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--- cyp18and306page [2025/07/25 06:10] – external edit 127.0.0.1
+++ cyp18and306page [2025/09/12 06:22] (current) – renefeyereisen
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 These two CYP2 clan P450s are closely related in sequence and result from a duplication event, forming a strongly supported monophyletic clade. They are also mostly present in close synteny, with the two genes head to head in //Drosophila// and the honey bee (Niwa et al., 2004; Claudianos et al., 2006) as well as in //Daphnia pulex// (Rewitz and Gilbert 2008). This arrangement is also found in Coleoptera, Hemiptera, Isoptera, //Calopteryx splendens//, and the collembolan //Holacanthella duospinosa// but the CYP306 and CYP18 genes are head to tail in another collembolan //Orchesella cincta// and in the amphipods //Hyalella azteca// and //Parhyale hawaiensis//. They are also head to tail in the millipede //Trogoniulus corallinus//, but tail to tail in another millipede, //Helicorthomorpha holstii//. This synteny of CYP306 and CYP18 maintained over 400 MY is remarkable, given that the function of the two genes is thought to be opposite (biosynthesis vs. inactivation - at least in Drosophila). Perhaps the risk of hormonal imbalance has favored their inheritance as a linked locus.
-CYP18 is found almost ubiquitously in arthropod genomes as a single copyy gene (see exceptions below). A CYP18 gene is even found in //[[euperipatoides|Euperipatoides rowelli]]//, (Onychophora, sister clade of Arthropoda). In stark contrast, no chelicerate has a CYP306 gene, indicating that the CYP18A1 / CYP306A1 gene duplication occurred at the base of Mandibulata (Myriapoda + Pancrustacea), see scheme below (taht does not show secondary losses in some lineages).{{ ::cyp18_306.png?400 |}}
+CYP18 is found almost ubiquitously in arthropod genomes as a single copyy gene (see exceptions below). A CYP18 gene is even found in //[[euperipatoides|Euperipatoides rowelli]]//, (Onychophora, sister clade of Arthropoda). In stark contrast, no chelicerate has a CYP306 gene, indicating that the CYP18A1 / CYP306A1 gene duplication occurred at the base of Mandibulata (Myriapoda + Pancrustacea), see scheme below (that does not show secondary losses in some lineages).{{ ::cyp18_306.png?400 |}}
 An interesting hypothesis (Ogihara et al.,2019; Dermauw et al., 2020) is that an ancestral CYP18 had both C-25 and C-26 hydroxylase activities (or even just C-25 hydroylase activity), and that upon duplication, subfunctionalization into C-25 (CYP306) and C-26 (CYP18) hydroxylase activities emerged. This would explain the presence of 25-hydroxylated ecdysteroids in Chelicerates: scorpions, spiders, ticks and some mites (Crosby et al., 1986; Chambers et al., 1996; Feldlaufer and Hartfelter 1997; Lomas et al., 1997; Miyashita et al., 2011; Honda et al., 2017) which have a CYP18 but no CYP306. Even pycnogonids make abundant C25 and C26-hydroxylated ecdysteroids (Bückmann et al, 1986), yet presumably lack CYP306 as the other Chelicerates (or pre-Chelicerates).