CHD7 and SOX2 act in a common gene regulatory network during mammalian semicircular canal and cochlear development

Inner ear morphogenesis requires tightly regulated epigenetic and transcriptional control of gene expression. CHD7, an ATP-dependent chromodomain helicase DNA-binding protein, and SOX2, an SRY-related HMG box pioneer transcription factor, are known to contribute to vestibular and auditory system development, but their genetic interactions in the ear have not been explored. Here, we analyzed inner ear development and the transcriptional regulatory landscapes in mice with variable dosages of Chd7 and/or Sox2. We show that combined haploinsufficiency for Chd7 and Sox2 results in reduced otic cell proliferation, severe malformations of semicircular canals, and shortened cochleae with ectopic hair cells. Examination of mice with conditional, inducible Chd7 loss by Sox2CreER reveals a critical period (~E9.5) of susceptibility in the inner ear to combined Chd7 and Sox2 loss. Data from genome-wide RNA-sequencing and CUT&Tag studies in the otocyst show that CHD7 regulates Sox2 expression and acts early in a gene regulatory network to control expression of key otic patterning genes, including Pax2 and Otx2. CHD7 and SOX2 directly bind independently and cooperatively at transcription start sites and enhancers to regulate otic progenitor cell gene expression. Together, our findings reveal essential roles for Chd7 and Sox2 in early inner ear development and may be applicable for syndromic and other forms of hearing or balance disorders.

Chromatin remodeling protein CHD4 regulates axon guidance of spiral ganglion neurons in developing cochlea

The chromodomain helicase binding protein 4 (CHD4) is an ATP-dependent chromatin remodeler. De-novo pathogenic variants of CHD4 cause Sifrim-Hitz-Weiss syndrome (SIHIWES). Patients with SIHIWES show delayed development, intellectual disability, facial dysmorphism, and hearing loss. Many cochlear cell types, including spiral ganglion neurons (SGNs), express CHD4. SGNs are the primary afferent neurons that convey sound information from the cochlea, but the function of CHD4 in SGNs is unknown. We employed the Neurog1(Ngn1) CreERT2 Chd4 conditional knockout animals to delete Chd4 in SGNs. SGNs are classified as type I and type II neurons. SGNs lacking CHD4 showed abnormal fasciculation of type I neurons along with improper pathfinding of type II fibers. CHD4 binding to chromatin from immortalized multipotent otic progenitor-derived neurons was used to identify candidate target genes in SGNs. Gene ontology analysis of CHD4 target genes revealed cellular processes involved in axon guidance, axonal fasciculation, and ephrin receptor signaling pathway. We validated increased Epha4 transcripts in SGNs from Chd4 conditional knockout cochleae. The results suggest that CHD4 attenuates the transcription of axon guidance genes to form the stereotypic pattern of SGN peripheral projections. The results implicate epigenetic changes in circuit wiring by modulating axon guidance molecule expression and provide insights into neurodevelopmental diseases.

Chromodomain helicase DNA binding protein 4 in cell fate decisions

Loss of spiral ganglion neurons (SGNs) in the cochlea causes hearing loss. Understanding the mechanisms of cell fate transition accelerates efforts that employ directed differentiation and lineage conversion to repopulate lost SGNs. Proposed strategies to regenerate SGNs rely on altering cell fate by activating transcriptional regulatory networks, but repressing networks for alternative cell lineages is also essential. Epigenomic changes during cell fate transitions suggest that CHD4 represses gene expression by altering the chromatin status. Despite limited direct investigations, human genetic studies implicate CHD4 function in the inner ear. The possibility of CHD4 in suppressing alternative cell fates to promote inner ear regeneration is discussed.

Alcohol reverses the effects of KCNJ6 (GIRK2) noncoding variants on excitability of human glutamatergic neurons

Synonymous and noncoding single nucleotide polymorphisms (SNPs) in the KCNJ6 gene, encoding G protein-gated inwardly rectifying potassium channel subunit 2 (GIRK2), have been linked with increased electroencephalographic frontal theta event-related oscillations (ERO) in subjects diagnosed with alcohol use disorder (AUD). To identify molecular and cellular mechanisms while retaining the appropriate genetic background, we generated induced excitatory glutamatergic neurons (iN) from iPSCs derived from four AUD-diagnosed subjects with KCNJ6 variants ("Affected: AF") and four control subjects without variants ("Unaffected: UN"). Neurons were analyzed for changes in gene expression, morphology, excitability and physiological properties. Single-cell RNA sequencing suggests that KCNJ6 AF variant neurons have altered patterns of synaptic transmission and cell projection morphogenesis. Results confirm that AF neurons express lower levels of GIRK2, have greater neurite area, and elevated excitability. Interestingly, exposure to intoxicating concentrations of ethanol induces GIRK2 expression and reverses functional effects in AF neurons. Ectopic overexpression of GIRK2 alone mimics the effect of ethanol to normalize induced excitability. We conclude that KCNJ6 variants decrease GIRK2 expression and increase excitability and that this effect can be minimized or reduced with ethanol.

shox2 is required for vestibular statoacoustic neuron development

Homeobox genes act at the top of genetic hierarchies to regulate cell specification and differentiation during embryonic development. We identified the short stature homeobox domain 2 (shox2) transcription factor that is required for vestibular neuron development. shox2 transcripts are initially localized to the otic placode of the developing inner ear where neurosensory progenitors reside. To study shox2 function, we generated CRISPR-mediated mutant shox2 fish. Mutant embryos display behaviors associated with vestibular deficits and showed reduced number of anterior statoacoustic ganglion neurons that innervate the utricle, the vestibular organ in zebrafish. Moreover, a shox2-reporter fish showed labeling of developing statoacoustic ganglion neurons in the anterior macula of the otic vesicle. Single cell RNA-sequencing of cells from the developing otic vesicle of shox2 mutants revealed altered otic progenitor profiles, while single molecule in situ assays showed deregulated levels of transcripts in developing neurons. This study implicates a role for shox2 in development of vestibular but not auditory statoacoustic ganglion neurons.

