Project description:The cochlear duct is tonotopically organized, such that the basal cochlea responds more sensitively to high frequency sounds and the apical cochlea to low frequency sounds. In effort to understand how the tonotopic organization is established in mammals, we searched for genes that are differentially expressed along the tonotopic axis during neonatal development.
Project description:The cochlear duct is tonotopically organized, such that the basal cochlea responds more sensitively to high frequency sounds and the apical cochlea to low frequency sounds. In effort to understand how the tonotopic organization is established in mammals, we searched for genes that are differentially expressed along the tonotopic axis during neonatal development. Eighty temporal bones were dissected from C57BL/6 mice at P0 and P8. The cochlear tissues were divided into three equal pieces representing the basal, middle and apical turns, and pooled separately. Six total RNA from the pooled samples were applied to 6 GeneChips.
Project description:In the mammalian auditory system, frequency discrimination depends on numerous morphological and physiological properties of the organ of Corti that gradually change along the longitudinal (tonotopic) axis of the organ. For example, the basilar membrane stiffness changes tonotopically, thus affecting the tuning properties of individual hair cells. At the molecular level, those frequency-specific characteristics are mirrored by gene expression gradients; however, the molecular mechanisms controlling tonotopic gene expression in the mouse cochlea remain elusive. Through analyzing scRNA-seq data from two developmental time points, we predicted that morphogens, rather than a timing-associated mechanism, confer spatial identity in the cochlea. Subsequently, we reconstructed the developing cochlea in 3D space from scRNA-seq data to investigate the molecular pathways mediating tonotopic information. The retinoic acid and sonic hedgehog pathways were found to form opposing tonotopic gradients, and functional interrogation using mouse cochlear explants suggested that both pathways jointly specify the tonotopic axis during development.
Project description:The role of the hippocampus in learning and memory has been widely studied. However, studies of differences along the longitudinal axis indicate that the hippocampus is perhaps not a singular structure, but instead it is thought that the dorsal and ventral poles of the hippocampus have functional differences. An anatomical gradient of hippocampal inputs along the dorsal-ventral axis supports this notion. It has been recently shown that there is transcriptional differentiation along the longitudinal axis of the adult hippocampus, coinciding with functional and anatomical gradients. Understanding the development of the dorsal-ventral hippocampal axis will further our understanding of the different hippocmapal functional contributions along the longitudinal axis. However, analysis of transcriptional gradients along the dorsal ventral axis have not been studied in the neonatal rat during development. We performed an extensive bead-chip based geneome-wide analysis of transcriptional differences in dorsal, intermediate, and ventral hippocampal tissue of rats aged postnatal day 0 (P0), P9, P18 and P60.
Project description:Precise frequency discrimination is a hallmark of auditory function in birds and mammals. In the cochlea, tuning and spectral separation result from longitudinal differences in basilar membrane stiffness and numerous individual gradiations in sensory hair cell phenotypes, but it is unknown what patterns those phenotypes. Hypothesizing that morphogen levels might differ along the longitudinal axis of the developing cochlea, we sequenced the transcriptomes of the proximal, middle, and distal thirds of the chicken cochlea at E6.5, when postmitotic hair cells first form. Embryonic day 6.5 chicken cochlea were dissected. Three samples were collected from each cochlear duct by cutting the duct into three approximately equal sized pieces to produce proximal, middle, and distal pieces. Each sample contained a portion of the future tegmentum vasculosum and the basilar papilla sensory epithelium. The distal piece also contained the region fo the future lagena.
Project description:Precise frequency discrimination is a hallmark of auditory function in birds and mammals. In the cochlea, tuning and spectral separation result from longitudinal differences in basilar membrane stiffness and numerous individual gradiations in sensory hair cell phenotypes, but it is unknown what patterns those phenotypes. Hypothesizing that morphogen levels might differ along the longitudinal axis of the developing cochlea, we sequenced the transcriptomes of the proximal, middle, and distal thirds of the chicken cochlea at E6.5, when postmitotic hair cells first form.
Project description:A cardinal feature of the auditory pathway is frequency selectivity represented in the form of a tonotopic map from the cochlea to the cortex. The molecular determinants of the auditory frequency map are unknown. Here, we discovered that the transcription factor ISL1 regulates features of auditory neurons, including the formation of the spiral ganglion neuron (SGN) and peripheral and central processes that shape the tonotopic representation of the auditory map. We selectively knocked out Isl1 in auditory neurons using Neurod1Cre strategies. In the absence of Isl1, SGNs migrate into the central cochlea and beyond. The cochlear wiring is profoundly reduced and disrupted. The central axons of Isl1 mutants lose their topographic projections and segregation at the cochlear nucleus. Transcriptome analysis of SGNs shows that Isl1 regulates neurogenesis, axonogenesis, migration, and the functional properties of neurons. Surprisingly, notable auditory processing features are preserved despite the significant hearing impairment, revealing central auditory pathway resilience and plasticity in mutant mice. Mutant mice demonstrate altered acoustic startle reflex, prepulse inhibition, characteristics of compensatory neural hyperactivity centrally. Our findings show that the Isl1 is one of the obligatory factors required to sculpt auditory structural and functional tonotopic maps. Still, upon Isl1 deletion, the ensuing compensatory plasticity of the auditory pathway does not suffice to overcome developmental changes at the peripheral sensory organ.
Project description:Transcriptional programs that regulate development are exquisitely controlled in space and time. Elucidating these programs that underlie development is essential to understanding the acquisition of cell and tissue identity. We present microarray expression profiles of a high resolution set of developmental time points within a single Arabidopsis root, and a comprehensive map of nearly all root cell-types. These cell-type specific transcriptional signatures often predict novel cellular functions. A computational pipeline identified dominant expression patterns that demonstrate transcriptional connections between disparate cell types. Dominant expression patterns along the rootâs longitudinal axis do not strictly correlate with previously defined developmental zones, and in many cases, expression fluctuation along this axis was observed. Both robust co-regulation of gene expression and potential phasing of gene expression were identified between individual roots. Methods that combine these two sets of profiles demonstrate transcriptionally rich and complex programs that define Arabidopsis root development in both space and time. We used microarrays to profile expression of nearly all cell types in the Arabidopsis root, and to profile at high resolution, developmental time points along the root's longitudinal axis. Experiment Overall Design: Microarray expression profiles of 8 new GFP marked lines with 2-3 replicates were used to augment existing microarray expression profiles of the root. RNA isolated from 13 cross sections along a single root's longitudinal axis were also profiled by microarray analysis. An independent root with 12 sections were used as a biological replicate.