Biology subjects

Schulte-Merker, S.

Publications and source records attributed to Schulte-Merker, S..

12 recordsLinked to original sources

bioRxiv2025

The protein-tyrosine phosphatase Shp2 is essential for lymphatic endothelial cell differentiation in zebrafish

Mutations in genes associated with the VEGFC/VEGFR3 signaling pathway are strongly linked to a range of developmental and functional defects in the lymphatic system. PTPN11 encodes SHP2, a protein-tyrosine phosphatase that plays a critical role in receptor protein-tyrosine kinase (RTK) signaling. In this study, we investigated lymphangiogenesis in mutant zebrafish embryos lacking functional Shp2 and demonstrate that Shp2 is essential for normal lymphatic development in the trunk and head regions of zebrafish embryos. Embryos lacking functional Shp2 failed to develop lymphatic vessels and lymphatic endothelial cells (LECs), whereas venous intersegmental vessel (vISV) formation remained unaffected. While endothelial cells sprouted normally from the posterior cardinal vein (PCV), they did not migrate to the horizontal myoseptum to form parachordal lymphangioblast (PL) cells. Rescue experiments using Shp2 mutants demonstrated that catalytic activity and signaling properties of Shp2 are required for restoration of normal lymphangiogenesis. These findings highlight a pivotal role for Shp2 signaling in the migration and differentiation of lymphatic endothelial cells without affecting venous angiogenesis.

developmental biology↗

bioRxiv2025

SVEP1 enables efficient binding of Angiopoietin-2 to the TIE1 receptor, allowing receptor phosphorylation and downstream signaling

The molecular mechanisms that drive (lymph-)angiogenesis are crucial to understand diseases, such as lymphedema, that are caused due to malformations of the lymphatic vasculature. Recently, an interaction between the secreted protein Svep1, a key regulator in lymphangiogenesis, and the transmembrane receptor Tie1 was shown in zebrafish, human, and mice. Here, guided by in silico AlphaFold-multimer structure predictions of SVEP1 complexes, we assert with protein binding studies that the human CCP20 domain is the primary binding site for TIE1. We further demonstrate that SVEP1 mediates strong binding of ANG2 and TIE1, and that combined stimulation of hdLECs with SVEP1 and ANG2 leads to phosphorylation of TIE1. TIE1 activation by SVEP1 and ANG2 enables downstream signaling and, in turn, potentiates nuclear exclusion of FOXO1 and phosphorylation of AKT compared to SVEP1 or ANG2 alone. We present a model in which ANG1/2 dimers bind to both SVEP1 and TIE1, resulting in the recruitment of multiple TIE1 receptor molecules to a multimeric complex at the cell membrane, potentially amplifying its signaling capacity.

developmental biology↗

bioRxiv2024

Integration of ATAC and RNA-sequencing identifies chromatin and transcriptomic signatures in classical and non-classical zebrafish osteoblasts and indicates mechanisms of entpd5a regulation

Two types of osteoblasts are required to assemble the zebrafish embryonic skeleton: classical osteoblasts homologous to the mammalian cell, and notochord sheath cells, which serve as non-classical osteoblasts. The gene entpd5a is critically required for ossification via both types of osteoblasts. Despite the indispensability of zebrafish models in vertebrate research, the genetic regulation of bone formation, as well as mechanisms of transcriptional control of entpd5a, remain largely unknown. Here, using a newly generated transgenic line, we isolate classical and non-classical osteoblasts from zebrafish embryos and performed both ATAC-seq and RNA-seq. We analysed results independently and integratively to understand those chromatin dynamics and accompanying transcriptomic changes that occur in different skeletal cell types. We show that although Dlx family factors are playing important roles in classical osteoblast regulation, Hox family factors are involved in governing spinal ossification via non-classical osteoblasts. We further present a resource-driven analysis of the entpd5a promoter, experimentally validating the ATAC-seq dataset and proposing mechanisms of regulating the complex entpd5a expression pattern during zebrafish osteogenesis. Our results thus provide a necessary comprehensive resource for the field of bone development and indicate spatio-temporally regulated promoter/enhancer interactions taking place in the entpd5a locus.

developmental biology↗

bioRxiv2023

Angpt1 binding to Tie1 regulates the signaling required for lymphatic vessel development in zebrafish

