Molecular Evolution and Functional Divergence of Trace Amine–Associated Receptors

Trace amine-associated receptors (TAARs) are a member of the G-protein-coupled receptor superfamily and are known to be expressed in olfactory sensory neurons. A limited number of molecular evolutionary studies have been done for TAARs so far. To elucidate how lineage-specific evolution contributed to their functional divergence, we examined 30 metazoan genomes. In total, 493 TAAR gene candidates (including 84 pseudogenes) were identified from 26 vertebrate genomes. TAARs were not identified from non-vertebrate genomes. An ancestral-type TAAR-like gene appeared to have emerged in lamprey. We found four therian-specific TAAR subfamilies (one eutherian-specific and three metatherian-specific) in addition to previously known nine subfamilies. Many species-specific TAAR gene duplications and losses contributed to a large variation of TAAR gene numbers among mammals, ranging from 0 in dolphin to 26 in flying fox. TAARs are classified into two groups based on binding preferences for primary or tertiary amines as well as their sequence similarities. Primary amine-detecting TAARs (TAAR1-4) have emerged earlier, generally have single-copy orthologs (very few duplication or loss), and have evolved under strong functional constraints. In contrast, tertiary amine-detecting TAARs (TAAR5-9) have emerged more recently and the majority of them experienced higher rates of gene duplications. Protein members that belong to the tertiary amine-detecting TAAR group also showed the patterns of positive selection especially in the area surrounding the ligand-binding pocket, which could have affected ligand-binding activities and specificities. Expansions of the tertiary amine-detecting TAAR gene family may have played important roles in terrestrial adaptations of therian mammals. Molecular evolution of the TAAR gene family appears to be governed by a complex, species-specific, interplay between environmental and evolutionary factors.     

PRR5, a novel component of mTOR complex 2, regulates platelet-derived growth factor receptor beta expression and signaling

The protein kinase mammalian target of rapamycin (mTOR) plays an important role in the coordinate regulation of cellular responses to nutritional and growth factor conditions. mTOR achieves these roles through interacting with raptor and rictor to form two distinct protein complexes, mTORC1 and mTORC2. Previous studies have been focused on mTORC1 to elucidate the central roles of the complex in mediating nutritional and growth factor signals to the protein synthesis machinery. Functions of mTORC2, relative to mTORC1, have remained little understood. Here we report identification of a novel component of mTORC2 named PRR5 (PRoline-Rich protein 5), a protein encoded by a gene located on a chromosomal region frequently deleted during breast and colorectal carcinogenesis (Johnstone, C. N., Castellvi-Bel, S., Chang, L. M., Sung, R. K., Bowser, M. J., Pique, J. M., Castells, A., and Rustgi, A. K. (2005) Genomics 85, 338-351). PRR5 interacts with rictor, but not raptor, and the interaction is independent of mTOR and not disturbed under conditions that disrupt the mTOR-rictor interaction. PRR5, unlike Sin1, another component of mTORC2, is not important for the mTOR-rictor interaction and mTOR activity toward Akt phosphorylation. Despite no significant effect of PRR5 on mTORC2-mediated Akt phosphorylation, PRR5 silencing inhibits Akt and S6K1 phosphorylation and reduces cell proliferation rates, a result consistent with PRR5 roles in cell growth and tumorigenesis. The inhibition of Akt and S6K1 phosphorylation by PRR5 knock down correlates with reduction in the expression level of platelet-derived growth factor receptor beta (PDGFRbeta). PRR5 silencing impairs PDGF-stimulated phosphorylation of S6K1 and Akt but moderately reduces epidermal growth factor- and insulin-stimulated phosphorylation. These findings propose a potential role of mTORC2 in the cross-talk with the cellular machinery that regulates PDGFRbeta expression and signaling.     

Genetic identification and molecular phylogeny of Pseudodiaptomus species (Calanoida, Pseudodiaptomidae) in Korean waters

Five species of the genus Pseudodiaptomus, P. inopinus, P. poplesia, P. marinus, P. nihonkaiensis, and P. sp. occur in Korea nearshore waters. Although the four species except for P. sp. have been classified into Lobus and Ramosus groups, two for each group, based on morphological characters, this classification had yet to be confirmed by molecular characters. Here, we determined molecular characters and phylogenetic relationships of the five species in order to evaluate the morphology-based groupings and the species identifications. For this, a 625-bp DNA region of the mitochondrial gene cytochrome oxidase subunit I (mtCOI) was sequenced and compared among the species. Intraspecific variation of the sequences is less than 0.6%, while interspecific variation ranges from 17.6-26.7%, indicating every species, including P. sp., is a genetically distinct, valid species. Phylogenetic trees of the mtCOI DNA reveal that the Lobus-group species including P. inopinus and P. poplesia form a well-supported clade and that P. sp. belongs to this group. On the other hand, the Ramosus group clade consisting of P. marinus and P. nihonkaiensis is not well supported by bootstrap analyses, suggesting that further evaluation of the validity of this group assignment is needed.