Tet controls axon guidance in early brain development through glutamatergic signaling

Mutations in ten-eleven translocation (TET) proteins are associated with human neurodevelopmental disorders. We find a function of Tet in regulating Drosophila early brain development. The Tet DNA-binding domain (TetAXXC) is required for axon guidance in the mushroom body (MB). Glutamine synthetase 2 (Gs2), a key enzyme in glutamatergic signaling, is significantly down-regulated in the TetAXXC brains. Loss of Gs2 recapitulates the TetAXXC phenotype. Surprisingly, Tet and Gs2 act in the insulin-producing cells (IPCs) to control MB axon guidance, and overexpression of Gs2 in IPCs rescues the defects of TetAXXC. Feeding TetAXXC with metabotropic glutamate receptor antagonist MPEP rescues the phenotype while glutamate enhances it. Mutants in Tet and Drosophila Fmr1, the homolog of human FMR1, have similar defects, and overexpression of Gs2 in IPCs also rescues the Fmr1 phenotype. We provide the first evidence that Tet controls the guidance of developing brain axons by modulating glutamatergic signaling.

Alzheimer's Incidence and Prevalence with and without Asthma: A Medicare cohort study

BACKGROUND

International data suggest that asthma, like other inflammatory diseases, might increase Alzheimer's disease (AD) risk.

OBJECTIVE

To explore risk pathways and future mitigation strategies by comparing diagnostic claims-based AD incidence and prevalence among US patients with asthma to non-asthma patients.

METHODS

This cohort study included a national Medicare 20% random sample 2013-2015. Adult patients with >12 months continuous Medicare with asthma were compared to non-asthma subjects overall and as matched. Asthma was defined by one inpatient or two outpatient codes for asthma. The main outcomes were two-year incident or prevalent AD defined as any codes for ICD-9 331.0 or ICD-10 G30.0, G30.1, G30.8, G30.9.

RESULTS

Among 5,460,732 total beneficiaries, 678,730 patients were identified with baseline asthma and more often identified as Black or Hispanic, were Medicaid eligible, or resided in a highly disadvantaged neighborhood than those without asthma. Two-year incidence of AD was 1.4% with asthma vs 1.1% without; prevalence was 7.8% vs 5.4% (both p=<0.001). Per 100,000 patients over two years, 303 more incident AD diagnoses occurred in asthma, with 2,425 more prevalent cases (p<0.001). Multivariable models showed asthma had greater odds of two-year AD incidence [AOR 1.33 (1.29-1.36); matched 1.2 (1.17-1.24)] and prevalence [AOR 1.48 (1.47-1.50); matched 1.25 (1.22-1.27)).

CONCLUSION

Asthma was associated with 20-33% increased two-year incidence and 25-48% increased prevalence of claims-based Alzheimer's disease in this nationally representative US sample. Future research should investigate risk pathways of underlying comorbidities and social determinants, as well as whether there are potential asthma treatments that may preserve brain health.

Receipt of rheumatology care and lupus-specific labs among young adults with systemic lupus erythematosus: A US Medicare retention in care cohort study

OBJECTIVE

In systemic lupus erythematosus, poor disease outcomes occur in young adults, patients identifying as Black or Hispanic, and socioeconomically disadvantaged patients. These identities and social factors differentially shape care access and quality that contribute to lupus health disparities in the US. Thus, our objective was to measure markers of care access and quality, including rheumatology visits (longitudinal care retention) and lupus-specific serology testing, by race and ethnicity, neighborhood disadvantage, and geographic context.

METHODS

This cohort study used a geo-linked 20% national sample of young adult Medicare beneficiaries (ages 18-35) with lupus-coded encounters and a 1-year assessment period. Retention in lupus care required a rheumatology visit in each 6-month period, and serology testing required ≥1 complement or dsDNA antibody test within the year. Multivariable logistic regression models were fit for visit-based retention and serology testing to determine associations with race and ethnicity, neighborhood disadvantage, and geography.

RESULTS

Among 1,036 young adults with lupus, 39% saw a rheumatologist every 6 months and 28% had serology testing. White beneficiaries from the least disadvantaged quintile of neighborhoods had higher visit-based retention than other beneficiaries (64% vs 30%-60%). Serology testing decreased with increasing neighborhood disadvantage quintile (aOR 0.80; 95% CI 0.71, 0.90) and in the Midwest (aOR 0.46; 0.30, 0.71).

CONCLUSION

Disparities in care, measured by rheumatology visits and serology testing, exist by neighborhood disadvantage, race and ethnicity, and region among young adults with lupus, despite uniform Medicare coverage. Findings support evaluating lupus care quality measures and their impact on US lupus outcomes.

Tet-dependent 5-hydroxymethyl-Cytosine modification of mRNA regulates axon guidance genes in Drosophila

Modifications of mRNA, especially methylation of adenosine, have recently drawn much attention. The much rarer modification, 5-hydroxymethylation of cytosine (5hmC), is not well understood and is the subject of this study. Vertebrate Tet proteins are 5-methylcytosine (5mC) hydroxylases and catalyze the transition of 5mC to 5hmC in DNA. These enzymes have recently been shown to have the same function in messenger RNAs in both vertebrates and in Drosophila. The Tet gene is essential in Drosophila as Tet knock-out animals do not reach adulthood. We describe the identification of Tet-target genes in the embryo and larval brain by mapping one, Tet DNA-binding sites throughout the genome and two, the Tet-dependent 5hmrC modifications transcriptome-wide. 5hmrC modifications are distributed along the entire transcript, while Tet DNA-binding sites are preferentially located at the promoter where they overlap with histone H3K4me3 peaks. The identified mRNAs are preferentially involved in neuron and axon development and Tet knock-out led to a reduction of 5hmrC marks on specific mRNAs. Among the Tet-target genes were the robo2 receptor and its slit ligand that function in axon guidance in Drosophila and in vertebrates. Tet knock-out embryos show overlapping phenotypes with robo2 and both Robo2 and Slit protein levels were markedly reduced in Tet KO larval brains. Our results establish a role for Tet-dependent 5hmrC in facilitating the translation of modified mRNAs primarily in cells of the nervous system.