Type-I-interferon signaling drives microglial dysfunction and senescence in human iPSC models of Down syndrome and Alzheimer's disease

Microglia are critical in brain development and Alzheimer's disease (AD) etiology. Down syndrome (DS) is the most common genetic developmental disorder and risk factor for AD. Surprisingly, little information is available on the impact of trisomy of human chromosome 21 (Hsa21) on microglial functions during DS brain development and in AD in DS. Using induced pluripotent stem cell (iPSC)-based organoid and chimeric mouse models, we report that DS microglia exhibit an enhanced synaptic pruning function, which alters neuronal synaptic functions. In response to human brain tissue-derived pathological tau, DS microglia undergo cellular senescence and exhibit elevated type-I-interferon signaling. Mechanistically, knockdown of Hsa21-encoded type I interferon receptors, IFNARs, rescues the DS microglial phenotypes both during brain development and in response to pathological tau. Our findings provide in vivo evidence that human microglia respond to pathological tau by exhibiting dystrophic phenotypes. Targeting IFNARs may improve DS microglial functions and prevent senescence.

Xrn1 is a deNADding enzyme modulating mitochondrial NAD-capped RNA

The existence of non-canonical nicotinamide adenine diphosphate (NAD) 5′-end capped RNAs is now well established. Nevertheless, the biological function of this nucleotide metabolite cap remains elusive. Here, we show that the yeast Saccharomyces cerevisiae cytoplasmic 5′-end exoribonuclease Xrn1 is also a NAD cap decapping (deNADding) enzyme that releases intact NAD and subsequently degrades the RNA. The significance of Xrn1 deNADding is evident in a deNADding deficient Xrn1 mutant that predominantly still retains its 5′-monophosphate exonuclease activity. This mutant reveals Xrn1 deNADding is necessary for normal growth on non-fermenting sugar and is involved in modulating mitochondrial NAD-capped RNA levels and may influence intramitochondrial NAD levels. Our findings uncover a contribution of mitochondrial NAD-capped RNAs in overall NAD regulation with the deNADding activity of Xrn1 fulfilling a central role.

The cytoplasmic Xrn1 protein has long been established as the predominate 5′ to 3′ exoribonuclease that cleaves RNAs with an unprotected 5′ monophosphate end. Here the authors demonstrate Xrn1 can also degrade RNAs harboring the noncanonical nicotinamide adenine diphosphate (NAD) 5′ cap by removing the NAD cap and degrading the RNA.

Understanding the differentiation and epigenetics of cochlear sensory progenitors in pursuit of regeneration

PURPOSE OF REVIEW

Sensory hair cells (HCs) of the inner ear are responsible for our ability to hear and balance. Loss of these cells results in hearing loss. Stem cell replacement and in situ regeneration have the potential to replace lost HCs. Newly discovered contributions of transcription factor regulatory networks and epigenetic mechanisms in regulating HC differentiation and regeneration are placed into context of the literature.

RECENT FINDINGS

A wealth of new data has helped to define cochlear sensory progenitors in their developmental trajectories. This includes transcription factor networks, epigenetic manipulations, and cochlear HC subtype specification.

SUMMARY

Understanding how sensory progenitors differ and how HC subtypes arise will substantially inform efforts in hearing restoration.

Single-Cell Fluorescence Analysis of Pseudotemporal Ordered Cells Provides Protein Expression Dynamics for Neuronal Differentiation

Stem cell replacement therapy is a potential method for repopulating lost spiral ganglion neurons (SGNs) in the inner ear. Efficacy of cell replacement relies on proper differentiation. Defining the dynamic expression of different transcription factors essential for neuronal differentiation allows us to monitor the progress and determine when the protein functions in differentiating stem cell cultures. Using immortalized multipotent otic progenitors (iMOPs) as a cellular system for SGN differentiation, a method for determining dynamic protein expression from heterogeneous cultures was developed. iMOP-derived neurons were identified and ordered by increasing neurite lengths to create a pseudotime course that reflects the differentiation trajectory. The fluorescence intensities of transcription factors SOX2 and NEUROD1 from individual pseudotemporally ordered cells were measured. Individual cells were grouped by K-means clustering and the mean fluorescence intensity for each cluster determined. Curve fit of the mean fluorescence represented the protein expression dynamics in differentiating cells. The method provides information about protein expression dynamics in differentiating stem cell cultures.

Activation of CHK1 in Supporting Cells Indirectly Promotes Hair Cell Survival

The sensory hair cells of the inner ear are exquisitely sensitive to ototoxic insults. Loss of hair cells after exposure to ototoxic agents causes hearing loss. Chemotherapeutic agents such as cisplatin causes hair cell loss. Cisplatin forms DNA mono-adducts as well as intra- and inter-strand DNA crosslinks. DNA cisplatin adducts are repaired through the DNA damage response. The decision between cell survival and cell death following DNA damage rests on factors that are involved in determining damage tolerance, cell survival and apoptosis. Cisplatin damage on hair cells has been the main focus of many ototoxic studies, yet the effect of cisplatin on supporting cells has been largely ignored. In this study, the effects of DNA damage response in cochlear supporting cells were interrogated. Supporting cells play a major role in the development, maintenance and oto-protection of hair cells. Loss of supporting cells may indirectly affect hair cell survival or maintenance. Activation of the Phosphoinositide 3-Kinase (PI3K) signaling was previously shown to promote hair cell survival. To test whether activating PI3K signaling promotes supporting cell survival after cisplatin damage, cochlear explants from the neural subset (NS) Cre Pten conditional knockout mice were employed. Deletion of Phosphatase and Tensin Homolog (PTEN) activates PI3K signaling in multiple cell types within the cochlea. Supporting cells lacking PTEN showed increased cell survival after cisplatin damage. Supporting cells lacking PTEN also showed increased phosphorylation of Checkpoint Kinase 1 (CHK1) levels after cisplatin damage. Nearest neighbor analysis showed increased numbers of supporting cells with activated PI3K signaling in close proximity to surviving hair cells in cisplatin damaged cochleae. We propose that increased PI3K signaling promotes supporting cell survival through phosphorylation of CHK1 and increased survival of supporting cells indirectly increases hair cell survival after cisplatin damage.

