RESUMO
Despite the availability of large molecular data sets, the position of the root of the eutherian tree remains a controversial issue. Depending on source data, taxon sampling and analytical approach, the root can be placed at either Afrotheria, Xenarthra, Afrotheria+Xenarthra, or murid rodents. We explored the phylogenetic potential of indels in four nuclear protein-coding genes (SCA1, PRNP, TNFalpha, and HspB3) with regard to a possible rooting at the murid branch. According to parsimony principles, five indels were interpreted to contradict such a rooting, and one indel to support it. The results illustrate that indels, despite the occurrence of homoplasy, can be convincing sources of independent molecular evidence to distinguish between alternative phylogenetic hypotheses.
Assuntos
Proteínas de Bactérias , Mamíferos/classificação , Mamíferos/genética , Filogenia , Mutação Puntual/genética , Sequência de Aminoácidos , Animais , Ataxinas , Teorema de Bayes , Primers do DNA , Proteínas de Choque Térmico/genética , Funções Verossimilhança , Dados de Sequência Molecular , Proteínas do Tecido Nervoso/genética , Proteínas Nucleares/genética , Fator de Necrose Tumoral alfa/genéticaRESUMO
The rudimentary eyes of the mole rat Spalax ehrenbergi have lost their visual function, but are still required for the control of circadian rhythms. It has previously been found that alphaA-crystallin, a major eye lens protein in other mammals, evolved much faster in the mole rat than in rodents with normal vision. Yet, although mole rat alphaA-crystallin seems superfluous as a lens protein, its rate of change is still much slower than that of pseudogenes, suggesting some remaining function. The authors therefore studied the structure and function of recombinant mole rat alphaA-crystallin. Circular dichroism (CD), tryptophan fluorescence and gel permeation analyses indicated that the overall structure and stability of mole rat alphaA-crystallin are comparable to that of rat alphaA-crystallin. However, the chaperone-like activity of mole rat alphaA-crystallin is considerably lower than that of its rat orthologue. Two-dimensional NMR spectroscopy of mole rat alphaA-crystallin suggests that this may be in part due to a diminished flexibility of the C-terminal extension, which is thought to be important for the chaperoning capacity. Overall, mole rat alphaA-crystallin appears to still be a viable protein, confirming that it has some as yet elusive role, despite the loss of its primary lens function.