Tet-dependent 5-hydroxymethyl-Cytosine modification of mRNA regulates axon guidance genes in Drosophila

Modifications of mRNA, especially methylation of adenosine, have recently drawn much attention. The much rarer modification, 5-hydroxymethylation of cytosine (5hmC), is not well understood and is the subject of this study. Vertebrate Tet proteins are 5-methylcytosine (5mC) hydroxylases and catalyze the transition of 5mC to 5hmC in DNA. These enzymes have recently been shown to have the same function in messenger RNAs in both vertebrates and in Drosophila. The Tet gene is essential in Drosophila as Tet knock-out animals do not reach adulthood. We describe the identification of Tet-target genes in the embryo and larval brain by mapping one, Tet DNA-binding sites throughout the genome and two, the Tet-dependent 5hmrC modifications transcriptome-wide. 5hmrC modifications are distributed along the entire transcript, while Tet DNA-binding sites are preferentially located at the promoter where they overlap with histone H3K4me3 peaks. The identified mRNAs are preferentially involved in neuron and axon development and Tet knock-out led to a reduction of 5hmrC marks on specific mRNAs. Among the Tet-target genes were the robo2 receptor and its slit ligand that function in axon guidance in Drosophila and in vertebrates. Tet knock-out embryos show overlapping phenotypes with robo2 and both Robo2 and Slit protein levels were markedly reduced in Tet KO larval brains. Our results establish a role for Tet-dependent 5hmrC in facilitating the translation of modified mRNAs primarily in cells of the nervous system.

Tet Controls Axon Guidance in Early Brain Development through Glutamatergic Signaling

Ten-eleven translocation (Tet) is an important gene in neurodevelopment, but how Tet regulates brain development is still under study. Mutations in human TET proteins have been found in individuals with neurodevelopmental disorders. Here we report a new function of Tet in regulating Drosophila early brain development. We found that mutation on the Tet DNA-binding domain ( Tet ^AXXC ) resulted in axon guidance defects in the mushroom body (MB). Tet is required in early brain development during the outgrowth of MB β axons. Transcriptomic study of Tet ^AXXC mutant and wild-type pupal brains shows that glutamine synthetase 2 (Gs2), a key enzyme in glutamatergic signaling, is the most significantly down-regulated gene in the Tet mutant brains. RNAi knockdown or CRISPR/Cas9 mutagenesis of Gs2 recapitulates the Tet ^AXXC phenotype. Surprisingly, Tet and Gs2 act in the insulin-producing cells (IPCs) to control MB axon guidance, and overexpression of Gs2 in the IPCs rescue the axonal defects of Tet ^AXXC . Treating Tet ^AXXC with the metabotropic glutamate receptor antagonist MPEP can also rescue the phenotype confirming Tet function in regulating glutamatergic signaling. Tet ^AXXC and the Drosophila homolog of Fragile X Messenger Ribonucleoprotein protein mutant ( Fmr1 ³ ) have similar mushroom body axonal defects and reduction in Gs2 transcription, and, importantly, overexpression of Gs2 in the IPCs of Fmr1 mutants also rescues the axonal defects. Our studies reveal a new function of Tet in regulating axon guidance in the brain via glutamatergic signaling and suggest overlapping functions between Tet and Fmr1.

Association of rurality and identifying as black with receipt of specialty care among patients hospitalized with a diabetic foot ulcer: a Medicare cohort study

INTRODUCTION

Rural patients with diabetic foot ulcers, especially those identifying as black, face increased risk of major amputation. Specialty care can reduce this risk. However, care disparities might beget outcome disparities. We aimed to determine whether a smaller proportion of rural patients, particularly those identifying as black, receive specialty care compared with the national proportion.

RESEARCH DESIGN AND METHODS

This 100% national retrospective cohort examined Medicare beneficiaries hospitalized with diabetic foot ulcers (2013-2014). We report observed differences in specialty care, including: endocrinology, infectious disease, orthopedic surgery, plastic surgery, podiatry, or vascular surgery. We used logistic regression to examine possible intersectionality between rurality and race, controlling for sociodemographics, comorbidities, and ulcer severity and including an interaction term between rurality and identifying as black.

RESULTS

Overall, 32.15% (n=124 487) of patients hospitalized with a diabetic foot ulcer received specialty care. Among rural patients (n=13 100), the proportion decreased to 29.57%. For patients identifying as black (n=21 649), the proportion was 33.08%. Among rural patients identifying as black (n=1239), 26.23% received specialty care. This was >5 absolute percentage points less than the overall cohort. The adjusted OR for receiving specialty care among rural versus urban patients identifying as black was 0.61 (95% CI 0.53 to 0.71), which was lower than that for rural versus urban patients identifying as white (aOR 0.85, 95% CI 0.80 to 0.89). This metric supported a role for intersectionality between rurality and identifying as black.

CONCLUSIONS

A smaller proportion of rural patients, particularly those identifying as black, received specialty care when hospitalized with a diabetic foot ulcer compared with the overall cohort. This might contribute to known disparities in major amputations. Future studies are needed to determine causality.

Tet-dependent 5-hydroxymethyl-Cytosine modification of mRNA regulates the axon guidance genes robo2 and slit in Drosophila

Modifications of mRNA, especially methylation of adenosine, have recently drawn much attention. The much rarer modification, 5-hydroxymethylation of cytosine (5hmC), is not well understood and is the subject of this study. Vertebrate Tet proteins are 5-methylcytosine (5mC) hydroxylases enzymes catalyzing the transition of 5mC to 5hmC in DNA and have recently been shown to have the same function in messenger RNAs in both vertebrates and in Drosophila. The Tet gene is essential in Drosophila because Tet knock-out animals do not reach adulthood. We describe the identification of Tet-target genes in the embryo and larval brain by determining Tet DNA-binding sites throughout the genome and by mapping the Tet-dependent 5hmrC modifications transcriptome-wide. 5hmrC-modified sites can be found along the entire transcript and are preferentially located at the promoter where they overlap with histone H3K4me3 peaks. The identified mRNAs are frequently involved in neuron and axon development and Tet knock-out led to a reduction of 5hmrC marks on specific mRNAs. Among the Tet-target genes were the robo2 receptor and its slit ligand that function in axon guidance in Drosophila and in vertebrates. Tet knock-out embryos show overlapping phenotypes with robo2 and are sensitized to reduced levels of slit. Both Robo2 and Slit protein levels were markedly reduced in Tet KO larval brains. Our results establish a role for Tet-dependent 5hmrC in facilitating the translation of modified mRNAs, primarily in developing nerve cells.

