Dosage effect of zero to three functional LBR-genes in vivo and in vitro

Abstract

The Lamin B receptor (LBR) is a pivotal architectural protein in the nuclear envelope. Mutations in the Lamin B receptor lead to nuclear hyposegmentation (Pelger-Huët anomaly). We have exactly quantified the nuclear lobulation in neutrophils from individuals with 0, 1, 2 and 3 functional copies of the lamin B receptor gene and analyzed the effect of different mutation types. Our data demonstrate that there is a highly significant gene-dosage effect between the gene copy number and the nuclear segmentation index of neutrophils. This finding is paralleled by a dose-dependent increase in LBR protein and staining intensity of the nuclear membrane in corresponding lymphoblastoid cell lines, which demonstrates a significant correlation on the protein level as well. We further show that LBR expression continually increases during granulopoiesis in vitro from human precursor cells with ovoid nuclei to multi-segmented neutrophil nuclei 11 days later, indicating relevance for regular human granulopoiesis. Altogether, LBR is a unique model that will allow the systematic study of gene-dosage effects and of modifying endogeneous and exogeneous factors on granulopoiesis.

Dicer1 deletion in myeloid-committed progenitors causes neutrophil dysplasia and blocks macrophage/dendritic cell development in mice

“…27 These mutations result in decreased expression of LBR, which is strongly correlated with hyposegmentation of the nucleus in neutrophils. [27][28] In our model, Dicer1-null neutrophils were hyposegmented, but LBR expression remained unchanged in Dicer1-null GMPs. This result suggests that other, as-yet-undefined mechanisms may be involved in the observed developmental abnormalities or that downstream LBR pathways are controlled by Dicer1 and may cause features of Pelger-Huët anomaly.…”

Intranuclear membranes induced by lipidated proteins are derived from the nuclear envelope

“…52 The multipass integral membrane protein LBR, for example, influences nuclear lobulation in a dosage dependent manner, i.e., nuclear segmentation is positively correlated with LBR protein levels. 53 Other examples are progerin, a permanently isoprenylated mutant version of lamin A and Kugelkern (Kuk/Char), a Drosophila protein. Knockdown of the kuk/char gene prevents nuclear elongation during cellularization in Drosophila while overexpression of the Kuk/Char protein leads to nuclear lobulation and intranuclear membrane growth.…”

“…Knockdown of the kuk/char gene prevents nuclear elongation during cellularization in Drosophila while overexpression of the Kuk/Char protein leads to nuclear lobulation and intranuclear membrane growth. 53,54 Nuclear growth and intranuclear membrane formation might therefore be two sides of the same coin.…”

1q42.12q42.2 Deletion in a Child with Midline Defects and Hypoplasia of the Corpus Callosum

“…LBR is also associated with 2 different recognized clinical conditions, Pelger-Huet anomaly and Greenberg skeletal dysplasia [Borovik et al, 2013]. Copy number of LBR and the nuclear segmentation index of neutrophils were highly correlated while the gene dosage could affect granulopoiesis [Gravemann et al, 2010]. Our index patient had features of LBR gene deletion manifesting as hypolobularity of the neutrophils (also known as the Pelger-Huet anomaly).…”