Functional Conservation of the Promoter Regions of Vertebrate Tyrosinase Genes

Abstract

Tyrosinase is the key enzyme for synthesizing melanin pigments, which primarily determine mammalian skin coloration. Considering the important roles of pigments in the evolution and the adaptation of vertebrates, phylogenetic changes in the coding and flanking regulatory sequences of the tyrosinase gene are particularly intriguing. We have now cloned cDNA encoding tyrosinase from Japanese quail and snapping turtle. These nonmammalian cDNA are highly homologous to those of the mouse and human tyrosinases, whereas the 5' flanking sequences are far less conserved except for a few short sequence motifs. Nevertheless, we demonstrate that the 5' flanking sequences from the quail or turtle tyrosinase genes are capable of directing the expression of a fused mouse tyrosinase cDNA when introduced into cultured mouse albino melanocytes. This experimental method, which reveals the functional conservation of regulatory sequences in one cell type (the melanocyte), may be utilized to evaluate phylogenetic differences in mechanisms controlling specific gene expression in many other types of cells. We also provide evidence that the 5' flanking sequences from these nonmammalian genes are functional in vivo by producing transgenic mice. Phylogenetic changes of vertebrate tyrosinase promoters and the possible involvement of conserved sequence motifs in melanocyte-specific expression of tyrosinase are discussed.

The tyrosinase enhancer is activated by Sox10 and Mitf in mouse melanocytes

“…Consistent with their high degree of conservation, mutation of the E-box elements also induced a decrease of enhancer activity indicating that they represent functional transcription factor binding sites. However, although, Mitf-mediated activation was abolished by the mutation of the second CAGCTG E-box (E2), it is unlikely that this represents a direct target for Mitf, since high affinity Mitf binding has only been demonstrated for CATGTG or CACGTG motifs in vitro (Bentley et al, 1994;Ganss et al, 1994b;Jackson et al, 1991;Lowings et al, 1992;Sato et al, 2001;Shibahara et al, 1991;Yasumoto et al, 1997), though we cannot rule out the possibility that in vivo modification of Mitf or its interaction with other factors leads to a change in its DNA-binding specificity. Interestingly, the effect of Sox10 was affected by the mutation of the E-box motif, suggesting that, in fibroblasts, Sox10 might activate Mitf or cooperate with whatever factor binds this element in vivo (Lee et al, 2000;Potterf et al, 2000;Verastegui et al, 2000b).…”

“…Mitf and USF-1 specifically bind E-box DNA motifs, which are characterized by a consensus CANNTG sequence (Aksan and Goding, 1998;Bentley et al, 1994;Galibert et al, 2001;Yasumoto et al, 1994), with preferences for CATGTG (Mitf) and CACGTG (USF-1) (Aksan and Goding, 1998;Corre and Galibert, 2005). In addition, Mitf preferentially interacts with an E-box containing motif termed the M-box (AGTCATGTGCT) (Bentley et al, 1994;Ganss et al, 1994c;Jackson et al, 1991;Lowings et al, 1992;Sato et al, 2001;Shibahara et al, 1991;Yasumoto et al, 1997). Sox10, which is a member of the HMG box family of transcription factors (Wegner, 2005), binds the consensus sequence A/T A/T CAA T/A (Mollaaghababa and Pavan, 2003).…”

Development of Pigment Cells in the Brain of Ascidian Tadpole Larvae: Insights into the Origins of Vertebrate Pigment Cells

“…It was found that a fragment corresponding to the region between positions − 111 and + 33 (144-bp fragment) is sufficient to direct lineage-specific and developmentally correct expression of HrTyr during embryogenesis. Surprisingly, the 144-bp fragment of HrTyr does not contain any cis-regulatory elements known to be conserved in vertebrate tyrosinase promoters, such as CATGTG-type E-box motifs to which the basic-helix-loop-helix-leucine-zipper (bHLH-LZ) transcription factor Mitf is known to bind (35,36). Rather, we found several putative Pax3-binding consensus sites scattered within the minimal promoter region.…”

Promoters with Cancer Cell-Specific Activity for Melanoma Gene Therapy

“…This motif was detected in TYR gene promoters in various animal species. A similar motif can be found within the M-box and the enhancer region of the tyrosinase gene [27]. Melanocyte-specific expression of the tyrosinase gene is activated upon the binding of the product of the MITF gene to the promoter region, including the M-box and the E-box starting region [24].…”

“…This promoter fragment contains three positive regulatory elements: the conservative element that is typical for melanocyte-specific promoters – M-box (-104/-37 from the TSS), linked with nine nucleotides that are known as CR1; the Sp1-site (-45/-37 from the TSS); and the evolutionarily conservative element CR2 consisting of the E-box motif and the octamer element (-14/+1 from the TSS) overlapping with it [ 24 ]. It is significant that the octamer element in the TYR promoter is degenerate in many mammals, including mice [ 27 ]. The E-box contains the CANNTG motif, which binds bHLH family transcription factors (basic-helix-loop-helix).…”