Graff Meyer, A. | Search bioRxiv

bioRxiv2026

Fine ultrastructural organization of glomerular neuropil in the developing zebrafish olfactory bulb

Across animal phyla, odor information is represented in the first olfactory processing center by combinatorial activation of discrete glomeruli. To examine how this organization of olfactory processing channels emerges during development we combined 2-photon calcium imaging, volume electron microscopy, and large-scale automated neuron reconstruction in zebrafish larvae. We focused on a developmental stage (130 hours post fertilization) when the olfactory bulb (OB) is structured into ~16 large neuropil regions referred to as protoglomeruli but most glomeruli are not yet differentiated. Our ultrastructural reconstructions revealed that protoglomeruli are organized into smaller units referred to as microglomeruli, each of which is defined by a distinct set of mitral cells with overlapping, spatially confined dendritic arbors. Neighboring microglomeruli were innervated by distinct subsets of sensory axons and activity was more highly correlated among mitral cells associated with the same microglomerulus than across microglomeruli of the same or different protoglomeruli. These results reveal a precise subcellular organization of the neuropil in the developing OB into distinct processing channels, indicating that the layout of the adult glomerular array is established already early in development.

neuroscience↗

bioRxiv2025

A model of apical-out human first trimester trophoblast organoids to study regeneration after syncytial damage

The villous syncytiotrophoblast in humans is the interface between maternal blood and the placenta and its functions are essential for a successful pregnancy. The syncytium can be damaged in vivo focally by high-velocity and turbulent maternal blood flow, or more globally by oxidative stress. It then quickly regenerates, a process critical for the maintenance of placental functions including nutrient transfer and protection from infections. To investigate this process, we developed apical-out trophoblast organoids from first-trimester placentas and induced mechanical damage to the syncytium. We observed spontaneous regeneration of syncytiotrophoblast both morphologically and functionally. TNFRSF12A, the TWEAK receptor, was identified as a potential enhancer of syncytiotrophoblast regeneration. Supplementation with recombinant TWEAK in organoids increased the expression of cell proliferation and fusion markers, promoting syncytiotrophoblast formation. The source of TWEAK was found to be macrophages derived from maternal blood monocytes that adhere to sites of syncytiotrophoblast damage in vivo. This in vitro model that allows the exploration of syncytial biology has relevance for important pregnancy disorders including pre-eclampsia, where breaks occur more often, and vertical infections, where maternal monocytes could be a source of transmission.

developmental biology↗

bioRxiv2021

Loss of hepatic Lgr4 and Lgr5 promotes nonalcoholic fatty liver disease

Background & AimsThe Rspo-Lgr4/5-Znrf3/Rnf43 module is a master regulator of hepatic Wnt/{beta}-catenin signaling and metabolic zonation, but its impact on nonalcoholic fatty liver disease (NAFLD) remains unclear. We studied whether liver-specific loss of the Wnt/{beta}-catenin modulators Leucine-Rich Repeat-Containing G Protein-Coupled Receptor 4/5 (Lgr4/5) promotes nonalcoholic fatty liver disease (NAFLD). MethodsMice with liver-specific deletion of both receptors Lgr4/5 (Lgr4/5dLKO) were fed with normal diet (ND) or high fat diet (HFD). Livers of these mice were analyzed for lipid and fibrotic content by tissue staining and immunohistochemistry (IHC), and lipoproteins, inflammation and liver enzyme markers were measured in blood. Mechanistic insights into hepatic lipid accumulation were obtained by using ex vivo primary hepatocyte cultures derived from the Lgr4/5dLKO mice. Lipid analysis of mouse livers was performed by mass spectrometry (MS)-based untargeted lipidomic analysis. ResultsWe demonstrated that liver-specific ablation of Lgr4/5-mediated Wnt signaling resulted in hepatic steatosis, impaired bile acid (BA) secretion and predisposition to liver fibrosis. Under HFD conditions, we observed progressive intrahepatic fat accumulation, developing into macro-vesicular steatosis. Serum lipoprotein levels in HFD-fed Lgr4/5dLKO mice were decreased, rather than increased, suggesting that accumulation of fat in the liver was due to impaired lipid secretion by hepatocytes. Our lipidome analysis revealed a severe alteration of several lipid species in livers of Lgr4/5dLKO mice, including triacylglycerol estolides (TG-EST), a storage form of bioactive free fatty acid (FA) esters of hydroxy FAs (FAHFAs). ConclusionsLoss of hepatic Wnt/{beta}-catenin activity by Lgr4/5 deletion led to deregulation of lipoprotein pathways, loss of BA secretion, intrinsic alterations of lipid homeostasis and the onset of NAFLD. Lay summaryThe Wnt/{beta}-catenin pathway plays an important role during development and tissue homeostasis. Loss of Wnt/{beta}-catenin activity in mouse liver leads to loss of liver zonation, but the impact on nonalcoholic fatty liver disease (NAFLD) remains unclear. We show that livers of mice developed steatosis upon deletion of the positive pathway regulators Lgr4/5. Livers of knock-out (KO) mice exhibited altered lipid composition due to impaired lipid secretion. Furthermore, livers of these mice developed a nonalcoholic steatohepatitis (NASH)-like phenotype and fibrotic features derived from activated hepatic stellate cells. Our data demonstrate a protective role of Wnt/{beta}-catenin pathway activity towards the development of NAFLD. HighlightsO_LIAbrogation of hepatic Wnt/{beta}-catenin activity and liver zonation upon Lgr4/5 deletion in mice led to hepatic steatosis. C_LIO_LILiver fat accumulation was caused by impaired lipid secretion from hepatocytes. C_LIO_LISteatotic livers contained increased levels of diverse lipid species, including polyunsaturated fatty acids and triglycerol-estolides. C_LIO_LIThese data confirmed that a decrease in Wnt/{beta}-catenin signaling led to the development of nonalcoholic fatty liver disease (NAFLD) in mice. C_LI

physiology↗