Prevention: Necessary But Insufficient? A 2-Year Follow-Up of an Effective First-Grade Mathematics Intervention.

We present first-grade, second-grade, and third-grade impacts for a first-grade intervention targeting the conceptual and procedural bases that support arithmetic. At-risk students (average age at pretest = 6.5) were randomly assigned to three conditions: a control group (n = 224) and two variants of the intervention (same conceptual instruction but different forms of practice: speeded [n = 211] vs. nonspeeded [n = 204]). Impacts on all first-grade content outcomes were significant and positive, but no follow-up impacts were significant. Many intervention children achieved average mathematics achievement at the end of third grade, and prior math and reading assessment performance predicted which students will require sustained intervention. Finally, projecting impacts 2 years later based on nonexperimental estimates of effects of first-grade math skills overestimates long-term intervention effects.

Does the Severity of Students' Pre-Intervention Math Deficits Affect Responsiveness to Generally Effective First-Grade Intervention?

The purpose of this analysis was to assess whether effects of 1st-grade mathematics intervention apply across the range of at-risk learners' initial skill levels. Students were randomly assigned to control (n=213) and 2 variants of intervention (n=385) designed to improve arithmetic. Of each 30-minute intervention session (48 over 16 weeks), 25 minutes were identical in the 2 variants, focused on number knowledge that provides the conceptual bases for arithmetic. The other 5 minutes provided non-speeded conceptual practice (n=196) or speeded strategic practice (n=199). Contrasts tested effects of intervention (combined across variants) versus control and effects between the variants. Moderation analysis indicated no significant interactions between at-risk children's pre-intervention mathematics skill and either contrast on any outcome. Across pre-intervention math skill, effects favored intervention over control on arithmetic and transfer to double-digit calculations and number knowledge and favored speeded over non-speeded practice on arithmetic.

Using Moderator Analysis to Identify the First-Grade Children Who Benefit More and Less from a Reading Comprehension Program: A Step Toward Aptitude-by-Treatment Interaction.

Because of the importance of teaching reading comprehension to struggling young readers and the infrequency with which it has been implemented and evaluated, we designed a comprehensive first-grade reading comprehension program. We conducted a component analysis of the program's decoding/fluency (DF) and reading comprehension (COMP) dimensions, creating DF and DF+COMP treatments to parse the value of COMP. Students (N = 125) were randomly assigned to the 2 active treatments and controls. Treatment children were tutored 3 times per week for 21 weeks in 45-min sessions. Children in DF and DF+COMP together performed more strongly than controls on word reading and comprehension. However, pretreatment word reading appeared to moderate these results such that children with weaker beginning word reading across the treatments outperformed similarly low-performing controls to a significantly greater extent than treatment children with stronger beginning word reading outperformed comparable controls. DF+COMP children did not perform better than DF children. Study limitations and implications for research and practice are discussed.

Rapid Evidence Review of Mobile Applications for Self-management of Diabetes.

BACKGROUND: Patients with diabetes lack information on which commercially available applications (apps) improve diabetes-related outcomes. We conducted a rapid evidence review to examine features, clinical efficacy, and usability of apps for self-management of type 1 and type 2 diabetes in adults. METHODS: Ovid/Medline and the Cochrane Database of Systematic Reviews were searched for systematic reviews and technology assessments. Reference lists of relevant systematic reviews were examined for primary studies. Additional searches for primary studies were conducted online, through Ovid/Medline, Embase, CINAHL, and ClinicalTrials.gov . Studies were evaluated for eligibility based on predetermined criteria, data were extracted, study quality was assessed using a risk of bias tool, information on app features was collected, and app usability was assessed. Results are summarized qualitatively. RESULTS: Fifteen articles evaluating 11 apps were identified: six apps for type 1 and five apps for type 2 diabetes. Common features of apps included setting reminders and tracking blood glucose and hemoglobin A1c (HbA1c), medication use, physical activity, and weight. Compared with controls, use of eight apps, when paired with support from a healthcare provider or study staff, improved at least one outcome, most often HbA1c. Patients did not experience improvements in quality of life, blood pressure, or weight, regardless of app used or type of diabetes. Study quality was variable. Of the eight apps available for usability testing, two were scored "acceptable," three were "marginal," and three were "not acceptable." DISCUSSION: Limited evidence suggests that use of some commercially available apps, when combined with additional support from a healthcare provider or study staff, may improve some short-term diabetes-related outcomes. The impact of these apps on longer-term outcomes is unclear. More rigorous and longer-term studies of apps are needed. REGISTRATION: This review was funded by the Agency for Healthcare Research and Quality (AHRQ). The protocol is available at: http://www.effectivehealthcare.ahrq.gov/topics/diabetes-mobile-devices/research-protocol .

