Nucleocytoplasmic connections and deafness

Puberty classifications in beef heifers are moderately to highly heritable and associated with candidate genes related to cyclicity and timing of puberty

Introduction: Pubertal attainment is critical to reproductive longevity in heifers. Previously, four heifer pubertal classifications were identified according to attainment of blood plasma progesterone concentrations > 1 ng/ml: 1) Early; 2) Typical; 3) Start-Stop; and 4) Non-Cycling. Early and Typical heifers initiated and maintained cyclicity, Start-Stop started and then stopped cyclicity and Non-Cycling never initiated cyclicity. Start-Stop heifers segregated into Start-Stop-Discontinuous (SSD) or Start-Stop-Start (SSS), with SSD having similar phenotypes to Non-Cycling and SSS to Typical heifers. We hypothesized that these pubertal classifications are heritable, and loci associated with pubertal classifications could be identified by genome wide association studies (GWAS). Methods: Heifers (n = 532; 2017 - 2022) genotyped on the Illumina Bovine SNP50 v2 or GGP Bovine 100K SNP panels were used for variant component estimation and GWAS. Heritability was estimated using a univariate Bayesian animal model. Results: When considering pubertal classifications: Early, Typical, SSS, SSD, and Non-Cycling, pubertal class was moderately heritable (0.38 ± 0.08). However, when heifers who initiated and maintained cyclicity were compared to those that did not cycle (Early+Typical vs. SSD+Non-Cycling) heritability was greater (0.59 ± 0.19). A GWAS did not identify single nucleotide polymorphisms (SNPs) significantly associated with pubertal classifications, indicating puberty is a polygenic trait. A candidate gene approach was used, which fitted SNPs within or nearby a set of 71 candidate genes previously associated with puberty, PCOS, cyclicity, regulation of hormone secretion, signal transduction, and methylation. Eight genes/regions were associated with pubertal classifications, and twenty-two genes/regions were associated with whether puberty was attained during the trial. Additionally, whole genome sequencing (WGS) data on 33 heifers were aligned to the reference genome (ARS-UCD1.2) to identify variants in FSHR, a gene critical to pubertal attainment. Fisher's exact test determined if FSHR SNPs segregated by pubertal classification. Two FSHR SNPs that were not on the bovine SNP panel were selected for additional genotyping and analysis, and one was associated with pubertal classifications and whether they cycled during the trial. Discussion: In summary, these pubertal classifications are moderately to highly heritable and polygenic. Consequently, genomic tools to inform selection/management of replacement heifers would be useful if informed by SNPs associated with cyclicity and early pubertal attainment.

Mouse screen reveals multiple new genes underlying mouse and human hearing loss

Adult-onset hearing loss is very common, but we know little about the underlying molecular pathogenesis impeding the development of therapies. We took a genetic approach to identify new molecules involved in hearing loss by screening a large cohort of newly generated mouse mutants using a sensitive electrophysiological test, the auditory brainstem response (ABR). We review here the findings from this screen. Thirty-eight unexpected genes associated with raised thresholds were detected from our unbiased sample of 1,211 genes tested, suggesting extreme genetic heterogeneity. A wide range of auditory pathophysiologies was found, and some mutant lines showed normal development followed by deterioration of responses, revealing new molecular pathways involved in progressive hearing loss. Several of the genes were associated with the range of hearing thresholds in the human population and one, SPNS2, was involved in childhood deafness. The new pathways required for maintenance of hearing discovered by this screen present new therapeutic opportunities.

This study uses an electrophysiological screen of over a thousand new mutant mouse lines to identify 38 new genes underlying deafness, some associated with human hearing function, revealing a wide range of molecular and pathological mechanisms.

Progressive hearing loss with age is extremely common in the population, leading to difficulties in understanding speech, increased social isolation, and associated depression. We know it has a significant heritability, but so far we know very little about the molecular pathways leading to hearing loss, hampering the development of treatments. Here, we describe a large-scale screen of 1,211 new targeted mouse mutant lines, resulting in the identification of 38 genes underlying hearing loss that were not previously suspected of involvement in hearing. Some of these genes reveal molecular pathways that may be useful targets for drug development. Our further analysis of the genes identified and the varied pathological mechanisms within the ear resulting from the mutations suggests that hearing loss is an extremely heterogeneous disorder and may have as many as 1,000 genes involved.

Human fetal inner ear involvement in congenital cytomegalovirus infection

Background

Congenital cytomegalovirus (CMV) infection is a leading cause of sensorineural hearing loss (SNHL). The mechanisms of pathogenesis of CMV-related SNHL are still unclear. The aim is to study congenital CMV-related damage in the fetal inner ear, in order to better understand the underlying pathophysiology behind CMV-SNHL.

Results

We studied inner ears and brains of 20 human fetuses, all at 21 week gestational age, with a high viral load in the amniotic fluid, with and without ultrasound (US) brain abnormalities. We evaluated histological brain damage, inner ear infection, local inflammatory response and tissue viral load.

Immunohistochemistry revealed that CMV was positive in 14/20 brains (70%) and in the inner ears of 9/20 fetuses (45%). In the cases with inner ear infection, the marginal cell layer of the stria vascularis was always infected, followed by infection in the Reissner’s membrane. The highest tissue viral load was observed in the inner ear with infected Organ of Corti. Vestibular labyrinth showed CMV infection of sensory cells in the utricle and in the crista ampullaris.

US cerebral anomalies were detected in 6 cases, and in all those cases, the inner ear was always involved. In the other 14 cases with normal brain scan, histological brain damage was present in 8 fetuses and 3 of them presented inner ear infection.

Conclusions

CMV-infection of the marginal cell layer of the stria vascularis may alter potassium and ion circulation, dissipating the endocochlear potential with consequent SNHL. Although abnormal cerebral US is highly predictive of brain and inner ear damage, normal US findings cannot exclude them either.