Complement facilitates developmental microglial pruning of astrocyte and vascular networks

Microglia, the resident immune cell of the central nervous system, play a pivotal role in facilitating neurovascular development through mechanisms that are not fully understood. This current work resolves a previously unknown role for microglia in facilitating the developmental pruning of the astrocytic template resulting in a spatially organized retinal vascular bed. Mechanistically, our study identified that local microglial expression of complement (C)3 and C3aR is necessary for the regulation of astrocyte patterning and vascular growth during retinal development. Ablation of retinal microglia, loss of C3 or C3aR reduced developmental pruning and clearance of astrocytic bodies leading to increased astrocyte density leading to altered vascular patterning during retinal vascular development. This data demonstrates that C3/C3aR signaling is an important checkpoint required for the finetuning of vascular density during neuroretinal development.

Coagulation Factor IIIa (f3a) Knockdown in Zebrafish Leads to Defective Angiogenesis and Mild Bleeding Phenotype

Aim: Tissue factor (TF), an initiator of the extrinsic coagulation pathway, is crucial for embryogenesis, as mice lacking TF are embryonically lethal (E10.5). This lethality may be attributed to defects in vascular development and circulatory failure, suggesting additional roles for TF in embryonic development beyond coagulation. In this study, we characterized the role of one of the TF paralogs (f3a) using a zebrafish model. Methods: To understand the TF evolution across different species, we performed molecular phylogenetic and sequence homology analysis. The expression of f3a during embryonic developmental stages was determined by RT-PCR. Endothelial-specific transgenic lines of zebrafish (flk1:egfp-NLS/kdrl:mCherry-CAAX) was used to image the vascular development. The role of f3a during embryonic development was investigated by mRNA knockdown using Morpholinos (MO), an antisense-based oligonucleotide strategy. The f3a morphants were examined at 52 hpf for defects in morphological appearance, bleeding, and vascular patterning. Results: Spatiotemporal expression of f3a by qPCR revealed expression in all developmental stages, suggesting that f3a transcripts are both maternally and zygotically expressed. High expression of f3a from 28 hpf to 36 hpf confirmed the role of in the development of the yolk sac, circulation, and fins. f3a MO-injected embryos showed morphological abnormalities, including shorter body lengths and crooked tails. O-dianisidine staining showed f3a MO-injected embryos exhibited bleeding in the trunk (5.44%) and head (9.52%) regions. Using endothelial-specific transgenic lines of zebrafish (flk1:egfp-NLS/kdrl:mCherry-CAAX), imaging of caudal vein plexus, which forms immediately following the onset of circulation and sprouting, showed a 3-fold decrease in f3a morphants versus controls at 48 hpf, suggesting a potential role for f3a in flow-induced angiogenesis.

Wasp controls oriented migration of endothelial cells to achieve functional vascular patterning

Endothelial cell migration and proliferation are essential for the establishment of a hierarchical organization of blood vessels and optimal distribution of blood. However, how these cellular processes are quantitatively coordinated to drive vascular network morphogenesis remains unknown. Here, using the zebrafish vasculature as a model system, we demonstrate that the balanced distribution of endothelial cells as well as the resulting regularity of vessel caliber, is a result of cell migration from veins towards arteries and cell proliferation in veins. We identify the Wiskott-Aldrich Syndrome protein (WASp) as an important molecular regulator of this process and show that loss of coordinated migration from veins to arteries upon wasb depletion results in aberrant vessel morphology and the formation of persistent arteriovenous shunts. We demonstrate that WASp achieves its function through the coordination of junctional actin assembly and PECAM1 recruitment and provide evidence that this is conserved in human. Overall, we demonstrate that functional vascular patterning in the zebrafish trunk is established through differential cell migration regulated by junctional actin, and that interruption of differential migration may represent a pathomechanism in vascular malformations.

Bilateral Corneal Ghost Vessels in an Otherwise Healthy Child

We report a rare case of bilateral corneal ghost vessels in a 6–year-old child with an unremarkable past ocular and past medical history. This study was a single observational case report. A 6-year-old girl was referred to our clinic for further evaluation, due to suboptimal visual acuity in both eyes. Her past medical and ocular history revealed no systemic, inflammatory, infectious, or degenerative disorders. Slit-lamp examination revealed regressed blood vessels (“ghost vessels”) in the anterior and mid-corneal stroma as the only pathologic finding. Confocal scanning microscopy of both corneas demonstrated scattered branching railroad-shaped ghost vessels at the level of the middle and anterior stroma. Complete systemic workup was performed for the patient. No identifiable risk factor for the development of corneal vascularization was found. According to our findings, we assume that in our patient, vasculogenesis occurred due to angioblast invasion to the presumptive cornea due to disequilibrium in mechanisms involved in vascular patterning during embryonic development.

Molecular Genetic Characteristics of Different Scenarios of Xylogenesis on the Example of Two Forms of Silver Birch Differing in the Ratio of Structural Elements in the Xylem

Silver birch (Betula pendula Roth) is an economically important species in Northern Europe. The current research focused on the molecular background of different xylogenesis scenarios in the birch trunks. The study objects were two forms of silver birch, silver birch trees, and Karelian birch trees; the latter form is characterized by the formation of two types of wood, non-figured (straight-grained) and figured, respectively, while it is currently not clear which factors cause this difference. We identified VND/NST/SND genes that regulate secondary cell wall biosynthesis in the birch genome and revealed differences in their expression in association with the formation of xylem with different ratios of structural elements. High expression levels of BpVND7 accompanied differentiation of the type of xylem which is characteristic of the species. At the same time, the appearance of figured wood was accompanied by the low expression levels of the VND genes and increased levels of expression of NST and SND genes. We identified BpARF5 as a crucial regulator of auxin-dependent vascular patterning and its direct target—BpHB8. A decrease in the BpARF5 level expression in differentiating xylem was a specific characteristic of both Karelian birch with figured and non-figured wood. Decreased BpARF5 level expression in non-figured trees accompanied by decreased BpHB8 and VND/NST/SND expression levels compared to figured Karelian birch trees. According to the results obtained, we suggested silver birch forms differing in wood anatomy as valuable objects in studying the regulation of xylogenesis.

Established, New and Emerging Concepts in Brain Vascular Development

In this review, we discuss the state of our knowledge as it relates to embryonic brain vascular patterning in model systems zebrafish and mouse. We focus on the origins of endothelial cell and the distinguishing features of brain endothelial cells compared to non-brain endothelial cells, which is revealed by single cell RNA-sequencing methodologies. We also discuss the cross talk between brain endothelial cells and neural stem cells, and their effect on each other. In terms of mechanisms, we focus exclusively on Wnt signaling and the recent developments associated with this signaling network in brain vascular patterning, and the benefits and challenges associated with strategies for targeting the brain vasculature. We end the review with a discussion on the emerging areas of meningeal lymphatics, endothelial cilia biology and novel cerebrovascular structures identified in vertebrates.