Diurnal gene expression patterns underlie time-of-the-day-specific functional specialization of tissues. However, available circadian gene expression atlases of a few organs are largely from nocturnal vertebrates. We report the diurnal transcriptome of 64 tissues, including 22 brain regions, sampled every 2 hours over 24 hours, from the primate (baboon). Genomic transcription was highly rhythmic, with up to 81.7% of protein-coding genes showing daily rhythms in expression. In addition to tissue-specific gene expression, the rhythmic transcriptome imparts another layer of functional specialization. Most ubiquitously expressed genes that participate in essential cellular functions exhibit rhythmic expression in a tissue-specific manner. The peak phases of rhythmic gene expression clustered around dawn and dusk, with a "quiescent period" during early night. Our findings also unveil a different temporal organization of central and peripheral tissues between diurnal and nocturnal animals.

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The current study describes, using immunohistochemical methods, the nuclear organization of the cholinergic, catecholaminergic and serotonergic systems within the brains of five microchiropteran species. For the vast majority of nuclei observed, direct homologies are evident in other mammalian species; however, there were several distinctions in the presence or absence of specific nuclei that provide important clues regarding the use of the brain in the analysis of chiropteran phylogenetic affinities. Within the five species studied, three specific differences (presence of a parabigeminal nucleus, dorsal caudal nucleus of the ventral tegmental area and the absence of the substantia nigra ventral) found in two species from two different families (Cardioderma cor; Megadermatidae, and Coleura afra; Emballonuridae), illustrates the diversity of microchiropteran phylogeny and the usefulness of brain characters in phylogenetic reconstruction. A number of distinct differences separate the microchiropterans from the megachiropterans, supporting the diphyletic hypothesis of chiropteran phylogenetic origins. These differences phylogenetically align the microchiropterans with the heterogenous grouping of insectivores, in contrast to the alignment of megachiropterans with primates. The consistency of the changes and stasis of neural characters with mammalian phylogeny indicate that the investigation of the microchiropterans as a sister group to one of the five orders of insectivores to be a potentially fruitful area of future research.