The fusiform gyrus exhibits differential gene-gene co-expression in Alzheimer's disease

Alzheimer's Disease (AD) is an irreversible neurodegenerative disease clinically characterized by the presence of β-amyloid plaques and tau deposits in various regions of the brain. However, the underlying factors that contribute to the development of AD remain unclear. Recently, the fusiform gyrus has been identified as a critical brain region associated with mild cognitive impairment, which may increase the risk of AD development. In our study, we performed gene co-expression and differential co-expression network analyses, as well as gene-expression-based prediction, using RNA-seq transcriptome data from post-mortem fusiform gyrus tissue samples collected from both cognitively healthy individuals and those with AD. We accessed differential co-expression networks in large cohorts such as ROSMAP, MSBB, and Mayo, and conducted over-representation analyses of gene pathways and gene ontology. Our results comprise four exclusive gene hubs in co-expression modules of Alzheimer's Disease, including FNDC3A, MED23, NRIP1, and PKN2. Further, we identified three genes with differential co-expressed links, namely FAM153B, CYP2C8, and CKMT1B. The differential co-expressed network showed moderate predictive performance for AD, with an area under the curve ranging from 0.71 to 0.76 (+/- 0.07). The over-representation analysis identified enrichment for Toll-Like Receptors Cascades and signaling pathways, such as G protein events, PIP2 hydrolysis and EPH-Epherin mechanism, in the fusiform gyrus. In conclusion, our findings shed new light on the molecular pathophysiology of AD by identifying new genes and biological pathways involved, emphasizing the crucial role of gene regulatory networks in the fusiform gyrus.

Microarray expression profiling of fndc3a zebrafish mutants

The group of Fibronectin type III domain-containing (FNDC; InterPro IPR003961) protein super family splits into a large number of gene-orthologues and mediates a variety of cellular functions during development and disease. They act as anti-inflammatory factors, are linked to cell-cell-interactions, regulate cell signaling and are associated with different cancer types, like cervical and colorectal. One member of this gene family is FNDC3A , which influences different developmental processes in vertebrates, like Sertoli cell/spermatid adhesion in mice testis, bone traits in chicken, and fin development in zebrafish. To identify downstream molecular processes during vertebrate development we investigated gene expression profiles in the previously established fndc3a zebrafish mutants via microarray analyses on 22 hpf embryos (26-somite stage). Our analyses imply distinct transcriptional profiles between genotype groups and hint to altered cell binding and catalytic activity in fndc3a mutants.

ECM alterations in Fndc3a (Fibronectin Domain Containing Protein 3A) deficient zebrafish cause temporal fin development and regeneration defects

Fin development and regeneration are complex biological processes that are highly relevant in teleost fish. They share genetic factors, signaling pathways and cellular properties to coordinate formation of regularly shaped extremities. Especially correct tissue structure defined by extracellular matrix (ECM) formation is essential. Gene expression and protein localization studies demonstrated expression of fndc3a (fibronectin domain containing protein 3a) in both developing and regenerating caudal fins of zebrafish (Danio rerio). We established a hypomorphic fndc3a mutant line (fndc3a^wue1/wue1) via CRISPR/Cas9, exhibiting phenotypic malformations and changed gene expression patterns during early stages of median fin fold development. These developmental effects are mostly temporary, but result in a fraction of adults with permanent tail fin deformations. In addition, caudal fin regeneration in adult fndc3a^wue1/wue1 mutants is hampered by interference with actinotrichia formation and epidermal cell organization. Investigation of the ECM implies that loss of epidermal tissue structure is a common cause for both of the observed defects. Our results thereby provide a molecular link between these developmental processes and foreshadow Fndc3a as a novel temporal regulator of epidermal cell properties during extremity development and regeneration in zebrafish.

