A study of the nature of embryonic lethality in LIS1-/- mice

Homozygous deletion of the Lis1 gene (Lis1(-/-)) in mouse resulted in early embryonic lethality immediately after embryo implantation by an undefined mechanism. We seek to define the nature of this demise. LIS1 (pafah1b1) is a 46 kDa protein with seven tryptophan-aspartate (WD) repeats. It docks with many proteins and has been implicated in microtubular function, cell division, intercellular transport, and nuclear and cellular motility. Combined Western and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analyses showed that LIS1 expression from the blastocyst stage required new transcription from the embryonic genome. Consequently, the death of post-implantation embryos may not reflect the first time during development that LIS1 was required, rather, it may reflect the first time following depletion of gametic stores that its actions were essential. Following culture of blastocysts in vitro for 96 hr the inner cell mass (ICM) of null embryos were significantly smaller than ICM of wild-type siblings. Normal blastocyst outgrowths after 96-hr culture had high levels of LIS1 expression in the outer cells of developing ICM and extensive expression in trophoblast cells. Lis1(-/-) embryos had significantly smaller trophoblast nuclei than wild-type embryos. The results show that LIS1 expression is required for the continued normal development of the ICM and optimal trophoblast giant cell formation.