Glycosylation orchestrates megakaryocytic fate of hematopoietic stem cells via Wnt-MUC13 signaling.

Hematopoietic stem and progenitor cells (HSPCs) sustain blood production through tightly regulated fate decisions. Disruption of this control underlies disorders such as myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), and inherited thrombocytopenias. While transcriptional and epigenetic regulation of HSPCs is well established, the contribution of glycosylation has remained largely unexplored. Here, we identify the glycosyltransferase B4GALT1 as a central regulator of hematopoiesis that integrates extrinsic niche cues with intrinsic transcriptional programs. B4GALT1 shapes the bone marrow microenvironment by generating complex glycan niches that support HSPC function. However, its deficiency produces oncogenic glycan signatures, disrupts HSPC niche integrity, and induces aberrant expression of Mucin 13 (MUC13). These changes expand stem and progenitor pools, enforce megakaryocyte lineage bias, and activate the Wnt-MUC13/β-catenin signaling axis, a pathway tightly linked to proliferation and malignant transformation. Consequently, B4GALT1 loss uncouples proliferation from self-renewal, altering key regulators of stem cell quiescence, lineage balance, and marrow homeostasis. Our findings define a previously unrecognized glycan-dependent regulatory axis that directs HSPC fate through coordinated transcriptional reprogramming, signaling modulation, and niche remodeling. This work establishes aberrant glycosylation as a driver of hematopoietic dysfunction and highlights B4GALT1 as a potential therapeutic target in stem cell-driven blood disorders.