Growth and morphogenesis of the gastropod shell
Growth and morphogenesis of the gastropod shell
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DOI：
10.1073/pnas.1816089116
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发表时间：
2019-04-02
影响因子：
11.1
通讯作者：
Lambert, J. David
中科院分区：
文献类型：
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作者：
Johnson, Adam B.;Fogel, Nina S.;Lambert, J. David
腹足类的外壳形态是众所周知的多样性，但通常有一个共同的几何形状，对数线圈。这种形态的变化已经通过数学和计算建模，但对贝壳形态发生的发育生物学仍然知之甚少。在这里，我们的特点的组织和生长模式的分泌上皮细胞的幼虫壳的篮子螺Tritia（也被称为Ilyanassa）。尽管幼虫壳的相对简单，我们发现一个令人惊讶的复杂组织的壳边缘行和区的细胞。我们研究了细胞分裂模式与EdU掺入试验，发现两个生长区内的壳边缘。在更前面的孔径生长区，我们发现，推断的分裂角是偏向于平行于壳边缘，这些部门发生在边缘的左侧。在更后的外套膜上皮生长区，推断师是显着偏右，相对于前后轴。这些生长区，以及它们显示的左右不对称的卵裂模式，可以在细胞行为水平上解释壳形态发生的主要模式。在具有不同卷曲几何形状的腹足类中，Planorbella sp.，我们发现了与Tritia相似的壳缘组织和生长区，但与我们在Tritia的螺旋盘绕壳中观察到的不同的左右不对称性。这些结果表明，在地幔边缘上皮细胞的差异生长模式，有助于在腹足类贝壳壳的形状和识别细胞机制，可能会有所不同，以产生壳的多样性在进化中。
Gastropod shell morphologies are famously diverse but generally share a common geometry, the logarithmic coil. Variations on this morphology have been modeled mathematically and computationally but the developmental biology of shell morphogenesis remains poorly understood. Here we characterize the organization and growth patterns of the shell-secreting epithelium of the larval shell of the basket whelk Tritia (also known as Ilyanassa). Despite the larval shell's relative simplicity, we find a surprisingly complex organization of the shell margin in terms of rows and zones of cells. We examined cell division patterns with EdU incorporation assays and found two growth zones within the shell margin. In the more anterior aperture growth zone, we find that inferred division angles are biased to lie parallel to the shell edge, and these divisions occur more on the margin's left side. In the more posterior mantle epithelium growth zone, inferred divisions are significantly biased to the right, relative to the anterior-posterior axis. These growth zones, and the left-right asymmetries in cleavage patterns they display, can explain the major modes of shell morphogenesis at the level of cellular behavior. In a gastropod with a different coiling geometry, Planorbella sp., we find similar shell margin organization and growth zones as Tritia, but different left-right asymmetries than we observed in the helically coiled shell of Tritia. These results indicate that differential growth patterns in the mantle edge epithelium contribute to shell shape in gastropod shells and identify cellular mechanisms that may vary to generate shell diversity in evolution.