DNA end resection by Dna2–Sgs1–RPA and its stimulation by Top3–Rmi1 and Mre11–Rad50–Xrs2

The repair of DNA double-strand breaks (DSBs) by homologous recombination requires processing of broken ends. For repair to start, the DSB must first be resected to generate a 3′-single-stranded DNA (ssDNA) overhang, which becomes a substrate for the DNA strand exchange protein, Rad51 (ref. 1). Genetic studies have implicated a multitude of proteins in the process, including helicases, nucleases and topoisomerases. Here we biochemically reconstitute elements of the resection process and reveal that it requires the nuclease Dna2, the RecQ-family helicase Sgs1 and the ssDNA-binding protein replication protein-A (RPA). We establish that Dna2, Sgs1 and RPA constitute a minimal protein complex capable of DNA resection in vitro. Sgs1 helicase unwinds the DNA to produce an intermediate that is digested by Dna2, and RPA stimulates DNA unwinding by Sgs1 in a species-specific manner. Interestingly, RPA is also required both to direct Dna2 nucleolytic activity to the 5′-terminated strand of the DNA break and to inhibit 3′ to 5′ degradation by Dna2, actions that generate and protect the 3′-ssDNA overhang, respectively. In addition to this core machinery, we establish that both the topoisomerase 3 (Top3) and Rmi1 complex and the Mre11–Rad50–Xrs2 complex (MRX) have important roles as stimulatory components. Stimulation of end resection by the Top3–Rmi1 heterodimer and the MRX proteins is by complex formation with Sgs1 (refs 5, 6), which unexpectedly stimulates DNA unwinding. We suggest that Top3–Rmi1 and MRX are important for recruitment of the Sgs1–Dna2 complex to DSBs. Our experiments provide a mechanistic framework for understanding the initial steps of recombinational DNA repair in eukaryotes

Bess and Hearing Screening: Portending the Challenges in Children

This article summarizes the significant contributions of Fred H. Bess to the early detection of hearing loss in infants and children. Based on public health and educational policy, Bess challenged audiologists to view hearing screening as a responsibility that brought with it the need to develop screening tools that are effective in identifying hearing loss - whether for use with infants, preschoolers, or school-age children - and that adhere to important screening principles. A review of his influence on pertinent guidelines, position statements, and recommendations highlights his belief that early identification of hearing loss is critical if children are to overcome the significant obstacles presented by even mild and unilateral hearing losses. This section is followed by a review of seminal papers that stimulated research in universal newborn hearing screening programs and the detection of unilateral and minimal hearing loss. We conclude with a review of selected studies that build on Bess\u27s earlier work and strive to drive our field forward to practices that are both evidence-based and effective in detecting hearing loss in children

The impact of otitis media with effusion on early phonetic inventories: A longitudinal prospective investigation

This prospective investigation examined the effects of otitis media with effusion (OME) on early speech production. Two groups of infants, the otitis media positive (OME+; n = 8), and the otitis media negative (OME-; n = 8) were defined according to otitis media (OM) history during the first year of life. OM documentation was based on results from tympanometry, pneumatic otoscopy, and behavioural audiometry collected bimonthly beginning at age 2 months. Phonetic transcriptions were completed from infants' recorded babbling samples at 10, 12 and 14 months of age. No differences were found between the two groups on rate of vocalizations (i.e. consonants produced per minute). Differences between the two groups were seen in place and manner of articulation. OME+ infants produced more bilabial stops than OME- infants who, in turn, produced more alveolar stops and nasals than did their OME+ counterparts. Furthermore, within the OME+ group, children with poorer hearing thresholds showed preference for bilabial stops, whereas children with better hearing thresholds showed more diversity in their phonetic inventories

Early Otitis Media with Effusion, Hearing Loss, and Auditory Processes at School Age

OBJECTIVES: To examine the effect of conductive hearing loss (HL) secondary to otitis media with effusion (OME) in the first 3 years of life on physiologic, peripheral, and higher-order behavioral auditory measures examined at school age. METHODS: Peripheral hearing sensitivity for conventional and extended high-frequency audiometric ranges, physiologic (distortion product otoacoustic emissions, contralateral and ipsilateral acoustic middle ear muscle reflexes), auditory brain stem response (ABR), and higher-order auditory processing measures (masking level difference; Virtual Auditory Localization, Speech Intelligibility Gain; adaptive Pediatric Speech Intelligibility task) were examined at the end of the second grade of elementary school in two cohorts (North Carolina, N = 73, and New York, N = 59). All participants (mean age, 8 years) were followed prospectively in infancy and early childhood (7 to 39 months) for middle ear status and hearing loss (using pneumatic otoscopy/tympanometry and repeated conditioned behavioral audiometric response procedures). Multivariate analyses were conducted to address whether early OME and early conductive HL were related to physiologic, peripheral, and higher-order auditory processes. RESULTS: Early hearing loss and OME were significantly associated with peripheral hearing at school age; extended high-frequency thresholds accounted for the result. Similarly, hearing loss in early life and OME were significantly associated with the acoustic middle ear muscle reflex: The contralateral stimulation condition accounted for the association. Significant associations with both early OME and early HL were also found for the auditory brain stem response measure and were explained by the correlations between early hearing loss and the ABR Wave V latency but not other ABR indices. There were no reliable associations between either early OME or early HL on any other auditory processes evaluated at the end of second grade. CONCLUSIONS: Extended high-frequency hearing and brain stem auditory pathway measures in childhood were significantly associated with children\u27s experiences with OME and hearing loss from 7 to 39 months of age. However, no significant associations were found for psychoacoustic measures of binaural processing or a behavioral adaptive speech-in-noise test at school age

A multisite study to examine the efficacy of the otoacousticemission/automated auditory brainstem response newborn hearing screening protocol: Results of visualreinforcement audiometry

Purpose: This 3rd of 4 articles on a study of the efficacy of the 2-stage otoacoustic emission/automated auditory brainstem response (OAE/A-ABR) newborn hearing screening protocol describes (a) the behavioral audiometric protocol used to validate hearing status at 8-12 months of age, (b) the hearing status of the sample, and (c) the success of the visual reinforcement audiometry (VRA) protocol across 7 sites. Method: A total of 973 infants who failed OAE but passed A-ABR, in one or both ears, during newborn screening were tested with a VRA protocol, supplemented by tympanometry and OAE screening at age 8-12 months. Results: VRA audiograms (1.0, 2.0, and 4.0 kHz) were obtained for 1,184 (82.7%) of the 1,432 study ears. Hearing loss was ruled out in another 100 ears by VRA in combination with OAE, for a total of 88.7% of the study sample. Permanent hearing loss was identified in 30 ears of 21 infants. Sites differed in their success with the VRA protocol. Conclusions: Continued monitoring of hearing beyond the newborn period is an important component of early detection of hearing loss. Using a structured protocol, VRA is an appropriate test method for most, but not all, infants. A battery of test procedures is often needed to adequately delineate hearing loss in infants. Examiner experience appears to be a factor in successful VRA