Fujian Key Laboratory on Conservation and Sustainable Utilization of Marine Biodiversity, College of Geography and Oceanography, Minjiang University, Fuzhou 350108, China
2.
College of Environmental and Safety Engineering, Fuzhou University, Fuzhou 350108, China
3.
SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou 510006, China
4.
National Marine Environmental Monitoring Center, Dalian 116023, China
Funds:
The National Natural Science Foundation of China under contract No. 42106119; the Department of Science and Technology of Fujian Province under contract Nos 2022J02052, 2020J05175 and 2020J05178; the Fujian Provincial Department of Ocean and Fisheries under contract No. FJHJF-L-2022-12; the Yancheng fishery high quality development project under contract No. YCSCYJ2021023).
In the coastal environment, the co-occurrence of antibiotic and nanoplastic pollution is common. Investigating their individual and combined toxicity to marine organisms is of great necessity. In the present study, the reproductive toxicity of sulfamethazine (SMZ) and nanoplastics (polystyrene, PS) via the dietary route on the spermatogenesis of marine medaka (Oryzias melastigma) was examined. After 30 days of dietary exposure, SMZ alone decreased the gonadosomatic index (GSI) value (~ 35%) and the proportion of undifferentiated type A spermatogonia (Aund) (~ 40%), probably by disrupting the testicular sex hormone production, the spermatogenesis-related growth factor network and the balance of apoptosis. Individual exposure to PS did not affect the GSI value or the proportions of germ cells at different developmental stages, but dysregulated the expression of several spermatogenesis-related genes. Interestingly, the presence of PS alleviated the decreased GSI value caused by SMZ. This alleviation effect was achieved by enhancing the spermatogonia differentiation instead of reversing the suppressed self-renewal of Aund, suggesting that the mixture of PS and SMZ could cause reproductive effects in a different way. These findings expand our knowledge of threats of ubiquitous antibiotic and nanoplastic pollution to fish reproduction and population.
Figure 1. Gonadosomatic indexes (GSI) in the sulfamethazine (SMZ) and nano polystyrene (PS) exposed male O. melastigma. Asterisks indicated significant differences (* p < 0.05, ** p ≤ 0.01, n ≥ 5).
Figure 2. Paraffin sections of testis from the Control (A), L-SMZ (B), H-SMZ (C), PS (D) and H-SMZ + PS (E) groups. No significant effects of PS, SMZ or their binary mixture on the morphological structure of testis were observed. Aund, undifferentiated type A spermatogonia; Adiff, differentiated type A spermatogonia; B, type B spermatogonia; SC, spermatocyte; ST, spermatids.
Figure 3. Relative expression of germ cell marker genes in the sulfamethazine (SMZ) and nano polystyrene (PS) exposed male O. melastigma. Representation of spermatogenesis from type A undifferentiated spermatogonia to spermatozoa was modified from Schulz et al., (2010) (A). The transcriptional expression levels of nanos2 (B), piwil1 (C), dazl (D), sycp3 (E), odf3b (F) and sept7 (G) were measured. Asterisks indicated significant differences (* p < 0.05, ** p ≤ 0.01, n ≥ 5). Aund, undifferentiated type A spermatogonia; Adiff, differentiated type A spermatogonia; B, type B spermatogonia; SC, spermatocyte; ST, spermatids; SZ, spermatozoa.
Figure 4. Relative expression of spermatogenesis related genes in the sulfamethazine (SMZ) and nano polystyrene (PS) exposed male O. melastigma. The values of four treatment groups were normalized to the control which was set to 0. Color bar from red to green represented the fold change from increasing to decreasing (n ≥ 5).
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