Delivery of nucleic acids to ex vivo porcine airways using electrospray.

AIM OF THE STUDY: Nucleic acid-based therapies have the potential to provide clinically meaningful benefit across a wide spectrum of lung disease. However, in vivo delivery remains a challenge. Here we examined the feasibility of using electrospray to deliver nucleic acids to both porcine tracheal tissue sections and whole lung ex vivo. MATERIALS AND METHODS: The effect of electrospray solution, emitter gauge, flow rate and voltage on plasmid DNA integrity was examined by analyzing supercoiled:open circle structure ratio by gel electrophoresis. Optimal parameters were used to deliver luciferase DNA and mRNA and siRNA-FITC to tracheal tissue sections. Luciferase mRNA was delivered to whole porcine lungs ex vivo using a catheter and bronchoscope system. Luciferase activity and fluorescence were analyzed by luminometry and microscopy respectively. RESULTS: The incidence of DNA plasmid nicking was greatest in a low salt solution without ethanol compared with 1% and 20% ethanol with salt. From a range of emitters tested, a 32 gauge emitter produced the best supercoiled:open circle structure ratio, likely because less voltage was required to produce a stable electrospray with this emitter. Lower flow rates also showed a trend towards reduced DNA nicking. GFP DNA electrosprayed at 5 kV and 6 kV resulted in lower levels of GFP expression in A549 lung cells following lipofection compared with 3 kV and 4 kV. Optimised parameters of 20% ethanol solution, 32 gauge emitter, low flow rates and voltages of 3-5 kV, nucleic acid molecules were successful for delivery of luciferase DNA and mRNA as well as siRNA-FITC to porcine tracheal tissue sections and for delivery of luciferase mRNA to whole porcine lungs via bronchoscope. CONCLUSIONS: We report ex vivo delivery of nucleic acids to porcine lung tissue via electrospray and bronchoscopic electrospray delivery of nucleic acid to an ex vivo porcine lung model.

Text Comprehension and Oral Language as Predictors of Word-Problem Solving: Insights into Word-Problem Solving as a Form of Text Comprehension.

This study was designed to deepen insights on whether word-problem (WP) solving is a form of text comprehension (TC) and on the role of language in WPs. A sample of 325 second graders, representing high, average, and low reading and math performance, was assessed on (a) start-of-year TC, WP skill, language, nonlinguistic reasoning, working memory, and foundational skill (word identification, arithmetic) and (b) year-end WP solving, WP-language processing (understanding WP statements, without calculation demands), and calculations. Multivariate, multilevel path analysis, accounting for classroom and school effects, indicated that TC was a significant and comparably strong predictor of all outcomes. Start-of-year language was a significantly stronger predictor of both year-end WP outcomes than of calculations, whereas start-of-year arithmetic was a significantly stronger predictor of calculations than of either WP measure. Implications are discussed in terms of WP solving as a form of TC and a theoretically coordinated approach, focused on language, for addressing TC and WP-solving instruction.

Hedonic Hunger Is Related to Increased Neural and Perceptual Responses to Cues of Palatable Food and Motivation to Consume: Evidence from 3 Independent Investigations.

BACKGROUND: The Power of Food Scale (PFS) seeks to identify individuals who experience high appetitive drive in response to food cues, which is a construct termed "hedonic hunger." OBJECTIVE: The purpose of this study was to assess cross-sectional correlates and predictive power of PFS scores to probe the construct of hedonic hunger. METHODS: Separate data from 3 studies (study 1, n = 44; study 2, n = 398; study 3, n = 100) were used to evaluate the construct of hedonic hunger. We examined the correlations between the PFS and neural responsivity during intake and anticipated intake of palatable foods, behavioral food reinforcement, perceptual hedonic ratings of food images, and change in body mass index (BMI) and binge eating over time. RESULTS: Hedonic hunger was strongly related to bilateral brain response in regions implicated in oral somatosensory processing during cue-elicited anticipation of food intake (study 1; right postcentral gyrus: r = 0.67, P < 0.001; left postcentral gyrus: r = 0.64, P < 0.001), and was correlated with behavioral food reinforcement (study 2; r = 0.31, P = 0.03) and perceptual hedonic ratings (study 3; r = 0.24, P = 0.02). Hedonic hunger was not associated with baseline BMI (studies 1-3: P = 0.14, 0.21, and 0.37, respectively) or change in BMI over the 2-y follow-up (studies 1 and 2: P = 0.14 and 0.37, respectively) but was significantly correlated with baseline binge eating in 2 samples (study 1: r = 0.58, P = 0.001; study 2: r = 0.31, P = 0.02; and study 3: P = 0.02). CONCLUSIONS: Hedonic hunger was not predictive of weight regulation. However, individuals who report high hedonic hunger are likely to show increased neural and perceptual responses to cues of palatable foods, increased motivation to consume such foods, and a greater likelihood of current binge eating.

