Gene transfer across species boundaries in bryophytes: evidence from major life cycle stages in Homalothecium lutescens and H. sericeum.

BACKGROUND AND AIMS: The mosses Homalothecium lutescens and H. sericeum are genetically, morphologically and ecologically differentiated; mixed populations sometimes occur. In sympatric populations, intermediate character states among gametophytes and sporophytes have been observed, suggesting hybridization and introgression in such populations. METHODS: We determined genotypes using bi-allelic co-dominant single nucleotide polymorphism (SNP) markers, specific to either H. lutescens or H. sericeum, to estimate the degree of genetic mixing in 449 moss samples collected from seven sympatric and five allopatric populations on the island of Öland, south Sweden. The samples represented three generations: haploid maternal gametophytes; diploid sporophytes; and haploid sporelings. KEY RESULTS: Admixture analyses of SNP genotypes identified a majority as pure H. lutescens or H. sericeum, but 76 samples were identified as mildly admixed (17 %) and 17 samples (3.8 %) as strongly admixed. Admixed samples were represented in all three generations in several populations. Hybridization and introgression were bidirectional. CONCLUSIONS: Our results demonstrate that admixed genomes are transferred between the generations, so that the populations behave as true hybrid zones. Earlier studies of sympatric bryophyte populations with admixed individuals have not been able to show that admixed alleles are transferred beyond the first generation. The presence of true hybrid zones has strong evolutionary implications because genetic material transferred across species boundaries can be directly exposed to selection in the long-lived haploid generation of the bryophyte life cycle, and contribute to local adaptation, long-term survival and speciation.

A retrospective study of the prescribing and outcomes of tyrosine kinase inhibitors in chronic myeloid leukaemia over a period of more than 10 years.

WHAT IS KNOWN AND OBJECTIVE: Since their introduction, tyrosine kinase inhibitors (TKIs) have been increasingly used in clinical practice. We describe the prescribing and the clinical and biological consequences of two such inhibitors, imatinib and erlotinib, in patients with chronic myeloid leukaemia (CML) in a practice setting over a period of more than 10 years. METHODS: All patients who received at least one TKI for chronic phase CML between 2001 and 2012 in our university hospital were included in the study. RESULTS AND DISCUSSION: Of the 139 patients, with a median age of 57 years, who were surveyed, imatinib and nilotinib were prescribed as the first TKI in 131 (94%) and 8 (6%) patients, respectively. With a median follow-up of 6 years, 342 treatment modifications were observed: 113 (33%) increased doses, 109 (32%) decreased doses, 89 (26%) TKI changes, 14 (4%) definitive discontinuations, 13 (4%) temporary discontinuations and 4 (1%) additions of IFN-α. The main reasons for the 342 treatment modifications were adverse events (n = 112, 33%), long-term optimal response (n = 58, 17%) and failure (n = 57, 17%). Eighty-five (61%), 31 (22%), 18 (13%) and 5 (4%) patients had no, 1, 2 and 3 TKI changes, respectively. Imatinib was the most prescribed TKI (75%). Adverse events resulting in treatment modifications occurred in 18% of patients for imatinib, 49% for nilotinib and 41% for dasatinib (P < 0·001). Median time to TKI change whatever the reason was >50 months (not achieved) for imatinib, 22 months for nilotinib and 27 months for dasatinib (log-rank test, P < 0·001). WHAT IS NEW AND CONCLUSION: Imatinib was the most prescribed TKI both in the first and in subsequent therapeutic lines for chronic phase CML. Our study showed a very good efficacy-safety profile for imatinib at a median follow-up of 6 years in an unselected French population.

Transatlantic spread of highly pathogenic avian influenza H5N1 by wild birds from Europe to North America in 2021.

Highly pathogenic avian influenza (HPAI) viruses of the A/Goose/Guangdong/1/1996 lineage (GsGd), which threaten the health of poultry, wildlife and humans, are spreading across Asia, Europe, Africa and North America but are currently absent from South America and Oceania. In December 2021, H5N1 HPAI viruses were detected in poultry and a free-living gull in St. John's, Newfoundland and Labrador, Canada. Our phylogenetic analysis showed that these viruses were most closely related to HPAI GsGd viruses circulating in northwestern Europe in spring 2021. Our analysis of wild bird migration suggested that these viruses may have been carried across the Atlantic via Iceland, Greenland/Arctic or pelagic routes. The here documented incursion of HPAI GsGd viruses into North America raises concern for further virus spread across the Americas by wild bird migration.

Contribution of aerobic photoheterotrophic bacteria to the carbon cycle in the ocean.

The vertical distribution of bacteriochlorophyll a, the numbers of infrared fluorescent cells, and the variable fluorescence signal at 880 nanometers wavelength, all indicate that photosynthetically competent anoxygenic phototrophic bacteria are abundant in the upper open ocean and comprise at least 11% of the total microbial community. These organisms are facultative photoheterotrophs, metabolizing organic carbon when available, but are capable of photosynthetic light utilization when organic carbon is scarce. They are globally distributed in the euphotic zone and represent a hitherto unrecognized component of the marine microbial community that appears to be critical to the cycling of both organic and inorganic carbon in the ocean.

Small extracellular particles with big potential for horizontal gene transfer: membrane vesicles and gene transfer agents.

