果蠅的萬聖節基因

雖然萬聖節已經過去快兩個月了，不過我這兩天才把這篇拿來看一下，看了才知道有 Halloween genes，他們是果蠅的一組控制胚胎生長的基因，包括有：

Gene	Gene Name	Function
spo	pook, Cyp307a1	converts 7-dehydrocholesterol (7dC) to Δ4-diketol
spok	spookier, Cyp207a2	works with gene product of spo
phm	phantom, Cyp306a1, exo	microsomal 25-hydroxylase, converts 2,22,25dE-ketodiol to 2,22dE-ketotriol (2,22dE)
dib	disembodied, Cyp302a1	converts 2,22,dE-ketotriol to 2-deoxyecdysone (2dE)
sad	shadow, Cyp315a1	converts 2-deoxyecdysone to ecdysone (E)
shd	shade, Cyp314a1	converts ecdysone to 20-hydroxyecdysone (20E)

酵素參與順序和功能如下圖。


(Figure: JT Warren et al, PNAS 2002)

這些基因屬於 cytochrome P450 superfamily (CYPs)，參與用膽固醇(cholesterol)製造蛻皮激素(ecdysteroid)的過程，這個過程最後的產品是 20E，是主要的 molting hormone。如果這些基因有突變，會造成生長過程中 exoskeleton 出現問題，胚胎會在 exoskeleton 成長完之前就死掉了，除此之外，在顯微鏡下，突變的幼蟲外皮因為沒有分化完成，外觀符合人們對萬聖節的想像而因此得名，發現這些基因的幾位也因此得了 1995 年的諾貝爾獎。

"no differentiation of cuticle and head skeleton” (disembodied), “only head skeleton visible” (haunted), and “mouth parts and denticles poorly differentiated” (mummy)



Article:

J Cohen, A gory tale behind the origin of ‘Halloween genes’. Science Magazine (2016)


Papers:

C Nüsslein-Volhard & E Wieschaus, Mutations affecting segment number and polarity in Drosophila. Nature (1980)

JT Warren et al, Molecular and biochemical characterization of two P450 enzymes in the ecdysteroidogenic pathway of Drosophilamelanogaster. PNAS (2002)

LI Gilbert, Halloween genes encode P450 enzymes that mediate steroid hormone biosynthesis in Drosophila melanogaster. Molecular & Cellular Endocrinology (2004)


Other references:

FlyBase: HALLOWEEN GENES