Pumilio is a member of the highly conserved PUF family of RNA-binding proteins 
that function as a developmental regulator in diverse animal species. Two 
Pumilio genes, Pum1 and Pum2, have been identified in mammals and are found to 
be involved in sperm development, neuron development as well as human diseases 
such as neurodegeneration. Generation of animal models disrupting different 
parts of Pum protein could help to further dissect their physiological function. 
Here we described characterization and analysis of a mouse line possessing a 
gene trap mutation of the Pumilio1 (Pum1) gene. Mice homozygous for the mutation 
(Pum1(XE002)) cannot be recovered in the adult offspring, at birth or at 
different time points of embryonic development (E18, E14, E12). Careful analysis 
of preimplantation embryos showed that no homozygous blastocysts could be 
detected on day 3.5 of gestation. 96-hr in vitro culture of 1-cell embryos 
either by natural mating or in vitro fertilization between heterozygotes failed 
to uncover any homozygous blastocysts, suggesting an early loss of homozygous 
preimplantation embryos. The lack of Pum1 gene trap homozygotes suggests a role 
of Pum1 in very early embryonic development or fertilization. This novel animal 
model affecting the beginning of embryonic development could help to understand 
not only the genetic mechanism underlying preimplantation embryonic development 
but also the translational regulation in development and diseases.