Temporal and spatial expression pattern of Nnat during mouse eye development

RNA-Seq Analysis Reveals an Essential Role of the cGMP-PKG-MAPK Pathways in Retinal Degeneration Caused by Cep250 Deficiency

Usher syndrome (USH) is characterised by degenerative vision loss known as retinitis pigmentosa (RP), sensorineural hearing loss, and vestibular dysfunction. RP can cause degeneration and the loss of rod and cone photoreceptors, leading to structural and functional changes in the retina. Cep250 is a candidate gene for atypical Usher syndrome, and this study describes the development of a Cep250 KO mouse model to investigate its pathogenesis. OCT and ERG were applied in Cep250 and WT mice at P90 and P180 to access the general structure and function of the retina. After recording the ERG responses and OCT images at P90 and P180, the cone and rod photoreceptors were visualised using an immunofluorescent stain. TUNEL assays were applied to observe the apoptosis in Cep250 and WT mice retinas. The total RNA was extracted from the retinas and executed for RNA sequencing at P90. Compared with WT mice, the thickness of the ONL, IS/OS, and whole retina of Cep250 mice was significantly reduced. The a-wave and b-wave amplitude of Cep250 mice in scotopic and photopic ERG were lower, especially the a-wave. According to the immunostaining and TUNEL stain results, the photoreceptors in the Cep250 retinas were also reduced. An RNA-seq analysis showed that 149 genes were upregulated and another 149 genes were downregulated in Cep250 KO retinas compared with WT mice retinas. A KEGG enrichment analysis indicated that cGMP-PKG signalling pathways, MAPK signalling pathways, edn2-fgf2 axis pathways, and thyroid hormone synthesis were upregulated, whereas protein processing in the endoplasmic reticulum was downregulated in Cep250 KO eyes. Cep250 KO mice experience a late-stage retinal degeneration that manifests as the atypical USH phenotype. The dysregulation of the cGMP-PKG-MAPK pathways may contribute to the pathogenesis of cilia-related retinal degeneration.

Joint dimension reduction and clustering analysis of single-cell RNA-seq and spatial transcriptomics data

Dimension reduction and (spatial) clustering is usually performed sequentially; however, the low-dimensional embeddings estimated in the dimension-reduction step may not be relevant to the class labels inferred in the clustering step. We therefore developed a computation method, Dimension-Reduction Spatial-Clustering (DR-SC), that can simultaneously perform dimension reduction and (spatial) clustering within a unified framework. Joint analysis by DR-SC produces accurate (spatial) clustering results and ensures the effective extraction of biologically informative low-dimensional features. DR-SC is applicable to spatial clustering in spatial transcriptomics that characterizes the spatial organization of the tissue by segregating it into multiple tissue structures. Here, DR-SC relies on a latent hidden Markov random field model to encourage the spatial smoothness of the detected spatial cluster boundaries. Underlying DR-SC is an efficient expectation-maximization algorithm based on an iterative conditional mode. As such, DR-SC is scalable to large sample sizes and can optimize the spatial smoothness parameter in a data-driven manner. With comprehensive simulations and real data applications, we show that DR-SC outperforms existing clustering and spatial clustering methods: it extracts more biologically relevant features than conventional dimension reduction methods, improves clustering performance, and offers improved trajectory inference and visualization for downstream trajectory inference analyses.

Lidocaine prevents breast cancer growth by targeting neuronatin to inhibit nerve fibers formation

Lidocaine has been shown to inhibit the invasion and metastasis of breast cancer, but the mechanism still remains unclear. This study explored the relationship between lidocaine and circulating seeding of breast cancer cells from the perspective of nerve fiber formation. The cell lines MDA-MB-231 and 4T1 were subcutaneously inoculated in mice to simulate the tumor self-seeding by circulating cancer cells. Lidocaine was used to treat these mice and tumor growth was observed. Silver staining was performed to observe the distribution of nerve fibers in tumor-bearing tissues, and immunohistochemical analysis was performed to observe the expression levels of nerve-related proteins. The results showed that lidocaine treatment effectively inhibited tumor growth and nerve fiber formation, and down-regulated the expression levels of protein gene product 9.5, neurofilament, nerve growth factor (NGF), and neuronatin (Nnat). Overexpression NGF and Nnat both could reverse the therapeutic effects of lidocaine. These results suggest that the effect of lidocaine on inhibiting breast cancer invasion and metastasis may be achieved by targeting Nnat, regulating the production of NGFs in cancer cells, and subsequently inhibiting the formation of nerve fibers.