1659. Association of Rurality and Identifying as Black with Receipt of Specialty Care among Patients Hospitalized with Diabetic Foot Ulcers: a Medicare cohort study

Background

Among those with diabetic foot ulcers, rural patients identifying as Black face at least 10% greater risk of major amputation or death compared to the US as a whole. As specialty care is associated with lower risk of major amputation, this difference could be driven by specialty care access. We hypothesize that rural patients and, particularly, rural patients identifying as Black, receive less inpatient specialty care compared to the overall cohort.

Methods

We built a cohort of all Medicare patients hospitalized with diabetic foot ulcers (2013–2014). Rurality was measured using Rural Urban Commuting Area codes. Race was categorized using the Research Triangle Institute algorithm. Specialty care was defined as receiving inpatient care from at least 1 of 6 relevant specialties to address diabetes, infection, biomechanics or vascular disease, per National Provider Taxonomy codes: endocrinology, infectious disease, orthopedic surgery, plastic surgery, podiatry, and vascular surgery. We reported observed differences in specialty care, overall and stratified by rurality, identifying as Black, and ulcer severity. Pearson X² tests were performed on observed frequencies.

Results

Overall, 32.2% of the cohort received inpatient specialty care. This proportion decreased to 29.6% for rural patients (X² = 36.2, p ≤ 0.001) and 26.2% for rural patients identifying as Black (X² = 19.5, p ≤ 0.001). Among those with osteomyelitis, 54.3% of the cohort received specialty care, while only 49.5% of rural patients, 50.8% of patients identifying as Black, and 37.6% of rural patients identifying as Black received specialty care; the disparity for rural patients identifying as Black was greater than the sum of rural and racial disparities (4.8% for rural + 3.5% for Blacks = 8.3% versus a 16.7% observed difference for rural Blacks; Figure 1). Notably, only 2.7% of patients presenting with osteomyelitis were seen by an infectious disease specialist. This proportion decreased to 2.5% for rural patients.

Observed Proportions of Patients Receiving Specialty Care Stratified by Rurality, Identifying as Black, and Ulcer Severity

Conclusion

A smaller proportion of rural patients received specialty care, and rural patients identifying as Black were half as likely to receive specialty care than the overall cohort. Improving specialty access for these high-risk patients may reduce disparities in major amputations.

Disclosures

All Authors: No reported disclosures.

Phase-stabilized UV light at 267 nm through twofold second harmonic generation

Providing phase stable laser light is important to extend the interrogation time of optical clocks towards many seconds and thus achieve small statistical uncertainties. We report a laser system providing more than 50 µW phase-stabilized UV light at 267.4 nm for an aluminium ion optical clock. The light is generated by frequency-quadrupling a fibre laser at 1069.6 nm in two cascaded non-linear crystals, both in single-pass configuration. In the first stage, a 10 mm long PPLN waveguide crystal converts 1 W fundamental light to more than 0.2 W at 534.8 nm. In the following 50 mm long DKDP crystal, more than 50 µW of light at 267.4 nm are generated. An upper limit for the passive short-term phase stability has been measured by a beat-node measurement with an existing phase-stabilized quadrupling system employing the same source laser. The resulting fractional frequency instability of less than 5×10^-17 after 1 s supports lifetime-limited probing of the ²⁷Al⁺ clock transition, given a sufficiently stable laser source. A further improved stability of the fourth harmonic light is expected through interferometric path length stabilisation of the pump light by back-reflecting it through the entire setup and correcting for frequency deviations. The in-loop error signal indicates an electronically limited instability of 1 × 10^-18 at 1 s.

Association of Race, Ethnicity, and Rurality With Major Leg Amputation or Death Among Medicare Beneficiaries Hospitalized With Diabetic Foot Ulcers

IMPORTANCE

Patients identifying as Black and those living in rural and disadvantaged neighborhoods are at increased risk of major (above-ankle) leg amputations owing to diabetic foot ulcers. Intersectionality emphasizes that the disparities faced by multiply marginalized people (eg, rural US individuals identifying as Black) are greater than the sum of each individual disparity.

OBJECTIVE

To assess whether intersecting identities of Black race, ethnicity, rural residence, or living in a disadvantaged neighborhood are associated with increased risk in major leg amputation or death among Medicare beneficiaries hospitalized with diabetic foot ulcers.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study used 2013-2014 data from the US National Medicare Claims Data Database on all adult Medicare patients hospitalized with a diabetic foot ulcer. Statistical analysis was conducted from August 1 to October 27, 2021.

EXPOSURES

Race was categorized using Research Triangle Institute variables. Rurality was assigned using Rural-Urban Commuting Area codes. Residents of disadvantaged neighborhoods comprised those living in neighborhoods at or above the national 80th percentile Area Deprivation Index.

MAIN OUTCOMES AND MEASURES

Major leg amputation or death during hospitalization or within 30 days of hospital discharge. Logistic regression was used to explore interactions among race, ethnicity, rurality, and neighborhood disadvantage, controlling for sociodemographic characteristics, comorbidities, and ulcer severity.

RESULTS

The cohort included 124 487 patients, with a mean (SD) age of 71.5 (13.0) years, of whom 71 286 (57.3%) were men, 13 100 (10.5%) were rural, and 21 649 (17.4%) identified as Black. Overall, 17.6% of the cohort (n = 21 919), 18.3% of rural patients (2402 of 13 100), and 21.9% of patients identifying as Black (4732 of 21 649) underwent major leg amputation or died. Among 1239 rural patients identifying as Black, this proportion was 28.0% (n = 347). This proportion exceeded the expected excess for rural patients (18.3% - 17.6% = 0.7%) plus those identifying as Black (21.9% - 17.6% = 4.3%) by more than 2-fold (28.0% - 17.6% = 10.4% vs 0.7% + 4.3% = 5.0%). The adjusted predicted probability of major leg amputation or death remained high at 24.7% (95% CI, 22.4%-26.9%), with a significant interaction between race and rurality.

CONCLUSIONS AND RELEVANCE

Rural patients identifying as Black had a more than 10% absolute increased risk of major leg amputation or death compared with the overall cohort. This study suggests that racial and rural disparities interacted, amplifying risk. Findings support using an intersectionality lens to investigate and address disparities in major leg amputation and mortality for patients with diabetic foot ulcers.

eCross-cultural adaptation of the spine oncology-specific SOSGOQ2.0 questionnaire to German language and the assessment of its validity and reliability in the clinical setting

Background

The recently developed Spine Oncology Study Group Outcomes Questionnaire (SOSGOQ2.0) was proven a valid and reliable instrument measuring health-related quality of life (HRQOL) for patients with spinal malignancies. A German version was not available.

