Data from: Cell turnover and detritus production in marine sponges from tropical and temperate benthic ecosystems

This study describes in vivo cell turnover (the balance between cell proliferation and cell loss) in eight marine sponge species from tropical coral reef, mangrove and temperate Mediterranean reef ecosystems. Cell proliferation was determined through the incorporation of 5-bromo-2′-deoxyuridine (BrdU) and measuring the percentage of BrdU-positive cells after 6 h of continuous labeling (10 h for Chondrosia reniformis). Apoptosis was identified using an antibody against active caspase-3. Cell loss through shedding was studied quantitatively by collecting and weighing sponge-expelled detritus and qualitatively by light microscopy of sponge tissue and detritus. All species investigated displayed substantial cell proliferation, predominantly in the choanoderm, but also in the mesohyl. The majority of coral reef species (five) showed between 16.1±15.9% and 19.0±2.0% choanocyte proliferation (mean±SD) after 6 h and the Mediterranean species, C. reniformis, showed 16.6±3.2% after 10 h BrdU-labeling. Monanchora arbuscula showed lower choanocyte proliferation (8.1±3.7%), whereas the mangrove species Mycale microsigmatosa showed relatively higher levels of choanocyte proliferation (70.5±6.6%). Choanocyte proliferation in Haliclona vansoesti was variable (2.8–73.1%). Apoptosis was negligible and not the primary mechanism of cell loss involved in cell turnover. All species investigated produced significant amounts of detritus (2.5–18% detritus bodyweight−1·d−1) and cell shedding was observed in seven out of eight species. The amount of shed cells observed in histological sections may be related to differences in residence time of detritus within canals. Detritus production could not be directly linked to cell shedding due to the degraded nature of expelled cellular debris. We have demonstrated that under steady-state conditions, cell turnover through cell proliferation and cell shedding are common processes to maintain tissue homeostasis in a variety of sponge species from different ecosystems. Cell turnover is hypothesized to be the main underlying mechanism producing sponge-derived detritus, a major trophic resource transferred through sponges in benthic ecosystems, such as coral reefs.本研究描述了采自热带珊瑚礁、红树林及温带地中海礁生态系统的8种海洋海绵的体内细胞更新过程——即细胞增殖与细胞丢失之间的动态平衡。细胞增殖通过掺入5-溴-2′-脱氧尿苷（5-bromo-2′-deoxyuridine，简称BrdU）进行测定，并在持续标记6小时（云形软海绵*Chondrosia reniformis*为10小时）后统计BrdU阳性细胞的百分比。凋亡通过靶向活化半胱天冬酶-3（active caspase-3）的抗体进行鉴定。细胞脱落引发的细胞丢失，通过收集并称重海绵排出的碎屑开展定量研究，同时通过光学显微镜观察海绵组织与碎屑进行定性分析。所有被研究的海绵物种均表现出显著的细胞增殖，主要分布于领细胞层（choanoderm），同时也存在于中胶层（mesohyl）。其中5种珊瑚礁物种在6小时标记后，领细胞增殖率介于16.1±15.9%至19.0±2.0%（平均值±标准差）之间；地中海物种云形软海绵*Chondrosia reniformis*经10小时BrdU标记后，领细胞增殖率为16.6±3.2%。树状单柄海绵*Monanchora arbuscula*的领细胞增殖率较低（8.1±3.7%），而红树林物种细点粘海绵*Mycale microsigmatosa*的领细胞增殖率则相对较高（70.5±6.6%）。凡氏小团扇海绵*Haliclona vansoesti*的领细胞增殖率波动较大，范围为2.8%~73.1%。凋亡程度极微，并非细胞更新过程中细胞丢失的主要机制。所有被研究物种均产生大量碎屑，产率为2.5%~18%（碎屑体重⁻¹·d⁻¹），且8种物种中有7种观察到细胞脱落现象。组织学切片中观察到的脱落细胞数量，可能与碎屑在海绵管道内的停留时间差异相关。由于排出的细胞碎片已发生降解，碎屑产生量无法直接与细胞脱落现象建立关联。本研究证实，在稳态条件下，经由细胞增殖与细胞脱落实现的细胞更新，是维持多种不同生态系统中海绵物种组织稳态的普遍过程。研究推测，细胞更新是产生海绵源性碎屑的核心潜在机制，而海绵源性碎屑是珊瑚礁等底栖生态系统中经由海绵传递的关键营养资源。