Homology-dependent interactions determine the order of strand exchange by IntDOT recombinase

The Bacteroides conjugative transposon CTnDOT encodes an integrase, IntDOT, which is a member of the tyrosine recombinase family. Other members of this group share a strict requirement for sequence identity within the region of strand exchange, called the overlap region. Tyrosine recombinases catalyze recombination by making an initial cleavage, strand exchange and ligation, followed by strand swapping isomerization requiring sequence identity in the overlap region, followed by the second cleavage, strand exchange and ligation. IntDOT is of particular interest because it has been shown to utilize a three-step mechanism: a sequence identity-dependent initial strand exchange that requires two base pairs of complementary DNA at the site of cleavage; a sequence identity-independent strand swapping isomerization, followed by a sequence identity-independent cleavage, strand exchange and ligation. In addition to the sequence identity requirement in the overlap region, Lambda Int interactions with arm-type sites dictate the order of strand exchange regardless of the orientation of the overlap region. Although IntDOT has an arm-binding domain, we show here that the location of sequence identity within the overlap region dictates where the initial cleavage takes place and that IntDOT can recombine substrates containing mismatches in the overlap region so long as a single base of sequence identity exists at the site of initial cleavage

Climate change and the long-term viability of the World’s busiest heavy haul ice road

Climate models project that the northern high latitudes will warm at a rate in excess of the global mean. This will pose severe problems for Arctic and sub-Arctic infrastructure dependent on maintaining low temperatures for structural integrity. This is the case for the economically important Tibbitt to Contwoyto Winter Road (TCWR)—the world’s busiest heavy haul ice road, spanning 400 km across mostly frozen lakes within the Northwest Territories of Canada. In this study, future climate scenarios are developed for the region using statistical downscaling methods. In addition, changes in lake ice thickness are projected based on historical relationships between measured ice thickness and air temperatures. These projections are used to infer the theoretical operational dates of the TCWR based on weight limits for trucks on the ice. Results across three climate models driven by four RCPs reveal a considerable warming trend over the coming decades. Projected changes in ice thickness reveal a trend towards thinner lake ice and a reduced time window when lake ice is at sufficient thickness to support trucks on the ice road, driven by increasing future temperatures. Given the uncertainties inherent in climate modelling and the resultant projections, caution should be exercised in interpreting the magnitude of these scenarios. More certain is the direction of change, with a clear trend towards winter warming that will reduce the operation time window of the TCWR. This illustrates the need for planners and policymakers to consider future changes in climate when planning annual haulage along the TCWR

Role of the core in CTnDOT integration

IntDOT is the tyrosine recombinase encoded by the Bacteroides conjugative transposon CTnDOT. It catalyzes integration and excision into and out of the bacterial host chromosome. Although it is a member of the well studied tyrosine recombinase family, IntDOT is of particular interest because it can catalyze recombination between substrates containing heterology in the overlap region. This tolerance for heterology suggests that IntDOT uses a different mechanism for recombination. IntDOT performs initial cleavage on the top strand adjacent to the D and B core sites. The first two bases within the overlap region are a conserved GC dinucleotide that provide the only sequence identity between the two substrates. I used complementary DNA oligonucleotides to invert the overlap region 180 degrees to relocate the GC dinucleotide to the bottom strand adjacent to the B’ core site of attB. I tested the inverted overlap attB site in an in vitro integration assay with wild-type attDOT and showed that integration still occurs, albeit in the opposite orientation relative to the wild type reaction. I used nicked attB substrates to show that initial cleavage of the inverted overlap attB substrate takes place on the bottom strand adjacent to the B’ core site, suggesting that the location of sequence identity within the overlap determines the site of initial cleavage. I confirmed this hypothesis by using an attB site containing a symmetric overlap sequence

