FIGURE 2. Fbn1 null phenotype.

A, left two panels, representative aneurysm of the ascending aorta in a newborn mouse with histological documentation (Weigert staining) of elastic fiber fragmentation and aortic wall rupture (arrow). Right four panels, top, right lungs of wild-type (+/+) and Fbn1 null (−/−) mice showing multiple blebs in the peripheral portion of the latter (arrow); bottom, partial views of the exposed thoraxes of wild-type and mutant mice showing thinner intercostal muscles and abnormal ribs in the latter compared with the former animal. B, cross-sections of aortic tissue around the lesions in mutant mice (−/−) and at corresponding levels in age and sex-matched wild-type littermates stained with H&E, Weigert, trichrome, or anti-MMP-9 antiserum. On the right side of the H&E panels is a magnification of the mutant tissue showing an altered architecture with loss of normal contacts between cells and with the surrounding matrix (yellow arrows). The immunoblot on the right further documents elevated MMP-9 compared with β-tubulin levels in the decaying post-mortem aorta of mutant mice. All the specimens are oriented with the lumen of the vessel at the top; scale bar = 100 μm.