Lymphatic vasculature in the central nervous system

The central nervous system (CNS) is considered as an immune privilege organ, based on experiments in the mid 20th century showing that the brain fails to mount an efficient immune response against an allogeneic graft. This suggests that in addition to the presence of the blood-brain barrier (BBB), the apparent absence of classical lymphatic vasculature in the CNS parenchyma limits the capacity for an immune response. Although this view is partially overturned by the recent discovery of the lymphatic-like hybrid vessels in the Schlemm’s canal in the eye and the lymphatic vasculature in the outmost layer of the meninges, the existence of lymphatic vessels in the CNS parenchyma has not been reported. Two potential mechanisms by which lymphatic vasculature may arise in the organs are: 1) sprouting and invasion of lymphatic vessels from the surrounding tissues into the parenchyma and 2) differentiation of blood endothelial cells into lymphatic endothelial cells in the parenchyma. Considering these mechanisms, we here discuss what causes the dearth of lymphatic vessels specifically in the CNS parenchyma

Peripheral nerve-derived VEGF promotes arterial differentiation via neuropilin 1-mediated positive feedback

In developing limb skin, peripheral nerves are required for arterial differentiation, and guide the pattern of arterial branching. In vitro experiments suggest that nerve-derived VEGF may be important for arteriogenesis, but its role in vivo remains unclear. Using a series of nerve-specific Cre lines, we show that VEGF derived from sensory neurons, motoneurons and/or Schwann cells is required for arteriogenesis in vivo. Arteriogenesis also requires endothelial expression of NRP1, an artery-specific coreceptor for VEGF^(164) that is itself induced by VEGF. Our results provide the first evidence that VEGF is necessary for arteriogenesis from a primitive capillary plexus in vivo, and show that in limb skin the nerve is indeed the principal source of this signal. They also suggest a model in which a `winner-takes-all' competition for VEGF may control arterial differentiation, with the outcome biased by a VEGF^(164)-NRP1 positive-feedback loop. Our results also demonstrate that nerve-vessel alignment is a necessary, but not sufficient, condition for nerve-induced arteriogenesis. Different mechanisms therefore probably underlie these endothelial patterning and differentiation processes

Neural crest stem cells undergo multilineage differentiation in developing peripheral nerves to generate endoneurial fibroblasts in addition to Schwann cells

Neural crest stem cells (NCSCs) persist in peripheral nerves throughout late gestation but their function is unknown. Current models of nerve development only consider the generation of Schwann cells from neural crest, but the presence of NCSCs raises the possibility of multilineage differentiation. We performed Cre-recombinase fate mapping to determine which nerve cells are neural crest derived. Endoneurial fibroblasts, in addition to myelinating and non-myelinating Schwann cells, were neural crest derived, whereas perineurial cells, pericytes and endothelial cells were not. This identified endoneurial fibroblasts as a novel neural crest derivative, and demonstrated that trunk neural crest does give rise to fibroblasts in vivo, consistent with previous studies of trunk NCSCs in culture. The multilineage differentiation of NCSCs into glial and non-glial derivatives in the developing nerve appears to be regulated by neuregulin, notch ligands, and bone morphogenic proteins, as these factors are expressed in the developing nerve, and cause nerve NCSCs to generate Schwann cells and fibroblasts, but not neurons, in culture. Nerve development is thus more complex than was previously thought, involving NCSC self-renewal, lineage commitment and multilineage differentiation

Essential role of the zinc finger transcription factor Casz1 for mammalian cardiac morphogenesis and development

Chromosome 1p36 deletion syndrome is one of the most common terminal deletions observed in humans and is related to congenital heart disease (CHD). However, the 1p36 genes that contribute to heart disease have not been clearly delineated. Human CASZ1 gene localizes to 1p36 and encodes a zinc finger transcription factor. Casz1 is required for Xenopus heart ventral midline progenitor cell differentiation. Whether Casz1 plays a role during mammalian heart development is unknown. Our aim is to determine 1p36 gene CASZ1 function at regulating heart development in mammals. We generated a Casz1 knock-out mouse using Casz1-trapped embryonic stem cells. Casz1 deletion in mice resulted in abnormal heart development including hypoplasia of myocardium, ventricular septal defect, and disorganized morphology. Hypoplasia of myocardium was caused by decreased cardiomyocyte proliferation. Comparative genome-wide RNA transcriptome analysis of Casz1 depleted embryonic hearts identifies abnormal expression of genes that are critical for muscular system development and function, such as muscle contraction genes TNNI2, TNNT1, and CKM; contractile fiber gene ACTA1; and cardiac arrhythmia associated ion channel coding genes ABCC9 and CACNA1D. The transcriptional regulation of some of these genes by Casz1 was also found in cellular models. Our results showed that loss of Casz1 during mouse development led to heart defect including cardiac noncompaction and ventricular septal defect, which phenocopies 1p36 deletion syndrome related CHD. This suggests that CASZ1 is a novel 1p36 CHD gene and that the abnormal expression of cardiac morphogenesis and contraction genes induced by loss of Casz1 contributes to the heart defect

