FIGURE 2.

Patterns of cell death and cell senescence in the developing autopod of chick embryos at incubation day 7.5. (A) areas of cell death (INZs) mapped by vital stained with neutral red. (B) Vibratome section of autopod at stage equivalent to that illustrate in (A) showing the pattern of SAβ-gal staining for cell senescence. Note the identical pattern of SAβ-gal and neutral red vital staining in (A). Note also the positivity for SAβ-gal in the developing tendons (arrow). (C) Semithin section of the third interdigital space stained with toluidine blue to show the structure of the regressing interdigits. Note the abundance of dark dying cells. Arrow shows a large macrophage containing phagocytosed dead cells. (D) Transverse vibratome section of digit 3 at id 8, showing SAβ-gal staining in the interdigital margins of the digit (arrows) and in the extensor and flexor tendons (arrow heads) in course of differentiation. (E) Transverse section of digit 3 stained with toluidine blue showing a detailed view of the digit flexor tendon. The level of the section is indicated by black arrows in (B). (F) longitudinal section of the autopod through the level of the flexor tendons after incubation for 30 min in bromodeoxyuridine (BrdU). Note the reduced proliferation in the interdigital regions (id) and in the core of the developing tendons (T) (originally published in Lorda-Diez et al., 2009).