Polyamine and Its Metabolite H2O2 Play a Key Role in the Conversion of Embryogenic Callus into Somatic Embryos in Upland Cotton (Gossypium hirsutum L.).

The objective of this study was to increase understanding about the mechanism by which polyamines (PAs) promote the conversion of embryogenic calli (EC) into somatic embryos in cotton (Gossypium hirsutum L.). We measured the levels of endogenous PAs and H2O2, quantified the expression levels of genes involved in the PAs pathway at various stages of cotton somatic embryogenesis (SE), and investigated the effects of exogenous PAs and H2O2 on differentiation and development of EC. Putrescine (Put), spermidine (Spd), and spermine (Spm) significantly increased from the EC stage to the early phase of embryo differentiation. The levels of Put then decreased until the somatic embryo stage whereas Spd and Spm remained nearly the same. The expression profiles of GhADC genes were consistent with changes in Put during cotton SE. The H2O2 concentrations began to increase significantly at the EC stage, during which time both GhPAO1 and GhPAO4 expressions were highest and PAO activity was significantly increased. Exogenous Put, Spd, Spm, and H2O2 not only enhanced embryogenic callus growth and embryo formation, but also alleviated the effects of D-arginine and 1, 8-diamino-octane, which are inhibitors of PA synthesis and PAO activity. Overall, the results suggest that both PAs and their metabolic product H2O2 are essential for the conversion of EC into somatic embryos in cotton.

Human microRNA clusters: genomic organization and expression profile in leukemia cell lines.

MicroRNAs (miRNAs) play an important role in diverse physiological and developmental processes by negatively regulating expression of target genes at the post-transcriptional level. Here, we globally analyzed the genomic organization of all registered 326 human miRNA genes in miRNA registry 7.1 and found that 148 human miRNA genes appeared in a total of 51 clusters. Alignment of the miRNA sequences in different clusters revealed a significant number of miRNA paralogs among the clusters, implying an evolution process targeting the potentially conserved roles of these molecules. Then we performed Northern blot analysis for expression profiling of all clustered miRNAs in several human leukemia cell lines. Consistent expression of the miRNAs in a single cluster was revealed in 39 clusters, while inconsistent expression of members in a single cluster was detected in the other 12 clusters. Meanwhile, we identified several hematopoietic lineage-specific or -enriched miRNA clusters (e.g., the mir-29c, mir-302, mir-98, mir-29a, and let-7a-1 clusters) and individual miRNAs (e.g., mir-181c, mir-181d, mir-191, and mir-136). These findings may suggest vital roles of these miRNA clusters or miRNAs in human hematopoiesis and oncogenesis, and provide clues for understanding the function and mechanism of miRNAs in various biological processes.