topographic segregation supports the notion that the two G cell types may serve different functions. A comparison of the antrum specific G cells with the two pan-gastrointestinal enteroendocrine cell types, somatostatin-secreting D cells and serotonin-secreting enterochromaffin (EC) cells, revealed a rather similar distribution pattern of G and D cells, but a fundamentally different distribution of EC cells. These observations suggest that distinct mechanisms govern the spatial segregation of enteroendocrine cells in the antrum mucosa.

Figure 1.

G cells are clearly confined to the antral region of the stomach. A-D) Longitudinal tissue sections of the antrum and the adjacent gastrointestinal tissues derived from mGAS-EGFP transgenic mice are shown; G cells are visible due to their intrinsic EGFP fluorescence (green). Tissue sections were immunostained using specific antibodies for histamine (A,B) and smoothelin (C,D) both labeled in red. A,C) To visualize the gastrointestinal tissues all cells were counterstained with DAPI (blue). A,B) The transition from the corpus to antrum (indicated by the yellow arrows) can be clearly determined by labeling ECL cells and G cells; both EEC populations are found in distinct compartments of the stomach and do not overlap; histamine-immunopositive cells are found in the corpus but absent in the antrum while EGFP-positive G cells are only present in the antrum. C,D) The transition from the antrum to the duodenum (indicated by the yellow arrows) can be visualized by labeling smooth muscle cells of the pylorus which separates the stomach from the small intestine; EGFP-positive G cells are scattered throughout the antrum reaching the pyloric region but are absent in the duodenum. Scale bars: 200 μm.

Figure 2.

G cells are less frequent in the distal antrum compared to the proximal antrum. A-C) Longitudinal tissue sections of the antrum of mGAS-EGFP transgenic mice are shown; G cells are visualized by green fluorescence; tissue sections were counterstained with DAPI (blue). A) The antral mucosa differs along the length of the antrum. Likewise, G cells were not evenly distributed. B,C) When counting G cells in the proximal (B) and distal antrum (C), normalized to 1000 nuclei 25.08±7.58 (D) and 13.77±4.13 G cells (E) were found in the mucosa of the proximal and distal antrum respectively. Scale bars: 200 μm.

Figure 3.

Distinct topographic distribution patterns for morphologically different G cells. A) A longitudinal tissue section of the antrum of a mGAS-EGFP transgenic mouse is shown in differential interference contrast (DIC); G cells are visible due to their intrinsic green fluorescence; the yellow dashed line separates the basal region from the upper region of the antral invaginations. While basally located G cells are pyramidal- or roundish-shaped (B), G cells in the upper region have a spindle-like contour and long processes (C). D) In the basal region the numbers of pyramidal-/roundish-shaped G cells was significantly higher in the proximal antrum (23.91±7.49) compared to the distal antrum (12.22±3.81). E) In the upper region the number of spindle-like G cells did not significantly differ between the proximal (1.17±0.25) and distal antrum (1.55±0.40). **P<0.01; ns, not significant. Scale bars: A) 20 μm; B) 5 μm; C) 10 μm.

Figure 4.

Similar topographic distribution patterns of G cells and D cells in the antrum. A,B) Longitudinal tissue sections of the proximal (A) and distal antrum (B) of mGASEGFP transgenic mice are shown; G cells are visualized by green fluorescence; D cells were immunostained using a specific antibody for somatostatin (red); tissue sections were counterstained with DAPI (blue). C) In the basal region of the antral invaginations, compared to G cells (grey bars), smaller D cell numbers (black bars) were counted; in the proximal antrum 7.36±0.70 D cells were found, while only 2.53±0.13 D cells were counted in the distal antrum. D) In the upper region, 0.44±0.23 and 0.54±0.25 D cells were found in the proximal and distal antrum respectively. ***P<0.001; **P<0.01; *P<0.05; ns, not significant. Scale bars: 200 μm.

Figure 5.

Different topographic distribution patterns of G cells and EC cells in the antrum. A,B) Longitudinal tissue sections of the proximal (A) and distal antrum (B) of mGAS-EGFP transgenic mice are shown; G cells are visible due to their intrinsic fluorescence (green), EC cells were immunostained using a specific antibody for 5-HT (red); tissue sections were counterstained with DAPI (blue). C) In the basal region of the antral invaginations, compared to G cells (grey bars), smaller EC cell numbers (white bars) were counted; 13.92±3.26 and 6.46±3.33 EC cells were counted in the proximal and distal antrum, respectively. D) In the upper region EC cells outnumbered G cells as 1.36±0.58 and 3.10±1.04 EC cells were found. ns, not significant. Scale bars: 200 μm.