Smoking and Cellular Telephone Use Among Pregnant Women Seeking Prenatal Care: Opportunities for Intervention.

OBJECTIVES: Although smoking during pregnancy is associated with poor pregnancy outcomes, many women continue to smoke throughout pregnancy. Behavioral interventions for smoking cessation yield modest benefits, particularly in lower socioeconomic groups. Pharmacotherapy, a first-line option for smoking cessation, has not shown clear benefits for pregnant smokers, partly due to limited adherence. We evaluated the feasibility of conducting a pharmacotherapy trial for smoking cessation in pregnant women, using text messaging to enhance medication adherence. METHODS: We surveyed 724 predominantly minority pregnant women to examine the prevalence and correlates of smoking and the use of cellular telephones and text messaging. RESULTS: Nearly 18% of the respondents were current smokers, with a majority (67.7%) expressing interest in participating in a smoking cessation trial. Only about 6% of women with a smoking history ever received nicotine dependence treatment. Smokers were significantly more likely to be depressed than non-smokers. The vast majority of respondents (92.1%) owned cell phones, with 93.2% having an unlimited text-messaging plan. CONCLUSIONS: These data support the feasibility of conducting a pharmacotherapy smoking cessation trial and using text messaging to enhance medication adherence in a predominantly minority population of pregnant smokers.

On the interactions between RNA and titrateable lipid layers: implications for RNA delivery with lipid nanoparticles.

Characterising the interaction between cationic ionisable lipids (CIL) and nucleic acids (NAs) is key to understanding the process of RNA lipid nanoparticle (LNP) formation and release of NAs from LNPs. Here, we have used different surface techniques to reveal the effect of pH and NA type on the interaction with a model system of DOPC and the CIL DLin-MC3-DMA (MC3). At only 5% MC3, differences in the structure and dynamics of the lipid layer were observed. Both pH and %MC3 were shown to affect the absorption behaviour of erythropoietin mRNA, polyadenylic acid (polyA) and polyuridylic acid (polyU). The adsorbed amount of all studied NAs was found to increase with decreasing pH and increasing %MC3 but with different effects on the lipid layer, which could be linked to the NA secondary structure. For polyA at pH 6, adsorption to the surface of the layer was observed, whereas for other conditions and NAs, penetration of the NA into the layer resulted in the formation of a multilayer structure. By comparison to simulations excluding the secondary structure, differences in adsorption behaviours between polyA and polyU could be observed, indicating that the NA's secondary structure also affected the MC3-NA interactions.

Evolution of the structure of lipid nanoparticles for nucleic acid delivery: From in situ studies of formulation to colloidal stability.

The development of lipid nanoparticle (LNP) based therapeutics for delivery of RNA has triggered the advance of new strategies for formulation, such as high throughput microfluidics for precise mixing of components into well-defined particles. In this study, we have characterised the structure of LNPs throughout the formulation process using in situ small angle x-ray scattering in the microfluidic chip, then by sampling in the subsequent dialysis process. The final formulation was investigated with small angle x-ray (SAXS) and neutron (SANS) scattering, dynamic light scattering (DLS) and cryo-TEM. The effect on structure was investigated for LNPs with a benchmark lipid composition and containing different cargos: calf thymus DNA (DNA) and two model mRNAs, polyadenylic acid (polyA) and polyuridylic acid (polyU). The LNP structure evolved during mixing in the microfluidic channel, however was only fully developed during the dialysis. The colloidal stability of the final formulation was affected by the type of incorporated nucleic acids (NAs) and decreased with the degree of base-pairing, as polyU induced extensive particle aggregation. The main NA LNP peak in the SAXS data for the final formulation were similar, with the repeat distance increasing from polyU

School Closure and Child Maltreatment During the COVID-19 Pandemic.

