The LPS signaling pathway has been analyzed using a combination of biochemical and genetic methods. Yet, to the present time, not all of the proteins that participate in LPS detection have been identified. In order to find more of them, a forward genetic strategy has been used. Germline mutations are induced in mice using N-ethyl-N-nitrosourea (ENU), and the mutants are systematically screened for their ability to respond to primary challenge with LPS, as well as their ability to develop LPS tolerance. Among the first 1365 F1 and 1686 F3 mice analyzed in this manner, three transmissible mutations have been detected. An autosomal recessive mutation, Lps2, abolishes the primary LPS response but does not reside in any of the genes that are presently known to be essential for LPS sensing. Two other mutations, one dominant and one recessive, block the development of LPS tolerance. Lps2 has been excluded from more than 99% of the genome by genetic mapping. In the present proposal, we outline plans for high-resolution mapping and cloning these mutations. Moreover, since germline mutagenesis is clearly an effective means of finding the essential cellular components of LPS sensing and feedback inhibition pathways, we will extend our effort to approach saturation, cloning all mutations that show a strong phenotypic effect. The existing mutations, and all future mutations that are acquired through this forward genetic approach, will be subjected to advanced phenotypic analysis to determine the level at which they affect LPS signaling. In the case of mutations that abolish LPS tolerance, we will attempt to determine the net impact on host resistance to infection.