Development of the vascular system is regulated by multiple signaling pathways mediated by receptor tyrosine kinases (RTKs). Among them, Angiopoietin (Ang)/Tie signaling regulates lymphatic and blood vessel development in mammals. Of the two Tie receptors, Tie2 is well known as a key mediator of Ang/Tie signaling, but unexpectedly, recent studies reveal that the Tie2 locus has been lost in many vertebrate species, while the Tie1 gene is more commonly present. However, Tie1-driven signaling pathways, including ligands and cellular functions, are not well understood. Here, we performed comprehensive mutant analyses of Angiopoietins and Tie receptors in zebrafish and found that only angpt1 and tie1 mutants show defects in trunk lymphatic vessel development. Among zebrafish Angiopoietins, only Angpt1 binds to Tie1 as a ligand. We indirectly monitored Ang1/Tie1 signaling and detected Tie1 activation in sprouting endothelial cells (ECs), where Tie1 inhibits nuclear import of EGFP-Foxo1a. Angpt1/Tie1 signaling functions in EC migration, proliferation, and lymphatic specification during early lymphangiogenesis, at least in part by modulating Vegfc/Vegfr3 signaling. Thus, we show Angpt1/Tie1 signaling to constitute an essential signaling pathway for lymphatic development in zebrafish. Brief Summary StatementZebrafish Angpt1/Tie1 signaling is characterized as an essential signaling pathway for trunk lymphatic development, with Tie1 regulating Foxo1 localization and modulating Vegfc/Vegfr3 signaling.

developmental biology↗

bioRxiv2022

svep1 and tie1 genetically interact and affect aspects of facial lymphatic development in a Vegfc-independent manner

Multiple factors are required to form functional lymphatic vessels. Here, we uncover an essential role for the secreted protein Svep1 and the transmembrane receptor Tie1 during the development of subpopulations of the zebrafish facial lymphatic network. This specific aspect of the facial network forms independently of Vegfc signalling, which otherwise is the most prominent signalling axis in all other lymphatic beds. Additionally, we find that multiple specific and newly uncovered phenotypic hallmarks of svep1 mutants are also present in tie1, but not in tie2 or vegfc mutants. These phenotypes are observed in the lymphatic vasculature of both head and trunk, as well as in the development of the dorsal longitudinal anastomotic vessel (DLAV) under reduced flow conditions. Furthermore, we show genetic interaction between svep1 and tie1 during the migration of parachordal lymphangioblasts (PLs). Therefore, our study demonstrates an important function for Tie1 signalling during lymphangiogenesis as well as blood vessel development in zebrafish and provides the first in vivo evidence for zebrafish Svep1 and Tie1 interaction. Since compound heterozygous mutations for SVEP1 and TIE2 have recently been reported in human glaucoma patients, our data have clinical relevance in demonstrating a role for Svep1 in Tie signalling in an in vivo setting.

developmental biology↗

bioRxiv2022

Neural plate progenitors give rise to both anterior and posterior pituitary cells

The pituitary is the master neuroendocrine gland, which regulates body homeostasis. It consists of the anterior pituitary/adenohypophysis (AH), which harbors hormones producing cells and the posterior pituitary/neurohypophysis (NH), which relays the direct passage of hormones from the brain to the periphery. It is widely accepted that the AH originates from the oral ectoderm (Rathkes pouch) whereas the neural ectoderm contributes to the NH. Using single cell transcriptomics of the zebrafish pituitary we characterized cyp26b1-positive pituicyte of the NH and prop1-positive adenohypophyseal progenitors. We found that these cell types expressed common markers implying lineage relatedness. Genetic tracing revealed that in contrast to the prevailing dogma, neural plate precursors of both zebrafish (her4.3+) and mouse (Sox1+) contribute to both the neurohypophyseal and adenohypophyseal cells. We further show that pituicytes and prop1+ progenitors reside in close anatomical proximity and pituicyte-derived RA-degrading enzyme Cyp26b1 fine-tunes differentiation of prop1+ progenitors into hormone-producing cells. These results challenge the notion that AH cells are exclusively derived from non-neural ectoderm and demonstrate that a cross-talk between neuro- and adeno-hypophyseal cells fine-tunes the development of pituitary neuroendocrine cells.

developmental biology↗

bioRxiv2021

Svep1 stabilizes developmental vascular anastomosis in reduced flow conditions.

