The molluscan larval shell formation is a complicated process. There is evidence that the mantle of the primary larva (trochophore) contains functionally different cell populations with distinct gene expression profiles. However, it remains unclear how these cells are specified. In the present study, we identified three cell populations from the shell gland in earlier stages (gastrula) from the bivalve mollusc Crassostrea gigas. These cell populations were determined by analyzing the co-expression relationships among six potential shell formation (pSF) genes using two-color hybridization. The three cell populations, which we designated as SGCPs (shell gland cell populations), formed a concentric-circle pattern from outside to inside of the shell gland. SGCP I was located in the outer edge of the shell gland and the cells expressed pax2/5/8, gata2/3, and bmp2/4. SGCP II was located more internally and the cells expressed two engrailed genes. The last population, SGCP III, was located in the central region of the shell gland and the cells expressed lox4. Determination of the gene expression profiles of SGCPs would help trace their origins and fates and elucidate how these cell populations are specified. Moreover, potential roles of the SGCPs, e.g., development of sensory cells and shell biogenesis, are suggested. Our results reveal the internal organization of the embryonic shell gland at the molecular level and add to the knowledge of larval shell formation.

中文翻译：

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从双壳贝类软体动物的壳腺中鉴定出三个细胞群。

软体动物幼虫壳的形成是一个复杂的过程。有证据表明，初级幼虫（次绒毛）的套层包含功能不同的细胞群，具有不同的基因表达谱。但是，仍然不清楚如何指定这些单元格。在本研究中，我们从双壳软体动物Crassostrea gigas的早期阶段（胃）中鉴定了壳腺的三个细胞群。通过使用双色杂交分析六个潜在壳形成（pSF）基因之间的共表达关系来确定这些细胞群。我们将这三个细胞群称为SGCP（壳腺细胞群），从壳腺的外部到内部形成同心圆图案。SGCP I位于壳腺的外边缘，细胞表达pax2 / 5/8，gata2 / 3和bmp2 / 4。SGCP II位于更内部，细胞表达两个参与基因。最后一个种群SGCP III位于壳腺的中央区域，细胞表达lox4。确定SGCPs的基因表达谱将有助于追踪其起源和命运，并阐明这些细胞群的指定方式。此外，建议了SGCPs的潜在作用，例如感觉细胞的发育和壳的生物发生。我们的结果揭示了在分子水平上胚壳腺的内部组织，并增加了幼虫壳形成的知识。