Hypomorphic mutation in hnRNP U results in post-implantation lethality

Abstract

The present study characterized an embryonic lethal mutation induced by insertion of the U3Neo gene trap retrovirus into an intron of the gene encoding heterogeneous ribonuclear protein U (Hnrnpu), which maps to the distal arm of mouse chromosome 1. Murine hnRNP U was found to be identical to the human protein at all but one of 341 amino acid residues. Embryos homozygous for the provirus showed obvious abnormalities after 6.5 days of development (E6.5) and were resorbed by E10.5. Expression of the inserted neomycin-resistance gene involved alternative splicing to a cryptic 3' splice site located in the neomycin resistance gene resulting in a hypomorphic mutation. Homozygous mutant cell lines isolated from preimplantation blastocysts expressed hnRNP U transcripts at levels 2 to 5 times lower than wild-type cells, suggesting that nearly wild-type levels of hnRNP U are required for embryonic development.

The Trithorax group protein Ash2l and Saf-A are recruited to the inactive X chromosome at the onset of stable X inactivation

“…Saf-A has been implicated in many processes, including transcription, RNA transport, DNA replication and circadian rhythm (Onishi et al, 2008). Saf-A is required for cell proliferation and a hypomorphic mutation in mice causes embryonic lethality (Roshon and Ruley, 2005). Although this precludes a direct genetic investigation of Saf-A function in X inactivation, our results suggest that Saf-A together with Ash2l could be components for either memory imposition or stabilization of the Xi.…”

Kisspeptin–GPR54 Signaling Is Essential for Preovulatory Gonadotropin-Releasing Hormone Neuron Activation and the Luteinizing Hormone Surge

“…The first is that the Dungan Gpr54 mutant mouse was generated by retroviral insertion into intron 2 (H. Dungan, personal communication) with no loss of Gpr54 coding sequence. There are cases in which retroviral insertion does not always produce a null mutation but can generate a hypomorphic allele with residual gene function (Couldrey et al, 1999;Roshon and Ruley, 2005). The extent to which this may occur in the Dungan Gpr54 transgenic line has not been reported.…”

The impact of alternative splicing in vivo: Mouse models show the way

“…Using gene-trap ES cell lines that carry disrupted hnRNP C or hnRNP U alleles, it was shown that these genes are indeed essential for embryonic development, as the lack of either of the two proteins proved to cause early embryonic lethality. In both cases, embryos developed normally through the egg cylinder stage (day 6.5) but failed to initiate gastrulation (Williamson et al 2000;Roshon and Ruley 2005). Interestingly, cell lines derived from early hnRNP C-deficient embryos were viable and, to some extent, able to differentiate and displayed no obvious defect in the expression or splicing of marker genes (Williamson et al 2000).…”