Single-Cell Transcriptome Analysis of Neural Stem Cells

Neural stem cells (NSCs) in the adult central nervous system play essential roles in both normal homeostasis and repair of damaged tissue after injury. The study of adult NSCs is hampered by the heterogeneous NSC population. In this review, we describe recent progresses in using single-cell RNA-sequencing (scRNA-seq) technique for the investigation of NSCs. The first part of this review focuses on the scRNA-seq techniques and bioinformatic analysis. The second part emphasizes the applications of scRNA-seq analysis in NSC research. Finally, we discuss the challenges and future directions of scRNA-seq technique for both basic research and regenerative medicine.

Transcriptional Regulation of Notch1 Expression by Nkx6.1 in Neural Stem/Progenitor Cells during Ventral Spinal Cord Development

Notch1 signaling plays a critical role in maintaining and determining neural stem/progenitor cell (NSPC) fate, yet the transcriptional mechanism controlling Notch1 specific expression in NSPCs remains incomplete. Here, we show transcription factor Nkx6.1 interacts with a cis-element (CR2, an evolutionarily conserved non-coding fragment in the second intron of Notch1 locus) and regulates the expression of Notch1 in ventral NSPCs of the developing spinal cord. We show that the Notch1 expression is modulated by the interaction of Nkx6.1 with a 139 bp enhancer sequence within CR2. Knockdown or overexpression of Nkx6.1 leads to down- or up-regulated Notch1 expression, respectively. In CR2-GFP transgenic mouse, GFP expression was found prominent in the ventricular zone and neural progenitor cells from embryonic day 9.5 to postnatal day 7. GFP+ cells were mainly neural progenitors for interneurons and not for motoneurons or glial cells. Moreover, GFP expression persisted in a subset of ependymal cells in the adult spinal cord, suggesting that CR2 is active in both embryonic and adult NSPCs. Together our data reveal a novel mechanism of Notch1 transcriptional regulation in the ventral spinal cord by Nkx6.1 via its binding with Notch1 enhancer CR2 during embryonic development.

Single-Cell Transcriptome Analysis of Developing and Regenerating Spiral Ganglion Neurons

The spiral ganglion neurons (SGNs) of the cochlea are essential for our ability to hear. SGN loss after exposure to ototoxic drugs or loud noise results in hearing loss. Pluripotent stem cell-derived and endogenous progenitor cell types have the potential to become SGNs and are cellular foundations for replacement therapies. Repurposing transcriptional regulatory networks to promote SGN differentiation from progenitor cells is a strategy for regeneration. Advances in the Fludigm C1 workflow or Drop-seq allow sequencing of single cell transcriptomes to reveal variability between cells. During differentiation, the individual transcriptomes obtained from single-cell RNA-seq can be exploited to identify different cellular states. Pseudotemporal ordering of transcriptomes describes the differentiation trajectory, allows monitoring of transcriptional changes and determines molecular barriers that prevent the progression of progenitors into SGNs. Analysis of single cell transcriptomes will help develop novel strategies for guiding efficient SGN regeneration.

Tryptophan-rich basic protein (WRB) mediates insertion of the tail-anchored protein otoferlin and is required for hair cell exocytosis and hearing

The transmembrane recognition complex (TRC40) pathway mediates the insertion of tail-anchored (TA) proteins into membranes. Here, we demonstrate that otoferlin, a TA protein essential for hair cell exocytosis, is inserted into the endoplasmic reticulum (ER) via the TRC40 pathway. We mutated the TRC40 receptor tryptophan-rich basic protein (Wrb) in hair cells of zebrafish and mice and studied the impact of defective TA protein insertion. Wrb disruption reduced otoferlin levels in hair cells and impaired hearing, which could be restored in zebrafish by transgenic Wrb rescue and otoferlin overexpression. Wrb-deficient mouse inner hair cells (IHCs) displayed normal numbers of afferent synapses, Ca²⁺ channels, and membrane-proximal vesicles, but contained fewer ribbon-associated vesicles. Patch-clamp of IHCs revealed impaired synaptic vesicle replenishment. In vivo recordings from postsynaptic spiral ganglion neurons showed a use-dependent reduction in sound-evoked spiking, corroborating the notion of impaired IHC vesicle replenishment. A human mutation affecting the transmembrane domain of otoferlin impaired its ER targeting and caused an auditory synaptopathy. We conclude that the TRC40 pathway is critical for hearing and propose that otoferlin is an essential substrate of this pathway in hair cells.

Activation of PI3K signaling prevents aminoglycoside-induced hair cell death in the murine cochlea

Loss of sensory hair cells of the inner ear due to aminoglycoside exposure is a major cause of hearing loss. Using an immortalized multipotent otic progenitor (iMOP) cell line, specific signaling pathways that promote otic cell survival were identified. Of the signaling pathways identified, the PI3K pathway emerged as a strong candidate for promoting hair cell survival. In aging animals, components for active PI3K signaling are present but decrease in hair cells. In this study, we determined whether activated PI3K signaling in hair cells promotes survival. To activate PI3K signaling in hair cells, we used a small molecule inhibitor of PTEN or genetically ablated PTEN using a conditional knockout animal. Hair cell survival was challenged by addition of gentamicin to cochlear cultures. Hair cells with activated PI3K signaling were more resistant to aminoglycoside-induced hair cell death. These results indicate that increased PI3K signaling in hair cells promote survival and the PI3K signaling pathway is a target for preventing aminoglycoside-induced hearing loss.

