The Hox gene labial (lab) governs the formation of the tritocerebral head segment in insects and spiders. However, the morphology that results from lab action is very different in the two groups. In insects, the tritocerebral segment (intercalary segment) is reduced and lacks appendages, whereas in spiders the corresponding segment (pedipalpal segment) is a proper segment including a pair of appendages (pedipalps). It is likely that this difference between lab action in insects and spiders is mediated by regulatory targets or interacting partners of lab. However, only a few such genes are known in insects and none in spiders. We have conducted a candidate gene screen in the spider Parasteatoda tepidariorum using as candidates Drosophila melanogaster genes known to (potentially) interact with lab or to be expressed in the intercalary segment. We have studied 75 P. tepidariorum genes (including previously published and duplicated genes). Only 3 of these (proboscipedia-A (pb-A) and two paralogs of extradenticle (exd)) showed differential expression between leg and pedipalp. The low success rate points to a weakness of the candidate gene approach when it is applied to lineage specific organs. The spider pedipalp has no counterpart in insects, and therefore relying on insect data apparently cannot identify larger numbers of factors implicated in its specification and formation. We argue that in these cases a de novo approach to gene discovery might be superior to the candidate gene approach.

中文翻译：

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候选基因筛选蜘蛛拟南芥中Hox基因唇的潜在相互作用伙伴和调控靶标。

Hox基因labial（实验室）控制着昆虫和蜘蛛中三脑头部的形成。但是，在两组中，由实验室作用产生的形态非常不同。在昆虫中，三脑段（inter间段）减少并且没有附肢，而在蜘蛛中，相应的段（al足段）是包括一对附属物（ped足）的适当段。昆虫和蜘蛛的实验行为之间的这种差异可能是由调控目标或实验室的相互作用伙伴介导的。但是，在昆虫中只有少数这样的基因是已知的，在蜘蛛中则没有。我们已经在蜘蛛中进行了候选基因筛选使用已知果蝇（可能）与实验室相互作用或在cal间节段中表达的果蝇果蝇基因作为候选拟青霉。我们已经研究了75个拟南芥体育基因（包括以前发表和复制的基因）。其中只有3个（原皮A（pb-A）和两个齿外旁系（exd））在小腿和pedipalp之间显示出差异表达。成功率低说明了将候选基因方法应用于谱系特定器官时的弱点。蜘蛛pedipalp在昆虫中没有对应物，因此依靠昆虫数据显然无法识别与其规格和形成有关的大量因素。我们认为在这些情况下，从头进行基因发现的方法可能优于候选基因方法。