We report the discovery that flow and Svep1 are modulator of vessel anastomosis during developmental angiogenesis in zebrafish embryos. We show that loss of Svep1 and blood flow reduction both contribute to defective anastomosis of intersegmental vessels. We show that this defect in primary angiogenic sprouts is associated with an expansion of Apelin-positive tip cells and with reduced formation and lumenisation of the dorsal longitudinal anastomotic vessel. Mechanistically, our results suggest that flow and Svep1 act synergistically to modulate vascular network formation in the zebrafish trunk.

developmental biology↗

bioRxiv2020

Zinc dysregulation in slc30a8 (znt8) mutant zebrafish leads to blindness and disrupts bone mineralisation

Zinc is an essential cofactor for many cellular processes including gene transcription, insulin secretion and retinal function. Excessive free Zn2+ is highly toxic and consequently intracellular zinc is tightly controlled by a system of transporters, metallothioneins (MTs) and storage vesicles. Here we describe the developmental consequences of a missense allele of zinc efflux transporter slc30a8 (znt8) in zebrafish. Homozygous slc30a8hu1798 larvae are virtually blind and develop very little or no bone mineral. We show that zinc is stored in pigmented cells (melanophores) of healthy larvae but in slc30a8hu1798 mutants it instead accumulates in the bone and brain. Supporting a role for pigment cells in zinc homeostasis, nacre zebrafish, which lack melanophores, also show disrupted zinc homeostasis. The photoreceptors of slc30a8hu1798 fish are severely depleted while those of nacre fish are enriched with zinc. We propose that developing zebrafish utilise pigmented cells as a zinc storage organ, and that Slc30a8 is required for transport of zinc into these cells and into photoreceptors.

physiology↗

bioRxiv2020

Phosphatidylinositol-3 kinase activity controls survival and stemness of zebrafish hematopoietic stem/progenitor cells

Hematopoietic Stem and Progenitor Cells (HSPCs) are multipotent cells giving rise to all blood lineages during life. HSPCs emerge from the ventral wall of the dorsal aorta (VDA) during a specific timespan in embryonic development through endothelial hematopoietic transition (EHT). We investigated the ontogeny of HSPCs in mutant zebrafish embryos lacking functional pten, an important tumor suppressor with a central role in cell signaling. Through in vivo live imaging, we discovered that in pten mutant embryos a proportion of the HSPCs died upon emergence from the VDA, an effect rescued by inhibition of phosphatidylinositol-3 kinase (PI3K). Surprisingly, inhibition of PI3K in wild type embryos also induced HSPC death. Surviving HSPCs colonized the caudal hematopoietic tissue (CHT) normally and committed to all blood lineages. Single cell RNA sequencing indicated that inhibition of PI3K enhanced survival of multi-potent progenitors, whereas the number of HSPCs with more stem-like properties was reduced. At the end of the definitive wave, loss of Pten caused a shift to more restricted progenitors at the expense of HSPCs. We conclude that PI3K signaling tightly controls HSPCs survival and both up- and downregulation of PI3K signaling reduces stemness of HSPCs. 2 Key pointsO_LILoss of Pten and inhibition of PI3K induced apoptosis of hematopoietic stem/progenitor cells upon endothelial to hematopoietic transition C_LIO_LISurviving hematopoietic stem/progenitor cells committed to all blood lineages but displayed reduced stemness C_LI

developmental biology↗

bioRxiv2019

Meningeal lymphatic endothelial cells fulfill scavenger endothelial cell function and employ Mrc1a for cargo uptake

Brain lymphatic endothelial cells (BLECs) constitute a group of loosely connected endothelial cells within the meningeal layer of the zebrafish brain. We previously reported that BLECs efficiently endocytose extracellular cargo molecules (van Lessen et al., 2017), but how this is accomplished and controlled on the molecular level remains unclear. We here compare BLECs to scavenging endothelial cells (SECs) in the embryonic cardinal vein and find them to accept an identical set of substrate molecules. While there is redundancy in the type of scavenger receptors being used, the two cell populations rely for specific substrate molecules on different cell surface receptors to mediate their physiological role: Stab2 appears more critical within SECs in the cardinal vein, while BLECs depend more on the Mrc1a receptor for internalization of cargo. Given the striking similarities to the substrate specificity of cardinal vein SECs, we postulate that BLECs qualify functionally as SECs of the brain.