SHIELD: an integrative gene expression database for inner ear research

The inner ear is a highly specialized mechanosensitive organ responsible for hearing and balance. Its small size and difficulty in harvesting sufficient tissue has hindered the progress of molecular studies. The protein components of mechanotransduction, the molecular biology of inner ear development and the genetic causes of many hereditary hearing and balance disorders remain largely unknown. Inner-ear gene expression data will help illuminate each of these areas. For over a decade, our laboratories and others have generated extensive sets of gene expression data for different cell types in the inner ear using various sample preparation methods and high-throughput genome-wide approaches. To facilitate the study of genes in the inner ear by efficient presentation of the accumulated data and to foster collaboration among investigators, we have developed the Shared Harvard Inner Ear Laboratory Database (SHIELD), an integrated resource that seeks to compile, organize and analyse the genomic, transcriptomic and proteomic knowledge of the inner ear. Five datasets are currently available. These datasets are combined in a relational database that integrates experimental data and annotations relevant to the inner ear. The SHIELD has a searchable web interface with two data retrieval options: viewing the gene pages online or downloading individual datasets as data tables. Each retrieved gene page shows the gene expression data and detailed gene information with hyperlinks to other online databases with up-to-date annotations. Downloadable data tables, for more convenient offline data analysis, are derived from publications and are current as of the time of publication. The SHIELD has made published and some unpublished data freely available to the public with the hope and expectation of accelerating discovery in the molecular biology of balance, hearing and deafness.

Database URL:https://shield.hms.harvard.edu

C-MYC transcriptionally amplifies SOX2 target genes to regulate self-renewal in multipotent otic progenitor cells

Sensorineural hearing loss is caused by the loss of sensory hair cells and neurons of the inner ear. Once lost, these cell types are not replaced. Two genes expressed in the developing inner ear are c-Myc and Sox2. We created immortalized multipotent otic progenitor (iMOP) cells, a fate-restricted cell type, by transient expression of C-MYC in SOX2-expressing otic progenitor cells. This activated the endogenous C-MYC and amplified existing SOX2-dependent transcripts to promote self-renewal. RNA-seq and ChIP-seq analyses revealed that C-MYC and SOX2 occupy over 85% of the same promoters. C-MYC and SOX2 target genes include cyclin-dependent kinases that regulate cell-cycle progression. iMOP cells continually divide but retain the ability to differentiate into functional hair cells and neurons. We propose that SOX2 and C-MYC regulate cell-cycle progression of these cells and that downregulation of C-MYC expression after growth factor withdrawal serves as a molecular switch for differentiation.

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A single factor, C-MYC, induces self-renewal in SOX2-expressing otic progenitors

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C-MYC transcriptionally amplifies SOX2 target genes

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SOX2 modulates transcription of cell-cycle genes

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Immortalized multipotent otic progenitors can differentiate into otic cell types

Abstract 5098: GFP compatibility with EdU cell proliferation assay

Examining cell proliferation in GFP expressing cells is of general interest in many aspects of biology including regenerative medicine, stem cells, developmental biology and some fields of cancer research. However, visualization of GFP expression is not readily compatible with commonly used proliferation assays which incorporate a thymidine analog to directly measure S-phase proliferation of DNA. With the BrdU (bromo-deoxyuridine) assay, an antibody based detection method, alcohol for fixation and hydrochloric acid for DNA denaturation is commonly used. Neither chemical is compatible with GFP fluorescence. For imaging applications there are some methods to avoid the use of HCl as a denaturant with the BrdU assay, however; they are typically “home-brew” methods used to partially digest the DNA, adding extra steps, and not easily performed.

The much faster and reliable EdU (ethynyl-deoxyuridine) cell proliferation assay which uses click chemistry for detection of S-phase proliferation of DNA, uses formaldehyde based fixation and avoids the use of HCl for DNA denaturation. However, the use of copper to catalyse the click reaction also negatively affects GFP fluorescence. Anti-GFP antibodies can be used in the click reaction work flow, to “retrieve” the lost GFP fluorescence but are not convenient and add extra steps.

We present recent improvements to the click chemistry based EdU cell proliferation assay which minimizes the loss of GFP and other fluorescent proteins signals and avoids the need for “work around” methods. The resulting click reaction is both more rapid and brighter than the “classic” click EdU assay. The modifications preserve most of the GFP fluorescence and permit multiplex detection with EdU with no change in the work flow of the classic click EdU assay.

We optimized components in the improved click reaction conditions and tested compatibility with various fluorescent proteins. Examples of click chemistry and GFP/RFP/mCherry compatibility are presented using the EdU cell proliferation assay in both cell culture and in GFP expressing tissue. Additionally, improvements are demonstrated in with other applications of click chemistry assays used for imaging as well as with on flow cytometry platforms where GFP, R-phycoerythrin (R-PE), or other fluorescent proteins are commonly combined with cell proliferation assays.

The use of the modified click reaction is an enabling improvement over originally described copper based click reactions and will further enhance the utility of EdU based cell proliferation.

Citation Format: Scott T. Clarke, Zhichao Song, Kelvin Y. Kwan, Carolyn DeMarco, Aleksey Rukavishnikov, Upinder Singh, Kyle Gee. GFP compatibility with EdU cell proliferation assay. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5098. doi:10.1158/1538-7445.AM2014-5098

The ion channel TRPA1 is required for normal mechanosensation and is modulated by algesic stimuli

BACKGROUND & AIMS

The transient receptor potential (TRP) channel family includes transducers of mechanical and chemical stimuli for visceral sensory neurons. TRP ankyrin 1 (TRPA1) is implicated in inflammatory pain; it interacts with G-protein-coupled receptors, but little is known about its role in the gastrointestinal (GI) tract. Sensory information from the GI tract is conducted via 5 afferent subtypes along 3 pathways.

METHODS

Nodose and dorsal root ganglia whose neurons innnervate 3 different regions of the GI tract were analyzed from wild-type and TRPA1(-/-) mice using quantitative reverse-transcription polymerase chain reaction, retrograde labeling, and in situ hybridization. Distal colon sections were analyzed by immunohistochemistry. In vitro electrophysiology and pharmacology studies were performed, and colorectal distension and visceromotor responses were measured. Colitis was induced by administration of trinitrobenzene sulphonic acid.