Objective

A cross-cultural adaptation of the SOSGOQ2.0 to the German language and its multicenter evaluation.

Methods

In a multistep process, a cross-cultural adaptation of the SOSGOQ2.0 was conducted. Subsequently, a multicenter, prospective observational cohort study was initiated to assess the reliability and validity of the German adaptation. To assess external construct validity of the cross-cultural adapted questionnaire, a comparison to the established questionnaire QLQ-C30 from the European Organisation for Research and Treatment of Cancer was conducted. Mean-difference plots were used to measure the agreement between the questionnaires in total score and by domain (deviation from mean up to 10% allowed). Further reliability and validity tests were carried out. Change to baseline was analysed 3–16 weeks later after different interventions occurred. Clinically relevant thresholds in comparison to the EORTC QLQ-C30 questionnaire were evaluated by ROC curve analysis.

Results

We could enroll 113 patients from four different university hospitals (58 females, 55 males). Mean age was 64.11 years (sd 11.9). 80 patients had an ECOG performance status of 2 or higher at baseline. External construct validity in comparison to the EORTC QLQ-C30 questionnaire in total score and by domain was confirmed (range of deviation 4.4 to 9.0%). Good responsiveness for the domains Physical Functioning (P < .001) and Pain (P < .001) could be shown. The group mean values also displayed a difference in the domains of Social Functioning (P = .331) and Mental Health (P = .130), but not significant. The minimum clinically relevant threshold values for the questionnaire ranged from 4.0 to 7.5 points.

Conclusions

According to our results, the cross-cultural adapted questionnaire is a reliable and valid tool to measure HRQOL in German speaking patients with spinal malignancies. Especially the domains Physical Functioning and Pain showed overall good psychometric characteristics. In this way, a generic questionnaire, such as the EORTC QLQ-C30, can be usefully supplemented by spine-specific questions to increase the overall accuracy measuring HRQOL in patients with spinal malignancies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08578-x.

Enabled/VASP is required to mediate proper sealing of opposing cardioblasts during Drosophila dorsal vessel formation

INTRODUCTION

The Drosophila dorsal vessel (DV) is comprised of two opposing rows of cardioblasts (CBs) that migrate toward the dorsal midline during development. While approaching the midline, CBs change shape, enabling dorsal and ventral attachments with their contralateral partners to create a linear tube with a central lumen. We previously demonstrated DV closure occurs via a "buttoning" mechanism where specific CBs advance ahead of their lateral neighbors, and attach creating transient holes, which eventually seal.

RESULTS

Here, we investigate the role of the actin-regulatory protein enabled (Ena) in DV closure. Loss of Ena results in DV cell shape and alignment defects. Live analysis of DV formation in ena mutants shows a reduction in CB leading edge protrusion length and gaps in the DV between contralateral CB pairs. These gaps occur primarily between a specific genetic subtype of CBs, which express the transcription factor seven-up (Svp) and form the ostia inflow tracts of the heart. In WT embryos these gaps between Svp⁺ CBs are observed transiently during the final stages of DV closure.

CONCLUSIONS

Our data suggest that Ena modulates the actin cytoskeleton in order to facilitate the complete sealing of the DV during the final stages of cardiac tube formation.

The gridded retarding ion drift sensor for the petitSat cubeSat mission

The Gridded Retarding Ion Drift Sensor (GRIDS) is a small sensor that will fly on the 6 U petitSat CubeSat. It is designed to measure the three-dimensional plasma drift velocity vector in the Earth's ionosphere. The GRIDS also supplies information about the ion temperature, ion density, and the ratio of light to heavy ions present in the ionospheric plasma. It utilizes well-proven techniques that have been successfully validated by similar instruments on larger satellite missions while meeting CubeSat-compatible requirements for low mass, size, and power consumption. GRIDS performs the functions of a Retarding Potential Analyzer (RPA) and an Ion Drift Meter (IDM) by combining the features of both types of instruments in a single package. The sensor alternates RPA and IDM measurements to produce the full set of measurement parameters listed above. On the petitSat mission, GRIDS will help identify and characterize a phenomenon known as plasma blobs (or enhancements).

C-24 Longitudinal Trajectories of Working Memory Performance in Typically Aging Older Adults

Objective

Cross-sectional studies have shown age-related differences in working memory (WM), but the trajectory is unclear due to the scarcity of longitudinal studies. Additional research is needed to better characterize the course of age-related changes in WM in older adults. The present study sought to address this gap in the literature by conducting serial assessments of WM in a longitudinally followed cohort of typically aging adults. We hypothesized a significant age × time interaction, such that WM would show pronounced declines with advancing age.

Methods

640 functionally intact participants in an aging cohort (clinical dementia rating = 0; age range 52-99, mean age = 75) completed a computerized WM measure, Running Letter Memory (RLM), every ~15 months for up to 8.5 years (mean follow-up = 1.9 years). Longitudinal changes in RLM scores were analyzed using linear mixed effects models, allowing for random slopes and intercepts. All models were adjusted for sex and education.

Results

RLM performance did not significantly decline over time (b = -.14, p = .43). As hypothesized, there was a significant age × time interaction predicting RLM scores (b = -.08, p = .006). Specifically, RLM performance remained relatively stable (or slightly improved) until around age 75, beyond which increasingly precipitous declines were observed with advancing age.

Conclusion

The present results suggest that WM performance does not evidence declines until the mid-70s in typically aging adults, at which point increasingly steep decline trajectories are observed with advancing age. These findings highlight that cognitive aging does not occur at a constant rate in late life.

Towards a transportable aluminium ion quantum logic optical clock

With the advent of optical clocks featuring fractional frequency uncertainties on the order of 10^-17 and below, new applications such as chronometric leveling with few-centimeter height resolution emerge. We are developing a transportable optical clock based on a single trapped aluminum ion, which is interrogated via quantum logic spectroscopy. We employ singly charged calcium as the logic ion for sympathetic cooling, state preparation, and readout. Here, we present a simple and compact physics and laser package for manipulation of ⁴⁰Ca⁺. Important features are a segmented multilayer trap with separate loading and probing zones, a compact titanium vacuum chamber, a near-diffraction-limited imaging system with high numerical aperture based on a single biaspheric lens, and an all-in-fiber ⁴⁰Ca⁺ repump laser system. We present preliminary estimates of the trap-induced frequency shifts on ²⁷Al⁺, derived from measurements with a single calcium ion. The micromotion-induced second-order Doppler shift for ²⁷Al⁺ has been determined to be δν_EMMν=-0.4_-0.3 ^+0.4×10^-18 and the black-body radiation shift is δν_BBR/ν = (-4.0 ± 0.4) × 10^-18. Moreover, heating rates of 30 (7) quanta per second at trap frequencies of ω_rad,Ca+ ≈ 2π × 2.5 MHz (ω_ax,Ca+ ≈ 2π × 1.5 MHz) in radial (axial) direction have been measured, enabling interrogation times of a few hundreds of milliseconds.