It is not known how school closure affected child maltreatment. We conducted a retrospective cohort, linear mixed-models study of 133 counties (comprising 8,582,479 children) in Virginia between 2018 and 2021. Exposure was the opening of schools at least 2 days a week. Outcomes were referrals and incidence of child maltreatment reported to the Department of Social Services. In 2020-2021, there were descriptively more referrals (in-person: 50.9 per 10,000 [95% CI: 47.9, 54.0]; virtual: 45.8 per 10,000 [95% CI: 40.7, 50.9]) and incidence (in-person: 3.7 per 10,000 [95% CI: 3.3, 4.2]; virtual: 2.9 per 10,000 [95% CI: 2.3, 3.5]) of child maltreatment in counties with in-person schooling, though these differences did not reach statistical significance. The referral rate variations (between pandemic and pre-pandemic eras) of counties with in-person schooling was significantly greater than rate changes in counties with virtual schooling during the summer period. There were no differences in incidence in any quarter. Higher poverty within a county was associated with both higher referrals and incidence. Our findings suggest that child maltreatment is driven primarily by underlying differences in counties (namely, poverty) rather than the type of schooling children receive.

Cation and buffer specific effects on the DNA-lipid interaction.

Knowledge of DNA - lipid layer interactions is key for the development of biosensors, synthetic nanopores, scaffolds, and gene-delivery systems. These interactions are strongly affected by the ionic composition of the solvent. We have combined quartz crystal microbalance (QCM) and ellipsometry measurements to reveal how pH, buffers and alkali metal chloride salts affect the interaction of DNA with lipid bilayers (DOTAP/DOPC 30:70 in moles). We found that the thickness of the DNA layer adsorbed onto the lipid bilayer decreased in the order citrate > phosphate > Tris > HEPES. The effect of cations on the thickness of the DNA layer decreased in the order (K+ > Na+ > Cs+ ∼ Li+). Rationalization of the experimental results requires that adsorption, due to cation specific charge screening, is driven by the simultaneous action of two mechanisms namely, the law of matching water affinities for kosmotropes (Li+) and ion dispersion forces for chaotropes (Cs+). The outcome of these two opposing mechanisms is a "bell-shaped" specific cations sequence. Moreover, a superimposed buffer specificity, which goes beyond the simple effect of pH regulation, further modulated cation specificity. In summary, DNA-lipid bilayer interactions are maximized if citrate buffer (50 mM, pH 7.4) and KCl (100 mM) are used.

Structural insights on ionizable Dlin-MC3-DMA lipids in DOPC layers by combining accurate atomistic force fields, molecular dynamics simulations and neutron reflectivity.

Ionizable lipids such as the promising Dlin-MC3-DMA (MC3) are essential for the successful design of lipid nanoparticles (LNPs) as drug delivery agents. Combining molecular dynamics simulations with experimental data, such as neutron reflectivity experiments and other scattering techniques, is essential to provide insights into the internal structure of LNPs, which is not fully understood to date. However, the accuracy of the simulations relies on the choice of force field parameters and high-quality experimental data is indispensable to verify the parametrization. For MC3, different parameterizations in combination with the CHARMM and the Slipids force fields have recently emerged. Here, we complement the existing efforts by providing parameters for cationic and neutral MC3 compatible with the AMBER Lipid17 force field. Subsequently, we carefully assess the accuracy of the different force fields by providing a direct comparison to neutron reflectivity experiments of mixed lipid bilayers consisting of MC3 and DOPC at different pHs. At low pH (cationic MC3) and at high pH (neutral MC3) the newly developed MC3 parameters in combination with AMBER Lipid17 for DOPC give good agreement with the experiments. Overall, the agreement is similar compared to the Park-Im parameters for MC3 in combination with the CHARMM36 force field for DOPC. The Ermilova-Swenson MC3 parameters in combination with the Slipids force field underestimate the bilayer thickness. While the distribution of cationic MC3 is very similar, the different force fields for neutral MC3 reveal distinct differences ranging from strong accumulation in the membrane center (current MC3/AMBER Lipid17 DOPC), over mild accumulation (Park-Im MC3/CHARMM36 DOPC) to surface accumulation (Ermilova-Swenson MC3/Slipids DOPC). These pronounced differences highlight the importance of accurate force field parameters and their experimental validation.

