Mouse ζ- and α-Globin Genes: Embryonic Survival, α-Thalassemia, and Genetic Background Effects

Abstract

A classical notion regarding the expression of murine embryonic ζ- and adult α-globin genes holds that there is a switch in globin production from the embryonic to the adult form during fetal development. Our previous in situ hybridization studies challenged this view, since both ζ- and α-globin mRNAs can be detected simultaneously in the earliest erythrocyte populations. This finding raises the possibility that ζ-globin production might be wholly or partially redundant in embryos in which the adult α-globin is also expressed. To test this possibility, we created a null mutation of the ζ-globin gene using homologous recombination in embryonic stem cells. Many outbred mice homozygous for the ζ-null mutation were able to develop normally, undermining the notion that there is an absolute need for ζ-globin and indicating that α-globin alone can serve the survival needs of the fetus. Interestingly, insertion of the PGK-Neo cassette (used to create the null mutation) into the ζ-globin gene appears to influence the expression of the nearby α-globin genes, giving rise to reduced α-globin production and to an α-thalassemia–like syndrome. There is also evidence indicating the strong influence of genetic background on the ζ-null and α1-null phenotypes, both of which are much more severe in the 129/SvEv inbred genetic background. These quantitative differences can potentially be exploited to identify genes important for erythropoiesis.

Chromatin interaction mechanism of transcriptional control invivo

“…There is indirect evidence for competition in the mouse α locus which may be indicative of an alternating transcriptional mechanism. Insertional mutation of the ζ gene with a PGK-Neo cassette results in decreased expression of the α genes in definitive erythroid cells when ζ would normally be silenced (Leder et al, 1997). Although the DRB results alone do not allow us to make firm conclusions regarding the mechanism of multiple α gene expression they do show a clear difference compared with the γ and β genes and exclude an artificial lag of reappearing double signals in cis as a consequence of the DRB treatment.…”

A retained selection cassette increases reporter gene expression without affecting tissue distribution in SPI3 knockout/GFP knock‐in mice

“…It is becoming apparent that retention of the selectable marker gene in knockout mice can lead to a confounding phenotype. In most cases the retained selectable marker gene affects the expression of neighbouring genes (Fiering et al, 1995;Hug et al, 1996;Pham et al, 1996;Leder et al, 1997;DeJarnette et al, 1998;.…”

Endothelial alpha globin is a nitrite reductase

“…There were no changes in erythrocyte size or volume upon Cdh5-Cre driven deletion ( Supplementary Figure 3 ); this is in contrast to the anemia and decreased red blood cell size in Hba1 global knockout animals ( Hba1 -/- , Supplemental Figures 3-4 ). Global recombination of our Hba1 conditional allele ( Hba1 fl/fl ; Sox2-Cre 29 ), hereafter Hba1 Δ/Δ , Supplemental Figure 4A-C ) produces an anemia phenotype that mirrors global loss of Hba1 through insertion of a neomycin resistance cassette 30 ( Supplemental Figure 4D-F ) with significant defects in blood hemoglobin and hematocrit without a statistically significant change in total red blood cells.…”