Mouse Sprr locus: a tandem array of coordinately regulated genes Satyakam Patel, Tonja Kartasova, Julia A. Segre Epithelial Biology Section, National Human Genome Research Institute, Bethesda, MD 20892-4442, USA Received: 11 June 2002 / Accepted: 4 October 2002 Abstract Small PRoline Rich (SPRR) proteins are primary constituents of the cornified cell envelope, necessary to create a permeability barrier across the body’s surface. The family of murine Sprr genes has diver- sified, enabling the body to construct slightly dif- ferent types of barriers as needed for backskin, mouth, tongue, etc. The Sprr genes have remained tandemly arrayed within 220 kb on mouse Chro- mosome (Chr) 3. On the basis of sequence similarity, we identified a novel member of the family, the murine ortholog of SPRR4. We present a sequence- verified physical map of the region and identify the complete coding sequence of the Sprr2 genes. Highly specific RNase protection assays based on the 3¢ untranslated sequences were used to query the expression of these genes in a model of barrier defi- ciency, mice with a targeted ablation of the tran- scription factor Kruppel-like factor 4 (Klf4)/)). Twelve of the 15 members of the Sprr family are upregulated in the Klf4)/) mice. The sequences upstream of the start of transcription of the Sprr2 genes contain common regulatory elements con- served with the human SPRR2 genes. The clustering of the genes and their misregulation suggest that these genes may be held together in a tandem array to allow coordinate regulation. Introduction An intriguing element of mammalian genomes is the retention of tandemly arrayed gene families. The globin and Hox genes are physically linked to allow coordinate regulation (Krumlauf 1994; Li et al. 1999). Other tandem arrays may be held together owing to recent gene conversion or duplication and insuffi- cient time to radiate onto different chromosomes. Comparison of related regions in mouse and human genomes has proved to be a valuable strategy to an- notate and analyze large, clustered gene families. One very large block of tissue-specific genes is the epidermal differentiation complex (EDC) on human Chr 1q21, mouse Chr 3. The EDC consists of more than 50 genes within 2.5 Mb that are expressed predominantly in the skin. The EDC contains many of the major structural proteins of the skin (loricrin, filaggrin, involucrin) necessary for terminal differ- entiation. The EDC also contains several gene fam- ilies, including at least 10 Small PRoline Rich (Sprr), 13 S100, and 18 late envelope protein (Lep) genes (Marshall et al. 2001; Song et al. 1999; South et al. 1999). The skin provides the two essential functions of protecting itself from mechanical stress and pro- tecting the body from dehydration and the entry of toxic agents (Fuchs and Raghavan 2002). Barrier function is attained by crosslinked cornified enve- lope (CE) proteins, which serve as a scaffold for ex- truded lipids (Steinert 2000). The primary role of the SPRR proteins is to serve as precursors for the CE, which forms directly underneath the plasma membrane of terminally differentiating cells of stratified squamous epithelia (Hohl et al. 1995). On the basis of the number of amino acids in the repeats of the protein’s central domain and the consensus of the sequence, they are divided into four families; SPRR1, 2, 3, and 4. There are two Sprr1 genes and just a single Sprr3 and Sprr4 gene. With 7 genes in humans and 11 in mouse, the SPRR2 proteins are the most diversified of the Sprr genes. Although the coding sequence of the various Sprr genes appears similar, their expression differs across the various regions of the body: backskin, palms, buckle, lips, etc. (Song et al. 1999). Similar to the temporal regu- lation of the globin genes, the Sprr gene expression may be regulated spatially to create different types of barriers across the body surface. It is intriguing to postulate that these genes may have diversified to code for slightly different proteins producing differ- ent types of barriers. These genes may then be held Correspondence to: J.A. Segre; E-mail: jsegre@nhgri.nih.gov 140 DOI: 10.1007/s00335-002-2205-4 • Volume 14, 140–148 (2003) •Ó Springer-Verlag New York, Inc. 2003