Golgi during development

The organization and function of the Golgi apparatus in dendrite development and neurological disorders

Dendrites are specialized neuronal compartments that sense, integrate and transfer information in the neural network. Their development is tightly controlled and abnormal dendrite morphogenesis is strongly linked to neurological disorders. While dendritic morphology ranges from relatively simple to extremely complex for a specified neuron, either requires a functional secretory pathway to continually replenish proteins and lipids to meet dendritic growth demands. The Golgi apparatus occupies the center of the secretory pathway and is regulating posttranslational modifications, sorting, transport, and signal transduction, as well as acting as a non-centrosomal microtubule organization center. The neuronal Golgi apparatus shares common features with Golgi in other eukaryotic cell types but also forms distinct structures known as Golgi outposts that specifically localize in dendrites. However, the organization and function of Golgi in dendrite development and its impact on neurological disorders is just emerging and so far lacks a systematic summary. We describe the organization of the Golgi apparatus in neurons, review the current understanding of Golgi function in dendritic morphogenesis, and discuss the current challenges and future directions.

On the use of QDE-SVM for gene feature selection and cell type classification from scRNA-seq data

Cell type identification is one of the fundamental tasks in single-cell RNA sequencing (scRNA-seq) studies. It is a key step to facilitate downstream interpretations such as differential expression, trajectory inference, etc. scRNA-seq data contains technical variations that could affect the interpretation of the cell types. Therefore, gene selection, also known as feature selection in data science, plays an important role in selecting informative genes for scRNA-seq cell type identification. Generally speaking, feature selection methods are categorized into filter-, wrapper-, and embedded-based approaches. From the existing literature, methods from filter- and embedded-based approaches are widely applied in scRNA-seq gene selection tasks. The wrapper-based method that gives promising results in other fields has yet been extensively utilized for selecting gene features from scRNA-seq data; in addition, most of the existing wrapper methods used in this field are clustering instead of classification-based. With a large number of annotated data available today, this study applied a classification-based approach as an alternative to the clustering-based wrapper method. In our work, a quantum-inspired differential evolution (QDE) wrapped with a classification method was introduced to select a subset of genes from twelve well-known scRNA-seq transcriptomic datasets to identify cell types. In particular, the QDE was combined with different machine-learning (ML) classifiers namely logistic regression, decision tree, support vector machine (SVM) with linear and radial basis function kernels, as well as extreme learning machine. The linear SVM wrapped with QDE, namely QDE-SVM, was chosen by referring to the feature selection results from the experiment. QDE-SVM showed a superior cell type classification performance among QDE wrapping with other ML classifiers as well as the recent wrapper methods (i.e., FSCAM, SSD-LAHC, MA-HS, and BSF). QDE-SVM achieved an average accuracy of 0.9559, while the other wrapper methods achieved average accuracies in the range of 0.8292 to 0.8872.

Congenital disorder of glycosylation caused by starting site-specific variant in syntaxin-5

The SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) protein syntaxin-5 (Stx5) is essential for Golgi transport. In humans, the STX5 mRNA encodes two protein isoforms, Stx5 Long (Stx5L) from the first starting methionine and Stx5 Short (Stx5S) from an alternative starting methionine at position 55. In this study, we identify a human disorder caused by a single missense substitution in the second starting methionine (p.M55V), resulting in complete loss of the short isoform. Patients suffer from an early fatal multisystem disease, including severe liver disease, skeletal abnormalities and abnormal glycosylation. Primary human dermal fibroblasts isolated from these patients show defective glycosylation, altered Golgi morphology as measured by electron microscopy, mislocalization of glycosyltransferases, and compromised ER-Golgi trafficking. Measurements of cognate binding SNAREs, based on biotin-synchronizable forms of Stx5 (the RUSH system) and Förster resonance energy transfer (FRET), revealed that the short isoform of Stx5 is essential for intra-Golgi transport. Alternative starting codons of Stx5 are thus linked to human disease, demonstrating that the site of translation initiation is an important new layer of regulating protein trafficking.

Progress in research into the role of abnormal glycosylation modification in tumor immunity

In abnormal glycosylation, molecules of glucose or other carbohydrates in living organisms are inappropriately attached to proteins, which causes protein denaturation. Abnormal glycosylation modification is known to directly or indirectly affect the tumor escape process, but very few studies have been performed on whether protein glycosylation changes the structure and function of immune cells and immune molecules and thereby regulates the occurrence and development of tumor escape. Therefore, this article summarizes the effect of the immune system on tumor escape in association with the abnormal glycosylation process from an immunological perspective.

