The copper transporter CTR1 provides an essential function in mammalian embryonic development

Abstract

Copper serves as an essential cofactor for a variety of proteins in all living organisms. Previously, we described a human gene (CTR1;SLC31A1) that encodes a high-affinity copper-uptake protein and hypothesized that this protein is required for copper delivery to mammalian cells. Here, we test this hypothesis by inactivating the Ctr1 gene in mice by targeted mutagenesis. We observe early embryonic lethality in homozygous mutant embryos and a deficiency in copper uptake in the brains of heterozygous animals. Ctr1 ؊/؊ embryos can be recovered at E8.5 but are severely developmentally retarded and morphologically abnormal. Histological analysis reveals discontinuities and variable thickness in the basement membrane of the embryonic region and an imperfect Reichert's membrane, features that are likely due to lack of activity in the collagen cross-linking cupro-enzyme lysyl oxidase. A collapsed embryonic cavity, the absence of an allantois, retarded mesodermal migration, and increased cell death are also apparent. In the brains of heterozygous adult mice, which at 16 months are phenotypically normal, copper is reduced to approximately half compared with control littermates, implicating CTR1 as the required port for copper entry into at least this organ. A study of the spatial and temporal expression pattern of Ctr1 during mouse development and adulthood further shows that CTR1 is ubiquitously transcribed with highest expression observed in the specialized epithelia of the choroid plexus and renal tubules and in connective tissues of the eye, ovary, and testes. We conclude that CTR1 is the primary avenue for copper uptake in mammalian cells.

Vertebrate Ctr1 coordinates morphogenesis and progenitor cell fate and regulates embryonic stem cell differentiation

“…Mouse embryos lacking the Ctr1 gene display clear defects in gastrulation and mesoderm formation and die in utero (31,32). Unfortunately, the early embryonic lethality of the Ctr1-null mutants precludes in-depth analysis of the function of this gene in cellular differentiation during murine embryogenesis.…”

Posttranslational regulation of copper transporters

“…Copper import in mammals is primarily mediated by the copper transporter (CTR) family of proteins that comprises the homologous CTR1 and CTR2. CTR1 is absolutely required for dietary copper absorption and is essential for cellular copper uptake [1][2][3][4][5][6][7]. Cellular copper export is equally important and is dependent on ATP7A and ATP7B [8][9][10][11][12].…”

“…hCTR1 was identified as a highaffinity CTR by functional complementation of a yeast strain deficient in high-affinity copper uptake [29][30][31][32]. The characterization of CTR1 as a high-affinity CTR marked the start of extensive studies on the structure, function, and cellular localization of the CTR protein family [2,6,7,[33][34][35][36][37][38][39][40][41][42]. Overexpression of hCTR1 in several cell lines results in a substantial, specific, and saturable induction of cellular copper import with a K m of approximately 1-5 lM [7,35,39].…”

“…Overexpression of hCTR1 in several cell lines results in a substantial, specific, and saturable induction of cellular copper import with a K m of approximately 1-5 lM [7,35,39]. Ctr1 knockout mice died during midgestation, indicating an essential role for Ctr1 in embryonic development [2,4]. Interestingly, Ctr1 ?/-mice that survived the embryonic stages displayed copper deficiencies in brain tissue, indicating that Ctr1 is indispensable for copper transport in mammals [2].…”

“…Ctr1 knockout mice died during midgestation, indicating an essential role for Ctr1 in embryonic development [2,4]. Interestingly, Ctr1 ?/-mice that survived the embryonic stages displayed copper deficiencies in brain tissue, indicating that Ctr1 is indispensable for copper transport in mammals [2]. Mouse embryonic fibroblasts isolated from Ctr1 knockout mice have a substantial defect in copper uptake and copper incorporation into cuproenzymes [3].…”