The Number of Larval Molts Is Controlled by Hox in Caterpillars
The Number of Larval Molts Is Controlled by Hox in Caterpillars
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DOI：
10.1016/j.cub.2020.11.017
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发表时间：
2021-02-22
期刊：
影响因子：
9.2
通讯作者：
Shinoda, Tetsuro
中科院分区：
文献类型：
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作者：
Daimon, Takaaki;Koyama, Takashi;Shinoda, Tetsuro
有外骨骼的动物为了进一步生长而蜕皮。在昆虫中，幼虫（或若虫）蜕皮的数量在种间和种内变化，并且广泛接受幼虫蜕皮数量的变化是对不同环境条件的适应性反应。(1-5)然而，幼虫蜕皮数量的多样性和可塑性的分子机制在很大程度上是未知的。在家蚕中，有蜕皮三次、四次或五次的品系，这些数量是由单个常染色体基因座上的等位基因变异决定的，即蜕皮（M）。(6-9)在这里，我们表明，Hox基因性梳减少（Scr）是负责的M位点的表型。Scr选择性表达于幼虫的前胸腺（PG），这是一种产生蜕皮激素的内分泌器官。(2)Scr抑制PG中蜕皮激素的生物合成，从而调节每个幼虫龄期期间身体大小的增量增加。我们的实验一致表明，三个M等位基因之间的Scr的差异表达水平导致不同的生长比率，最终导致不同数量的幼虫蜕皮。尽管Hox基因在赋予沿着体轴的节段身份和在发育后期塑造节段特异性结构中的作用已经得到了很好的确立，（10-13）本研究确定了Hox基因在激素生物合成中的意想不到的作用。这种新的作用意味着，除了塑造特定的片段形态外，Hox基因还通过调节动物生理学来驱动生活史性状的进化。
Animals with exoskeletons molt for further growth. In insects, the number of larval (or nymphal) molts varies inter- and intra-specifically, and it is widely accepted that the variation in the number of larval molts is an adaptive response to diverse environmental conditions. (1-5) However, themolecular mechanism that underlies the variety and plasticity in the number of larval molts is largely unknown. In the silkworm, Bombyx mori, there are strains that molt three, four, or five times, and these numbers are determined by allelic variation at a single autosomal locus, Moltinism (M).(6-9) Here, we demonstrate that the Hox gene Sex combs reduced (Scr) is responsible for the phenotypes of the M locus. Scr is selectively expressed in the larval prothoracic gland (PG), an endocrine organ that produces molting hormones.(2) Scr represses the biosynthesis of molting hormones in the PG, thereby regulating the incremental increase in body size during each larval instar. Our experiments consistently suggest that the differential expression levels of Scr among the three M alleles result in different growth ratios that ultimately lead to the different number of larval molts. Although the role of Hox genes in conferring segmental identity along the body axis and in molding segment-specific structure later in development has been well established,(10-13) the present study identifies an unexpected role of Hox gene in hormone biosynthesis. This new role means that, in addition to shaping segment-specific morphology, Hox genes also drive the evolution of life history traits by regulating animal physiology.