Aim: 

Among invertebrates, steroids, enzymes of steroid metabolism and steroid receptors have been identified in molluscs. However, their role in modulating gene expression is still unknown. In this work, the effects of the natural estrogen 17b-estradiol (E₂) in the bivalve Mytilus were investigated in the hepatopancreas, a tissue playing a central role in metabolism and in gametogenesis.

Methods: 

Mussels were injected with 25 pmoles of E₂ and tissues sampled at 24 hrs post-injection. The expression of selected Mytilus genes was evaluated by quantitative RT-PCR. Moreover, global gene expression was evaluated by a Mytilus cDNA microarray. Functional parameters (lysosomal parameters, antioxidant enzyme activities) were also assessed.

Results: 

E₂ induced up-regulation of the Estrogen Receptors in Mytilus, as well as of catalase, MT-20 and GST-p. The microarray data showed significant changes in expression of 34 gene sequences. Among up-regulated genes, sequences coding for proteins involved in lysosomal function, lipid signalling and metabolism, and glutathione metabolism were identified. Down-regulation of extracellular matrix components and vitellogenesis system was observed. These effects were accompanied by changes in lysosomal parameters and antioxidant enzyme activities.

Conclusions: 

The results demonstrate for the first time that E₂ affects gene expression and function in molluscan hepatopancreas. In particular, components involved in lysosomal function and maintenance of redox balance are affected.