Loss of UGP2 in brain leads to a severe epileptic encephalopathy, emphasizing that bi-allelic isoform-specific start-loss mutations of essential genes can cause genetic diseases

Developmental and/or epileptic encephalopathies (DEEs) are a group of devastating genetic disorders, resulting in early-onset, therapy-resistant seizures and developmental delay. Here we report on 22 individuals from 15 families presenting with a severe form of intractable epilepsy, severe developmental delay, progressive microcephaly, visual disturbance and similar minor dysmorphisms. Whole exome sequencing identified a recurrent, homozygous variant (chr2:64083454A > G) in the essential UDP-glucose pyrophosphorylase (UGP2) gene in all probands. This rare variant results in a tolerable Met12Val missense change of the longer UGP2 protein isoform but causes a disruption of the start codon of the shorter isoform, which is predominant in brain. We show that the absence of the shorter isoform leads to a reduction of functional UGP2 enzyme in neural stem cells, leading to altered glycogen metabolism, upregulated unfolded protein response and premature neuronal differentiation, as modeled during pluripotent stem cell differentiation in vitro. In contrast, the complete lack of all UGP2 isoforms leads to differentiation defects in multiple lineages in human cells. Reduced expression of Ugp2a/Ugp2b in vivo in zebrafish mimics visual disturbance and mutant animals show a behavioral phenotype. Our study identifies a recurrent start codon mutation in UGP2 as a cause of a novel autosomal recessive DEE syndrome. Importantly, it also shows that isoform-specific start-loss mutations causing expression loss of a tissue-relevant isoform of an essential protein can cause a genetic disease, even when an organism-wide protein absence is incompatible with life. We provide additional examples where a similar disease mechanism applies.

Dynamic Changes in the Localization of Neuronatin-Positive Cells during Neurogenesis in the Embryonic Rat Brain

Neuronatin (NNAT) was first identified as a gene selectively and abundantly expressed in the cytoplasm of the newborn mouse brain, and involved in neonatal neurogenesis. However, the particular roles of NNAT in the developing prenatal brain have not been identified, especially in mid to late stages. In this study, we performed immunohistochemical analyses of NNAT and SOX2 proteins, a nuclear transcription factor and neural stem/progenitor marker, in the rat brain on embryonic days 13.5, E16.5, and E20.5. NNAT signals were broadly observed across the developing brain on E13.5 and gradually more localized in later stages, eventually concentrated in the alar and basal parts of the terminal hypothalamus, the alar plate of prosomere 2 of the thalamus, and the choroid plexus in the lateral and fourth ventricles on E20.5. In particular, the mammillary body in the basal part of the terminal hypothalamus, a region with a high number of SOX2-positive cells, evidenced intense NNAT signals on E20.5. The intracellular localization of NNAT showed diverse profiles, suggesting that NNAT was involved in various cellular functions, such as cell differentiation and functional maintenance, during prenatal neurogenesis in the rat brain. Thus, the present observations suggested diverse and active roles of the NNAT protein in neurogenesis. Determining the function of this molecule may assist in the elucidation of the mechanisms involved in brain development.

Characteristic Localization of Neuronatin in Rat Testis, Hair Follicle, Tongue, and Pancreas

Neuronatin (Nnat) is expressed in the pituitary, pancreas, and other tissues; however, the function of NNAT is still unclear. Recent studies have demonstrated that NNAT is localized in the sex-determining region Y-box 2-positive stem/progenitor cells in the developing rat pituitary primordium and is downregulated during differentiation into mature hormone-producing cells. Moreover, NNAT is widely localized in subcellular organelles, excluding the Golgi. Here, we further evaluated NNAT-positive cells and intracellular localization in embryonic and postnatal rat tissues such as the pancreas, tongue, whisker hair follicle, and testis. Immunohistochemistry revealed that NNAT was localized in undifferentiated cells (i.e., epithelial basal cells and basement cells in the papillae of the tongue and round and elongated spermatids of the testis) as well as in differentiated cells (insulin-positive cells and exocrine cells of the pancreas, taste receptor cells of the fungiform papilla, the inner root sheath of whisker hair follicles, and spermatozoa). In addition, NNAT exhibited novel intracellular localization in acrosomes in the spermatozoa. Because the endoplasmic reticulum (ER) is excluded from spermatozoa and sarco/ER Ca²⁺-ATPase isoform 2 (SERCA2) is absent from the inner root sheath, these findings suggested that NNAT localization in the ER and its interaction with SERCA2 are cell- or tissue-specific properties.