Lamins Regulate Cell Trafficking and Lineage Maturation of Hematopoietic Cells

Abstract

Hematopoietic stem and progenitor cells reside preferentially in adult marrow microenvironments together with nucleated erythroblasts and megakaryocytes, whereas other blood cells readily cross the endothelial barrier into the circulation. Since the nucleus is the largest organelle in blood cells, we hypothesized that [1] cell sorting across microporous barriers is regulated by nuclear deformability as controlled by lamin-A and -B, and [2] lamin levels directly modulate hematopoietic programs. Mass spectrometry-calibrated intracellular flow cytometry indeed reveals a lamin expression map that partitions human blood lineages between marrow and circulating compartments (P = 0.00006). B-type lamins are highly variable and predominate only in CD34+ cells, but migration through micropores and nuclear flexibility in micropipette aspiration both appear limited by lamin-A:B stoichiometry across hematopoietic lineages. Differentiation is also modulated by overexpression or knockdown of lamins as well as retinoic acid addition, which regulates lamin-A transcription. In particular, erythroid differentiation is promoted by high lamin-A and low lamin-B1 expression, whereas megakaryocytes of high ploidy are inhibited by lamin suppression. Lamins thus contribute to both trafficking and differentiation.