Bacteria are known to release different types of particles that serve various purposes such as the processing of metabolites, communication, and the transfer of genetic material. One of the most interesting aspects of the production of such particles is the biogenesis and trafficking of complex particles that can carry DNA, RNA, proteins or toxins into the surrounding environment to aid in bacterial survival or lead to gene transfer. Two important bacterial extracellular complexes are membrane vesicles and gene transfer agents. In this review, we will discuss the production, contents and functions of these two types of particles as related to their abilities to facilitate horizontal gene transfer.

A novel pathway producing dimethylsulphide in bacteria is widespread in soil environments.

The volatile compound dimethylsulphide (DMS) is important in climate regulation, the sulphur cycle and signalling to higher organisms. Microbial catabolism of the marine osmolyte dimethylsulphoniopropionate (DMSP) is thought to be the major biological process generating DMS. Here we report the discovery and characterization of the first gene for DMSP-independent DMS production in any bacterium. This gene, mddA, encodes a methyltransferase that methylates methanethiol and generates DMS. MddA functions in many taxonomically diverse bacteria including sediment-dwelling pseudomonads, nitrogen-fixing bradyrhizobia and cyanobacteria, and mycobacteria including the pathogen Mycobacterium tuberculosis. The mddA gene is present in metagenomes from varied environments, being particularly abundant in soil environments, where it is predicted to occur in up to 76% of bacteria. This novel pathway may significantly contribute to global DMS emissions, especially in terrestrial environments and could represent a shift from the notion that DMSP is the only significant precursor of DMS.

Genotypic and allelic frequencies of SULT1A1 polymorphisms in women receiving adjuvant tamoxifen therapy.

Human sulfotransferase 1A1 (SULT1A1) is involved in the metabolism of a number of substances including 4-hydroxytamoxifen. It has been shown that patients who are homozygous for the variant SULT1A1 *2/*2 have lower catalytic activity. Previous data has suggested that patients with this particular genotype may be at a greater risk of developing breast cancer or not responding to tamoxifen therapy. To date, there is no data within the Hispanic population on the genotypic and allelic frequencies of the SULT1A1 gene. Two hundred and ninety-six patients were genotyped by either restriction fragment length polymorphism (RFLP) or Pyrosequencing for the SULT1A1 exon 7 polymorphism. The genotypic frequency was 0.47 (*1/*1), 0.40 (*1/*2) and 0.13 (*2/*2) in Caucasians and 0.37 (*1/*1), 0.45 (*1/*2) and 0.18 (*2/*2) in Hispanics. Although Hispanics have a higher genotypic frequency of variant genotypes this difference was not statistically significant (p=0.26). SULT1A1 genotype did not correlate with any prognostic or predictive markers associated with breast cancer. Future evaluations will assess the functional significance of this polymorphism on survival.

The gene transfer agent of Rhodobacter capsulatus and "constitutive transduction" in prokaryotes.

Transduction, bacteriophage-mediated gene transfer, is thought to play an important role in the evolution of prokaryote genomes. Several gene transfer agents that resemble transducing phages have been found in diverse prokaryotes. This mini-review discusses these interesting agents of genetic exchange with a focus on the gene transfer agent (GTA) of Rhodobacter capsulatus, at present the only member of this group for which genetic information exists about the production of transducing particles. Production of GTA results from expression of genes that are similar to phage genes, yet transcription of these genes is dependent upon cellular (two-component) signaling proteins. The significance of these relationships, as well as the finding of GTA gene homologues in the bacterium Rhodopseudomonas palustris, is discussed.

Genetic analysis of a bacterial genetic exchange element: the gene transfer agent of Rhodobacter capsulatus.

An unusual system of genetic exchange exists in the purple nonsulfur bacterium Rhodobacter capsulatus. DNA transmission is mediated by a small bacteriophage-like particle called the gene transfer agent (GTA) that transfers random 4.5-kb segments of the producing cell's genome to recipient cells, where allelic replacement occurs. This paper presents the results of gene cloning, analysis, and mutagenesis experiments that show that GTA resembles a defective prophage related to bacteriophages from diverse genera of bacteria, which has been adopted by R. capsulatus for genetic exchange. A pair of cellular proteins, CckA and CtrA, appear to constitute part of a sensor kinase/response regulator signaling pathway that is required for expression of GTA structural genes. This signaling pathway controls growth-phase-dependent regulation of GTA gene messages, yielding maximal gene expression in the stationary phase. We suggest that GTA is an ancient prophage remnant that has evolved in concert with the bacterial genome, resulting in a genetic exchange process controlled by the bacterial cell.

Transcript cleavage, attenuation, and an internal promoter in the Rhodobacter capsulatus puc operon.

The stoichiometry of the structural proteins of the photosynthetic apparatus in purple photosynthetic bacteria is achieved primarily by complex regulation of the levels of mRNA encoding the different proteins, which has been studied in the greatest detail in the puf operon. Here we investigated the transcriptional and posttranscriptional regulation of the puc operon, which encodes the peripheral light harvesting complex LHII. We show that, analogous to the puf operon, a primary transcript encoding five puc genes is rapidly processed to generate more stable RNA subspecies. Contrary to previous hypotheses, translational coupling and regulation of puc transcription by puc gene products were found not to occur. A putative RNA stem-loop structure appears to attenuate transcription initiated at the puc operon major promoter. We also found that a minor pucD-internal promoter contributes to the levels of a message that encodes the LHII 14-kDa gamma (PucE) protein.