Single-cell transcriptomics identifies new blood cell populations in Drosophila released at the onset of metamorphosis

Drosophila blood cells called hemocytes form an efficient barrier against infections and tissue damage. During metamorphosis, hemocytes undergo tremendous changes in their shape and behavior, preparing them for tissue clearance. Yet, the diversity and functional plasticity of pupal blood cells have not been explored. Here, we combine single-cell transcriptomics and high-resolution microscopy to dissect the heterogeneity and plasticity of pupal hemocytes. We identified undifferentiated and specified hemocytes with different molecular signatures associated with distinct functions such as antimicrobial, antifungal immune defense, cell adhesion or secretion. Strikingly, we identified a highly migratory and immuneresponsive pupal cell population expressing typical markers of the posterior signaling center (PSC), which is known to be an important niche in the larval lymph gland. PSC-like cells become restricted to the abdominal segments and are morphologically very distinct from typical Hemolectin (Hml)-positive plasmatocytes. G-TRACE lineage experiments further suggest that PSC-like cells can transdifferentiate to lamellocytes triggered by parasitoid wasp infestation. In summary, we present the first molecular description of pupal Drosophila blood cells, providing insights into blood cell functional diversification and plasticity during pupal metamorphosis. Three replicates of single cell RNA-sequencing of 2-10h APF Drosophila pupae using the Takara ICELL8 platform.

果蝇（Drosophila）的血细胞（hemocytes）是抵御感染与组织损伤的有效屏障。在变态发育过程中，血胞的形态与行为会发生剧烈变化，为组织清除工作做好准备。然而，蛹期血细胞的多样性与功能可塑性尚未得到深入探究。
本研究结合单细胞转录组学（single-cell transcriptomics）与高分辨率显微成像技术，解析了蛹期血胞的异质性与可塑性。研究团队鉴定出未分化与已特化的血胞群体，它们携带有与不同功能相关的独特分子特征，涵盖抗菌、抗真菌免疫防御、细胞黏附以及分泌等功能。
值得注意的是，本研究发现了一类高迁移性、免疫响应活跃的蛹期细胞群体，该群体表达幼虫淋巴腺中重要微环境（niche）——后部信号中心（posterior signaling center, PSC）的典型标志物。类PSC细胞仅分布于腹部体节，且在形态上与典型的血凝集素（Hemolectin, Hml）阳性浆细胞（plasmatocytes）差异显著。G-TRACE谱系示踪实验进一步表明，类PSC细胞在寄生蜂侵染的诱导下可转分化为片状细胞（lamellocytes）。
综上，本研究首次从分子层面解析了果蝇蛹期血细胞，为揭示变态发育过程中血细胞的功能分化与可塑性提供了重要见解。本研究采用Takara ICELL8平台，对化蛹后2-10小时（APF, After Puparium Formation）的果蝇蛹开展了单细胞RNA测序，共设置三次生物学重复。