Figure 4. Expression of the R26R Cre Reporter Gene in Pomc- or Agrp-Specific Tfam Mutant Animals.

Animals carrying the PomcCre or AgrpCre transgene together with the lacZ reporter allele for Cre recombination Gt(Rosa)26Sor^tm1Sor (R26R) were intercrossed with Tfam ^flox/^flox animals. F2 progeny of the indicated genotype were sacrificed at 7 mo of age, and hypothalamic coronal sections stained for Xgal. In this situation, Xgal staining serves as an autonomous histologic marker, and loss of Xgal staining in Tfam mutant animals is therefore secondary to cell death. Sections are representative of three to four per genotype group that were examined. The panel on the lower right shows the number of Agrp-expressing neurons in the control and Agrp-Tfam mutants as determined by fluorescence in situ hybridization to Agrp mRNA.

**, p ≤ 0.01. Error bars = standard error of the mean.