Fig. 2.

In vivo longitudinal imaging of islet growth. (A) Islets from 4-wk-old mice were transplanted into the anterior chamber of the eye of control and ob/ob mice at the age of 4 wk. Photography of transplanted eyes at different time points shows that individual islets can be identified and followed longitudinally (see yellow dashed circle). (B) Magnified views of islet grafts (marked by red frames in A) show the clearly visible large and tortuous blood vessels in the islet engrafted onto the iris of ob/ob recipient. (C) In vivo imaging of single islets 1 mo after transplantation by confocal microscopy shows morphological differences between islet grafts in control versus ob/ob mice. Vascularization is visualized by i.v. injection of FITC-labeled dextran prior to imaging. Note differences in backscatter intensity and vessel diameters. (D) In vivo imaging of islet grafts at different time points after transplantation by confocal microscopy. (E) Quantification of islet volumes by analysis of backscatter images reveals a significantly increased growth in ob/ob (solid lines) compared with control (dashed lines). Gray lines represent average islet volumes in single mice; black lines represent averaged values obtained per genotype (n = 3). (F) Immunohistochemistry analysis shows a strong proliferation of beta cells in both ob/ob transplanted eye and pancreas, as seen by insulin and Ki67 staining. (G) Average beta cell area was quantified from insulin and DAPI staining, demonstrating that beta cells from ob/ob mice (solid lines) were significantly larger than those from their control littermates (dashed lines). This hypertrophy was similar and independent of whether the islets were located in situ in the pancreas or in the transplanted eye (no significant differences). All images are representative. Confocal images are displayed as maximum intensity projections (MIPs) of optical Z-stacks. Immunohistochemistry experiments were performed using 4-mo-old mice (n ≥ 3 per group). Error bars represent SEM. *P < 0.05; **P < 0.01. (Scale bars: 100 µm.)