Targeted mutation of Apob . Model for human hypobetalipoproteinemia. Homozygotes characterized by exencephalus of varying severity that appears to be the result of abnormal supporting mesenchyme. Targeted mutation in Csk . Homozygotes deficient for CSK, a negative regulator of Src family tyrosine kinases, die in utero .
Homozygotes show circling, head-tossing, deafness, and hyperactivity.
Mutants also have abnormal development of membranous labyrinths with possible hydrocephalus of the hind brain. Homozygotes die within a few hours postnatally. Heterozygotes have varying numbers of extra digits on preaxial side of feet. Homozygotes die in utero with multiple abnormalities. Excessively large pharyngeal arches and an open neural tube are evident at E9.