Otic Neurogenesis in Xenopus laevis: Proliferation, Differentiation, and the Role of Eya1

Transcriptomic Analysis Identifies Candidate Genes for Differential Expression during Xenopus laevis Inner Ear Development

Background

The genes involved in inner ear development and maintenance of the adult organ have yet to be fully characterized. Previous genetic analysis has emphasized the early development that gives rise to the otic vesicle. This study aimed to bridge the knowledge gap and identify candidate genes that are expressed as the auditory and vestibular sensory organs continue to grow and develop until the systems reach postmetamorphic maturity.

Methods

Affymetrix microarrays were used to assess inner ear transcriptome profiles from three Xenopus laevis developmental ages where all eight endorgans comprise mechanosensory hair cells: larval stages 50 and 56, and the post-metamorphic juvenile. Pairwise comparisons were made between the three developmental stages and the resulting differentially expressed X. laevis Probe Set IDs (Xl-PSIDs) were assigned to four groups based on differential expression patterns. DAVID analysis was undertaken to impart functional annotation to the differentially regulated Xl-PSIDs.

Results

Analysis identified 1510 candidate genes for differential gene expression in one or more pairwise comparison. Annotated genes not previously associated with inner ear development emerged from this analysis, as well as annotated genes with established inner ear function, such as oncomodulin, neurod1, and sp7. Notably, 36% of differentially expressed Xl-PSIDs were unannotated.

Conclusions

Results draw attention to the complex gene regulatory patterns that characterize Xenopus inner ear development, and underscore the need for improved annotation of the X. laevis genome. Outcomes can be utilized to select candidate inner ear genes for functional analysis, and to promote Xenopus as a model organism for biomedical studies of hearing and balance.

Appropriate Vestibular Stimulation in Children and Adolescents-A Prerequisite for Normal Cognitive, Motor Development and Bodily Homeostasis-A Review

The structural development of the vestibular part of the inner ear is completed by birth but its central connections continue to develop until adolescence. Their development is dependent on vestibular stimulation-vestibular experience. Studies have shown that vestibular function, modulated by experience and epigenetic factors, is not solely an instrument for body position regulation, navigation, and stabilization of the head and images but also influences cognition, emotion, the autonomous nervous system and hormones. To emphasize the importance of appropriate vestibular stimulation, we present a literature review of its effect on bodily homeostasis, cognition and emotion.

YTHDF1 phase separation triggers the fate transition of spermatogonial stem cells by activating the IκB-NF-κB-CCND1 axis

N6-methyladenosine (m6A) modification controls cell fate determination. Here, we show that liquid-liquid phase separation (LLPS) of YTH N6-methyladenosine RNA binding protein 1 (YTHDF1), a pivotal m6A "reader" protein, promotes the transdifferentiation of spermatogonial stem cells (SSCs) into neural stem cell-like cells by activating the IκB-nuclear factor κB (NF-κB)-CCND1 axis. The inhibition of IκBα/β mRNA translation mediated by YTHDF1 LLPS is the key to the activation of the IκB-NF-κB-CCND1 axis. Disrupting either YTHDF1 LLPS or NF-κB activation inhibits transdifferentiation efficiency. Moreover, overexpression of the YTH domain of YTHDF1 inhibits the activation of the IκB-NF-κB-CCND1 axis by promoting IκBα/β mRNA translation. Overexpression of the tau-YTH fusion protein reactivates IκB-NF-κB-CCND1 axis by inhibiting the translation of IκBα/β mRNAs, and tau LLPS is observed, which can restore transdifferentiation efficiency. Our findings demonstrate that the protein-RNA LLPS plays essential roles in cell fate transition and provide insights into translational medicine and the therapy of neurological diseases.

Normal Table of Xenopus development: a new graphical resource

Normal tables of development are essential for studies of embryogenesis, serving as an important resource for model organisms, including the frog Xenopus laevis. Xenopus has long been used to study developmental and cell biology, and is an increasingly important model for human birth defects and disease, genomics, proteomics and toxicology. Scientists utilize Nieuwkoop and Faber's classic 'Normal Table of Xenopus laevis (Daudin)' and accompanying illustrations to enable experimental reproducibility and reuse the illustrations in new publications and teaching. However, it is no longer possible to obtain permission for these copyrighted illustrations. We present 133 new, high-quality illustrations of X. laevis development from fertilization to metamorphosis, with additional views that were not available in the original collection. All the images are available on Xenbase, the Xenopus knowledgebase (http://www.xenbase.org/entry/zahn.do), for download and reuse under an attributable, non-commercial creative commons license. Additionally, we have compiled a 'Landmarks Table' of key morphological features and marker gene expression that can be used to distinguish stages quickly and reliably (https://www.xenbase.org/entry/landmarks-table.do). This new open-access resource will facilitate Xenopus research and teaching in the decades to come.

Eya1 protein distribution during embryonic development of Xenopus laevis

Eya1 and other Eya proteins are important regulators of progenitor proliferation, cell differentiation and morphogenesis in all three germ layers. At present, most of our knowledge of Eya1 distribution is based on in situ hybridization for Eya1 mRNA. However, to begin to dissect the mechanisms underlying Eya1 functions, we need a better understanding of the spatiotemporal distribution of Eya1 proteins during embryonic development, their subcellular localization and their levels of expression in various tissues. Here we report the localization of Eya1 protein throughout embryonic development from neural plate stages to tadpole stages of Xenopus laevis using a specific antibody for Xenopus Eya1. Our study confirms the expression of Eya1 protein in cranial placodes, placodally derived sensory primordia (olfactory epithelium, otic vesicle, lateral line primordia) and cranial ganglia, as well as in somites, secondary heart field and pharyngeal endoderm. In addition, we report here a novel expression of Eya1 proteins in scattered epidermal cells in Xenopus. Our findings also reveal that, while being predominantly expressed in nuclei in most expression domains, Eya1 protein is also localized to the cytoplasm, in particular in the early preplacodal ectoderm, some placode-derived ganglia and a subset of epidermal cells. While some cytoplasmic roles of Eya1 have been previously described in other contexts, the functions of cytoplasmic Eya1 in the preplacodal ectoderm, cranial ganglia and epidermal cells remain to be investigated.