The chloroplast ribosome is a large and dynamic ribonucleoprotein machine that is composed of the 30S and 50S subunits. Although the components of the chloroplast ribosome have been identified in the last decade, the molecular mechanisms driving chloroplast ribosome biogenesis remain largely elusive. Here, we show that RNA helicase 22 (RH22), a putative DEAD RNA helicase, is involved in chloroplast ribosome assembly in Arabidopsis (Arabidopsis thaliana). A loss of RH22 was lethal, whereas a knockdown of RH22 expression resulted in virescent seedlings with clear defects in chloroplast ribosomal RNA (rRNA) accumulation. The precursors of 23S and 4.5S, but not 16S, rRNA accumulated in rh22 mutants. Further analysis showed that RH22 was associated with the precursors of 50S ribosomal subunits. These results suggest that RH22 may function in the assembly of 50S ribosomal subunits in chloroplasts. In addition, RH22 interacted with the 50S ribosomal protein RPL24 through yeast two-hybrid and pull-down assays, and it was also bound to a small 23S rRNA fragment encompassing RPL24-binding sites. This action of RH22 may be similar to, but distinct from, that of SrmB, a DEAD RNA helicase that is involved in the ribosomal assembly in Escherichia coli, which suggests that DEAD RNA helicases and rRNA structures may have coevolved with respect to ribosomal assembly and function.Given the prokaryotic origin of chloroplasts, the protein-synthesizing systems of chloroplasts are often considered to be very similar to those of bacteria. Chloroplasts contain 70S ribosomes, which are similar to prokaryotic ribosomes and distinct from their cytosolic counterparts, 80S ribosomes. The ribosomal RNAs (rRNAs) of higher plant chloroplasts are highly conserved and are most closely related to bacterial sequences (Branlant et al., 1981;Harris et al., 1994). The 30S subunit comprises 16S rRNA in chloroplasts and Escherichia coli. However, the 50S subunit of chloroplast ribosomes is composed of three rRNAs (23S, 4.5S, and 5S rRNAs), rather than the 23S and 5S rRNAs of E. coli (Harris et al., 1994). In chloroplasts, the 16S, 23S, 4.5S, and 5S rRNAs are encoded in an operon and are synthesized as a single large precursor (Edwards and Kö ssel, 1981

Neurofibromatosis type 1 associates with multiple neoplasms, and the Schwann cell tumor neurofibroma is the most prevalent. A hallmark feature of neurofibroma is mast cell infiltration, which is recruited by chemoattractant stem cell factor (SCF) and has been suggested to sustain neurofibroma tumorigenesis. In the present study, we use new, genetically engineered Scf mice to decipher the contributions of tumor-derived SCF and mast cells to neurofibroma development. We demonstrate that mast cell infiltration is dependent on SCF from tumor Schwann cells. However, removal of mast cells by depleting the main SCF source only slightly affects neurofibroma progression. Other inflammation signatures show that all neurofibromas are associated with high levels of macrophages regardless of Scf status. These findings suggest an active inflammation in neurofibromas and partly explain why mast cell removal alone is not sufficient to relieve tumor burden in this experimental neurofibroma model. Furthermore, we show that plexiform neurofibromas are highly associated with injury-prone spinal nerves that are close to flexible vertebras. In summary, our study details the role of inflammation in neurofibromagenesis. Our data indicate that prevention of inflammation and possibly also nerve injury at the observed tumor locations are therapeutic approaches for neurofibroma prophylaxis and that such treatment should be explored.

