Fgf3 and Fgf16 expression patterns define spatial and temporal domains in the developing chick inner ear

Decoding FGF/FGFR Signaling: Insights into Biological Functions and Disease Relevance

Fibroblast Growth Factors (FGFs) and their cognate receptors, FGFRs, play pivotal roles in a plethora of biological processes, including cell proliferation, differentiation, tissue repair, and metabolic homeostasis. This review provides a comprehensive overview of FGF-FGFR signaling pathways while highlighting their complex regulatory mechanisms and interconnections with other signaling networks. Further, we briefly discuss the FGFs involvement in developmental, metabolic, and housekeeping functions. By complementing current knowledge and emerging research, this review aims to enhance the understanding of FGF-FGFR-mediated signaling and its implications for health and disease, which will be crucial for therapeutic development against FGF-related pathological conditions.

The role of FGF15/FGF19 in the development of the central nervous system, eyes and inner ears in vertebrates

Fibroblast growth factor 19 (FGF19), and its rodent ortholog FGF15, is a member of a FGF subfamily directly involved in metabolism, acting in an endocrine way. During embryonic development, FGF15/FGF19 also functions as a paracrine or autocrine factor, regulating key events in a large number of organs. In this sense, the Fgf15/Fgf19 genes control the correct development of the brain, eye, inner ear, heart, pharyngeal pouches, tail bud and limbs, among other organs, as well as muscle growth in adulthood. These growth factors show relevant differences according to molecular structures, signalling pathway and function. Moreover, their expression patterns are highly dynamic at different stages of development, in particular in the central nervous system. The difficulty in understanding the action of these genes increases when comparing their expression patterns and regulatory mechanisms between different groups of vertebrates. The present review will address the expression patterns and functions of the Fgf15/Fgf19 genes at different stages of vertebrate embryonic development, with special attention to the regulation of the early specification, cell differentiation, and morphogenesis of the central nervous system and some sensory organs such as eye and inner ear. The most relevant anatomical aspects related to the structures analysed have also been considered in detail to provide an understandable context for the molecular and cellular studies shown.

A primer for Fibroblast Growth Factor 16 (FGF16)

During the discovery of the Fibroblast Growth Factor superfamily, scientists were determined to uncover all the genes that encoded FGF proteins. In 1998, FGF16 was discovered with classical cloning techniques in human and rat heart samples. FGF16 loss- and gain-of-function experiments in several organisms demonstrated a conserved function in vertebrates, and as a component of the FGF9 subfamily of ligands (FGF-E/-9/-20), is functionally conserved and sufficient to rescue loss-of-function phenotypes in invertebrates, like C. elegans. FGF16 has a broad expression pattern, predominantly expressed in brown adipose tissue, heart, with low but detectable levels in the brain, olfactory bulb, inner ear, muscle, thymus, pancreas, spleen, stomach, small intestine, and gonads (testis and ovary). FGF16 is also expressed moderately in the late developing limb bud. Despite its expression levels, this ligand plays notable roles in autopod metacarpal development; loss of one allele causes congenital metacarpal 4-5 fusion and hand deformities in humans. The broad expression pattern of FGF16 in several tissues underscores its multifaceted roles in stem cell maintenance, proliferation, cell fate specification, and metabolism.

Shared features in ear and kidney development - implications for oto-renal syndromes

The association between ear and kidney anomalies has long been recognized. However, little is known about the underlying mechanisms. In the last two decades, embryonic development of the inner ear and kidney has been studied extensively. Here, we describe the developmental pathways shared between both organs with particular emphasis on the genes that regulate signalling cross talk and the specification of progenitor cells and specialised cell types. We relate this to the clinical features of oto-renal syndromes and explore links to developmental mechanisms.

Regulation of otic neurosensory specification by Notch and Wnt signalling: insights from RNA-seq screenings in the embryonic chicken inner ear