developmental biology↗

bioRxiv2018

Endothelin receptor Aa regulates proliferation and differentiation of Erb-dependant pigment progenitors in zebrafish

Skin pigment patterns are important, being under strong selection for multiple roles including camouflage and UV protection. Pigment cells underlying these patterns form from adult pigment stem cells (APSCs). In zebrafish, APSCs derive from embryonic neural crest cells, but sit dormant until activated to produce pigment cells during metamorphosis. The APSCs are set-aside in an ErbB signaling dependent manner, but the mechanism maintaining quiescence until metamorphosis remains unknown. Mutants for a pigment pattern gene, parade, exhibit ectopic pigment cells localised to the ventral trunk. We show that parade encodes Endothelin receptor Aa, expressed in the blood vessels. Using chemical genetics, coupled with analysis of cell fate studies, we show that the ectopic pigment cells derive from APSCs. We propose that a novel population of APSCs exists in association with medial blood vessels, and that their quiescence is dependent upon Endothelin-dependent factors expressed by the blood vessels.\n\nLay AbstractPigment patterns are crucial for the many aspects of animal biology, for example, providing camouflage, enabling mate selection and protecting against UV irradiation. These patterns are generated by one or more pigment cell-types, localised in the skin, but derived from specialised stem cells (adult pigment stem cells, APSCs). In mammals, such as humans, but also in birds and fish, these APSCs derive from a transient population of multipotent progenitor cells, the neural crest. Formation of the adult pigment pattern is perhaps best studied in the zebrafish, where the adult pigment pattern is formed during a metamorphosis beginning around 21 days of development. The APSCs are set-aside in the embryo around 1 day of development, but then remain inactive until that metamorphosis, when they become activated to produce the adult pigment cells. We know something of how the cells are set-aside, but what signals maintain them in an inactive state is a mystery. Here we study a zebrafish mutant, called parade, which shows ectopic pigment cells in the embryo. We clone the parade gene, identifying it as ednraa encoding a component of a cell-cell communication process, which is expressed in blood vessels. By characterising the changes in the neural crest and in the pigment cells formed, and by combining this with an innovative assay identifying drugs that prevent the ectopic cells from forming, we deduce that the ectopic cells in the larva derive from precocious activation of APSCs to form pigment cells. We propose that a novel population of APSCs are associated with the blood vessels, that these are held in a quiescent state by signals coming from these vessels, and that these signals depend upon ednraa. Together this opens up an exciting opportunity to identify the signals maintaining APSC quiescence in zebrafish.

developmental biology↗

bioRxiv2017

Wilms Tumor 1b defines a wound-specific sheath cell subpopulation associated with notochord repair

Regenerative therapy for degenerative spine disorders requires the identification of cells that can slow down and possibly reverse degenerative processes. Here, we identify a novel and unanticipated wound-specific notochord sheath cell subpopulation that expresses Wilms Tumor (WT) 1b following injury. Using live imaging in zebrafish, we show that localized damage leads to Wt1b expression in the sheath, and that wt1b+ cells migrate into the wound to form a stopper-like structure, likely to maintain structural integrity. At the wound wt1b+ and entpd5+ cells constitute distinct subpopulations, and mark the site of an extra vertebra that forms in an untypical manner via a cartilage intermediate. Surprisingly, wt1b+ cells become closely associated with the chordacentra and sustain wt1b expression for over 35 days during vertebra formation. Given that remnants of notochord cells remain in the adult intervertebral disc, the identification of novel subpopulations may have important implications for regenerative treatments for spine disorders.\n\nHighlightsO_LINotochord injury triggers wound-specific expression of wt1b in novel sheath subpopulation\nC_LIO_LIWT1b notochord sheath cells fill injury site and form stopper-like structure\nC_LIO_LIWT1b subpopulation marks site of a new vertebra that forms via a cartilage intermediate\nC_LIO_LIWT1b wound-specific subpopulation perdures throughout and after vertebra repair\nC_LI

developmental biology↗