Function of Arl4aa in the Initiation of Hematopoiesis in Zebrafish by Maintaining Golgi Complex Integrity in Hemogenic Endothelium

ADP-ribosylation factor-like 4aa (Arl4aa) is a member of the ADP-ribosylation factor family. It is expressed in hematopoietic tissue during embryonic development, but its function was unknown. Zebrafish arl4aa is preferentially expressed in the ventral wall of the dorsal aorta (VDA) at 24 and 36 hpf and in caudal hematopoietic tissue at 48 hpf. Morpholino knockdown and transcription activator-like effector nuclease (TALEN) knockout of arl4aa significantly reduced expression of genes associated with definitive hematopoietic stem cells (HSCs). Golgi complex integrity in VDA was disrupted as shown by transmission electron microscopy and immunostaining of Golgi membrane Giantin. Mechanistically, arl4aa knockdown reduced Notch signaling in the VDA and its target gene expression. Protein expression of NICD was also reduced. Effects of arl4aa knockdown on definitive hematopoiesis could be restored by NICD expression. This study identified arl4aa as a factor regulating initiation of definitive HSCs by maintaining the integrity of Golgi complex and, secondarily, maturation of the Notch receptor.

Ratiometric fluorescence imaging of Golgi H2O2 reveals a correlation between Golgi oxidative stress and hypertension

Based on a novel Golgi-targeting phenylsulfonamide group, a two-photon (TP) fluorescent probe, Np-Golgi, was developed for in situ H₂O₂ ratiometric imaging in living systems.

Golgi oxidative stress is significantly associated with the occurrence and progression of hypertension. Notably, the concentration of hydrogen peroxide (H₂O₂) is directly proportional to the degree of Golgi oxidative stress. Therefore, based on a novel Golgi-targeting phenylsulfonamide group, we developed a two-photon (TP) fluorescent probe, Np-Golgi, for in situ H₂O₂ ratiometric imaging in living systems. The phenylsulfonamide moiety effectively assists Np-Golgi in the precise location of Golgi apparatus. In addition, the raw material of phenylsulfonamide is easily available, and chemical modification is easily implemented. By application of Np-Golgi, we explored the generation of H₂O₂ during Golgi oxidative stress, and also successfully revealed increases on the levels of Golgi H₂O₂ in the kidneys of mice with hypertension. This work provides an ideal tool to monitor Golgi oxidative stress for the first time and novel drug targets for the future treatment of hypertension.

DISTAG/TBCCd1 Is Required for Basal Cell Fate Determination in Ectocarpus

Brown algae are one of the most developmentally complex groups within the eukaryotes. As in many land plants and animals, their main body axis is established early in development, when the initial cell gives rise to two daughter cells that have apical and basal identities, equivalent to shoot and root identities in land plants, respectively. We show here that mutations in the Ectocarpus DISTAG (DIS) gene lead to loss of basal structures during both the gametophyte and the sporophyte generations. Several abnormalities were observed in the germinating initial cell in dis mutants, including increased cell size, disorganization of the Golgi apparatus, disruption of the microtubule network, and aberrant positioning of the nucleus. DIS encodes a TBCCd1 protein, which has a role in internal cell organization in animals, Chlamydomonas reinhardtii, and trypanosomes. Our study highlights the key role of subcellular events within the germinating initial cell in the determination of apical/basal cell identities in a brown alga and emphasizes the remarkable functional conservation of TBCCd1 in regulating internal cell organization across extremely distant eukaryotic groups.

The Golgi matrix protein giantin is required for normal cilia function in zebrafish

The Golgi is essential for glycosylation of newly synthesised proteins including almost all cell-surface and extracellular matrix proteoglycans. Giantin, encoded by the golgb1 gene, is a member of the golgin family of proteins that reside within the Golgi stack, but its function remains elusive. Loss of function of giantin in rats causes osteochondrodysplasia; knockout mice show milder defects, notably a cleft palate. In vitro, giantin has been implicated in Golgi organisation, biosynthetic trafficking, and ciliogenesis. Here we show that loss of function of giantin in zebrafish, using either morpholino or knockout techniques, causes defects in cilia function. Giantin morphants have fewer cilia in the neural tube and those remaining are longer. Mutants have the same number of cilia in the neural tube but these cilia are also elongated. Scanning electron microscopy shows that loss of giantin results in an accumulation of material at the ciliary tip, consistent with a loss of function of retrograde intraflagellar transport. Mutants show milder defects than morphants consistent with adaptation to loss of giantin.

Summary: Morpholino knockdown of Golgb1/giantin leads to a severe cilopathy phenotype twinned with longer, misshapen cilia. Stable mutants have a very mild phenotype, indicative of compensation, but still have longer cilia.

