Expression of one isoform of GTP cyclohydrolase I coincides with the larval black markings of the swallowtail butterfly, Papilio xuthus

The larva of the swallowtail butterfly Papilio xuthus changes its body markings during the fourth ecdysis. We found that stage-specific cuticular black markings are mainly regulated by co-localization of two melanin synthesis enzymes; tyrosine hydroxylase (TH) and dopa decarboxylase (DDC). TH converts tyrosine to dihydroxyphenylalanine (dopa), and tyrosine itself is converted from phenylalanine by phenylalanine hydroxylase (PAH). Guanosine triphosphate cyclohydrolase I (GTPCHI) is essential for the synthesis of tetrahydrobiopterin (BH4) that is a cofactor of TH and PAR In this report, we found that a GTPCHI inhibitor prevents pigmentation in Cultured integuments, Suggesting that the GTPCH1 I activity is also involved ill Cuticle pigmentation. We have cloned GTPCHI and PAH cDNAs from P. xuthus and investigated their spatial expression patterns in epidermis by whole-mount in situ hybridization. There are two isoforms of GTPCHI in larval epidermis (GTPCH1a and GTPCH1b). GTPCH1a is expressed at the black markings of the Subsequent instar, similar to TH, whereas GTPCH1b is expressed uniformly. similar to PAH. This Suggests that the region-specific expression of GTPCHIa supplies sufficient BH4 reinforcing the TH activity in black marking area. Our results imply that larval markings are regulated by not only melanin synthesis enzymes but also the cofactor supplying enzyme. (C) 2005 Elsevier Ltd. All rights reserved.