ChIP-cloning analysis uncovers centromere-specific retrotransposons in Brassica nigra and reveals their rapid diversification in Brassica allotetraploids.

Centromeres are indispensable functional units of chromosomes. The evolutionary mechanisms underlying the rapid evolution of centromeric repeats, especially those following polyploidy, remain unknown. In this study, we isolated centromeric sequences of Brassica nigra, a model diploid progenitor (B genome) of the allopolyploid species B. juncea (AB genome) and B. carinata (BC genome) by chromatin immunoprecipitation of nucleosomes containing the centromere-specific histone CENH3. Sequence analysis detected no centromeric satellite DNAs, and most B. nigra centromeric repeats were found to originate from Tyl/copia-class retrotransposons. In cytological analyses, six of the seven analyzed repeat clusters had no FISH signals in A or C genomes of the related diploid species B. rapa and B. oleracea. Notably, five repeat clusters had FISH signals in both A and B subgenomes in the tetraploid B. juncea. In the tetraploid B. carinata, only CL23 displayed three pairs of signals in terminal or interstitial regions of the C-derived chromosome, and no evidence of colonization of CLs onto C-subgenome centromeres was found in B. carinata. This observation suggests that centromeric repeats spread and proliferated between genomes after polyploidization. CL3 and CRB are likely ancient centromeric sequences arising prior to the divergence of diploid Brassica which have detected signals across the genus. And in allotetraploids B. juncea and B. carinata, the FISH signal intensity of CL3 and CRB differed among subgenomes. We discussed possible mechanisms for centromeric repeat divergence during Brassica speciation and polyploid evolution, thus providing insights into centromeric repeat establishment and targeting.

Karyotypes and Distribution of Tandem Repeat Sequences in Brassica nigra Determined by Fluorescence in situ Hybridization.

Whole-genome shotgun reads were analyzed to determine the repeat sequence composition in the genome of black mustard, Brassica nigra (L.) Koch. The analysis showed that satellite DNA sequences are very abundant in the black mustard genome. The distribution pattern of 7 new tandem repeats (BnSAT13, BnSAT28, BnSAT68, BnSAT76, BnSAT114, BnSAT180, and BnSAT200) on black mustard chromosomes was visualized using fluorescence in situ hybridization (FISH). The FISH signals of BnSAT13 and BnSAT76 provided useful cytogenetic markers; their position and fluorescence intensity allowed for unambiguous identification of all 8 somatic metaphase chromosomes. A karyotype showing the location and fluorescence intensity of these tandem repeat sequences together with the position of rDNAs and centromeric retrotransposons of Brassica (CRB) was constructed. The establishment of the FISH-based karyotype in B. nigra provides valuable information that can be used in detailed analyses of B. nigra accessions and derived allopolyploid Brassica species containing the B genome.

Right Atrial Evaluation in Patients With Pulmonary Hypertension: A Real-time 3-Dimensional Transthoracic Echocardiographic Study.

OBJECTIVES: The purpose of this study was to investigate the changes in the morphologic characteristics and performance of the right atrium (RA) that occur secondary to structural remodeling of the right ventricle (RV) in patients with pulmonary hypertension by real-time 3-dimensional echocardiography (3DE). METHODS: Comprehensive 2-dimensional echocardiography and real-time 3DE were performed in 112 patients and 30 healthy control participants. Patients with pulmonary hypertension were divided into 3 subgroups: 1, normal RV dimension (n = 34); 2, RV enlargement and preserved systolic function (n = 36); and 3, RV enlargement and systolic dysfunction (n = 42). RESULTS: Patients had larger RA volume parameters and lower RA passive emptying fractions than controls (P< .01). The RA active emptying fraction was higher in patient groups 1 (mean ± SD, 45.5% ± 10.7%) and 2 (40.1% ± 4.0%) and lower in group 3 (19.3% ± 4.3%) compared to controls (35.4% ± 3.5%). The RA total emptying fraction was similar between groups 1 and 2 (59.3% ± 9.7% and 52.6% ± 3.4%, respectively) but was significantly lower in group 3 compared to controls (26.8% ± 5.1% versus 55.2% ± 5.1%). Right atrial volume and phasic function were substantially affected by RV structure and function. CONCLUSIONS: Real-time 3DE is a feasible, repeatable, and noninvasive method for accessing cyclic RA volume and function changes, such as those that occur with varying RV status in patients with pulmonary hypertension.

[The pairing, synapsis and recombination of meiosis in plant].

Meiosis is the crucial step for sexual reproduction, while the pairing, synapsis and recombination are the key events in this process and have become the hotspots in meiosis studies. In recent years, with the development of the molecular biology and cell biology, associated with the mutant screened from mutant libraries, much advances were achieved in pairing, synapsis and recombination of meiosis in plant. In this review, we have gave an overview of the genes identification in this field and further studies of its molecular mechanism in plant.