Nuclear isoform of FGF13 regulates post-natal neurogenesis in the hippocampus through an epigenomic mechanism

Ceramide-induced FGF13 impairs systemic metabolic health

Ceramide accumulation impairs adipocytes' ability to efficiently store and utilize nutrients, leading to energy and glucose homeostasis deterioration. Using a comparative transcriptomic screen, we identified the non-canonical, non-secreted fibroblast growth factor FGF13 as a ceramide-regulated factor that impairs adipocyte function. Obesity robustly induces FGF13 expression in adipose tissue in mice and humans and is positively associated with glycemic indices of type 2 diabetes. Pharmacological or genetic inhibition of ceramide biosynthesis reduces FGF13 expression. Using mice with loss and gain of function of FGF13, we demonstrate that FGF13 is both necessary and sufficient to impair energy and glucose homeostasis independent of ceramides. Mechanistically, FGF13 exerts these effects by inhibiting mitochondrial content and function, metabolic elasticity, and caveolae formation, which cumulatively impairs glucose utilization and thermogenesis. These studies suggest the therapeutic potential of targeting FGF13 to prevent and treat metabolic diseases.

A temporal cortex cell atlas highlights gene expression dynamics during human brain maturation

The human brain undergoes protracted postnatal maturation, guided by dynamic changes in gene expression. Most studies exploring these processes have used bulk tissue analyses, which mask cell-type-specific gene expression dynamics. Here, using single-nucleus RNA sequencing on temporal lobe tissue, including samples of African ancestry, we build a joint pediatric and adult atlas of 75 cell subtypes, which we verify with spatial transcriptomics. We explore the differences between pediatric and adult cell subtypes, revealing the genes and pathways that change during brain maturation. Our results highlight excitatory neuron subtypes, including the LTK and FREM subtypes, that show elevated expression of genes associated with cognition and synaptic plasticity in pediatric tissue. The resources we present here improve our understanding of the brain during its development and contribute to global efforts to build an inclusive brain cell map.

Fibroblast Growth Factor (FGF) 13

Fibroblast Growth Factor (FGF) 13, also referred to as FGF homologous factor (FHF) 2, is a member of the FGF11 subfamily that is characterized as having sequence similarities to classical FGF receptor (FGFR)-binding FGFs, but functionally do not bind FGFRs. In this primer mini-review, we summarize current knowledge regarding FGF13 expression, mutant analyses, and gene and protein structure. Similar to other FHFs, FGF13 has been considered a non-secreted protein that lacks an amino signal and is prominently expressed in developing and mature neurons of the central and peripheral nervous systems, as well as the heart. The expression of FGF13 is not limited to early embryonic stages and has been shown to persist in adult tissues. As well, FGF13 is known to localize subcellularly, both within the cytoplasm and the nucleus. FGF13 is extremely adaptable, as it interacts with MAPK scaffolding protein islet brain 2 (IB2), stabilizes microtubules, or binds to voltage-gated sodium channels. Fgf13 mutant mouse lines display various neurological pathologies. Through sequence mapping, FGF13 is considered a candidate causative gene that is mutated in multiple human X-linked neurological diseases.

FGF13 enhances the function of TRPV1 by stabilizing microtubules and regulates acute and chronic itch

Itching is an aversive somatosensation that triggers the desire to scratch. Transient receptor potential (TRP) channel proteins are key players in acute and chronic itch. However, whether the modulatory effect of fibroblast growth factor 13 (FGF13) on acute and chronic itch is associated with TRP channel proteins is unclear. Here, we demonstrated that conditional knockout of Fgf13 in dorsal root ganglion neurons induced significant impairment in scratching behaviors in response to acute histamine-dependent and chronic dry skin itch models. Furthermore, FGF13 selectively regulated the function of the TRPV1, but not the TRPA1 channel on Ca2+ imaging and electrophysiological recordings, as demonstrated by a significant reduction in neuronal excitability and current density induced by TRPV1 channel activation, whereas TRPA1 channel activation had no effect. Changes in channel currents were also verified in HEK cell lines. Subsequently, we observed that selective modulation of TRPV1 by FGF13 required its microtubule-stabilizing effect. Furthermore, in FGF13 knockout mice, only the overexpression of FGF13 with a tubulin-binding domain could rescue TRP channel function and the impaired itch behavior. Our findings reveal a novel mechanism by which FGF13 is involved in TRPV1-dependent itch transduction and provide valuable clues for alleviating pathological itch syndrome.

