title: Role of GTP-CHI links PAH and TH in melanin synthesis in silkworm, Bombyx mori.
abstract: In insects, pigment patterns are formed by melanin, ommochromes, and pteridines. Here, the effects of pteridine synthesis on melanin formation were studied using 4th instar larvae of a wild-type silkworm strain, dazao (Bombyx mori), with normal color and markings. Results from injected larvae and in vitro integument culture indicated that decreased activity of guanosine triphosphate cyclohydrolase I (GTP-CH I, a rate-limiting enzyme for pteridine synthesis), lowers BH4 (6R-l-erythro-5,6,7,8-tetrahydrobiopterin, a production correlated with GTP-CH I activity) levels and eliminates markings and coloration. The conversion of phenylalanine and tyrosine to melanin was prevented when GTP-CH I was inhibited. When BH4 was added, phenylalanine was converted to tyrosine, and the tyrosine concentration increased. Tyrosine was then converted to melanin to create normal markings and coloration. Decreasing GTP-CH I activity did not affect L-DOPA (3,4-l-dihydroxyphenylalanine). GTP-CH I affected melanin synthesis by generating the BH4 used in two key reaction steps: (1) conversion of phenylalanine to tyrosine by PAH (phenylalanine hydroxylase) and (2) conversion of tyrosine to L-DOPA by TH (tyrosine hydroxylase). Expression profiles of BmGTPCH Ia, BmGTPCH Ib, BmTH, and BmPAH in the integument were consistent with the current findings.
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China. Electronic address: chenping1918@swu.edu.cn.
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China.
authors.forename: Jiying
authors.initials: J
authors.lastname: Wang
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China.
authors.forename: Haiyin
authors.initials: H
authors.lastname: Li
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Chen
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China.
authors.forename: Tian
authors.initials: T
authors.lastname: Li
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China.
authors.forename: Junjie
authors.initials: J
authors.lastname: Xiao
authors.affiliation: College of Biotechnology, Southwest University, Chongqing 400716, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhang
mesh_terms: D000818:Animals; D053898:Biosynthetic Pathways; D012831:Bombyx / Q000201:enzymology* / Q000254:growth & development; D006136:GTP Cyclohydrolase / Q000502:physiology*; D006160:Guanosine Triphosphate; D019476:Insect Proteins / Q000502:physiology*; D008543:Melanins / Q000096:biosynthesis*; D018978:Molting; D010651:Phenylalanine Hydroxylase / Q000502:physiology*; D012880:Skin Pigmentation; D046509:Tissue Culture Techniques; D014446:Tyrosine 3-Monooxygenase / Q000502:physiology*
chemical_list: D019476:Insect Proteins; D008543:Melanins; D006160:Guanosine Triphosphate; D010651:Phenylalanine Hydroxylase; D014446:Tyrosine 3-Monooxygenase; D006136:GTP Cyclohydrolase
keywords: Guanosine triphosphate cyclohydrolase I (GTP-CH I); Melanin synthesis; Phenylalanine hydroxylase (PAH); Silkworm; Tyrosine hydroxylase (TH)