A Type 1 Diabetes Genetic Risk Score Predicts Progression of Islet Autoimmunity and Development of Type 1 Diabetes in Individuals at Risk

OBJECTIVE

We tested the ability of a type 1 diabetes (T1D) genetic risk score (GRS) to predict progression of islet autoimmunity and T1D in at-risk individuals.

RESEARCH DESIGN AND METHODS

We studied the 1,244 TrialNet Pathway to Prevention study participants (T1D patients' relatives without diabetes and with one or more positive autoantibodies) who were genotyped with Illumina ImmunoChip (median [range] age at initial autoantibody determination 11.1 years [1.2-51.8], 48% male, 80.5% non-Hispanic white, median follow-up 5.4 years). Of 291 participants with a single positive autoantibody at screening, 157 converted to multiple autoantibody positivity and 55 developed diabetes. Of 953 participants with multiple positive autoantibodies at screening, 419 developed diabetes. We calculated the T1D GRS from 30 T1D-associated single nucleotide polymorphisms. We used multivariable Cox regression models, time-dependent receiver operating characteristic curves, and area under the curve (AUC) measures to evaluate prognostic utility of T1D GRS, age, sex, Diabetes Prevention Trial-Type 1 (DPT-1) Risk Score, positive autoantibody number or type, HLA DR3/DR4-DQ8 status, and race/ethnicity. We used recursive partitioning analyses to identify cut points in continuous variables.

RESULTS

Higher T1D GRS significantly increased the rate of progression to T1D adjusting for DPT-1 Risk Score, age, number of positive autoantibodies, sex, and ethnicity (hazard ratio [HR] 1.29 for a 0.05 increase, 95% CI 1.06-1.6; P = 0.011). Progression to T1D was best predicted by a combined model with GRS, number of positive autoantibodies, DPT-1 Risk Score, and age (7-year time-integrated AUC = 0.79, 5-year AUC = 0.73). Higher GRS was significantly associated with increased progression rate from single to multiple positive autoantibodies after adjusting for age, autoantibody type, ethnicity, and sex (HR 2.27 for GRS >0.295, 95% CI 1.47-3.51; P = 0.0002).

CONCLUSIONS

The T1D GRS independently predicts progression to T1D and improves prediction along T1D stages in autoantibody-positive relatives.

Oxidative Stress and Cardiovascular Risk in Type 1 Diabetes Mellitus: Insights From the DCCT/EDIC Study

Background

Hyperglycemia leading to increased oxidative stress is implicated in the increased risk for the development of macrovascular and microvascular complications in patients with type 1 diabetes mellitus.

Methods and Results

A random subcohort of 349 participants was selected from the DCCT / EDIC (Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications) cohort. This included 320 controls and 29 cardiovascular disease cases that were augmented with 98 additional known cases to yield a case cohort of 447 participants (320 controls, 127 cases). Biosamples from DCCT baseline, year 1, and closeout of DCCT , and 1 to 2 years post‐ DCCT ( EDIC years 1 and 2) were measured for markers of oxidative stress, including plasma myeloperoxidase, paraoxonase activity, urinary F 2α isoprostanes, and its metabolite, 2,3 dinor‐8 iso prostaglandin F 2α . Following adjustment for glycated hemoblobin and weighting the observations inversely proportional to the sampling selection probabilities, higher paraoxonase activity, reflective of antioxidant activity, and 2,3 dinor‐8 iso prostaglandin F 2α , an oxidative marker, were significantly associated with lower risk of cardiovascular disease (−4.5% risk for 10% higher paraoxonase, P <0.003; −5.3% risk for 10% higher 2,3 dinor‐8 iso prostaglandin F 2α , P =0.0092). In contrast, the oxidative markers myeloperoxidase and F 2α isoprostanes were not significantly associated with cardiovascular disease after adjustment for glycated hemoblobin. There were no significant differences between DCCT intensive and conventional treatment groups in the change in all biomarkers across time segments.

Conclusions

Heightened antioxidant activity (rather than diminished oxidative stress markers) is associated with lower cardiovascular disease risk in type 1 diabetes mellitus, but these biomarkers did not change over time with intensification of glycemic control.

Clinical Trial Registration

URL : https://www.clinicaltrials.gov . Unique identifiers: NCT 00360815 and NCT 00360893.

Deep digital flexor tendon shortening as a treatment for distal interphalangeal joint hyperextension in a 2-year-old mare

Shortening of the deep digital flexor tendon was performed by tenotomy, overlapping and anastomosis. The procedure was performed on a two-year-old Quarter Horse Mare with distal interphalangeal joint hyperextension with subluxation and metatarsophalangeal joint hyperextension. These problems originated from damage to the digital flexor tendons, presumably due to previous distal limb trauma. The procedure markedly improved the mare's level of comfort, degree of ambulation and limb conformation. Two years following surgery the mare was comfortable at pasture.

Aktuelle Diagnostik der Hüftkopf-nekrose

Die neue S3-Leitlinie zur atraumatischen Femurkopfosteonekrose (aFKON) des Erwachsenen fasst nicht nur den aktuellen Wis-sensstand zur Diagnostik der aFKON zusammen, sondern positioniert sich auch kritisch und klar zu verschiedenen Therapien und the-rapeutischen Ansätzen. In der vorliegenden Übersichtsarbeit werden die Kernaussagen der neuen Leitlinie zur Diagnostik der aFKON unter Berücksichtigung neuester Literatur erörtert. Die korrekte Zuordnung zu einem Stadium der Erkrankung ist Dreh- und Angel-punkt einer modernen Therapieentscheidung für jeden einzelnen Patienten. Hierzu wird eine pragmatische und moderne Nutzung der 1993 vorgelegten ARCO-Klassifikation empfohlen und beschrieben sowie Kriterien für die Einordnung in die einzelnen Stadien definiert. Die Diagnostik und die Klassifizierung der aFKON beruht heute praktisch ausschließlich auf den Ergebnissen der bildgebenden Diagnostik. Die Magnetresonanztomografie und in einzelnen Fällen die ergänzende Computer -tomografie sind die Eckpfeiler der Klassifikation. Die Radiografie des Beckens a. p. und einer zweiten Ebene der betroffenen Hüfte ist als Basisuntersuchung bei Verdacht auf eine aFKON anzusehen und dient auch dem Aus-schluss anderer Erkrankungen.

