Futahashi Ryo, Fujiwara Haruhiko
Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Bioscience Building 501, Kashiwa, Chiba 277-8562, Japan.
Insect Biochem Mol Biol. 2006 Jan;36(1):63-70. doi: 10.1016/j.ibmb.2005.11.002. Epub 2005 Dec 5.
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 PAH. In this report, we found that a GTPCHI inhibitor prevents pigmentation in cultured integuments, suggesting that the GTPCHI activity is also involved in 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 (GTPCHIa and GTPCHIb). GTPCHIa is expressed at the black markings of the subsequent instar, similar to TH, whereas GTPCHIb is expressed uniformly, similar to PAH. This suggests that the region-specific expression of GTPCHIa supplies sufficient BH(4) 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.
柑橘凤蝶幼虫在第四次蜕皮时会改变其体表斑纹。我们发现特定阶段的表皮黑色斑纹主要由两种黑色素合成酶的共定位调控，即酪氨酸羟化酶（TH）和多巴脱羧酶（DDC）。TH将酪氨酸转化为二羟基苯丙氨酸（多巴），而酪氨酸本身由苯丙氨酸羟化酶（PAH）从苯丙氨酸转化而来。鸟苷三磷酸环化水解酶I（GTPCHI）对于合成四氢生物蝶呤（BH4）至关重要，BH4是TH和PAH的一种辅因子。在本报告中，我们发现一种GTPCHI抑制剂可阻止培养的体表色素沉着，这表明GTPCHI活性也参与表皮色素沉着。我们已从柑橘凤蝶中克隆出GTPCHI和PAH的cDNA，并通过整装原位杂交研究了它们在表皮中的空间表达模式。幼虫表皮中有两种GTPCHI同工型（GTPCHIa和GTPCHIb）。GTPCHIa在后续龄期的黑色斑纹处表达，类似于TH，而GTPCHIb则均匀表达，类似于PAH。这表明GTPCHIa的区域特异性表达提供了足够的BH4，增强了黑色斑纹区域的TH活性。我们的结果表明，幼虫斑纹不仅受黑色素合成酶调控，还受辅因子供应酶调控。
