Modification of the larval swimming behavior in Oikopleura dioica, a chordate with a miniaturized central nervous system by dsRNA injection into fertilized eggs.

Using RNA interference, we have selectively perturbed neurotransmitter-related features of the larval swimming behavior of Oikopleura dioica, a tunicate with a central nervous system comprising about 130 neurons. We injected dsRNA into fertilized eggs to knockdown the expression of the genes, respectively, encoding ChAT (choline acetyltransferase) and GAD (glutamic acid decarboxylase), enzymes critical for the biosynthesis of acetylcholine and GABA. These two neurotransmitters have conserved roles during evolution, particularly within chordate motor systems, where they mediate respectively neuromuscular and central inhibitory signals. In Oikopleura, interference with ChAT expression prevented the normal bidirectional, propagating tail movement characteristic of swimming, permitting only repeated unilateral tail bends. Proper swimming was never observed, and the resting period between episodes of activity was lengthened. This phenotype is most likely caused by the reduction of transcription observed for both the targeted ChAT gene and the VAChT gene (Vesicular Acetylcholine Transporter), both genes being transcribed from the same operon. Interference with GAD expression led to an uncoordinated version of swimming with a spiral movement trajectory, but with episodes similar in duration and cycle frequency to those of normal swimming. Our results suggest locomotor functions for ChAT and GABA that are more subtle than previously proposed for tunicates and opens the way for a genetic dissection of Oikopleura neuronal circuits, which are likely to be among the most simplified in the chordate phylum.

Estrogen-induced alterations in amh and dmrt1 expression signal for disruption in male sexual development in the zebrafish.

Dmrt1 and amh are genes involved in vertebrate sex differentiation. In this study, we cloned dmrt1 and amh cDNAs in zebrafish (Danio rerio) and investigated the effects of exposure to 17a-ethinylestradiol (EE2), during early life on their patterns of expression and impact on the subsequent gonadal phenotype. Expression of both amh and dmrt1 in embryos was detected as early as at 1 day post fertilization (dpf) and enhanced expression of amh from 25 dpf was associated with the period of early gonadal differentiation. Sex-dependent differences in enhanced green fluorescent protein transgene expression driven by the promoter of the germ cell-specific vas gene were exploited to show that at 28dpf and 56dpf both amh and dmrt1 mRNA were overexpressed in males compared with females. Exposure during early life to environmentally relevant concentrations of EE2 had a suppressive effect on the expression of both amh and dmrt1 mRNAs and this was associated with a cessation/retardation in male gonadal sex development. Our findings indicate that estrogen-induced suppression in expression of dmrt1 and amh during early life correlate with subsequent disruptive effects on the sexual phenotype in males.