An endophenotype approach to the genetics of alcohol dependence: a genome wide association study of fast beta EEG in families of African ancestry

Fast beta (20-28 Hz) electroencephalogram (EEG) oscillatory activity may be a useful endophenotype for studying the genetics of disorders characterized by neural hyperexcitability, including substance use disorders (SUDs). However, the genetic underpinnings of fast beta EEG have not previously been studied in a population of African-American ancestry (AA). In a sample of 2382 AA individuals from 482 families drawn from the Collaborative Study on the Genetics of Alcoholism (COGA), we performed a genome-wide association study (GWAS) on resting-state fast beta EEG power. To further characterize our genetic findings, we examined the functional and clinical/behavioral significance of GWAS variants. Ten correlated single-nucleotide polymorphisms (SNPs) (r²>0.9) located in an intergenic region on chromosome 3q26 were associated with fast beta EEG power at P<5 × 10^-8. The most significantly associated SNP, rs11720469 (β: -0.124; P<4.5 × 10^-9), is also an expression quantitative trait locus for BCHE (butyrylcholinesterase), expressed in thalamus tissue. Four of the genome-wide SNPs were also associated with Diagnostic and Statistical Manual of Mental Disorders Alcohol Dependence in COGA AA families, and two (rs13093097, rs7428372) were replicated in an independent AA sample (Gelernter et al.). Analyses in the AA adolescent/young adult (offspring from COGA families) subsample indicated association of rs11720469 with heavy episodic drinking (frequency of consuming 5+ drinks within 24 h). Converging findings presented in this study provide support for the role of genetic variants within 3q26 in neural and behavioral disinhibition. These novel genetic findings highlight the importance of including AA populations in genetics research on SUDs and the utility of the endophenotype approach in enhancing our understanding of mechanisms underlying addiction susceptibility.

Feasibility of the Participatory Experience Survey and the Setting Affordances Survey for use in evaluation of programmes serving youth with intellectual and developmental disabilities

BACKGROUND

Participation by youth with disabilities in recreational activities has been shown to promote the development of important skills needed for transition to adulthood. The Participatory Experience Survey (PES) and the Setting Affordances Survey (SAS) were developed for use by recreational programmes serving youth with significant intellectual and developmental disabilities (SIDD) to assess participant experiences and ensure that participants are afforded optimal opportunities to develop these skills. This paper presents a feasibility evaluation to determine the appropriateness of the PES and the SAS for use in a programme evaluation context.

METHOD

The PES and the SAS were used to evaluate a programme serving youth with SIDD in the greater northwest region of the United States. Three recreational activities were evaluated: an art project, trip to a zoo and a track practice. Programme volunteers used the SAS to assess opportunities and affordances offered within each activity. The PES was then given to 10 young people in each activity to capture their experiences. It was hypothesized that each setting would afford different experiences and developmental opportunities because of the differing nature of the activities.

RESULTS

The PES and SAS were found to be feasible for conducting a programme evaluation. All three settings offered varying types of experiences and affordances. Notably, as measured by the SAS, opportunity for skill development was greater in more structured activities; the zoo had the fewest opportunities for skill development and the art project had the most skill development opportunities. Youth answered 'no' most often to 'asking for help' and 'helping a kid', suggesting changes to offer more opportunities to develop these skills would be beneficial in all three activities.

CONCLUSION

These new instruments offer programmes a means to more fully include young people with disabilities during programme evaluations, leading to better-structured, more supportive programmes.

Percutaneous Irreversible Electroporation: Long-term survival analysis of 71 patients with inoperable malignant hepatic tumors

Aim of this retrospective analysis was to evaluate the survival times after percutaneous irreversible electroporation (IRE) in inoperable liver tumors not amenable to thermal ablation. 71 patients (14 females, 57 males, median age 63.5 ± 10.8 years) with 103 liver tumors were treated in 83 interventions using IRE (NanoKnife® system). The median tumor short-axis diameter was 1.9 cm (minimum 0.4 cm, maximum 4.5 cm). 35 patients had primary liver tumors and 36 patients had liver metastases. The Kaplan-Meier method was employed to calculate the survival rates, and the different groups were compared using multivariate log-rank and Wilcoxon tests. The overall median survival time was 26.3 months; the median survival of patients with primary land secondary liver cancer did not significantly differ (26.8 vs. 19.9 months; p = 0.41). Patients with a tumor diameter >3 cm (p < 0.001) or more than 2 lesions (p < 0.005) died significantly earlier than patients with smaller or fewer tumors. Patients with hepatocellular carcinoma and Child-Pugh class B or C cirrhosis died significantly earlier than patients with Child-Pugh class A (p < 0.05). Patients with very early stage HCC survived significantly longer than patients with early stage HCC with a median survival of 22.3 vs. 13.7 months (p < 0.05).

Abstract P6-16-03: Phase 2 trial of everolimus and/or trastuzumab in hormone refractory, hormone receptor (HR)-positive, HER2-normal metastatic breast cancer (MBC)

Background: Increased signaling through growth factor pathways including PI3K/Akt/mTOR and HER2 have been implicated in hormone resistance. Everolimus (EVE) improves outcomes when added to endocrine therapy for patients with HR-positive MBC. This study evaluated the efficacy of everolimus (EVE) and trastuzumab (TRAS) in hormone refractory HER2-normal metastatic breast cancer.

Methods: Eligible patients had HR-positive, HER2/neu-negative (IHC +1 or +2, HER2-non-amplified) MBC that had progressed within 6 months of the most recent endocrine therapy. Patients continued on the most recent endocrine therapy they received and were randomized to receive EVE 10 mg oral daily or TRAS IV (8 mg/kg loading dose followed by 6 mg/kg every 3 weeks). At progression, the other agent was added (TRAS in the EVE arm and EVE in the TRAS arm). Patients were followed until disease progression or death.