Novel stem/progenitor cell population from murine tracheal submucosal gland ducts with multipotent regenerative potential.

The airway epithelium is in direct contact with the environment and therefore constantly at risk for injury. Basal cells (BCs) have been found to repair the surface epithelium (SE), but the contribution of other stem cell populations to airway epithelial repair has not been identified. We demonstrated that airway submucosal gland (SMG) duct cells, in addition to BCs, survived severe hypoxic-ischemic injury. We developed a method to isolate duct cells from the airway. In vitro and in vivo models were used to compare the self-renewal and differentiation potential of duct cells and BCs. We found that only duct cells were capable of regenerating SMG tubules and ducts, as well as the SE overlying the SMGs. SMG duct cells are therefore a multipotent stem cell for airway epithelial repair This is of importance to the field of lung regeneration as determining the repairing cell populations could lead to the identification of novel therapeutic targets and cell-based therapies for patients with airway diseases.

Reliability of a complication classification system for orthopaedic surgery.

BACKGROUND: Quality of health care and safety have been emphasized by various professional and governmental groups. However, no standardized method exists for grading and reporting complications in orthopaedic surgery. Conclusions regarding outcomes are incomplete without a standardized, objective complication grading scheme applied concurrently. The general surgery literature has the Clavien-Dindo classification that meets the above criteria. QUESTIONS/PURPOSES: We asked whether a previously reported classification would show high intraobserver and interobserver reliabilities when modified for orthopaedic surgery specifically looking at hip preservation surgery. We therefore determined the interreader and intrareader reliabilities of the adapted classification scheme as applied to hip preservation surgery. METHODS: We adapted the validated Clavien-Dindo complication classification system and tested its reliability for orthopaedic surgery, specifically hip preservation surgery. There are five grades based on the treatment required to manage the complication and the potential for long-term morbidity. Forty-four complication scenarios were created from a prospective multicenter database of hip preservation procedures and from the literature. Ten readers who perform hip surgery at eight centers in three countries graded the scenarios at two different times. Fleiss' and Cohen's κ statistics were performed for interobserver and intraobserver reliabilities, respectively. RESULTS: The overall Fleiss' κ value for interobserver reliability was 0.887 (95% CI, 0.855-0.891). The weighted κ was 0.925 (95% CI, 0.894-0.956) for Grade I, 0.838 (95% CI, 0.807-0.869) for Grade II, 0.87 (95% CI, 0.835-0.866) for Grade III, and 0.898 (95% CI, 0.866-0.929) for Grade IV. The Cohen's κ value for intraobserver reliability was 0.891 (95% CI, 0.857-0.925). CONCLUSIONS: The adapted classification system shows high interobserver and intraobserver reliabilities for grading of complications when applied to orthopaedic surgery looking at complications of hip preservation surgery. This grading scheme may facilitate standardization of complication reporting and make outcome studies more comparable.

Effect of encapsulated protein on the dynamics of lipid sponge phase: a neutron spin echo and molecular dynamics simulation study.

Lipid membranes are highly mobile systems with hierarchical, time and length scale dependent, collective motions including thickness fluctuations, undulations, and topological membrane changes, which play an important role in membrane interactions. In this work we have characterised the effect of encapsulating two industrially important enzymes, ß-galactosidase and aspartic protease, in lipid sponge phase nanoparticles on the dynamics of the lipid membrane using neutron spin echo (NSE) spectroscopy and molecular dynamics (MD) simulations. From NSE, reduced membrane dynamics were observed upon enzyme encapsulation, which were dependent on the enzyme concentration and type. By fitting the intermediate scattering functions (ISFs) with a modified Zilman and Granek model including nanoparticle diffusion, an increase in membrane bending rigidity was observed, with a larger effect for ß-galactosidase than aspartic protease at the same concentration. MD simulations for the system with and without aspartic protease showed that the lipids relax more slowly in the system with protein due to the replacement of the lipid carbonyl-water hydrogen bonds with lipid-protein hydrogen bonds. This indicates that the most likely cause of the increase in membrane rigidity observed in the NSE measurements was dehydration of the lipid head groups. The dynamics of the protein itself were also studied, which showed a stable secondary structure of protein over the simulation, indicating no unfolding events occurred.

