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Articles by Z Ni
Total Records ( 3 ) for Z Ni
  Z Ni , C Gunraj , A. J Nelson , I J Yeh , G Castillo , T Hoque and R. Chen
 

Interhemispheric inhibition (IHI) refers to the neurophysiological mechanism in which one hemisphere of the brain inhibits the opposite hemisphere. IHI can be studied by transcranial magnetic stimulation using a conditioning-test paradigm. We investigated IHI from 5 motor related cortical areas in the right hemisphere to the left primary motor cortex (M1). These areas are hand and face representations of M1, dorsal premotor cortex, somatosensory cortex, and dorsolateral prefrontal cortex. Test stimulus was delivered to the left M1 and conditioning stimulus (CS) was delivered to one of 5 motor related cortical areas in the right hemisphere. The time course of IHI, effects of different CS intensities and current directions on IHI were tested. Maximum IHI was found at interstimulus intervals of ~10 ms (short latency IHI, SIHI) and ~50 ms (long latency IHI, LIHI) for the motor related areas tested. LIHI could be elicited over a wide range of CS intensities, whereas SIHI required higher CS intensities. We conclude that there are 2 distinct phases of IHI from motor related cortical areas to the opposite M1 through the corpus callosum, and they are mediated by different neuronal populations.

  S Hu , G Yao , X Guan , Z Ni , W Ma , E. M Wilson , F. S French , Q Liu and Y. Zhang
 

Epididymal function depends on androgen signaling through the androgen receptor (AR), although most of the direct AR target genes in epididymis remain unknown. Here we globally mapped the AR binding regions in mouse caput epididymis in which AR is highly expressed. Chromatin immunoprecipitation sequencing indicated that AR bound selectively to 19,377 DNA regions, the majority of which were intergenic and intronic. Motif analysis showed that 94% of the AR binding regions harbored consensus androgen response elements enriched with multiple binding motifs that included nuclear factor 1 and activator protein 2 sites consistent with combinatorial regulation. Unexpectedly, AR binding regions showed limited conservation across species, regardless of whether the metric for conservation was based on local sequence similarity or the presence of consensus androgen response elements. Further analysis suggested the AR target genes are involved in diverse biological themes that include lipid metabolism and sperm maturation. Potential novel mechanisms of AR regulation were revealed at individual genes such as cysteine-rich secretory protein 1. The composite studies provide new insights into AR regulation under physiological conditions and a global resource of AR binding sites in a normal androgen-responsive tissue.

  Z Ni , Z Bikadi , X Cai , M. F Rosenberg and Q. Mao
 

The human breast cancer resistance protein (BCRP/ABCG2) mediates efflux of drugs and xenobiotics. In this study, we investigated the role of polar residues within or near the predicted transmembrane -helices 1 and 6 of BCRP in drug transport. We substituted Asn387, Gln398, Asn629, and Thr642 with Ala, Thr402 with Ala and Arg, and Tyr645 with Phe, and the mutants were stably expressed in human embryonic kidney-293 or Flp-In-293 cells. Immunoblotting and confocal microscopy analysis revealed that all of the mutants were well expressed and predominantly targeted to the plasma membrane. While T402A and T402R showed a significant global reduction in the efflux of mitoxantrone, Hoechst 33342, and BODIPY-prazosin, N629A exhibited significantly increased efflux activities for all of the substrates. N387A and Q398A displayed significantly impaired efflux for mitoxantrone and Hoechst 33342, but not for BODIPY-prazosin. In contrast, T642A and Y645F showed a moderate reduction in Hoechst 33342 efflux only. Drug resistance profiles of human embryonic kidney-293 cells expressing the mutants generally correlated with the efflux data. Furthermore, N629A was associated with a marked increase, and N387A and T402A with a significant reduction, in BCRP ATPase activity. Mutations of some of the polar residues may cause conformational changes, as manifested by the altered binding of the 5D3 antibody to BCRP in the presence of prazosin. The inward-facing homology model of BCRP indicated that Thr402 within transmembrane 1 may be important for helical interactions, and Asn629 may be involved in BCRP-substrate interaction. In conclusion, we have demonstrated the functional importance of some of these polar residues in BCRP activity.

 
 
 
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