RNA-DNA hybrids promote the expansion of Friedreich's ataxia (GAA)n repeats via break-induced replication.

Expansion of simple DNA repeats is responsible for numerous hereditary diseases in humans. The role of DNA replication, repair and transcription in the expansion process has been well documented. Here we analyzed, in a yeast experimental system, the role of RNA-DNA hybrids in genetic instability of long (GAA)n repeats, which cause Friedreich's ataxia. Knocking out both yeast RNase H enzymes, which counteract the formation of RNA-DNA hybrids, increased (GAA)n repeat expansion and contraction rates when the repetitive sequence was transcribed. Unexpectedly, we observed a similar increase in repeat instability in RNase H-deficient cells when we either changed the direction of transcription-replication collisions, or flipped the repeat sequence such that the (UUC)n run occurred in the transcript. The increase in repeat expansions in RNase H-deficient strains was dependent on Rad52 and Pol32 proteins, suggesting that break-induced replication (BIR) is responsible for this effect. We conclude that expansions of (GAA)n repeats are induced by the formation of RNA-DNA hybrids that trigger BIR. Since this stimulation is independent of which strand of the repeat (homopurine or homopyrimidine) is in the RNA transcript, we hypothesize that triplex H-DNA structures stabilized by an RNA-DNA hybrid (H-loops), rather than conventional R-loops, could be responsible.

Correlating Psychotropic Use to Major Depressive Disorder and ADHD Research Diagnoses: Trends in a Prospective Pediatric Cohort From Ages 3 to 21.

Objective: To examine the associations of psychotropic usage to clinical characteristics in a pediatric research cohort with research diagnoses and severity scores.Methods: The cohort (N = 348) was enriched for children with mood and externalizing symptoms. Prospective longitudinal data were collected from ages 3 to 21 (September 2003-December 2019). At up to 10 time points, data on psychotropic medication use were collected by caregiver- and self-report from the MacArthur Health and Behavior Questionnaire, Parent Version and as part of the diagnostic interview, and research diagnoses (DSM-IV and DSM-5) and disease severity scores were acquired using an age-appropriate standardized research interview (Preschool Age Psychiatric Assessment, Child and Adolescent Psychiatric Assessment, Kiddie-Schedule for Affective Disorders and Schizophrenia).Results: The percentage of children with attention-deficit/hyperactivity disorder (ADHD) taking ADHD medications was preschool, 20.7%; school-age, 65.4%; and adolescence/early adulthood, 84.0%. The percentage with major depressive disorder (MDD) who were taking antidepressants was preschool, 0%; school-age, 21.6%; and adolescence/early adulthood, 42.6%. Antipsychotic use in children with research diagnoses of ADHD or MDD peaked in school-age: ADHD, 30.8%, and MDD, 21.6%. Children who were taking an antipsychotic concurrently with an ADHD medication or antidepressant had more comorbid conditions and higher disease severity than those taking ADHD medications or antidepressants without concurrent antipsychotics. Black children with MDD used antidepressants significantly less than White children with MDD (Black = 12.1%, White = 31.9%, FDR P = .0495).Conclusions: Concordance between research diagnosis and psychotropic use increased with age. Antipsychotic use was quite high, though more frequent in children with higher disease severity. Both findings suggest that psychotropic use is less tied to discrete diagnoses at earlier ages and that antipsychotic medication use may be motivated by severity/impairment rather than diagnosis.

Stem cell and niche regulation in human short bowel syndrome.

Loss of functional small bowel surface area following surgical resection for disorders such as Crohn's disease, intestinal ischemic injury, radiation enteritis, and in children, necrotizing enterocolitis, atresia, and gastroschisis, may result in short bowel syndrome, with attendant high morbidity, mortality, and health care costs in the United States. Following resection, the remaining small bowel epithelium mounts an adaptive response, resulting in increased crypt cell proliferation, increased villus height, increased crypt depth, and enhanced nutrient and electrolyte absorption. Although these morphologic and functional changes are well described in animal models, the adaptive response in humans is less well understood. Clinically the response is unpredictable and often inadequate. Here we address the hypotheses that human intestinal stem cell populations are expanded and that the stem cell niche is regulated following massive gut resection in short bowel syndrome (SBS). We use intestinal enteroid cultures from patients with SBS to show that the magnitude and phenotype of the adaptive stem cell response are both regulated by stromal niche cells, including intestinal subepithelial myofibroblasts, which are activated by intestinal resection to enhance epithelial stem and proliferative cell responses. Our data suggest that myofibroblast regulation of bone morphogenetic protein signaling pathways plays a role in the gut adaptive response after resection.