Refinement of Megakaryocyte Lineage Commitment in Hematopoietic Stem and Progenitor Cells During Postnatal and Adult Hematopoiesis

Mammalian hematopoiesis ensures the continuous production of specialized blood cells, yet the mechanisms that govern megakaryocyte/erythroid (MK/E) bifurcation remain incompletely understood. While HSPCs sustain all blood lineages, how transient waves of progenitors arise and adapt from fetal to adult stages is less clear. This gap in knowledge limits our capacity to precisely manipulate platelet and red blood cell outputs in both developmental and therapeutic contexts. Using refined gating strategies and various bulk- and single-cell transcriptomics, we dissected the traditional “common myeloid progenitor” and Multipotent Progenitor (MPP) compartment into multiple functionally distinct subsets (C1, C2, C3). Within C1, an ESAM⁺ fraction exhibited robust MK/E potential in vitro and in vivo, whereas the ESAM⁻ fraction and other subsets displayed predominantly myeloid outputs. Upstream, MPP3 emerged as a critical branch point for MK/E fate commitment, while MPP4 contributed largely to myeloid and lymphoid lineages. These findings reveal a previously unappreciated heterogeneity in adult progenitors, spotlighting new avenues for controlling lineage specification. Developmentally, we observed transient α-catulin-GFP⁺ subsets in neonatal mice that preferentially yielded polyploid megakaryocytes. Over the first few postnatal weeks, these α-catulin-GFP⁺ cells declined, correlating with a shift to more balanced hematopoiesis. Furthermore, maternal dietary supplementation with trans-vaccenic acid (TVA) subtly altered MPP frequencies and α-catulin-GFP⁺ progenitors in offspring, suggesting that extrinsic factors intersect with intrinsic developmental programs to influence early-life MK/E output. Collectively, our data refine existing models of hematopoiesis by pinpointing distinct branching events that drive MK/E specialization in adult progenitors and uncovering specialized transient waves of MK/E-biased cells during the neonatal period. Understanding these dynamics enhances our capacity to modulate lineage commitment throughout development and may inform future strategies for treating platelet deficiencies and other hematologic disorders.