Results: 54 eligible patients were included in the analysis, and were randomized to EVE (n=30) or TRAS (n=24). 33% of patients were on fulvestrant, 31% exemestane, 22% tamoxifen and 7% letrozole, which were continued. The median PFS was 5.7 months for EVE vs. 2 months for TRAS until first progression or death with hazard ratio of 0.45 (95% CI 0.25-0.81, p=0.008). Among 48 patients who had disease progression, EVE was added to 16 patients who were originally treated by TRAS, and TRAS was added to 12 patients who were originally treated by EVE; the median time to the second progression was 6.3 months for the arm where EVE was added vs. 3.1 months in the arm where TRAS was added. Three patients were taken off study due to decrease in ejection fraction.

Conclusions: This trial demonstrates the efficacy of EVE alone or in combination with TRAS in patients with hormone refractory HR-positive, HER2-negative metastatic breast cancer, who remained on the endocrine therapy they had experienced disease progression on. This suggests that mTOR inhibition has the potential of restoring sensitivity to endocrine therapy and potentially allows the re-use of endocrine agents. Updated results and correlative studies will be presented. Clinical trial information: NCT00912340.

Citation Format: Paplomata E, Gogineni K, Meisel J, Santa-Maria C, Yuan L, Kramer J, Bill Li X, Zelnak A, Pakkala S, Kaklamani V, O'Regan R. Phase 2 trial of everolimus and/or trastuzumab in hormone refractory, hormone receptor (HR)-positive, HER2-normal metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-16-03.

Differences of cell surface marker expression between bone marrow- and kidney-derived murine mesenchymal stromal cells and fibroblasts

Mesenchymal stromal cells (MSC) are undifferentiated, multipotent adult cells with regenerative properties. They are particularly relevant for therapeutic approaches due to the simplicity of their isolation and cultivation. Since MSC show an expression pattern of cell surface marker, which is almost identical to fibroblasts, many attempts have been made to address the similarities and differences between MSC and fibroblasts. In this study we aimed to isolate murine MSC from bone marrow (BM) and kidney to characterize them in comparison to fibroblasts. Cells were isolated from murine kidney, BM and abdominal skin by plastic adherence and subsequently characterized by analysing their capability to build colony-forming unit-fibroblasts (CFU-F), their morphology, their proliferation, expression of telomerase activity and cell surface antigens as well as their differentiation capacity. Plastic adherent cells from the 3 mouse tissues showed similar morphology, proliferation profiles and CFU-F building capacities. However, while MSC from BM and kidney differentiated into the adipogenic, chondrogenic and osteogenic direction, fibroblasts were not able to do so efficiently. In addition, a tendency for lower expression of telomerase was found in the fibroblast population. Proliferating cells from kidney and BM expressed the MSC-specific cell surface markers CD105 and Sca-1 on a significantly higher and CD117 on a significantly lower level compared to fibroblasts and were thereby distinguishable from fibroblasts. Furthermore, we found that certain CD markers were specifically expressed on a higher level, either in BM-derived cells or fibroblasts. This study demonstrates that murine MSC isolated from different organs express certain specific markers, which enable their discrimination.

Epidemiology and outcomes of hepatitis C infection in elderly US Veterans

The chronic hepatitis C (CHC) cohort in the United States is getting older. Elderly patients with CHC may be at a high risk of cirrhosis and hepatocellular carcinoma (HCC), but also other nonhepatic comorbidities that negatively impact their likelihood of receiving or responding to antiviral treatment. There is little information on the clinical epidemiology or outcomes of CHC and its treatment in the elderly. We conducted a retrospective cohort study of 1 61 744 patients with a positive Hepatitis C virus RNA in the Veterans Health Administration Hepatitis C Clinical Case Registry to examine the association between age subgroups (20-49, 50-64, 65-85 years) and risk of cirrhosis, HCC or death using Cox proportional hazards models. We also examined the effect of treatment with a sustained viral response (SVR) on these outcomes in each age subgroup. The age distribution was 36.8% 20- to 49-year-olds, 57.6% 50- to 64-year-olds and 5.6% 65- to 85-year-olds (i.e. elderly). Risk of cirrhosis, HCC and death was significantly elevated in elderly patients [HR cirrhosis = 1.14 (1.00-1.29), HR HCC = 2.44 (1.99-2.99); HR death 2.09 (1.98-2.22)] compared with younger patients. The incidence of HCC was than 8.4 per 1000 PY in the elderly compared with 2.6 per 1000 PY and 5.7 per 1000 PY, among the 20-49 and 50-64 age groups, respectively. Elderly patients were significantly less likely to receive antiviral treatment (3.8% vs 14.8% and 19.1%, P < 0.0001), but among those who received treatment SVR was not different among the age groups (33.5% vs 33.2% and 32.1%). In an analysis limited to those who received treatment, SVR compared to treatment receipt with no SVR was associated with a reduction in risk of developing cirrhosis (HR = 0.34; 0.18-0.66) and HCC (HR = 0.60; 0.22-1.61) and all-cause mortality risk (HR = 0.52, 0.33-0.82). Elderly patients with CHC are more likely to develop HCC than younger patients but have traditionally received less antiviral treatment than younger patients. However, receipt of curative treatment is associated with a benefit in reducing cirrhosis, HCC and overall mortality, irrespective of age.

Cranial MR Imaging and Cerebral 99MTC HM-PAO-Spect in Patients with Subacute or Chronic Severe Closed Head Injury and Normal CT Examinations

Eighteen patients in the subacute or chronic state following severe closed head injury with normal cranial CT scans were examined by MR and 99mTc HM-PAO SPECT. Correlations were sought between these 2 imaging modalities and the clinical outcome, as defined by the Glasgow Outcome Scale (GOS) score. Both MR and SPECT revealed cerebral damage in all patients examined but structural and functional alterations did not coincide topographically in 64.9% of lesions. Nevertheless, complementary injury patterns suggesting poor recovery were found; cortical contusions and diffuse axonal injury (MR) in conjunction with cortical and thalamic hypoperfusion (SPECT) were noticed in 8 out of 12 patients with unfavorable outcome (GOS = III and IV). The synthesis of MR and SPECT information clearly enhanced the ability both to accurately assess posttraumatic brain damage and to improve patients' outcome prediction.