The Notch and Wnt signalling pathways play key roles in the formation of inner ear sensory organs, but little is known about their transcriptional effectors and targets in this context. Here, we perturbed Notch and Wnt activities in the embryonic chicken otic vesicle using pharmacological treatment or in ovo electroporation of plasmid DNA, and used RNA-Seq to analyse the resulting changes in gene expression. Compared to pharmacological treatments, in ovo electroporation changed the expression of fewer genes, a likely consequence of the variability and mosaicism of transfection. The pharmacological inhibition of Notch activity induced a rapid change in the expression of known effectors of this pathway and genes associated with neurogenesis, consistent with a switch towards an otic neurosensory fate. The Wnt datasets contained many genes associated with a neurosensory biological function, confirming the importance of this pathway for neurosensory specification in the otocyst. Finally, the results of a preliminary gain-of-function screening of selected transcription factors and Wnt signalling components suggest that the endogenous programs of otic neurosensory specification are very robust, and in general unaffected by the overexpression of a single factor. Altogether this work provides new insights into the effectors and candidate targets of the Notch and Wnt pathways in the early developing inner ear and could serve as a useful reference for future functional genomics experiments in the embryonic avian inner ear.

Origin of Neuroblasts in the Avian Otic Placode and Their Distributions in the Acoustic and Vestibular Ganglia

The inner ear is a complex three-dimensional sensorial structure with auditory and vestibular functions. This intricate sensory organ originates from the otic placode, which generates the sensory elements of the membranous labyrinth, as well as all the ganglionic neuronal precursors. How auditory and vestibular neurons establish their fate identities remains to be determined. Their topological origin in the incipient otic placode could provide positional information before they migrate, to later segregate in specific portions of the acoustic and vestibular ganglia. To address this question, transplants of small portions of the avian otic placode were performed according to our previous fate map study, using the quail/chick chimeric graft model. All grafts taking small areas of the neurogenic placodal domain contributed neuroblasts to both acoustic and vestibular ganglia. A differential distribution of otic neurons in the anterior and posterior lobes of the vestibular ganglion, as well as in the proximal, intermediate, and distal portions of the acoustic ganglion, was found. Our results clearly show that, in birds, there does not seem to be a strict segregation of acoustic and vestibular neurons in the incipient otic placode.

CRABP-I Expression Patterns in the Developing Chick Inner Ear

The vertebrate inner ear is a complex three-dimensional sensorial structure with auditory and vestibular functions, regarded as an excellent system for analyzing events that occur during development, such as patterning, morphogenesis, and cell specification. Retinoic acid (RA) is involved in all these development processes. Cellular retinoic acid-binding proteins (CRABPs) bind RA with high affinity, buffering cellular free RA concentrations and consequently regulating the activation of precise specification programs mediated by particular regulatory genes. In the otic vesicle, strong CRABP-I expression was detected in the otic wall's dorsomedial aspect, where the endolymphatic apparatus develops, whereas this expression was lower in the ventrolateral aspect, where part of the auditory system forms. Thus, CRABP-I proteins may play a role in the specification of the dorsal-to-ventral and lateral-to-medial axe of the otic anlagen. Regarding the developing sensory patches, a process partly involving the subdivision of a ventromedial pro-sensory domain, the CRABP-I gene displayed different levels of expression in the presumptive territory of each sensory patch, which was maintained throughout development. CRABP-I was also relevant in the acoustic-vestibular ganglion and in the periotic mesenchyme. Therefore, CRABP-I could protect RA-sensitive cells in accordance with its dissimilar concentration in specific areas of the developing chick inner ear.

Comparative assessment of Fgf's diverse roles in inner ear development: A zebrafish perspective

Progress in understanding mechanisms of inner ear development has been remarkably rapid in recent years. The research community has benefited from the availability of several diverse model organisms, including zebrafish, chick, and mouse. The complexity of the inner ear has proven to be a challenge, and the complexity of the mammalian cochlea in particular has been the subject of intense scrutiny. Zebrafish lack a cochlea and exhibit a number of other differences from amniote species, hence they are sometimes seen as less relevant for inner ear studies. However, accumulating evidence shows that underlying cellular and molecular mechanisms are often highly conserved. As a case in point, consideration of the diverse functions of Fgf and its downstream effectors reveals many similarities between vertebrate species, allowing meaningful comparisons the can benefit the entire research community. In this review, I will discuss mechanisms by which Fgf controls key events in early otic development in zebrafish and provide direct comparisons with chick and mouse.