Patient Preferences for Discussing and Acting on Health-Related Needs in Primary Care.

BACKGROUND: Addressing social needs, health behaviors, and mental health may help patients more than traditional medical care. However, these root causes of poor health are difficult to address and the role of primary care is unclear. This qualitative study assesses patient's willingness and motivations to discuss and accept assistance for these needs from their primary care team. METHODS: In July and August of 2020, semi-structured virtual interviews were conducted with family medicine patients (n = 6) and residents of low resource neighborhoods (n = 11) in Richmond, Virginia. Interviews were conducted over Zoom. We conducted a qualitative analysis of patient and resident interview transcripts. A rapid qualitative analysis approach and immersion-crystallization processes were used to identify themes and categories. RESULTS: Interviewees reported varying degrees of comfort discussing topics with their health care team. They were less comfortable discussing needs they considered outside the realm of "traditional primary care" including finances, transportation, and housing, but interviewees expressed willingness to discuss these needs under certain conditions. Important factors were a strong patient-clinician relationship to create a trusted and safe space for discussion, adequate time for discussion during visits, communication of practices' ability to provide resources to help patients, and ensuring appropriate high quality referrals. CONCLUSIONS: Primary care provides opportunity for identifying and addressing needs that adversely impact health. Some needs are more sensitive for patients to work with their care team on, though, there was willingness to work on any need when a strong provider relationship and clinic structure for providing support were in place. This study highlights critical care delivery factors which may be used to enhance patient comfort accepting support for their needs and ultimately improve clinical care and chronic disease management.

Word and Person Effects on Decoding Accuracy: A New Look at an Old Question.

The purpose of this study was to extend the literature on decoding by bringing together two lines of research, namely person and word factors that affect decoding, using a crossed random-effects model. The sample was comprised of 196 English-speaking grade 1 students. A researcher-developed pseudoword list was used as the primary outcome measure. Because grapheme-phoneme correspondence (GPC) knowledge was treated as person and word specific, we are able to conclude that it is neither necessary nor sufficient for a student to know all GPCs in a word before accurately decoding the word. And controlling for word-specific GPC knowledge, students with lower phonemic awareness and slower rapid naming skill have lower predicted probabilities of correct decoding than counterparts with superior skills. By assessing a person-by-word interaction, we found that students with lower phonemic awareness have more difficulty applying knowledge of complex vowel graphemes compared to complex consonant graphemes when decoding unfamiliar words. Implications of the methodology and results are discussed in light of future research.

Cement-Augmented and Dual-Headed Posterior Screw Reconstruction After Corpectomy for Metastatic Tumor Resection.

BACKGROUND: Metastatic spinal tumors have a well-documented deleterious effect on the overall strength of the bony spine. Surgical interventions must address not only removal of the tumor itself, but the integrity of reconstructive hardware constructs as well. METHODS: We present a series of 8 patients with metastatic spine tumors who were successfully treated with tumor resection and reconstruction of residual 3-column defect with cement-augmented fenestrated pedicle screws and dual-rod posterior stabilization. RESULTS: All patients demonstrated resolution of their presenting neurologic symptoms. CONCLUSIONS: This series supports the use of the aforementioned constructs in conjunction to provide added stability and reduce hardware failure when treating a diversity of spinal tumors.

Morphogenesis of the Islets of Langerhans Is Guided by Extraendocrine Slit2 and Slit3 Signals.

The spatial architecture of the islets of Langerhans is vitally important for their correct function, and alterations in islet morphogenesis often result in diabetes mellitus. We have previously reported that Roundabout (Robo) receptors are required for proper islet morphogenesis. As part of the Slit-Robo signaling pathway, Robo receptors function in conjunction with Slit ligands to mediate axon guidance, cell migration, and cell positioning in development. However, the role of Slit ligands in islet morphogenesis has not yet been determined. Here, we report that Slit ligands are expressed in overlapping and distinct patterns in both endocrine and nonendocrine tissues in late pancreas development. We show that the function of either Slit2 or Slit3, which are predominantly expressed in the pancreatic mesenchyme, is required and sufficient for islet morphogenesis, while Slit1, which is predominantly expressed in the ß cells, is dispensable for islet morphogenesis. We further show that Slit functions as a repellent signal to ß cells. These data suggest that clustering of endocrine cells during islet morphogenesis is guided, at least in part, by repelling Slit2/3 signals from the pancreatic mesenchyme.