RESULTS

TRPA1 is required for normal mechano- and chemosensory function in specific subsets of vagal, splanchnic, and pelvic afferents. The behavioral responses to noxious colonic distension were substantially reduced in TRPA1(-/-) mice. TRPA1 agonists caused mechanical hypersensitivity, which increased in mice with colitis. Colonic afferents were activated by bradykinin and capsaicin, which mimic effects of tissue damage; wild-type and TRPA1(-/-) mice had similar direct responses to these 2 stimuli. After activation by bradykinin, wild-type afferents had increased mechanosensitivity, whereas, after capsaicin exposure, mechanosensitivity was reduced: these changes were absent in TRPA1(-/-) mice. No interaction between protease-activated receptor-2 and TRPA1 was evident.

CONCLUSIONS

These findings demonstrate a previously unrecognized role for TRPA1 in normal and inflamed mechanosensory function and nociception within the viscera.

The micromachinery of mechanotransduction in hair cells

Mechanical stimuli generated by head movements and changes in sound pressure are detected by hair cells with amazing speed and sensitivity. The mechanosensitive organelle, the hair bundle, is a highly elaborated structure of actin-based stereocilia arranged in precise rows of increasing height. Extracellular linkages contribute to its cohesion and convey forces to mechanically gated channels. Channel opening is nearly instantaneous and is followed by a process of sensory adaptation that keeps the channels poised in their most sensitive range. This process is served by motors, scaffolds, and homeostatic mechanisms. The molecular constituents of this process are rapidly being elucidated, especially by the discovery of deafness genes and antibody targets.

Development of autoimmunity in mice lacking DNA topoisomerase 3beta

Mice lacking DNA topoisomerase 3beta are predisposed to a shortened lifespan, infertility, and lesions in multiple organs resulting from inflammatory responses. Examination of the immune system of 6- and 52-week-old top3beta(-/-) mice revealed no significant aberrations in their central and peripheral tolerance or in T lymphocyte activation. However, the older but not the younger cohort shows a high incidence of serum autoantibodies relative to their TOP3beta(+/+) age-mates. The mutant mice also show an increase in numerical aberrations of chromosomes in splenocytes and bone marrow cells, as well as an increase in apoptotic cells in the thymus. Thus, it appears plausible that the inflammatory lesions in top3beta(-/-) mice are caused by the development of autoimmunity as they age: Chromosomal abnormalities in top3beta(-/-) mice might lead to a persistent increase in apoptotic cells, which might in turn lead to the progression of autoimmunity.

TRPA1 Contributes to Cold, Mechanical, and Chemical Nociception but Is Not Essential for Hair-Cell Transduction

TRPA1, a member of the transient receptor potential (TRP) family of ion channels, is expressed by dorsal root ganglion neurons and by cells of the inner ear, where it has proposed roles in sensing sound, painful cold, and irritating chemicals. To test the in vivo roles of TRPA1, we generated a mouse in which the essential exons required for proper function of the Trpa1 gene were deleted. Knockout mice display behavioral deficits in response to mustard oil, to cold ( approximately 0 degrees C), and to punctate mechanical stimuli. These mice have a normal startle reflex to loud noise, a normal sense of balance, a normal auditory brainstem response, and normal transduction currents in vestibular hair cells. TRPA1 is apparently not essential for hair-cell transduction but contributes to the transduction of mechanical, cold, and chemical stimuli in nociceptor sensory neurons.

TRPA1 is a candidate for the mechanosensitive transduction channel of vertebrate hair cells

Mechanical deflection of the sensory hair bundles of receptor cells in the inner ear causes ion channels located at the tips of the bundle to open, thereby initiating the perception of sound. Although some protein constituents of the transduction apparatus are known, the mechanically gated transduction channels have not been identified in higher vertebrates. Here, we investigate TRP (transient receptor potential) ion channels as candidates and find one, TRPA1 (also known as ANKTM1), that meets criteria for the transduction channel. The appearance of TRPA1 messenger RNA expression in hair cell epithelia coincides developmentally with the onset of mechanosensitivity. Antibodies to TRPA1 label hair bundles, especially at their tips, and tip labelling disappears when the transduction apparatus is chemically disrupted. Inhibition of TRPA1 protein expression in zebrafish and mouse inner ears inhibits receptor cell function, as assessed with electrical recording and with accumulation of a channel-permeant fluorescent dye. TRPA1 is probably a component of the transduction channel itself.

Infertility and aneuploidy in mice lacking a type IA DNA topoisomerase III beta

We report that disruption of the mouse TOP3 beta gene encoding DNA topoisomerase III beta, one of the two mammalian type IA DNA topoisomerases, leads to a progressive reduction in fecundity. The litter size in crosses of top3 beta(-/-) mice decreases over time and through successive generations, and this decrease seems to reflect embryonic death rather than impaired fertilization. These observations are suggestive of a gradual accumulation of chromosomal defects in germ cells lacking DNA topoisomerase III beta, and this interpretation is supported by the observation of a high incidence of aneuploidy in the spermatocytes of infertile top3 beta(-/-) males. Cytogenetic examination of spermatocytes of wild-type mice also indicates that DNA topoisomerase III beta becomes prominently associated with the asynaptic regions of the XY bivalents during pachytene, and that there is a time lag between the appearance of chromosome-bound DNA topoisomerase III beta and Rad51, a protein known to be involved in an early step of homologous recombination. We interpret these findings, together with the known mechanistic characteristics of different subfamilies of DNA topoisomerases, in terms of a specific role of a type IA DNA topoisomerase in the resolution of meiotic double-Holliday junctions without crossing over. This interpretation is most likely applicable to mitotic cells as well and can explain the universal presence of at least one type IA DNA topoisomerase in all organisms.

Who are the residents of a nursing home in Singapore?

AIM OF STUDY

To describe the residents of a nursing home for the elderly in terms of their socio-demographic profile, mental and physical attributes, functional abilities and existing medical problems.

METHOD

A random sample of 120 subjects was obtained from a total of 350 residents in a voluntary welfare nursing home. Two subjects were excluded as they did not satisfy inclusion criteria (age > or = 60 years). The subjects' biodata, social background, medical problems and functional status at the time of admission were obtained by a review of the case records. Each of the subjects was examined with attention to their general condition, hearing and vision, presence of postural hypotension, cognition and ability to perform basic activities of daily living (ADL).

