Connecting Mammalian Genome with Phenome by ENU Mouse Mutagenesis: Gene Combinations Specifying the Immune System

Abstract

The human and mouse genome sequences bring closer the goal of understanding how characteristics of adult mammalian physiology and pathology are encoded by DNA. Here we review the challenge of understanding how genes specify mammalian traits, with particular focus on the cells and behavior of the immune system. Summarized is the emerging experience, advantages, and limitations of using ethylnitrosourea (ENU) to modify the mouse genome and select informative variants by phenotypic screens, yielding two main conclusions. First, ENU-induced variation provides an eminently feasible route to understanding how the genome encodes important mammalian processes without any prior assumptions about genes, their chromosomal locations, or expression patterns. Second, ENU alleles match those arising by natural variation. By changing individual protein domains or splice products, these alleles reveal separate gene functions specified through protein combinations.

VACTERL/caudal regression/Currarino syndrome-like malformations in mice with mutation in the proprotein convertasePcsk5

“…ENU results in loss-of-function, partial loss-of-function (i.e., hypomorphic) and gain-of-function alleles that are similar to the spectrum observed in the naturally occurring mutants causing human disease. These alleles can also allow in vivo investigation of the functional consequences of abnormal protein structure (for review, see Papathanasiou and Goodnow 2005).…”

Uncovering the uncharacterized and unexpected: Unbiased phenotype‐driven screens in the mouse

“…Such grass-roots screens are performed on a small scale in terms of cage numbers and cost and have proven to be cost-efficient. In some cases, these screens have been carried out in individual labs (Kasarskis et al, 1998;Herron et al, 2002;Zarbalis et al, 2004;Garcia-Garcia et al, 2005;Papathanasiou and Goodnow, 2005). In other cases, collaborations among neighboring labs that are interested in complementary phenotypes have been particularly productive (Pask et al, 2005;Timmer et al, 2005;Kennedy et al, 2006).…”

“…The Goodnow lab's first screen identified 11 mutant lines with defective T-cell formation and all 11 lines have molecularly identified the responsible gene variant (Nelms and Goodnow, 2001;Jun et al, 2003;Papathanasiou and Goodnow, 2005). Several of these have revealed unsuspected players.…”

“…Several of these have revealed unsuspected players. The screen identified a hypomorphic allele of Slp76, which bypassed its earlier requirement in development and thus revealed a specific function in T-cells (Papathanasiou and Goodnow, 2005). Another T-cell immunity mutant affected a protein that was previously only known for a function in chromosome maintenance (Papathanasiou and Goodnow, 2005).…”

“…As these reviews describe the basic methods used in forward genetic screens, including the types of screens that can be done, the sophisticated manipulations one can build into a screen to facilitate mapping, and the benefits of having a easily discernible phenotype, we will not focus on those topics (for examples, see Clark et al, 2004;Kile and Hilton, 2005;Papathanasiou and Goodnow, 2005). Here, we first illustrate how genome sequence information provides a molecular grounding for mouse forward genetics and then focus on the new aspects of biology that have been revealed in these screens.…”