Deletion of TLR2⁺ erythro‐myeloid progenitors leads to embryonic lethality in mice

Abstract

Early embryonic hematopoiesis in mammals is defined by three successive waves of hematopoietic progenitors which exhibit a distinct hematopoietic potential and provide continuous support for the development of the embryo and adult organism. Although the functional importance of each of these waves has been analyzed, their spatio-temporal overlap and the lack of wave-specific markers hinders the accurate separation and assessment of their functional roles during early embryogenesis. We have recently shown that TLR2, in combination with c-kit, represents the earliest signature of emerging precursors of the second hematopoietic wave, erythro-myeloid precursors (EMPs). Since the onset of Tlr2 expression distinguishes EMPs from primitive progenitors which coexist in the yolk sac from E7.5, we generated a novel transgenic "knock in" mouse model, Tlr2 Dtr , suitable for inducible targeted depletion of TLR2 + EMPs. In this model, the red fluorescent protein and diphtheria toxin receptor sequences are linked via a P2A sequence and inserted into the Tlr2 locus before its stop codon. We show that a timely controlled deletion of TLR2 + EMPs in Tlr2 Dtr embryos results in a marked decrease in both erythroid as well as myeloid lineages and, consequently, in embryonic lethality peaking before E13.5. These findings validate the importance of EMPs in embryonic development.

Limitations of Tamoxifen Application for In Vivo Genome Editing Using Cre/ERT2 System

“…Many genes are critically important for different stages of embryonic development and therefore animals with their constitutive knockout die during embryonic development [1][2][3]. Conditional knockout organisms are required to study the functions of the affected genes on later stages of development and throughout the adult lifespan.…”