Expression Analysis of Fibronectin Type III Domain-Containing (FNDC) Genes in Inflammatory Bowel Disease and Colorectal Cancer

Background

Fibronectin type III domain-containing (FNDC) proteins fulfill manifold functions in tissue development and regulation of cellular metabolism. FNDC4 was described as anti-inflammatory factor, upregulated in inflammatory bowel disease (IBD). FNDC signaling includes direct cell-cell interaction as well as release of bioactive peptides, like shown for FNDC4 or FNDC5. The G-protein-coupled receptor 116 (GPR116) was found as a putative FNDC4 receptor. We here aim to comprehensively analyze the mRNA expression of FNDC1, FNDC3A, FNDC3B, FNDC4, FNDC5, and GPR116 in nonaffected and affected mucosal samples of patients with IBD or colorectal cancer (CRC).

Methods

Mucosa samples were obtained from 30 patients undergoing diagnostic colonoscopy or from surgical resection of IBD or CRC. Gene expression was determined by quantitative real-time PCR. In addition, FNDC expression data from publicly available Gene Expression Omnibus (GEO) data sets (GDS4296, GDS4515, and GDS5232) were analyzed.

Results

Basal mucosal expression revealed higher expression of FNDC3A and FNDC5 in the ileum compared to colonic segments. FNDC1 and FNDC4 were significantly upregulated in IBD. None of the investigated FNDCs was differentially expressed in CRC, just FNDC3A trended to be upregulated. The GEO data set analysis revealed significantly downregulated FNDC4 and upregulated GPR116 in microsatellite unstable (MSI) CRCs. The expression of FNDCs and GPR116 was independent of age and sex.

Conclusions

FNDC1 and FNDC4 may play a relevant role in the pathobiology of IBD, but none of the investigated FNDCs is regulated in CRC. GPR116 may be upregulated in advanced or MSI CRC. Further studies should validate the altered FNDC expression results on protein levels and examine the corresponding functional consequences.

Miles to go (mtgo) encodes FNDC3 proteins that interact with the chaperonin subunit CCT3 and are required for NMJ branching and growth in Drosophila

Analysis of mutants that affect formation and function of the Drosophila larval neuromuscular junction (NMJ) has provided valuable insight into genes required for neuronal branching and synaptic growth. We report that NMJ development in Drosophila requires both the Drosophila ortholog of FNDC3 genes; CG42389 (herein referred to as miles to go; mtgo), and CCT3, which encodes a chaperonin complex subunit. Loss of mtgo function causes late pupal lethality with most animals unable to escape the pupal case, while rare escapers exhibit an ataxic gait and reduced lifespan. NMJs in mtgo mutant larvae have dramatically reduced branching and growth and fewer synaptic boutons compared with control animals. Mutant larvae show normal locomotion but display an abnormal self-righting response and chemosensory deficits that suggest additional functions of mtgo within the nervous system. The pharate lethality in mtgo mutants can be rescued by both low-level pan- and neuronal-, but not muscle-specific expression of a mtgo transgene, supporting a neuronal-intrinsic requirement for mtgo in NMJ development. Mtgo encodes three similar proteins whose domain structure is most closely related to the vertebrate intracellular cytosolic membrane-anchored fibronectin type-III domain-containing protein 3 (FNDC3) protein family. Mtgo physically and genetically interacts with Drosophila CCT3, which encodes a subunit of the TRiC/CCT chaperonin complex required for maturation of actin, tubulin and other substrates. Drosophila larvae heterozygous for a mutation in CCT3 that reduces binding between CCT3 and MTGO also show abnormal NMJ development similar to that observed in mtgo null mutants. Hence, the intracellular FNDC3-ortholog MTGO and CCT3 can form a macromolecular complex, and are both required for NMJ development in Drosophila.

Associations between single-nucleotide polymorphism in the FNDC3A and autism spectrum disorder in a Korean population

Autism spectrum disorder (ASD) is a neurodevelopmental syndrome associated with impairments of reciprocal communication and cognitive function. Associations between single-nucleotide polymorphisms (SNPs) and ASD were analysed by logistic regression. Polymorphisms in fibronectin type III domain-containing 3A (FNDC3A) exhibited significant associations in genotype and diplotype analyses. We conclude that FNDC3A influences the prevalence of ASD.