RESULTS

Results were available for 106 out of the 118 subjects as the rest were either discharged in the course of the study or had died. Single (36%), widowed (41%), female (71%) and age > or = 75 years (73%) consisted the majority. Most subjects (43%) were admitted because of both medical and social factors. Twenty-two percent appeared undernourished and of those who could be assessed, 14% had postural hypotension, 18% were hearing impaired and 53% had visual impairment. Fifty-two per cent suffered from mental problems while 46% and 40% had been diagnosed with hypertension and stroke respectively. Forty-eight percent had probable cognitive impairment (according to ECAQ scores) and 41% were very severely disabled (according to Barthel Index). Fifty-five percent were dependent in bathing, 50% dependent in dressing, 50% incontinent of urine (and requiring diapers), 48% were non-ambulant and 21% dependent in feeding.

CONCLUSION

With a significant proportion of the population requiring nursing home care in the future, a closer review of the situation is needed. This study has identified malnutrition, urinary incontinence, falls, functional decline and impaired vision/hearing as issues that deserve greater attention and, where necessary, intervention. Whether implementing recognised effective interventions will truly benefit our nursing home residents would warrant more local studies.

Clinical features of 46 eyes with calcified hydrogel intraocular lenses

PURPOSE

To clarify the clinical features of delayed calcification of hydrogel intraocular lenses (IOLs) based on observation of a large case series.

SETTING

Ophthalmology department of 2 university teaching hospitals, Hong Kong, China.

METHODS

The first 44 patients with a known diagnosis of calcified IOL were recruited. Medical and ophthalmic histories were obtained. Surgical details, surgical complications, and visual acuity before and after IOL implantation were also retrieved. Patients then had a visual acuity test, a slitlamp examination of the features of the IOL calcification, and a fundus examination for clarity of view.

RESULTS

Forty-six eyes of 44 patients had IOL calcification. All had a Hydroview IOL. The onset was from 4 to 26 months after surgery. Ninety-three percent of eyes had generalized IOL calcification, and 96% had forceps marks on the IOL. Mean visual acuity deteriorated from 0.4 at 3 months to 0.13 at 19 months. Visual loss was more severe in patients with diabetes mellitus or ischemic heart disease and in those in which the IOL calcified earlier after implantation.

CONCLUSION

All cases of IOL calcification were delayed in onset. The presence of forceps marks may provide a clue to the pathogenesis. Bilateral but asymmetric involvement in 2 patients suggests that the IOL was involved in the pathogenesis. Affected patients lost an average of 2.8 Snellen lines of visual acuity. Some eyes progressed more rapidly; however, the modulating factors remain unknown.

Accumulation and apparent oxidation of cis,trans-18 : 2 isomers relative to linoleic acid in rats

Dietary cis,trans-18 : 2 isomers impair desaturation and elongation of linoleic acid (Delta9cis,12cis-18 : 2), but little is known of their proportional partitioning between accumulation and oxidation. The present study was therefore designed to assess the accumulation and apparent oxidation of cis,trans-18 : 2 isomers compared with that of trans-18 : 1 isomers and Delta9cis,12cis-18 : 2 in rats. Accumulation is defined as whole-body increase in a fatty acid during a given period (i.e. final body content-initial body content). The apparent oxidation (disappearance) is defined as whole-body utilization of a fatty acid relative to its intake for a given period (intake-excretion-accumulation-longer-chain products)/intakex100). The animals were fed on a diet containing 15 % (w/w) partially hydrogenated rapeseed oil with 1.72 % energy as cis,trans-18 : 2 isomers and varying amounts of Delta9cis,12cis-18 : 2. The apparent oxidation of total cis,trans-18 : 2 isomers (72-76 % dietary intake) was greater than that of Delta9cis,12cis-18 : 2 (38-51 % dietary intake) but it was similar to that of total trans-18 : 1 isomers (78-82 % dietary intake). Among the four isomers, the apparent oxidation of Delta9trans,12trans-18 : 2 was greater than that of the other isomers including Delta9trans,12cis-18 : 2, Delta9cis,12trans-18 : 2 and Delta9cis,13trans-18 : 2. Accumulation of Delta5cis,8cis,11cis,15trans-20 : 4 and Delta5cis,8cis,11cis,14trans-20 : 4 derived from chain-elongation and desaturation of Delta9cis,13trans-18 : 2 and Delta9cis,12trans-18 : 2 was decreased when the dietary Delta9cis,12cis-18 : 2 supply was increased.

Mice lacking DNA topoisomerase IIIbeta develop to maturity but show a reduced mean lifespan

Targeted gene disruption in the murine TOP3beta gene-encoding DNA topoisomerase IIIbeta was carried out. In contrast to the embryonic lethality of mutant mice lacking DNA topoisomerase IIIalpha, top3beta(-/-) nulls are viable and grow to maturity with no apparent defects. Mice lacking DNA topoisomerase IIIbeta have a shorter life expectancy than their wild-type littermates, however. The mean lifespan of the top3beta(-/-) mice is about 15 months, whereas that of their wild-type littermates is longer than 2 years. Mortality of the top3beta(-/-) nulls appears to correlate with lesions in multiple organs, including hypertrophy of the spleen and submandibular lymph nodes, glomerulonephritis, and perivascular infiltrates in various organs. Because the DNA topoisomerase III isozymes are likely to interact with helicases of the RecQ family, enzymes that include the determinants of human Bloom, Werner, and Rothmund-Thomson syndromes, the shortened lifespan of top3beta(-/-) mice points to the possibility that the DNA topoisomerase III isozymes might be involved in the pathogenesis of progeroid syndromes caused by defective RecQ helicases.

