Maternal cadmium exposure induces mt2 and smtB mRNA expression in zebrafish (Danio rerio) females and their offspring

The present study aimed to identify the effects of maternal cadmium (Cd2+) exposure on the mRNA expression of mt2 (metallothionein-2) and smtB (similar to metallothionein-B) in female zebrafish (Danio rerio) and their offspring (F1 larvae). Zebrafish females were exposed to 0, 8.9, 17.8, and 35.6 μM Cd2+ for 72 h, and their ovaries and F1 larvae were collected to measure their Cd2+ contents and their smtB and mt2 mRNA expression. Cd2+ contents and the mRNA expression of smtB and mt2 in F1 larvae all showed positive correlations with the maternal Cd2+ treatment dose. The mt2 was 1.9- to 3.4-fold higher than smtB in F1 larvae. Furthermore, F1 larvae had noticeably enhanced Cd2+ tolerance after maternal Cd2+ treatment. These results demonstrate that maternal Cd2+ was transferred to larval fish and induced mt2 and smtB mRNA expression to protect larva against the impacts of Cd2+. In female ovaries, mt2 expression showed a noticeable increase after exposure to a metal environment, while smtB did not show exactly the same effect. The study can only conclude that smtB might have a much different role other than just protecting against the impacts of metals.