Gene regulation in temporally and spatially precise patterns is integral to normal developmental processes. Hormonal, tissue-specific and developmental regulation can be analyzed by molecular and genetic approaches in the C4/Slp gene family of the mouse major histocompatibility complex. C4, the fourth component of complement, is essential in the effector mechanism of humoral immunity. During evolution, the C4 gene has undergone duplication, allowing divergence with respect to function and regulation. The product of the duplicate gene, Slp (sex-limited protein), is structurally similar to C4, but does not participate in the complement pathway and is regulated by androgen. Extensive homology at the DNA level occurs in coding regions and upstream and downstream of these neighboring genes. Regulatory differences of both genes are found in congenic mouse strains and are due to allelic variation as well as nonlinked genes. Thus this serves as a model system in which to correlate differences in DNA sequence with differences in regulation; further comparison allows identification of specific factors in gene control.
The specific aims of this proposal are to define at the molecular level: I) cis-acting sequences involved in hormonal regulation; II) trans-acting factors that interact directly or indirectly with these sequences; III) interactions of cis and trans elements that specify developmental regulation. Cis-acting sequences will be defined by transfection of cloned genes and gene constructs. Hormonal regulation of Slp is due to an upstream enhancer element that derives from a proviral LTR; this element will be mutagenized to define internal domains and exact sequence requirements. Trans-acting factors will be identified by virtue of their sequence- specific binding. Biochemical characterization will aid isolation of genes encoding these proteins, whose function and regulation may then be more readily examined. Developmental regulation is particularly accessible to analysis in the C4/Slp system due to its genetics and because the major site of expression is liver, which is fully differentiated before, during and after transcriptional activation of Slp by androgen. Illumination of the molecular basis of Slp and C4 regulation will be relevant to general mechanisms of gene expression, hormonal control and evolution.
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