Fig. 5.

Deficient DA neuron development and selective increase in apoptosis in the midbrain dopaminergic area in p57^Kip2-null mutant pups. (A–D) Coronal sections of E18.5 wild-type (A and C) and p57^Kip2-null mutant (B and D) pups showing TH immunoreactivity (A and B) and Nurr1 mRNA expression (C and D). Expression patterns of TH and Nurr1 appear abnormal in the p57^Kip2 mutant ventral midbrain. TH- and Nurr1-expressing cells are almost entirely absent in the lateral regions, and the morphology appears disorganized. Both markers were normally distributed in other brain areas. (C and D Insets) Normal Nurr1 expression in p57^Kip2 mutant cortex. (E–G) TH was normally expressed in other catecholaminergic groups, e.g., the locus coeruleus (E and F) and olfactory bulb (G and H). (I–K) A combined TH-staining/TUNEL assay was used on coronal sections to detect apoptotic cells in the E18.5 wild-type and p57^Kip2-null mutant ventral midbrain. TUNEL-positive cells in the area of midbrain DA cells were observed and counted in wild-type and p57^Kip2 mutant mice. An increase in apoptotic cells in the entire dopaminergic area was observed in the mutant (J) as compared with the wild type (I) as exemplified by these high-magnification images of the medial ventral midbrain. The increase in the mutant was >2-fold greater than the wild type (K) (E18.5, p57^Kip2+/+, n = 3; –/–, n = 3; **, P < 0,005). (Scale bars: A–D, 100 μm; Insets, 300 μm; E–J, 200 μm.)