Bacillus amyloliquefaciens TL Downregulates the Ileal Expression of Genes Involved in Immune Responses in Broiler Chickens to Improve Growth Performance

Bacillus amyloliquefaciens TL promotes broiler chicken performance by improving nutrient absorption and utilization and reducing intestinal inflammation. In this study, RNA-sequencing (RNA-seq)-based transcriptomes of ileal tissues collected from probiotic-fed and control broiler chickens were analyzed to elucidate the effects of the probiotic B. amyloliquefaciens TL, as a feed additive, on the gut immune function. In total, 475 genes were significantly differentially expressed between the ileum of probiotic-fed and control birds. The expression of genes encoding pyruvate kinase, prothymosin-α, and heat stress proteins was high in the ileum of probiotic-fed birds (FPKM > 500), but not in the control group. The gene ontology functional enrichment and pathway enrichment analyses revealed that the uniquely expressed genes in the control group were mostly involved in immune responses, whereas those in the probiotic group were involved in fibroblast growth factor receptor signaling pathways and positive regulation of cell proliferation. Bacillus amyloliquefaciens TL downregulated the expression of certain proinflammatory factors and affected the cytokine–cytokine receptor interaction pathway. Furthermore, B. amyloliquefaciens TL in broiler diets altered the expression of genes involved in immune functions in the ileum. Thus, it might contribute to improved broiler growth by regulating the immune system and reducing intestinal damage in broilers.

Molecular characterization of fibroblast growth factor-16 and its role in promoting the differentiation of intramuscular preadipocytes in goat

Fat metabolism is an important and complex biochemical reaction in vivo and is regulated by many factors. Recently, the findings on high expression of fibroblast growth factor-16 (FGF16) in brown adipose tissue have led to an interest in exploring its role in lipogenesis and lipid metabolism. The study cloned the goat's FGF16 gene 624 bp long, including the complete open reading frame that encodes 207 amino acids. We found that FGF16 expression is highest in goat kidneys and hearts, followed by subcutaneous fat and triceps. Moreover, the expression of FGF16 reached its peak on the 2nd day of adipocyte differentiation (P < 0.01) and then decreased significantly. We used overexpression and interference to study the function of FGF16 gene in goat intramuscular preadipocytes. Silencing of FGF16 decreased adipocytes lipid droplet aggregation and triglyceride synthesis. This is in contrast to the situation where FGF16 is overexpressed. Furthermore, knockdown of FGF16 also caused down-regulated expression of genes associated with adipocyte differentiation including CCAAT enhancer-binding protein beta (P < 0.01), fatty acid-binding protein-2 (P < 0.01) and sterol regulatory element binding protein-1 (P < 0.05), but the preadipocyte factor-1 was up-regulated. At the same time, the genes adipose triglyceride lipase (P < 0.01) and hormone-sensitive lipase (P < 0.05) associated with triglyceride breakdown were highly expressed. Next, we locked the fibroblast growth factor receptor-4 (FGFR4) through the protein interaction network and interfering with FGF16 to significantly reduce FGFR4 expression. It was found that the expression profile of FGFR4 in adipocyte differentiation was highly similar to that of FGF16. Overexpression and interference methods confirmed that FGFR4 and FGF16 have the same promoting function in adipocyte differentiation. Finally, using co-transfection technology, pc-FGF16 and siRNA-FGFR4, siRNA2-FGF16 and siRNA-FGFR4 were combined to treat adipocytes separately. It was found that in the case of overexpression of FGF16, cell lipid secretion and triglyceride synthesis showed a trend of first increase and then decrease with increasing interference concentration. In the case of interference with FGF16, lipid secretion and triglyceride synthesis showed a downward trend with the increase of interference concentration. These findings illustrated that FGF16 mediates adipocyte differentiation via receptor FGFR4 expression and contributed to further study of the functional role of FGF16 in goat fat formation.

Cyp1B1 expression patterns in the developing chick inner ear

BACKGROUND

Retinoic acid (RA) plays an important role in organogenesis as a paracrine signal through transcriptional regulation of an increasing number of known downstream target genes, regulating cell proliferation, and differentiation. During the development of the inner ear, RA directly governs the morphogenesis and specification processes mainly by means of RA-synthesizing retinaldehyde dehydrogenase (RALDH) enzymes. Interestingly, CYP1B1, a cytochrome P450 enzyme, is able to mediate the oxidative metabolisms also leading to RA generation, its expression patterns being associated with many known sites of RA activity.

RESULTS

This study describes for the first time the presence of CYP1B1 in the developing chick inner ear as a RALDH-independent RA-signaling mechanism. In our in situ hybridization analysis, Cyp1B1 expression was first observed in a domain located in the ventromedial wall of the otic anlagen, being included within the rostralmost aspect of an Fgf10-positive pan-sensory domain. As development proceeds, all identified Fgf10-positive areas were Cyp1B1 stained, with all sensory patches being Cyp1B1 positive at stage HH34, except the macula neglecta.