Cell type-specific gene expression dynamics during human brain maturation

The human brain undergoes protracted post-natal maturation, guided by dynamic changes in gene expression. Most studies exploring these processes have used bulk tissue analyses, which mask cell type-specific gene expression dynamics. Here, using single nucleus (sn)RNA-seq on temporal lobe tissue, including samples of African ancestry, we build a joint paediatric and adult atlas of 75 cell subtypes, which we verify with spatial transcriptomics. We explore the differences between paediatric and adult cell types, revealing the genes and pathways that change during brain maturation. Our results highlight excitatory neuron subtypes, including the LTK and FREM subtypes, that show elevated expression of genes associated with cognition and synaptic plasticity in paediatric tissue. The new resources we present here improve our understanding of the brain during its development and contribute to global efforts to build an inclusive brain cell map.

ASH2L regulates postnatal neurogenesis through Onecut2-mediated inhibition of TGF-β signaling pathway

The ability of neural stem/progenitor cells (NSPCs) to proliferate and differentiate is required through different stages of neurogenesis. Disturbance in the regulation of neurogenesis causes many neurological diseases, such as intellectual disability, autism, and schizophrenia. However, the intrinsic mechanisms of this regulation in neurogenesis remain poorly understood. Here, we report that Ash2l (Absent, small or homeotic discs-like 2), one core component of a multimeric histone methyltransferase complex, is essential for NSPC fate determination during postnatal neurogenesis. Deletion of Ash2l in NSPCs impairs their capacity for proliferation and differentiation, leading to simplified dendritic arbors in adult-born hippocampal neurons and deficits in cognitive abilities. RNA sequencing data reveal that Ash2l primarily regulates cell fate specification and neuron commitment. Furthermore, we identified Onecut2, a major downstream target of ASH2L characterized by bivalent histone modifications, and demonstrated that constitutive expression of Onecut2 restores defective proliferation and differentiation of NSPCs in adult Ash2l-deficient mice. Importantly, we identified that Onecut2 modulates TGF-β signaling in NSPCs and that treatment with a TGF-β inhibitor rectifies the phenotype of Ash2l-deficient NSPCs. Collectively, our findings reveal the ASH2L-Onecut2-TGF-β signaling axis that mediates postnatal neurogenesis to maintain proper forebrain function.

m6A regulation of cortical and retinal neurogenesis is mediated by the redundant m6A readers YTHDFs

m⁶A modification plays an important role in regulating mammalian neurogenesis. However, whether and how the major cytoplasmic m⁶A readers, YTHDF1, YTHDF2, and YTHDF3 mediate this process is still not clear. Here, we demonstrate that Ythdf1 and Ythdf2 double deletion but not individual knockout recapitulates the phenotype of Mettl14 knockout in cortex. In addition, we find that Mettl14 knockout in retina causes protracted proliferation of retinal progenitors, decreased numbers of retinal neurons, and disturbed laminar structure. This phenotype is only reproduced when Ythdf1, Ythdf2, and Ythdf3 are knocked out simultaneously in retina. Analysis of YTHDF target mRNAs in mouse cortex and retina reveals abundant overlapping mRNAs related to neurogenesis that are recognized and regulated by both YTHDF1 and YTHDF2. Together our results demonstrate that the functionally redundant YTHDFs mediate m⁶A regulation of cortical and retinal neurogenesis.

The genetic basis of spatial cognitive variation in a food-caching bird

Spatial cognition is used by most organisms to navigate their environment. Some species rely particularly heavily on specialized spatial cognition to survive, suggesting that a heritable component of cognition may be under natural selection. This idea remains largely untested outside of humans, perhaps because cognition in general is known to be strongly affected by learning and experience.^1-4 We investigated the genetic basis of individual variation in spatial cognition used by non-migratory food-caching birds to recover food stores and survive harsh montane winters. Comparing the genomes of wild, free-living birds ranging from best to worst in their performance on a spatial cognitive task revealed significant associations with genes involved in neuron growth and development and hippocampal function. These results identify candidate genes associated with differences in spatial cognition and provide a critical link connecting individual variation in spatial cognition with natural selection.