| Heavy metal pollution is one of the most common pollution in modern society.Heavy metal pollution of mangrove areas is serious.Geloina erosa is a bivalve inhabiting in mangroves.The living conditions of G.erosa are facing multiple challenges from heavy metal pollution and human activities.The overall goal is to investigate Cr（Ⅵ）response mechanisms of G.erosa and the applicability of the G.erosa as a bioindicator to evaluate the health status of mangrove ecosystems.Our specific objectives were to observe the gill histological changes induced by the Cr（Ⅵ）exposure,to identify the differential expression genes of G.erosa upon the Cr（Ⅵ）exposure through transcriptome,and to investigate the transcriptional response of commonly molecular biomarkers of Cr（Ⅵ）-exposed G.erosa.The main research contents and results were as follows:（1）To observe the toxicological changes of the gill tissue of G.erosa after hexavalent chromium [Cr（Ⅵ）] exposure by histological section.Histological observation of the gill tissues of G.erosa exposed to 100 μmol · L-1 Cr（Ⅵ）for 48 h showed that Cr（Ⅵ）exposure led to the ciliary epithelial swelling and other pathological changes in G.erosa gill.The results showed that Cr（Ⅵ）exposure could damage the cilia of the gills of G.erosa and adversely affect the physiological function of the gills.（2）Transcriptome sequencing technology was used to screen out key genes and biomarkers related to heavy metal toxicology of G.erosa in response to Cr（Ⅵ）exposure.A total of 134,817 Unigenes were obtained after assembly,with an average length of 1,185 bp.The GO analysis of Unigenes showed that " biological regulation "," cell component structure or synthesis" and " cell process " were the dominant subgroups of " biological process ",and " cell and cell membrane part " were the dominant subgroups of " cell component ".A total of 31,384 differentially expressed genes were found in the transcripts of this study.GO analysis of differentially expressed genes showed that DEGs were involved in a variety of physiological processes through up-regulation or down-regulation.In the “ biological processes ” categories,the item of cellular processes was the most dominant of 1,043 contigs.Membrane（1,300 contigs）and binding（1,668 contigs）were the most dominant for cellular component and molecular functions respectively,and so on.In the KEGG pathways,several immune and apoptosis related pathways were significantly enriched,including some calcium signaling pathway,drug metabolism pathway,toll-like receptor signaling pathway,protein processing in endoplasmic reticulum pathway and MAPK signaling pathway.The results showed that Cr（Ⅵ）exposure induced the activation of immune system and cell apoptosis,and enhanced TLR signal transduction.（3）The expression of biomarkers related to heavy metal toxicology and key genes related to the response of G.erosa to Cr（Ⅵ）exposure was studied by q RT-PCR.Among eight genes of the selected biomarkers,Calm,HSP70,CYP450,ATG5,TLR2,MYD88 and CASP8 were up-regulated,while TLR4 was down-regulated in response to the Cr（Ⅵ）exposure.The results showed that TLR2,ATG5,MYD88,CYP450,HSP70,CALM,CAPS8 and TLR4 were all sensitive to Cr（Ⅵ）exposure.Combined with histological observations,Cr（Ⅵ）exposure damaged gill cilia and induced epithelial cells swelling in G.erosa while Cr（Ⅵ）damaged cell membrane and disturbed endoplasmic reticulum Ca2+homeostasis in the gills. |