Unique functions for Notch4 in murine embryonic lymphangiogenesis

Publisher Copyright: © 2021, The Author(s).In mice, embryonic dermal lymphatic development is well understood and used to study gene functions in lymphangiogenesis. Notch signaling is an evolutionarily conserved pathway that modulates cell fate decisions, which has been shown to both inhibit and promote dermal lymphangiogenesis. Here, we demonstrate distinct roles for Notch4 signaling versus canonical Notch signaling in embryonic dermal lymphangiogenesis. Actively growing embryonic dermal lymphatics expressed NOTCH1, NOTCH4, and DLL4 which correlated with Notch activity. In lymphatic endothelial cells (LECs), DLL4 activation of Notch induced a subset of Notch effectors and lymphatic genes, which were distinctly regulated by Notch1 and Notch4 activation. Treatment of LECs with VEGF-A or VEGF-C upregulated Dll4 transcripts and differentially and temporally regulated the expression of Notch1 and Hes/Hey genes. Mice nullizygous for Notch4 had an increase in the closure of the lymphangiogenic fronts which correlated with reduced vessel caliber in the maturing lymphatic plexus at E14.5 and reduced branching at E16.5. Activation of Notch4 suppressed LEC migration in a wounding assay significantly more than Notch1, suggesting a dominant role for Notch4 in regulating LEC migration. Unlike Notch4 nulls, inhibition of canonical Notch signaling by expressing a dominant negative form of MAML1 (DNMAML) in Prox1+ LECs led to increased lymphatic density consistent with an increase in LEC proliferation, described for the loss of LEC Notch1. Moreover, loss of Notch4 did not affect LEC canonical Notch signaling. Thus, we propose that Notch4 signaling and canonical Notch signaling have distinct functions in the coordination of embryonic dermal lymphangiogenesis.Peer reviewe

Tissue Specific Origin, Development, and Pathological Perspectives of Pericytes

Pericytes are mural cells surrounding blood vessels, adjacent to endothelial cells. Pericytes play critical roles in maturation and maintenance of vascular branching morphogenesis. In the central nervous system (CNS), pericytes are necessary for the formation and regulation of the blood-brain barrier (BBB) and pericyte deficiency accompanies CNS diseases including multiple sclerosis, diabetic retinopathy, neonatal intraventricular hemorrhage, and neurodegenerative disorders. Despite the importance of pericytes, their developmental origins and phenotypic diversity remain incompletely understood. Pericytes express multiple markers and the origin of pericytes differs by tissue, which may cause difficulty for the identification and understanding of the ontogeny of pericytes. Also, pericytes have the potential to give rise to different tissue

Whole-mount Confocal Microscopy for Adult Ear Skin: A Model System to Study Neuro-vascular Branching Morphogenesis and Immune Cell Distribution.

Here, we present a protocol of a whole-mount adult ear skin imaging technique to study comprehensive three-dimensional neuro-vascular branching morphogenesis and patterning, as well as immune cell distribution at a cellular level. The analysis of peripheral nerve and blood vessel anatomical structures in adult tissues provides some insights into the understanding of functional neuro-vascular wiring and neuro-vascular degeneration in pathological conditions such as wound healing. As a highly informative model system, we have focused our studies on adult ear skin, which is readily accessible for dissection. Our simple and reproducible protocol provides an accurate depiction of the cellular components in the entire skin, such as peripheral nerves (sensory axons, sympathetic axons, and Schwann cells), blood vessels (endothelial cells and vascular smooth muscle cells), and inflammatory cells. We believe this protocol will pave the way to investigate morphological abnormalities in peripheral nerves and blood vessels as well as the inflammation in the adult ear skin under different pathological conditions