Global Analysis Reveals the Crucial Roles of DNA Methylation during Rice Seed Development.

Seed development is an important process of reproductive development and consists of embryo and endosperm development; both comprise several key processes. To determine and investigate the functions of the dynamic DNA methylome during seed development, we profiled the DNA methylation genome wide in a series of developmental stages of rice (Oryza sativa) embryo and endosperm by methylcytosine immunoprecipitation followed by Illumina sequencing. The results showed that embryo is hypermethylated predominantly around non-transposable element (TE) genes, short DNA-TEs, and short interspersed TEs compared with endosperm, and non-TE genes have the most diverse methylation status across seed development. In addition, lowly expressed genes are significantly enriched in hypermethylated genes, but not vice versa, confirming the crucial role of DNA methylation in suppressing gene transcription. Further analysis revealed the significantly decreased methylation at early developing stages (from 2 to 3 d after pollination), indicating a predominant role of demethylation during early endosperm development and that genes with a consistent negative correlation between DNA methylation change and expression change may be potentially directly regulated by DNA methylation. Interestingly, comparative analysis of the DNA methylation profiles revealed that both rice indica and japonica subspecies showed robust fluctuant profiles of DNA methylation levels in embryo and endosperm across seed development, with the highest methylation level at 6 d after pollination (2 d after pollination of endosperm in japonica as well), indicating that a complex and finely controlled methylation pattern is closely associated with seed development regulation. The systemic characterization of the dynamic DNA methylome in developing rice seeds will help us understand the effects and mechanism of epigenetic regulation in seed development.

[Comparison between pathological findings and MR diffusion-weighted imaging in primary hepatocellular carcinoma after transcatheter arterial chemoembolization].

OBJECTIVE: To explore the pathological basis of diffusion-weighted imaging (DWI) findings in hepatocellular carcinoma (HCC) after transcatheter arterial chemoembolization (TACE). METHODS: DWI was performed in 15 patients with HCC treated by TACE within 24 - 48 hours before II-phase operation. The DWI findings of the liver lesions were analyzed and correlated with pathological findings including macroscopic observation, HE staining and immunohistochemical staining for bFGF. RESULTS: (1) The viable tumor area showed mostly hypersignal intensity (12/15), whereas coagulative necrotic lesions showed hyposignal (8/15) or isosignal intensity (6/15). The ADC values of zones of viable tumor and necrosis in tumor were (1.42 +/- 0.16) x 10(-3) mm(2)/s and (1.58 +/- 0.18) x 10(-3) mm(2)/s, respectively. There was a significant difference of ADC values between the two zones (t = 2.618, P < 0.05). (2) There was a significant difference in ADC values of viable tumor between well and poorly differentiated tumors (t = -2.646, P < 0.05). The distinction of ADC values of the whole tumor was significant among tumors with different degree of necrosis (chi(2) = 7.236, P < 0.05). (3) A negative correlation was observed between bFGF protein expression index and ADC values of viable parts of the tumors in the study group (r = -0.552, P = 0.033). CONCLUSION: DWI shows certain characteristic features of the HCC after TACE, and can be used to distinguish viable and necrotic tumor tissues in HCC after TACE.