Biomedical subjects

Sheng Cui

Publications and source records attributed to Sheng Cui.

22 records · Page 2Linked to original sources

PubMed2004

Immunohistochemical detection of islet-1 and neuronal nitric oxide synthase in the dorsal root ganglia (DRG) of sheep fetuses during gestation.

This study first investigated the ontogeny of Islet-1 and neuronal nitric oxide synthase (nNOS) expression and their co-localization in the DRG of sheep fetuses during gestation by immunohistochemistry (IHC). The results showed that Islet-1 and nNOS were located in the nuclei and cytoplasm of DRG neurons, respectively. The relative percentages of Islet-1-immunopositive (Islet-1(+)) neurons accounting for the total DRG neurons were 90%, 79%, 66%, and 53% at days 60, 90, and 120 of gestation and postnatally, respectively. The percentage of nNOS-immunopositive (nNOS(+)) neurons was 94% at day 60 and declined to approximately 30% at day 90, with no obvious further change until the postnatal period. Dual IHC showed that approximately 69% Islet-1(+) neurons express nNOS at day 60 of gestation. This proportion declined to approximately 24% at day 90, after which there was no significant change until birth. We also observed that most Islet-1(+) and nNOS(+) neurons belonged to small and medium-sized DRG neurons from day 90 of gestation to the postnatal period. These results suggest that both Islet-1 and nNOS are important for the differentiation and maintenance of some specific phenotypes of DRG neurons during late gestation of sheep fetuses, although the related mechanisms need to be further elucidated.

Animals↗

PubMed2002

Characterization of the DNA-unwinding activity of human RECQ1, a helicase specifically stimulated by human replication protein A.

The RecQ helicases are involved in several aspects of DNA metabolism. Five members of the RecQ family have been found in humans, but only two of them have been carefully characterized, BLM and WRN. In this work, we describe the enzymatic characterization of RECQ1. The helicase has 3' to 5' polarity, cannot start the unwinding from a blunt-ended terminus, and needs a 3'-single-stranded DNA tail longer than 10 nucleotides to open the substrate. However, it was also able to unwind a blunt-ended duplex DNA with a "bubble" of 25 nucleotides in the middle, as previously observed for WRN and BLM. We show that only short DNA duplexes (<30 bp) can be unwound by RECQ1 alone, but the addition of human replication protein A (hRPA) increases the processivity of the enzyme (>100 bp). Our studies done with Escherichia coli single-strand binding protein (SSB) indicate that the helicase activity of RECQ1 is specifically stimulated by hRPA. This finding suggests that RECQ1 and hRPA may interact also in vivo and function together in DNA metabolism. Comparison of the present results with previous studies on WRN and BLM provides novel insight into the role of the N- and C-terminal domains of these helicases in determining their substrate specificity and in their interaction with hRPA.

Adenosine Triphosphatases↗

PubMed2002

Differences in neuronal differentiation between the transient cranial (Frorieps') and normal dorsal root ganglia.

The Frorieps' ganglia are dorsal root ganglia (DRG) that form, grow slowly compared to normal DRG, and then degenerate during normal embryonic development of amniotes. Their fate has been shown to be regulated by the Hox family and other genes involved in pattern formation, and by the mesodermal microenvironment of the cranial somites in which they develop. Neurons are known to differentiate within the Frorieps' DRG in the course of their short life span. In this study, we compared several aspects of neural differentiation between the longest-lived Frorieps' ganglia, DRG2, and normal trunk DRG in chick embryos. The expression of transcription factor Islet-1 and the RNA-binding protein Hu differ between normal and Frorieps' DRG at St. 23 (embryonic day 4). Islet-1 is expressed in a higher proportion of cells in DRG2 than DRG5, suggesting that cells in DRG2 differentiate more rapidly into neurons than in normal DRG. This molecular difference appears at the same developmental stage as overt morphological differences between DRG2 and normal DRG. Other LIM-homeobox proteins (Lim-1, -2 and -3 and Islet-2) are not expressed either in normal or Frorieps' DRG at early stages of development. Somite-grafting experiments reveal that the increased proportion of Isl-1(+) in DRG2 is due to the special microenvironment of the cranial somites. In contrast to Islet-1, the Hu antigen is expressed in a slightly lower proportion of cells in DRG2 at St. 23. At St. 28, there is a significant population of neurons in DRG2 that are Isl-1(+)/Hu(-). Since Islet-1 is normally expressed before Hu in DRG cells, it is possible that the reduced growth rate of the DRG2 ganglion may partially result from the inability of precociously differentiating Islet-1(+) neurons to further mature, as reflected by Hu antigen expression. In contrast to the neuronal markers examined, the satellite cell marker 7B3 is expressed at similar levels in DRG2 and DRG5.

Animals↗

PubMed2002

Studies on the mode of Ku interaction with DNA.

The Ku heterodimer plays a central role in non-homologous end-joining. The binding of recombinant Ku to DNA has been investigated by dynamic light scattering, double-filter binding, fluorescence spectroscopy, and band shift assays. The hydrodynamic radius of Ku in solution is 5.2 nm and does not change when a 25-bp double-strand DNA (dsDNA) fragment (D25) is added, indicating that only one Ku molecule binds to a 25-bp fragment. The dissociation constant (k(d)) for the binding to D25 is 3.8 +/- 0.9 nm. If both ends of the substrate are closed with hairpin loops, Ku is still able to bind with little change in the k(d). The k(d) is not affected by ATP, Mg(2+), or ionic strength. However, the addition of bovine serum albumin decreases the k(d) by 2-fold. DNA substrates of 50 bp can bind two Ku molecules, whereas three molecules are bound to a 75-bp substrate. Data analysis with the Hill equation yields a value of the Hill coefficient (n) close to 1, and the k(d) values for the binding of Ku to both ends of these substrates are the same. Thus, we demonstrate that there is no cooperative interaction among the Ku heterodimers binding longer substrates.

Adenosine Triphosphate↗