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Articles by J Qi
Total Records ( 3 ) for J Qi
  F Zhao , J Qi and S. C. Schuster
 

The woolly mammoth (Mammuthus primigenius) died out about several thousand years ago, yet recent paleogenomic studies have successfully recovered genetic information from both the mitochondrial and nuclear genomes of this extinct species. Mammoths belong to Afrotheria, a group of mammals exhibiting extreme morphological diversity and large genome sizes. In this study, we found that the mammoth genome contains a larger proportion of interspersed repeats than any other mammalian genome reported so far, in which the proliferation of the RTE family of retrotransposons (covering 12% of the genome) may be the main reason for an increased genome size. Phylogenetic analysis showed that RTEs in mammoth are closely related to the family BovB/RTE. The incongruence of the reconstructed RTE phylogeny indicates that RTEs in mammoth may be acquired through an ancient lateral gene transfer event. A recent proliferation of SINEs was also found in the probocidean lineage, whereas the Afrotherian-wide SINEs in mammoth have undergone a rather flat and stepwise expansion. Comparisons of the transposable elements (TEs) between mammoth and other mammals may shed light on the evolutionary history of TEs in various mammalian lineages.

  Y Zhang , X Li , J Qi , J Wang , X Liu , H Zhang , S. C Lin and A. Meng
 

The Rho-associated serine/threonine kinases Rock1 and Rock2 play important roles in cell contraction, adhesion, migration, proliferation and apoptosis. Here we report that Rock2 acts as a negative regulator of the TGFβ signaling pathway. Mechanistically, Rock2 binds to and accelerates the lysosomal degradation of TGFβ type I receptors internalized from the cell surface in mammalian cells. The inhibitory effect of Rock2 on TGFβ signaling requires its kinase activity. In zebrafish embryos, injection of rock2a mRNA attenuates the expression of mesodermal markers during late blastulation and blocks the induction of mesoderm by ectopic Nodal signals. By contrast, overexpression of a dominant negative form of zebrafish rock2a, dnrock2a, has an opposite effect on mesoderm induction, suggesting that Rock2 proteins are endogenous inhibitors for mesoderm induction. Thus, our data have unraveled previously unidentified functions of Rock2, in controlling TGFβ signaling as well as in regulating embryonic patterning.

  J. J Zhou , M. S Li , J Qi and P. Linsdell
 

Rapid chloride permeation through the cystic fibrosis transmembrane conductance regulator (CFTR) Cl channel is dependent on the presence of fixed positive charges in the permeation pathway. Here, we use site-directed mutagenesis and patch clamp recording to show that the functional role played by one such positive charge (K95) in the inner vestibule of the pore can be "transplanted" to a residue in a different transmembrane (TM) region (S1141). Thus, the mutant channel K95S/S1141K showed Cl conductance and open-channel blocker interactions similar to those of wild-type CFTR, thereby "rescuing" the effects of the charge-neutralizing K95S mutation. Furthermore, the function of K95C/S1141C, but not K95C or S1141C, was inhibited by the oxidizing agent copper(II)-o-phenanthroline, and this inhibition was reversed by the reducing agent dithiothreitol, suggesting disulfide bond formation between these two introduced cysteine side chains. These results suggest that the amino acid side chains of K95 (in TM1) and S1141 (in TM12) are functionally interchangeable and located closely together in the inner vestibule of the pore. This allowed us to investigate the functional effects of increasing the number of fixed positive charges in this vestibule from one (in wild type) to two (in the S1141K mutant). The S1141K mutant had similar Cl conductance as wild type, but increased susceptibility to channel block by cytoplasmic anions including adenosine triphosphate, pyrophosphate, 5-nitro-2-(3-phenylpropylamino)benzoic acid, and Pt(NO2)42– in inside-out membrane patches. Furthermore, in cell-attached patch recordings, apparent voltage-dependent channel block by cytosolic anions was strengthened by the S1141K mutation. Thus, the Cl channel function of CFTR is maximal with a single fixed positive charge in this part of the inner vestibule of the pore, and increasing the number of such charges to two causes a net decrease in overall Cl transport through a combination of failure to increase Cl conductance and increased susceptibility to channel block by cytosolic substances.

 
 
 
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