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Extended-spectrum b-lactamase (ESBL)-producing Escherichia coli has spread rapidly worldwide and poses a serious threat to human and animal health. This study collected 51 nonreplicate E. coli isolates from 14 different chicken farms in Henan Province in China from December 2007 to August 2008. The prevalence of ESBL-producing E. coli, molecular characterization of the ESBL-related bla genes, including bla TEM , bla SHV and bla CTX-M , and the susceptibilities of these bacteria to various antimicrobial agents were determined. Thirty-one of the 51 isolates were positive for an ESBL phenotype and 29 of these isolates carried one or more bla genes. Twenty-two isolates harboured bla TEM genes and 15 isolates carried bla CTX-M genes (one CTX-M-14, three CTX-M-24 and 11 CTX-M-65). One isolate carried bla ; the remaining bla TEM isolates carried bla TEM-1 with one silent nucleotide base variation (T18C). We believe that this is the first study to report TEM-57 in E. coli isolates. All isolates harbouring bla CTX-M-24 and bla CTX-M-14 and five of the bla CTX-M-65 isolates also harboured the bla TEM-1 gene. To our knowledge, this study is the first to describe detection of CTX-M-65-producing E. coli isolated from chickens. None of the isolates contained the bla SHV gene. Conjugation experiments demonstrated that bla CTX-M and bla TEM genes could be transferred to E. coli DH5a. The results indicate that ESBL frequency has reached an alarming level in chicken isolates in China, with TEM-1 and CTX-M-65 enzymes being the two predominant b-lactamases detected. INTRODUCTIONExtended-spectrum b-lactamases (ESBLs) are rapidly spreading worldwide (Tenover et al., 1999) and presently comprise over 500 variants (http://www.lahey.org/Studies), which are frequently encountered among human and animal clinical Enterobacteriaceae isolates (Bradford, 2001). A typical characteristic of ESBLs is their ability to hydrolyse oxyimino-cephalosporins, which can be inhibited by blactamase inhibitors (Paterson & Bonomo, 2005). ESBLs, particularly TEM, SHV and CTX-M enzymes, exhibit a high degree of diversity (Bonnet, 2004;Livermore et al., 2007). ESBL genes are usually carried by plasmids, facilitating their spread among Gram-negative bacilli. Several surveillance studies have revealed a relatively high prevalence of ESBL-producing organisms in the AsiaPacific area (Hirakata et al., 2005;Wang et al., 2005). In particular, the CTX-M family is believed to be dominant in Asia, as it has appeared or caused outbreaks in many countries (Bonnet, 2004;Munday et al., 2004;Ryoo et al., 2005;Kiratisin et al., 2008;Xiao et al., 2008).Since 1994, ESBL-producing bacteria have become widely disseminated in the People's Republic of China and their molecular characterization has focused mainly on human clinical isolates (Cheng & Chen, 1994;Chanawong et al., 2002;Wang et al., 2005;Xiao et al., 2008;Liu et al., 2009). Several studies worldwide have studied the epidemiology and molecular characterization of ESBL-producing animal clinical isolates (Batchelor et al., ...

Sigma factors are the predominant factors involved in transcription regulation in bacteria. These factors can recruit the core RNA polymerase to promoters with specific DNA sequences and initiate gene transcription. The plastids of higher plants originating from an ancestral cyanobacterial endosymbiont also contain sigma factors that are encoded by a small family of nuclear genes. Although all plastid sigma factors contain sequences conserved in bacterial sigma factors, a considerable number of distinct traits have been acquired during evolution. The present review summarises recent advances concerning the regulation of the structure, function and activity of plastid sigma factors since their discovery nearly 40 years ago. We highlight the specialised roles and overlapping redundant functions of plastid sigma factors according to their promoter selectivity. We also focus on the mechanisms that modulate the activity of sigma factors to optimise plastid function in response to developmental cues and environmental signals. This article is part of a Special Issue entitled: Chloroplast Biogenesis.

Neurofibromatosis type 1 (NF1) is a cancer predisposition disorder that results from inactivation of the tumor-suppressor Neurofibromin, a negative regulator of RAS signaling. NF1 patients present with a wide range of clinical manifestations and the tumor with highest prevalence is cutaneous neurofibroma (cNF). Most patients harboring cNF suffer greatly from the burden of those tumors, which have no effective medical treatment. Ironically, none of the numerous NF1 mouse models developed so far recapitulate cNF. Here, we discovered that Hoxb7 serves as a lineage marker to trace the developmental origin of cNF neoplastic cells. Ablating Nf1 in the Hoxb7 lineage faithfully recapitulates both human cutaneous and plexiform neurofibroma. In addition, we discovered that modulation of the Hippo pathway acts as a “modifier” for neurofibroma tumorigenesis. This mouse model opens the doors for deciphering the evolution of cNF to identify effective therapies, where none exist today.

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