Esam On The Cells Of Endothelial Lineage Plays An Important Role In The Development Of Definitive Hematopoiesis

Endothelial cell-selective adhesion molecule (ESAM) is lifelong marker of hematopoietic stem cells (HSCs) (Yokota Blood 2009) and endothelial cells (ECs) (Hirarta JBC 2001). Although we previously elucidated the functional importance of ESAM on HSCs in stress-induced hematopoiesis in adults (Sudo J Immunol 2012; PLoS One 2016), how ESAM affect hematopoietic development during fetal life remained unknown. To address this issue, we analyzed the fetuses of conventional ESAM knockout mice. Approximately half of the ESAM-null fetuses exhibited severe anemia and died after mid-gestation. RNA-sequence analyses exhibited downregulation of adult-type globin genes and Alas2, which encodes the first, rate-limiting enzyme in the heme biosynthesis pathway in the ESAM-null fetal liver (FL). Culture and transplantation experiments demonstrated that these abnormalities were attributable to the malfunctioning of ESAM-null HSCs. In addition, cross-linking ESAM with an anti-ESAM antibody influenced the transcription of hemoglobin synthesis-related genes in HSCs, indicating the significance of ESAMs on HSCs for the development of definitive hematopoiesis. However, it was unclear whether ESAM expression on only HSCs was critical or if ESAM expression on ECs was also involved. To examine this, we generated ESAM-flox mice using the innovative CLICK (CRISPR with lssDNA inducing conditional knockout alleles) method that was recently developed by our group (Miyasaka BMC Genomics 2018), and analyzed the results.