Targeted disruption of the Walker–Warburg syndrome gene Pomt1 in mouse results in embryonic lethality

Abstract

O-mannosylation is an important protein modification in eukaryotes that is initiated by an evolutionarily conserved family of protein O -mannosyltransferases. The first mammalian protein O -mannosyltransferase gene described was the human POMT1 . Mutations in the hPOMT1 gene are responsible for Walker–Warburg syndrome (WWS), a severe recessive congenital muscular dystrophy associated with defects in neuronal migration that produce complex brain and eye abnormalities. During embryogenesis, the murine Pomt1 gene is prominently expressed in the neural tube, the developing eye, and the mesenchyme. These sites of expression correlate with those in which the main tissue alterations are observed in WWS patients. We have inactivated a Pomt1 allele by gene targeting in embryonic stem cells and produced chimeras transmitting the defect allele to offspring. Although heterozygous mice were viable and fertile, the total absence of Pomt1 – / – pups in the progeny of heterozygous intercrosses indicated that this genotype is embryonic lethal. An analysis of the mutant phenotype revealed that homozygous Pomt1 – / – mice suffer developmental arrest around embryonic day (E) 7.5 and die between E7.5 and E9.5. The Pomt1 – / – embryos present defects in the formation of Reichert's membrane, the first basement membrane to form in the embryo. The failure of this membrane to form appears to be the result of abnormal glycosylation and maturation of dystroglycan that may impair recruitment of laminin, a structural component required for the formation of Reichert's membrane in rodents. The targeted disruption of mPomt1 represents an example of an engineered deletion of a known glycosyltransferase involved in O -mannosyl glycan synthesis.

Mechanisms of Disease: congenital muscular dystrophies—glycosylation takes center stage

“…44 Pomt1 has also been eliminated in mice. 45 The phenotype of these animals-embryonic lethality due to disruption of REICHERT'S MEMBRANE-is the same phenotype that is found in mice lacking Dag1. 46 Reichert's membrane is a structure that is specific to rodent embryos, so it is unclear whether embryonic lethality in Dag1-deficient mice would be reflective of a similarly lethal phenotype in humans.…”

TheO-Mannosyltransferase PMT4 Is Essential for Normal Appressorium Formation and Penetration inUstilago maydis

“…initial PMT-catalyzed O-mannosylation step is a prerequisite for the addition of further mannose residues by members of the KRE2/MNT1 family, which add second and third mannose residues to target proteins (Willer et al, 2003). Thus, we wanted to determine if the U. maydis equivalents of the KRE2/MNT1 family might also have a role in pathogenesis.…”

“…Glycosylation is an extremely common and highly conserved type of protein modification involving the addition of carbohydrate residues to target proteins (Willer et al, 2003). It plays a critical role in determining the structure and function of numerous secreted and membrane-bound proteins.…”

“…In eukaryotic cells, N-and O-glycosylation occurs within the endoplasmic reticulum and Golgi apparatus and can take place as either a cotranslational or posttranslational process . Both pathways are highly conserved between species from prokaryotes to humans, including plants, although they can differ in the class, number, and location of carbohydrate residues added (Burda and Aebi, 1999;Willer et al, 2003).…”

Therapeutic Possibilities in the Autosomal Recessive Limb-Girdle Muscular Dystrophies

“…95 Attempts to model LGMD2K and 2M and the allelic congenital muscular dystrophies by the generation of mice null for fukutin or Pomt1 have resulted in early embryonic lethality attributed to basement membrane defects. 97,98 Moving closer to the human disease situation, however, a chimeric mouse deficient in fukutin escapes embryonic lethality to develop a Fukuyama congenital muscular dystrophy phenotype, 99,100 similar to that observed in the Large myd mouse harbouring a deletion in the mouse Large gene. 101 In Large myd mice, one of the few viable animal models for the dystroglycanopathies, Barresi et al 102 found that overexpression of transduced Large ameliorated the dystrophic phenotype and induced synthesis of glycan-enriched alpha-dystroglycan with high affinity for extracellular ligands.…”