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The evolution of the main regulatory region (D-loop) of the mammalian mitochondrial genome was analyzed by comparing the sequences of eight mammalian species: human, common chimpanzee, pygmy chimpanzee, dolphin, cow, rat, mouse, and rabbit. The best alignment of the sequences was obtained by optimization of the sequence similarities common to all these species. The two peripheral left and right D-loop domains, which contain the main regulatory elements so far discovered, evolved rapidly in a species-specific manner generating heterogeneity in both length and base composition. They are prone to the insertion and deletion of elements and to the generation of short repeats by replication slippage. However, the preservation of some sequence blocks and similar cloverleaf-like structures in these regions, indicates a basic similarity in the regulatory mechanisms of the mitochondrial genome in all mammalian species. We found, particularly in the right domain, significant similarities to the telomeric sequences of the mitochondrial (mt) and nuclear DNA of Tetrahymena thermophila. These sequences may be interpreted as relics of telomeres present in ancestral linear forms of mtDNA or may simply represent efficient templates of RNA primase-like enzymes. Due to their peculiar evolution, the two peripheral domains cannot be used to estimate in a quantitative way the genetic distances between mammalian species. On the other hand the central domain, highly conserved during evolution, behaves as a good molecular clock. Reliable estimates of the times of divergence between closely and distantly related species were obtained from the central domain using a Markov model and assuming nonhomogeneous evolution of nucleotide sites.

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Eukaryotic cells contain a population of mitochondria, variable in number and shape, which in turn contain multiple copies of a tiny compact genome (mtDNA) whose expression and function is strictly coordinated with the nuclear one. mtDNA copy number varies between different cell or tissues types, both in response to overall metabolic and bioenergetics demands and as a consequence or cause of specific pathological conditions. Here we present a novel and reliable methodology to assess the effective mtDNA copy number per diploid genome by investigating off-target reads obtained by whole-exome sequencing (WES) experiments. We also investigate whether and how mtDNA copy number correlates with mitochondrial mass, respiratory activity and expression levels. Analyzing six different tissues from three age- and sex-matched human individuals, we found a highly significant linear correlation between mtDNA copy number estimated by qPCR and the frequency of mtDNA off target WES reads. Furthermore, mtDNA copy number showed highly significant correlation with mitochondrial gene expression levels as measured by RNA-Seq as well as with mitochondrial mass and respiratory activity. Our methodology makes thus feasible, at a large scale, the investigation of mtDNA copy number in diverse cell-types, tissues and pathological conditions or in response to specific treatments.

p63 belongs to a family of transcription factors, which, while demonstrating striking conservation of functional domains, regulate distinct biological functions. Its principal role is in the regulation of epithelial commitment, differentiation and maintenance programs, during embryogenesis and in adult tissues. The p63 gene has a complex transcriptional pattern, producing two subclasses of N-terminal isoforms (TA and ΔN) which are alternatively spliced at the C-terminus. Here, we report the identification of two new C-terminus p63 variants, we named p63 δ and ε, that increase from 6 to 10 the number of the p63 isoforms. Expression analysis of all p63 variants demonstrates a tissue/cell-type-specific nature of p63 alternative transcript expression, probably related to their different cellular functions. We demonstrate that the new p63 variants as ΔN isoforms are active as transcription factors as they have nuclear localization and can modulate the expression of p63 target genes. Moreover, we report that, like ΔNp63α, ΔNp63δ and ε sustain cellular proliferation and that their expression decreases during keratinocyte differentiation, suggesting their involvement in this process. Taken together, our results demonstrate the existence of novel p63 proteins whose expression should be considered in future studies on the roles of p63 in the regulation of cellular functions.

A detailed comparative study of the regions surrounding the origin of replication in vertebrate mitochondrial DNA (mtDNA) has revealed a number of interesting properties. This region, called the D-loop-containing region, can be divided into three domains. The left (L) and right (R) domains, which have a low G content and contain the 5' and the 3' D-loop ends, respectively, are highly variable for both base sequence and length. They, however, contain thermodynamically stable secondary structures which include the conserved sequence blocks called CSB-1 and TAS which are associated with the start and stop sites, respectively, for D-loop strand synthesis. We have found that a "mirror symmetry" exists between the CSB-1 and TAS elements, which suggests that they can act as specific recognition sites for regulatory, probably dimeric, proteins. Long, statistically significant repeats are found in the L and R domains. Between the L and R domains we observed in all mtDNA sequences a region with a higher G content which was apparently free of complex secondary structure. This central domain, well preserved in mammals, contains an open reading frame of variable length in the organisms considered. The identification of common features well preserved in evolution despite the high primary structural divergence of the D-loop-containing region of vertebrate mtDNA suggests that these properties are of prime importance for the mitochondrial processes that occur in this region and may be useful for singling out the sites on which one should operate experimentally in order to discover functionally important elements.

A novel p53-inducible gene, PAG608, encodes a nuclear zinc finger protein whose overexpression promotes apoptosis interactions between p53 and these genes are generally