Identification of novel MYO18A interaction partners required for myoblast adhesion and muscle integrity

The unconventional myosin MYO18A that contains a PDZ domain is required for muscle integrity during zebrafish development. However, the mechanism by which it functions in myofibers is not clear. The presence of a PDZ domain suggests that MYO18A may interact with other partners to perform muscle-specific functions. Here we performed double-hybrid screening and co-immunoprecipitation to identify MYO18A-interacting proteins, and have identified p190RhoGEF and Golgin45 as novel partners for the MYO18A PDZ domain. We have also identified Lurap1, which was previously shown to bind MYO18A. Functional analyses indicate that, similarly as myo18a, knockdown of lurap1, p190RhoGEF and Golgin45 by morpholino oligonucleotides disrupts dystrophin localization at the sarcolemma and produces muscle lesions. Simultaneous knockdown of myo18a with either of these genes severely disrupts myofiber integrity and dystrophin localization, suggesting that they may function similarly to maintain myofiber integrity. We further show that MYO18A and its interaction partners are required for adhesion of myoblasts to extracellular matrix, and for the formation of the Golgi apparatus and organization of F-actin bundles in myoblast cells. These findings suggest that MYO18A has the potential to form a multiprotein complex that links the Golgi apparatus to F-actin, which regulates muscle integrity and function during early development.

Golgb1 regulates protein glycosylation and is crucial for mammalian palate development

Cleft palate is a common major birth defect for which currently known causes account for less than 30% of pathology in humans. In this study, we carried out mutagenesis screening in mice to identify new regulators of palatogenesis. Through genetic linkage mapping and whole-exome sequencing, we identified a loss-of-function mutation in the Golgb1 gene that co-segregated with cleft palate in a new mutant mouse line. Golgb1 is a ubiquitously expressed large coiled-coil protein, also known as giantin, that is localized at the Golgi membrane. Using CRISPR/Cas9-mediated genome editing, we generated and analyzed developmental defects in mice carrying additional Golgb1 loss-of-function mutations, which supported a crucial requirement for Golgb1 in palate development. Through maxillary explant culture assays, we demonstrate that the Golgb1 mutant embryos have intrinsic defects in palatal shelf elevation. Just prior to the developmental stage of palatal shelf elevation in wild-type littermates, Golgb1 mutant embryos exhibit increased cell density, reduced hyaluronan accumulation and impaired protein glycosylation in the palatal mesenchyme. Together, these results demonstrate that, although it is a ubiquitously expressed Golgi-associated protein, Golgb1 has specific functions in protein glycosylation and tissue morphogenesis.

The PDZ-containing unconventional myosin XVIIIA regulates embryonic muscle integrity in zebrafish

Myosin XVIIIA, or MYO18A, is a unique PDZ domain-containing unconventional myosin and is evolutionarily conserved from Drosophila to vertebrates. Although there is evidence indicating its expression in the somites, whether it regulates muscle function remains unclear. We show that the two zebrafish myo18a genes (myo18aa and myo18ab) are predominantly expressed at somite borders during early developmental stages. Knockdown of these genes or overexpression of the MYO18A PDZ domain disrupts myofiber integrity, induces myofiber lesions, and compromises the localization of dystrophin, α-dystroglycan (α-DG) and laminin at the myotome boundaries. Cell transplantation experiments indicate that myo18a morphant myoblasts fail to form elongated myofibers in the myotomes of wild-type embryos, which can be rescued by the full-length MYO18A protein. These results suggest that MYO18A likely functions in the adhesion process that maintains the stable attachment of myofibers to ECM (extracellular matrix) and muscle integrity during early development.

Characterization of Golgi scaffold proteins and their roles in compartmentalizing cell signaling

Subcellular compartmentalization has become an important theme in cell signaling. In particular, the Golgi apparatus (GA) plays a prominent role in compartmentalizing signaling cascades that originate at the plasma membrane or other organelles. To precisely regulate this process, cells have evolved a unique class of organizer proteins, termed "scaffold proteins". Sef, PAQR3, PAQR10 and PAQR11 are scaffold proteins that have recently been identified on the GA and are referred to as Golgi scaffolds. The major cell growth signaling pathways, such as Ras/MAPK, PI3K/AKT, insulin and VEGF (vascular endothelial growth factor), are tightly regulated spatially and temporally by these Golgi scaffolds to ensure a physiologically appropriate outcome. Here, we discuss the subcellular localization and characterization of the topology and functional domains of these Golgi scaffolds and summarize their roles in the compartmentalization of cell signaling. We also highlight the physiological and pathological roles of these Golgi scaffolds in tumorigenesis and developmental disorders.