van Es, J. | Search bioRxiv

bioRxiv2025

Human embryo implantation involves Syncytin-2/MFSD2A-mediated heterokaryon formation with maternal endometrium

Human embryo implantation involves attachment of the blastocyst to the endometrial epithelium to subsequently gain access to the underlying stromal compartment. The blastocyst is believed to cross the epithelium either by migration through, or upon apoptosis of, the endometrial epithelial cell layer. Yet, how the blastocyst exactly traverses the endometrial epithelium remains unknown. Here, we describe an in vitro implantation model of human blastoids and hormonally matured endometrial organoids amenable to high-resolution live imaging. We demonstrate that the initial step of implantation is mediated by the direct fusion of blastoid cells with endometrial epithelial cells. Blastoids express the fusion proteins Syncytin-1 and -2, while the endometrial epithelium mainly expresses the fusion co-receptor for Syncytin-2, called MFSD2A. CRISPR-induced loss of MFSD2A in the endometrial epithelium prevents blastoids from attaching and abolishes fusion. Together, these findings support a model in which fetal-maternal cell fusion constitutes the critical initiating mechanism of human embryo implantation, with endometrial MFSD2A playing an indispensable role in this process.

developmental biology↗

bioRxiv2025

BEST4/CA7+ and goblet cells are interdependent regulators of intestinal mucus homeostasis

The intestinal mucus layer is essential for the integrity of the intestinal barrier. It is produced by goblet cells, whose depletion is common in colonic inflammation but remains poorly understood. Here, we show that goblet cell survival relies on a reciprocal dependence with newly discovered BEST4/CA7+ cells. We developed a method to follow BEST4/CA7+ and goblet cells in time from birth to death in human colon organoids. Notably, goblet cells induce BEST4/CA7+ fates in sister cells and other neighbors, using DLL1-mediated lateral activation of Notch-signaling. BEST4/CA7+ cells in turn promote goblet survival, with the latter depleting rapidly after differentiation in absence of BEST4/CA7+ cells. This apoptosis inhibition does not require direct cell-cell contact and instead depends on their shared lumen. Such differentiation and survival interdependencies may be relevant beyond the maintenance of mucosal homeostasis.

cell biology↗

bioRxiv2025

A collection of patient-derived intestinal organoid lines reveals epithelial phenotypes associated with genetic drivers of pediatric inflammatory bowel disease

Pediatric Inflammatory Bowel Disease (IBD) is a chronic condition characterized by per-sistent intestinal inflammation in children and adolescents. Despite a rising global incidence, the underlying causes and optimal management strategies for pediatric IBD are still not fully understood. Compared to adult IBD, pediatric IBD frequently presents with distinct disease phenotypes, and is more commonly linked to rare monogenic variants that cause intestinal epithelial barrier dysfunction or affect the function of mucosal immune cells. While more than 100 genes have been associated with early-onset IBD, the roles of many of these genes in the intestinal epithelium and the mechanisms by which genetic variants contribute to disease remain poorly defined. Here we aimed to improve our understanding of intestinal epithelium dysfunction in early-onset IBD by conducting extensive molecular and cellular characterization to gain insights into patient-specific epithelial phenotypes and identify therapeutic targets. We generated intestinal epithelial organoids (IEOs) from 94 pediatric IBD patients, representing diverse clinical characteristics and including those with monogenic variants (BTK n=4, TTC7A n=3, IL10RA n=1, LRBA n=1, STXBP2 n=1, TTC37 n=1, TRNT1 n=1, PLCG2 n=1, DKC1 n=1, POLA1 n=1), and 46 non-IBD controls. This effort resulted in the largest RNA-seq dataset of pediatric IBD intestinal epithelial organoids to date, encompassing both baseline conditions and post-immunological stimulation, serving as a valuable resource for future research. We observed that IEOs effectively initiate inflammation upon stimulation with bacterial lysate, regardless of disease status, origin, or mutation status. Inflammatory stimulation triggered single-gene upregulation of IBD-linked SERPINA1 and LIFR across the IBD population compared to controls, suggesting their role in intestinal epithelial innate immune responses. However, co-expression network analysis showed no consistent transcriptional signatures across the entire IBD group at the systems level. Instead, differences emerged between controls and specific genotypes (TTC7A, STXBP2, LRBA), with STXBP2 and LRBA sharing an upregulated transcriptional response of IL-1 and SLC30-mediated zinc trafficking pathways. These findings underscore the potential of IEOs as a valuable model for studying IBD and offer key insights that could guide the development of targeted therapies for both monogenic and non-monogenic forms of IBD. O_FIG O_LINKSMALLFIG WIDTH=158 HEIGHT=200 SRC="FIGDIR/small/659052v2_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@10a4d9org.highwire.dtl.DTLVardef@b6cdadorg.highwire.dtl.DTLVardef@179216dorg.highwire.dtl.DTLVardef@181a4e4_HPS_FORMAT_FIGEXP M_FIG C_FIG

genetics↗