Conditional control of selectin ligand expression and global fucosylation events in mice with a targeted mutation at the FX locus

Abstract

Glycoprotein fucosylation enables fringe-dependent modulation of signal transduction by Notch transmembrane receptors, contributes to selectin-dependent leukocyte trafficking, and is faulty in leukocyte adhesion deficiency (LAD) type II, also known as congenital disorder of glycosylation (CDG)-IIc, a rare human disorder characterized by psychomotor defects, developmental abnormalities, and leukocyte adhesion defects. We report here that mice with an induced null mutation in the FX locus, which encodes an enzyme in the de novo pathway for GDP–fucose synthesis, exhibit a virtually complete deficiency of cellular fucosylation, and variable frequency of intrauterine demise determined by parental FX genotype. Live-born FX(−/−) mice exhibit postnatal failure to thrive that is suppressed with a fucose-supplemented diet. FX(−/−) adults suffer from an extreme neutrophilia, myeloproliferation, and absence of leukocyte selectin ligand expression reminiscent of LAD-II/CDG-IIc. Contingent restoration of leukocyte and endothelial selectin ligand expression, general cellular fucosylation, and normal postnatal physiology is achieved by modulating dietary fucose to supply a salvage pathway for GDP–fucose synthesis. Conditional control of fucosylation in FX(−/−) mice identifies cellular fucosylation events as essential concomitants to fertility, early growth and development, and leukocyte adhesion.

Regulation of Notch signaling by glycosylation

“…Transport of GDP-Fucose may also be mediated by another transporter [43]. Inhibition of GDP-Fucose synthesis leads to a subset of Notch signaling defects in Drosophila [13-15] but no visible Notch phenotype in mice [44], potentially because of maternal sources of GDP-Fucose. Clearly none of these strategies uniquely targets Notch receptors since a number of proteins have EGF repeats with the consensus recognized by OFUT1/Pofut1 [45], and all glycoproteins acted on by any fucosyltransferase will be affected by the loss of GDP-Fucose or the GDP-Fucose transporter.…”

Dysregulation of TGF-β1 receptor activation leads to abnormal lung development and emphysema-like phenotype in core fucose-deficient mice

“…In contrast to Fut8 Ϫ/Ϫ mice, embryonic lethality was observed in mutant mice deficient in the FX gene, which encodes an enzyme in the de novo pathway for GDP-fucose synthesis and is responsible for all cellular fucosylation, e.g., ␣1,2; ␣1,3; ␣1,6; etc. (23). The appearance of Fut8 Ϫ/Ϫ mice could not be distinguished from Fut8 ϩ/Ϫ and Fut8 ϩ/ϩ mice within 3 days of age, but Ϸ70% of them died during this period (Fig.…”

Differential Terminal Fucosylation of N-Linked Glycans Versus Protein O-Fucosylation in Leukocyte Adhesion Deficiency Type II (CDG IIc)

“…Total radioactivity recovery after chromatography ranged between 90 and 95% for each sample. PNGaseresistant glycoproteins eluted from fractions [5][6][7][8][9][10]. N-linked oligosaccharides eluted from fractions 11-28.…”

“…Alterations in the production of fucosylated glycoconjugates have been observed in development and differentiation, and in pathological conditions as well, including inflammation and tumor progression (1)(2)(3)(4)(5). Disruption of the FX gene, which codes for a key enzyme in fucose metabolism, results in mice that require fucose in their diet for survival, demonstrating the essential nature of fucosylation (6).…”