Family planning in carriers of BRCA1 and BRCA2 pathogenic variants

BRCA1 and BRCA2 pathogenic variant carriers have a high lifetime risk of developing breast and ovarian malignancies. Given the risks and significant ramifications of undergoing risk-reducing surgeries, many pathogenic variant carriers unaffected by cancer (previvors) struggle with family planning and reproductive decision making. The objective of this study was to determine the attitudes and practices of BRCA1 and BRCA2 pathogenic variant carriers with respect to family planning decision making. A cross-sectional survey was conducted of BRCA1 and BRCA2 previvors at four Northeastern medical centers. The survey was administered electronically via email using REDCap. The survey included demographic information as well as questions about genetic testing, prophylactic surgeries, family planning, and partnering. Data were analyzed with Fisher\u27s exact tests and t tests. The survey was completed by 139 of 422 BRCA1 and BRCA2 pathogenic variant carriers (response rate 33%). Thirteen were excluded from analysis due to self-reported cancer history. Of the remaining 126, 21 (16.7%) were male and 105 (83.3%) were female. Female participants (p \u3c 0.0001). Younger women also reported their genetic status had a stronger impact on their romantic relationships (p = 0.029). Men were significantly more likely to report that they felt no urgency to have a family compared to women (p \u3c 0.0001). Our study reflects the complex decision making for previvors and the intricacies of family planning in this population. Providers can use this knowledge as a guide to counsel patients about reproductive options

Choosing high-risk screening vs. surgery and the effect of treatment modality on anxiety and breast-specific sensuality in BRCA mutation carriers

Background: We have previously shown that breast cancer surgery affects breast specific sensuality, and that women who undergo mastectomy may have worse sexual function outcomes than those who undergo lumpectomy. It is less clear if patients who undergo prophylactic mastectomy are equally as affected as those with a cancer diagnosis. We sought to compare sexual function outcomes and their relationship to depression and anxiety between BRCA mutation carriers (mBRCA) with and without cancer in order to guide surgical counseling and improve survivorship outcomes. Methods: A confidential, cross-sectional survey was distributed electronically to mBRCA at least 18 years of age. The survey included investigator-generated questions, the Female Sexual Function Index (FSFI), and the Hospital Anxiety and Depression Scale (HADS) surveys. Responses were analyzed in total and divided into two subgroups: those with and without breast cancer. Results: Sixty-three mBRCA responded (37%) of 170 email addresses were identified, and 77% were postmenopausal. Although more than half of all mBRCA reported that the role of the breast in intimacy was important, most patients without cancer and all of those with cancer experienced an impressive decline in certain breast-specific sensuality parameters postoperatively. Among those without cancer, anxiety scores were not different between those choosing prophylactic mastectomy and high-risk screening (HRS). Sexual function as measured by the FSFI was negatively correlated with depression and anxiety in mBRCA. FSFI scores were not significantly different between those with and without cancer. However, the median FSFI of mBRCA with cancer, those undergoing HRS, and those who underwent prophylactic mastectomy indicated sexual dysfunction. Conclusions: As the availability of genetic testing increases, more women are found to harbor BRCA mutations and must choose between HRS and prophylactic surgery. Women with BRCA mutations, both with and without breast cancer, are susceptible to derangements in sexual function during the course of both screening or treatment, and this appears to be negatively correlated to depression and anxiety

Barriers to hormone therapy following prophylactic bilateral salpingo-oophorectomy in BRCA1/2 mutation carriers

OBJECTIVE: This study aimed to identify barriers to hormone therapy (HT) use among women with BRCA1/2 mutations after prophylactic bilateral salpingo-oophorectomy (BSO). METHODS: A cross-sectional, electronic survey was conducted of BRCA1/2 mutation carriers at Women and Infants Hospital, Yale Medical Center, Hartford Healthcare, and Maine Medical Center. This study was a subanalysis of a subset of female BRCA1/2 mutation carriers who had undergone a prophylactic BSO. Data were analyzed using the Fisher\u27s exact test or t test. RESULTS: We performed a subanalysis of 60 BRCA mutation carriers who underwent a prophylactic BSO. Only 24 women (40%) reported ever using HT. HT use was higher in women who underwent their prophylactic BSO at age younger than 45 years (51% vs. 25%, P = 0.06). Among all women who had a prophylactic BSO, the majority (73%) reported that a provider talked to them about using HT. Two thirds reported having seen contradictory information in the media about long-term consequences of HT. Seventy percent listed their provider as the primary influence in their decision to start HT. The most common reasons for not starting HT included it not being recommended by their physician (46%) and that it was not necessary (37%). CONCLUSIONS: BRCA mutation carriers frequently undergo prophylactic BSO at young ages, and less than half report using HT. This study highlights barriers to HT use, such as patient fears and physician discouragement, and identifies potential areas to improve educational efforts