Distinct clinical features associated with microsatellite instability in colorectal cancers of young patients

The Hong Kong Chinese population has an unusually high incidence of colorectal cancer in the young, suggestive of hereditary susceptibility. To search for a genetic basis for this predisposition, we studied the incidence of microsatellite instability (MSI) in paraffin-embedded colectomy specimens of 124 young (<50 years old) Chinese colorectal cancer patients referred to the Hong Kong Hereditary Gastrointestinal Cancer Registry from 1995 to 1998. By medical record review and personal interview, we searched for distinct clinical features associated with the manifestation of MSI in this group of patients. For patients with MSI tumours, blood was taken for detection of germline mutation in 2 mismatch repair (MMR) genes. MSI was present in 33 tumours from 23 males and 10 females (26.6%). Ongoing mutation analysis has so far identified MMR gene mutations in 8 patients with MSI tumours. The incidence of MSI increased significantly with decreasing age at cancer diagnosis. For patients aged 30 to 49, MSI tumours were located mainly at the proximal colon. However, for exceptionally young patients (<30 years), MSI tumours tended to be at the distal large bowel. This observation suggested a differential activity of the MMR pathway in colorectal carcinogenesis in different age groups. On multivariate analysis, young age at cancer diagnosis, proximal tumour location, a strong family history of colorectal cancer, and a personal history of metachronous cancer were independent predictors for MSI status. This knowledge may have an impact on the management of young colorectal cancer patients and their families.

Frequent microsatellite instability and mismatch repair gene mutations in young Chinese patients with colorectal cancer

BACKGROUND

The incidence of colorectal cancer in persons under 46 years of age is substantially higher in Hong Kong than in Scotland and many other countries. Consequently, we examined whether there is a hereditary predisposition for colorectal cancer in this Southern Chinese population.

METHODS

We investigated the incidence of microsatellite instability (MSI) at 10 DNA sites in 117 colorectal cancer specimens from Chinese patients of various ages. Those tumors with new alleles at 40% or more of the sites investigated were identified as highly unstable MSI (MSI-H). In young patients, we also searched for germline mutations in three mismatch repair genes (hMSH2, hMLH1, and hMSH6).

RESULTS

The incidence of MSI-H varied statistically significantly with age, being observed in more than 60% of those younger than age 31 years at diagnosis and in fewer than 15% of those age 46 years or older. In 15 patients (<46 years old) whose colorectal cancers showed MSI-H, eight possessed germline mutations in either hMSH2 or hMLH1. When mutations in hMSH6 were included, more than 80% of Chinese colorectal cancer patients younger than 31 years had germline mutations in mismatch repair genes. We found a novel germline missense mutation in hMSH6 in a 29-year-old man whose tumor showed no MSI. Two patients had a 4-base-pair insertion in exon 10 causing a truncated protein; this insertion is a common polymorphism with a population allele frequency in Chinese of 5.6%.

CONCLUSIONS

Our results indicate that germline mutations in mismatch repair genes contribute substantially to the pathogenesis and high incidence of colorectal cancer in young Hong Kong Chinese. However, because young Chinese and Caucasians show similar proportions of colorectal cancers with MSI-H, despite the higher incidence in the former, additional factors may underlie the high susceptibility of young Chinese to colorectal cancer.

Interleukin-10 inhibits inducible nitric oxide synthase in an animal model of necrotizing enterocolitis

BACKGROUND

Nitric oxide (NO) and its role in surgical inflammation are well documented; demonstrating the role of NO in necrotizing enterocolitis (NEC) and ways in which it may be suppressed may provide avenues for immune modulation in the treatment of NEC.

AIMS

We sought to demonstrate an increase in inducible nitric oxide synthase (iNOS) mRNA and nitric oxide in an experimental model of necrotizing enterocolitis. In addition, we hypothesized that interleukin-10 (IL-10) would attenuate this response.

METHODS

Newborn rats were treated with 25 microliters intraperitoneal IL-10 or vehicle prior to laparotomy, 1 h superior mesenteric artery (SMA) occlusion, 50 micrograms/kg intraluminal platelet activating factor administration, and SMA reperfusion. iNOS mRNA and nitric oxide levels were measured in the liver, small bowel, and serum and compared using Student's t-test.

RESULTS

Small bowel iNOS mRNA increased after NEC induction from 0.058 +/- 0.02 to 0.144 +/- 0.05 relative intensity units (RIU) at 2 h (p < 0.01) and from 0 to 0.09 +/- 0.02 RIU at 6 h (p < 0.03). Liver mRNA increased from 0.026 +/- 0.002 to 0.485 +/- 0.09 RIU (p < 0.002) and from 0 to 0.069 +/- 0.02 RIU (p < 0.0001) at 2 and 6 h, respectively. Serum nitric oxide increased in NEC induced animals at 2 h from 28.04 +/- 10.5 to 45.18 +/- 6.8 microM (p < 0.001). IL-10 suppressed iNOS mRNA and nitric oxide expression at 2 h in small bowel, liver, and serum by 60%, 89%, and 11%, respectively.

CONCLUSIONS

IL-10 decreases iNOS mRNA response in experimental NEC. This down-regulation may be an avenue for anti-inflammatory intervention in NEC.

Endothelium-dependent relaxation induced by hawthorn extract in rat mesenteric artery

The extract prepared from hawthorn (Crataegus fruit) was examined for its relaxant effect in rat isolated mesenteric arteries. Hawthorn extract induced concentration-dependent relaxation of the U46619-precontracted artery with an IC50 of 0.22 +/- 0.02 mg/ml. Removal of the functional endothelium reduced by approximately 85% the maximum relaxant response to hawthorn extract. Pretreatment of the arterial tissues with N(G)-nitro-L-arginine methyl ester (3-10 microM) or methylene blue (3-10 microM) inhibited the relaxation induced by hawthorn extract, while indomethacin (10 microM) had no effect. L-arginine (3 mM) did not affect the relaxation induced by hawthorn extract but partially reversed the effect of 10 microM N(G)-nitro-L-arginine methyl ester. Iberiotoxin (100 nM) slightly but significantly inhibited the relaxant effect of hawthorn extract whilst glibenclamide (3 microM) was ineffective. Glibenclamide at 3 microM reversed the relaxation induced by pinacidil. N(G)-nitro-L-arginine methyl ester and methylene blue markedly inhibited acetylcholine-induced relaxation in endothelium-intact arteries. Hawthorn extract also reduced the contraction induced by phenylephrine (1 microM) or high Ki (60 mM) with respective IC50 values of 0.13 +/- 0.01 mg/ml and 0.11 +/- 0.01 mg/ml. In high K+-contracted arteries, hawthorn extract induced only 55% of relaxation while it caused a complete inhibition of the U46619- or phenylephrine-induced contraction. These results suggest that hawthorn contains active components which cause vasorelaxation in rat isolated mesenteric arteries. Nitric oxide but not other endothelium-derived vasoactive factors was probably involved in the relaxation induced by hawthorn extract.

