Hemocyte proliferation is associated with blood color shade variation in the blood clam, Tegillarca granosa

Abstract

Blood color shade is closely related to the health status and nutritional value of the blood clam, Tegillarca granosa. The blood color shade of T. granosa shows great variation and is considered as an economically importantly trait. However, the molecular regulatory mechanism of blood color shade variation is unclear. In this study, the total hemocyte count (THC) and hemoglobin concentration (HGC) were verified to be related to blood color shade. RNA-seq analysis was performed to explore the blood color shade-related genes in T. granosa. Transcriptome analysis revealed 399 and 467 genes that were exclusively highly expressed in light-blood clams (HGC > 45.7 g/L, designated TL) and dark-blood clams (HGC < 31.3 g/L, designated TH), respectively. Differentially expressed genes were enriched in cell cycle, and several key genes (such as CDC42 and CDC20) involved in hematopoietic processes were upregulated in the TH group, which means that the variation of blood color shade is probably related to hematopoietic cell proliferation. Knockdown of CDC42 gene expression resulted in a significant reduction in THC in blood clams, and EdU staining revealed that cell proliferation activity of the clam gills is higher in the TH group than in the TL group, which confirmed our assumption. The present study improves our understanding of the molecular mechanisms underlying blood color shade variation in marine clams and facilitates the selection of blood clams with higher hemoglobin contents.