A postimplantation lethal mutation induced by transgene insertion on mouse chromosome 8

Area of Science:

• Genetics
• Developmental Biology
• Molecular Biology

Background:

• Transgenic mouse models are crucial for studying gene function and developmental processes.
• Understanding gene regulation and the impact of gene copy number variations is essential for developmental biology.

Purpose of the Study:

• To investigate the effects of increased phosphoglycerate kinase 1 (Pgk1) gene dosage in transgenic mice.
• To determine the cause of embryonic lethality observed in specific transgenic mouse lines.
• To characterize the integration site and potential disruption of endogenous genes by the transgene insertion.

Main Methods:

• Generation of transgenic mice with additional copies of the mouse Pgk1 gene.
• Genotyping of embryos at midgestation to assess viability and transgene carriage.
• Analysis of transgene expression levels to rule out gene toxicity.
• Cloning and characterization of transgene-flanking genomic DNA to investigate integration patterns.
• Chromosomal mapping of transgene insertion sites using mouse-hamster somatic cell hybrids and backcross panels.

Main Results:

• Two transgenic mouse lines (94-A and 94-K) exhibited embryonic lethality in homozygous or compound heterozygous states (A/A, K/K, A/K).
• Embryos with two copies of the transgene (A/K) died by Embryonic Day 10.
• Pgk1 toxicity was ruled out as the cause of death; insertional mutagenesis disrupting essential genes was implicated.
• Structural analysis suggested a single integration event for the 94-A and 94-K transgenes, with rearrangements.
• The 94-A transgene insertion was associated with a significant deletion and located near a highly transcribed endogenous gene on mouse chromosome 8.

Conclusions:

• Increased Pgk1 gene dosage itself does not cause the observed embryonic lethality.
• Insertional mutagenesis resulting from the transgene integration disrupts essential genes required for embryogenesis.
• The integration site on chromosome 8 is critical, suggesting disruption of a gene vital for embryonic development.
• Further investigation into the disrupted endogenous gene(s) is warranted to understand early embryogenesis.