High-Resolution Real-Time Sonography and MR Imaging in Assessment of Osteocartilaginous Exostoses

High-resolution real-time ultrasonography (US) and MR imaging, using both spin-echo (SE) and gradient-echo (GE) sequences, were performed prospectively in 14 patients with solitary osteocartilaginous exostoses to assess cartilage cap thickness and bursa formation. Results were compared to surgical and histopathologic findings in all cases. Both US and MR imaging were useful in evaluating exostotic cartilage cap thickness, which is supposed to be the most reliable sign of malignant transformation. Hyaline cartilage matrix had distinctive features in US and MR imaging caused by its specific histologic composition. The formation of bursae over the protruding exostoses, which results in pain and clinically could raise the suspicion of growth and malignant transformation, was demonstrated best using GE sequences. MR imaging was thus superior to US in the detection of bursa formation.

Photo-spectroscopy of mixtures of catalyst particles reveals their age and type

Within a fluid catalytic cracking (FCC) unit, a mixture of catalyst particles that consist of either zeolite Y (FCC-Y) or ZSM-5 (FCC-ZSM-5) is used in order to boost the propylene yield when processing crude oil fractions. Mixtures of differently aged FCC-Y and FCC-ZSM-5 particles circulating in the FCC unit, the so-called equilibrium catalyst (Ecat), are routinely studied to monitor the overall efficiency of the FCC process. In this study, the age of individual catalyst particles is evaluated based upon photographs after selective staining with substituted styrene molecules. The observed color changes are linked to physical properties, such as the micropore volume and catalytic cracking activity data. Furthermore, it has been possible to determine the relative amount of FCC-Y and FCC-ZSM-5 in an artificial series of physical mixtures as well as in an Ecat sample with unknown composition. As a result, a new practical tool is introduced in the field of zeolite catalysis to evaluate FCC catalyst performances on the basis of photo-spectroscopic measurements with an off-the-shelf digital single lens reflex (DSLR) photo-camera with a macro lens. The results also demonstrate that there is an interesting time and cost trade-off between single catalyst particle studies, as performed with e.g. UV-vis, synchrotron-based IR and fluorescence micro-spectroscopy, and many catalyst particle photo-spectroscopy studies, making use of a relatively simple DSLR photo-camera. The latter approach offers clear prospects for the quality control of e.g. FCC catalyst manufacturing plants.

Genome-wide association data suggest ABCB1 and immune-related gene sets may be involved in adult antisocial behavior

Adult antisocial behavior (AAB) is moderately heritable, relatively common and has adverse consequences for individuals and society. We examined the molecular genetic basis of AAB in 1379 participants from a case-control study in which the cases met criteria for alcohol dependence. We also examined whether genes of interest were expressed in human brain. AAB was measured using a count of the number of Antisocial Personality Disorder criteria endorsed under criterion A from the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV). Participants were genotyped on the Illumina Human 1M BeadChip. In total, all single-nucleotide polymorphisms (SNPs) accounted for 25% of the variance in AAB, although this estimate was not significant (P=0.09). Enrichment tests indicated that more significantly associated genes were over-represented in seven gene sets, and most were immune related. Our most highly associated SNP (rs4728702, P=5.77 × 10(-7)) was located in the protein-coding adenosine triphosphate-binding cassette, sub-family B (MDR/TAP), member 1 (ABCB1). In a gene-based test, ABCB1 was genome-wide significant (q=0.03). Expression analyses indicated that ABCB1 was robustly expressed in the brain. ABCB1 has been implicated in substance use, and in post hoc tests we found that variation in ABCB1 was associated with DSM-IV alcohol and cocaine dependence criterion counts. These results suggest that ABCB1 may confer risk across externalizing behaviors, and are consistent with previous suggestions that immune pathways are associated with externalizing behaviors. The results should be tempered by the fact that we did not replicate the associations for ABCB1 or the gene sets in a less-affected independent sample.

Five population-based interventions for smoking cessation: a MOST trial

Little is known about the relative, additive, and interactive effects of different population-based treatments for smoking cessation. The goal of this study was to evaluate the main and interactive effects of five different smoking interventions. Using the multiphase optimization strategy (MOST), 1,034 smokers who entered a Web site for smokers (smokefree.gov) were randomly assigned to the "on" and "off" conditions of five smoking cessation interventions: the National Cancer Institute's (NCI) Web site (www.smokefree.gov vs a "lite" Web site), telephone quitline counseling (vs none), a smoking cessation brochure (vs a lite brochure), motivational e-mail messages (vs none), and mini-lozenge nicotine replacement therapy (NRT vs none). Analyses showed that the NCI Web site and NRT both increased abstinence; however, the former increased abstinence significantly only when it was not used with the e-mail messaging intervention (messaging decreased Web site use). The other interventions showed little evidence of effectiveness. There was evidence that mailed nicotine mini-lozenges and the NCI Web site (www.smokefree.gov) provide benefit as population-based smoking interventions.

Cdc42 is required in a genetically distinct subset of cardiac cells during Drosophila dorsal vessel closure

The embryonic heart tube is formed by the migration and subsequent midline convergence of two bilateral heart fields. In Drosophila the heart fields are organized into two rows of cardioblasts (CBs). While morphogenesis of the dorsal ectoderm, which lies directly above the Drosophila dorsal vessel (DV), has been extensively characterized, the migration and concomitant fundamental factors facilitating DV formation remain poorly understood. Here we provide evidence that DV closure occurs at multiple independent points along the A-P axis of the embryo in a "buttoning" pattern, divergent from the zippering mechanism observed in the overlying epidermis during dorsal closure. Moreover, we demonstrate that a genetically distinct subset of CBs is programmed to make initial contact with the opposing row. To elucidate the cellular mechanisms underlying this process, we examined the role of Rho GTPases during cardiac migration using inhibitory and overexpression approaches. We found that Cdc42 shows striking cell-type specificity during DV formation. Disruption of Cdc42 function specifically prevents CBs that express the homeobox gene tinman from completing their dorsal migration, resulting in a failure to make connections with their partnering CBs. Conversely, neighboring CBs that express the orphan nuclear receptor, seven-up, are not sensitive to Cdc42 inhibition. Furthermore, this phenotype was specific to Cdc42 and was not observed upon perturbation of Rac or Rho function. Together with the observation that DV closure occurs through the initial contralateral pairing of tinman-expressing CBs, our studies suggest that the distinct buttoning mechanism we propose for DV closure is elaborated through signaling pathways regulating Cdc42 activity in this cell type.