Biomedical subjects

Ning Lei

Publications and source records attributed to Ning Lei.

3 recordsLinked to original sources

PubMed2006

Direct Bragg-peak phase retrieval by a hybrid-input-output algorithm with proper intensity normalization.

A hybrid-input-output algorithm is applied to reconstruct hypothetical carbon cluster crystals in both two and three dimensions. It is shown that normalizing the Bragg peaks to those from a cluster of solid spheres or discs with uniform electron density can often lead to faithfully reconstructed objects at both atomic and low resolutions. It is shown that, even without the central peak, low-resolution structures can still be reconstructed with good fidelity. The effect of Bragg-peak noise on object reconstruction is examined throughout the paper. Successful reconstructions of 500- and 1000-atom carbon cluster crystal structures at both atomic and low resolutions are given.

Algorithms↗

PubMed2004

Gata4 regulates testis expression of Dmrt1.

The doublesex and mab-3 related transcription factor 1 (Dmrt1) is a putative transcriptional regulator that is expressed exclusively in the gonads and is required for postnatal testis differentiation. Here we describe the transcriptional mechanisms regulating testis-specific expression of the Dmrt1 gene. Transient-transfection analysis identified a region of the promoter between kb -3.2 and -2.8 that is important for Sertoli cell-specific expression. DNase I footprinting revealed four sites of DNA-protein interaction within this region, three of which were prominent in primary Sertoli cells. Analysis of these sites, using electrophoretic mobility shift assays, revealed that Gata4 and another unknown factor bound within these regions. Further transient-transfection assays of various mutant promoters established the functional relevance of the Gata4-response and unknown factor-response elements, while studies of Dmrt1 expression in 13.5 days postcoitum Fog2 null gonads supported the in vivo importance of Gata4's regulation. As a whole, these studies identify Gata4 as an important regulator in the Dmrt1 transcriptional machinery that is responsible for robust expression of Dmrt1 in the testis.

Animals↗

PubMed2002

Sp1 and Egr1 regulate transcription of the Dmrt1 gene in Sertoli cells.

Dmrt1 is a recently described gene that is specifically expressed in the gonads and is required for postnatal testis differentiation. Here, we describe the transcriptional mechanisms regulating the Dmrt1 proximal promoter in testicular Sertoli cells. A genomic clone containing exon 1 of the rat Dmrt1 gene and more than 9 kilobases of 5' flanking sequence was isolated and characterized. Several prominent transcriptional start sites were identified, with the major site located 102 bases from the translational start. The Dmrt1 5' flanking region from -5000 to +74 was transcriptionally active in primary Sertoli cells, and deletion analysis of this fragment identified 2 major regions needed for full Dmrt1 promoter function. These regions were located between -3200 and -2000 base pairs (bp) and downstream of -150 bp relative to the major transcriptional start site. DNase I footprint analysis of the region downstream of -150 bp revealed 3 regions that are bound by proteins from Sertoli cell nuclear extracts. Site-directed mutagenesis of these regions identified 2 elements that activate the Dmrt1 promoter and 2 that repress it. The positive elements bind the transcription factors Sp1, Sp3, and Egr1, suggesting that these transcription factors play a critical role in Dmrt1 regulation in the testis.

Animals↗