Inhibitory effect of linoleic acid on chain elongation and desaturation of 18:2 c,t isomers in lactating and neonatal rats

The previous studies showed that dietary 18:2 c,t isomers could be chain-elongated and desaturated to produce unusual 20:4 isomers. The present study was undertaken to determine the minimal amount of 18:2n-6 required to suppress the chain elongation and desaturation of 18:2 c,t isomers in the lactating and neonatal rats when animals were fed 15% partially hydrogenated canola oil diet containing 1.72% energy as 18:2 c,t isomers and varying amounts of free 18:2n-6. These diets induced marginal essential fatty acid (EFA) deficiency states (0.56% energy 18:2n-6) to EFA adequacy (2.56% energy 18:2n-6). After feeding for 50 d, the female animals were mated with males by overnight pairing. After conception, the lactating rats were killed, together with one pup from each dam, at term and day 26 of lactation. Two unusual 20:4 isomers in both maternal and neonatal liver phospholipids were identified as 20:4delta5c,8c,11c,14t and 20:4delta5c,8c,11c,15t, which were derived from 18:2delta9c,12t and 18:2delta9c,13t, respectively. The results showed that 18:2n-6 at about 2.0% of total energy in maternal diet was required to block the production of 20:4delta5c,8c,11c,14t and 20:4delta5c,8c,11c,15t in the maternal liver, whereas 18:2n-6 at about 2.5% of total energy in maternal diet was required to suppress production of these unusual 20:4 isomers in the neonatal liver.

Breast milk fatty acid composition: a comparative study between Hong Kong and Chongqing Chinese

The fatty acids of milk samples obtained from 51 Hong Kong Chinese and 33 Chongqing Chinese (Si Chuan Province, China) were analyzed by gas-liquid chromatography. Compared with those of published data for Canadian and other Western countries, the Chinese milk from both Hong Kong and Chongqing contained higher levels of longer-chain polyunsaturated fatty acids, particularly docosahexaenoic acid (22:6n-3) and arachidonic acid (20:4n-6). In contrast, the content of trans fatty acids in the Chinese milk was lower compared with those for Canadian and other Western countries. Longitudinally, the concentrations of 22:6n-3 and 20:4n-6 gradually decreased when lactation progressed from colostrum (week 1) to mature (week 6). Over the same interval, linoleic acid (18:2n-6) remained unchanged in Chongqing Chinese but significantly increased in Hong Kong Chinese. Unlike 18:2n-6, linolenic acid (18:3n-3) increased in Chongqing Chinese but remained unchanged in Hong Kong Chinese throughout the study. The total milk fat also increased with the duration of lactation. In addition, the milk of Chongqing Chinese had higher total milk fat than that of Hong Kong Chinese and Canadians. The content of erucic acid (22:1n-9) increased with the progression of lactation in Chongqing Chinese, indicating that there was a switch in dietary consumption from fats of animal origin to rapeseed oil when lactation reached week 6. The present study showed that Hong Kong and Chongqing Chinese had a different fatty acid profile in many ways, which largely reflected a different dietary habit and life-style in these two places.

Depletion of linoleate induced by weight cycling is independent of extent of calorie restriction

Recent epidemiological studies have suggested that weight cycling induced by repeated dieting over time may increase the risk of cardiovascular disease. It is speculated that the increased mortality from coronary heart disease for people with a history of excessive weight cycling could be attributed to change in lipid metabolism. Previous studies have demonstrated that repeated cycling of 100% food restriction followed by ad libitum refeeding caused a depletion of linoleate and alpha-linolenate in rats. The objective of the present study was to test the hypothesis that the weight cycling-induced reduction in linoleate and alpha-linolenate is independent of extent of calorie restriction. Two consecutive weight cycles in three experiments were induced by 100% calorie restriction, 60% calorie restriction, and 36% calorie restriction, respectively, followed by ad libitum refeeding. As the consequence of the two weight cycles, linoleate and linolenate were decreased, whereas myristate, palmitate, and palmitoleate were proportionally increased in carcass and adipose tissue lipids. The results of all three experiments showed a preferential depletion of linoleate and alpha-linolenate without changes in final body weight, total body fat, and adipose tissue pads in the weight-cycled rats. In addition, the triacylglycerol species profile in the adipose tissue of weight-cycled rats was significantly remodeled, with a proportional depletion of linoleate-enriched triacylglycerol species (LLL, LLO, and LLP, where L, O, and P are linoleic, oleic, and palmitic acid, respectively) and a proportional accumulation of palmitate-enriched triacylglycerol species (OPPo, PPPo, and PPP, where Po is palmitoleic acid). We conclude that weight cycling changes the ratio of polyunsaturated fatty acids to saturated fatty acids and remodels the adipose tissue triacylglycerol species profile in rats.

Color duplex sonographically guided obliteration of pseudoaneurysm

Over a 21 month period, 112 patients were seen in the vascular laboratory for evaluation and therapy of possible pseudoaneurysm. Pseudoaneurysm was confirmed by color flow sonographic imaging in 31 patients. Twenty-eight of these patients underwent sonographically monitored extrinsic manual compression to induce thrombosis and subsequent obliteration. Complete manual thrombosis was achieved in 17 patients while partial thrombosis with subsequent spontaneous closure developed in three patients, for a total success rate of 71% (20/28). In eight patients attempts to thrombose the pseudoaneurysm failed (29%). Induction of thrombosis by manual compression was successful in the presence of oral and intravenous anticoagulants. No therapeutic complications were encountered. Under proper sonographic guidance, the technique of manual obliteration of pseudoaneurysms provides a safe and effective alternative to surgical intervention.