CONCLUSIONS

Cyp1B1 expression suggested a possible contribution of CYP1B1 action in the specification of the lateral-to-medial and dorsal-to-ventral axes of the developing chick inner ear.

Shaping of inner ear sensory organs through antagonistic interactions between Notch signalling and Lmx1a

The mechanisms of formation of the distinct sensory organs of the inner ear and the non-sensory domains that separate them are still unclear. Here, we show that several sensory patches arise by progressive segregation from a common prosensory domain in the embryonic chicken and mouse otocyst. This process is regulated by mutually antagonistic signals: Notch signalling and Lmx1a. Notch-mediated lateral induction promotes prosensory fate. Some of the early Notch-active cells, however, are normally diverted from this fate and increasing lateral induction produces misshapen or fused sensory organs in the chick. Conversely Lmx1a (or cLmx1b in the chick) allows sensory organ segregation by antagonizing lateral induction and promoting commitment to the non-sensory fate. Our findings highlight the dynamic nature of sensory patch formation and the labile character of the sensory-competent progenitors, which could have facilitated the emergence of new inner ear organs and their functional diversification in the course of evolution.

Clinical, pathological, and genetic evaluations of Chinese patient with otodental syndrome and multiple complex odontoma: Case report

Otodental syndrome is a rare autosomal-dominant disease characterized by globodontia, associated with sensorineural, high-frequency hearing loss. Here, we describe the clinical, pathological, and genetic evaluations of a 9-year-old girl with otodental syndrome and multiple complex odontoma.The patient presented with a draining sinus tract in her left cheek, globodontia, and hearing loss. The odontomas which caused the cutaneous sinus tracts were extracted because of the odontogenic infection. The extracted odontoma and primary tooth was studied by micro-CT and further observed histopathologically. The micro-CT findings revealed that the primary tooth had three crowns with two separated pulp chambers, and their root canals were partially fused. The histological findings showed abnormal morphologies of odontoblasts and dentin, hyperplasia of enamel, and malformation of odontogenic epithelium. Furthermore, DNA sequencing and analyze of deafness associated gene GJB2, GJB3, and PDS had not revealed any SNP or mutation; but exon 3 of the causative gene FGF3 could not be amplified, which may be associated with the microdeletion at chromosome 11q13.3. Three month after surgery, the patient was found to be asymptomatic and even the evidence of the extra-oral sinus had disappeared.The dental abnormality of otodental syndrome included congenital missing teeth, globodontia, and multiple complex odontoma. Globodontia exhibited characteristic features of fusion teeth. In addition, gene FGF3 haploinsufficiency was likely to be the cause of otodental syndrome. The report provides some new information in the field of otodental syndrome, which would make dentists more familiar with this disease.

Lectins selectively label cartilage condensations and the otic neuroepithelium within the embryonic chicken head

Cartilage morphogenesis during endochondral ossification follows a progression of conserved developmental events. Cells are specified towards a prechondrogenic fate and subsequently undergo condensation followed by overt differentiation. Currently available molecular markers of prechondrogenic and condensing mesenchyme rely on common regulators of the chondrogenic program that are not specific to the tissue type or location. Therefore tissue-specific condensations cannot be distinguished based on known molecular markers. Here, using the chick embryo model, we utilized lectin labeling on serial sections, demonstrating that differential labeling by peanut agglutinin (PNA) and Sambucus nigra agglutinin (SNA) successfully separates adjacently located condensations in the proximal second pharyngeal arch. PNA selectively labels chick middle ear columella and basal plate condensation, whereas SNA specifically marks extracolumella and the ventro-lateral part of the otic capsule. We further extended our study to examine lectin-binding properties of the different parts of the inner ear epithelium, neural tube and notochord. Our results show that SNA labels the auditory and vestibular hair cells of the inner ear, whereas PNA specifically recognizes the statoacoustic ganglion. PNA is also highly specific for the floor plate of the neural tube. Additionally, wheat germ agglutinin (WGA) labels the basement membrane of the notochord and is a marker of the apical-basal polarity of the cochlear duct. Overall, this study indicates that selective lectin labeling is a promising approach to differentiate between contiguously located mesenchymal condensations and subregions of epithelia globally during development.