Expression of mapk1 and egr1 genes in Onchidium reevesii under tidal stimulation

Previous studies have speculated that tidal rhythm of Onchidium reevesii was linked to its memory ability, which has not been well explained. Mapk1 and egr1 genes are closely related to memory formation in the MAPK signaling pathway that have been extensively studied in vertebrates. These two genes are involved in Long-term potentiation (LTP), which is generally regarded as one of the main molecular mechanisms underlying learning and memory. To investigate the relationship between tidal rhythm of O. reevesii and its memory ability, we studied the molecular mechanism of mapk1 and egr1 genes cooperating with tidal rhythm. The full-length cDNA sequence of mapk1 gene was cloned by RACE method and analyzed by bioinformatics, then qRT-PCR was used to analyze its expression levels in each tissue. A homology analysis and phylogenetic tree reconstruction revealed that O. reevesii is most closely related to the Biomphalaria glabrata. The qRT-PCR showed that mapk1 was expressed in all the tissues, but the highest expression was in the ganglion. We speculated that mapk1 is related to memory formation of O. reevesii. Then we used qRT-PCR to detect the expression of mapk1 and egr1 in ganglion of O. reevesi under tidal stimulation. The expression of mapk1 and egr1 at the rising tide points were significantly higher (P < 0.05) than that at the previous one lowest tide points on May 15–21, except the rising tide point on May 20 and May 21 of mapk1. The expression of mapk1 and egr1 genes in the ganglion sampled for 7-day were basically the same as that of the tide change of the same day. The expression of the two genes were upregulated at raising tide and downregulated at the lowest tide, it is presumed that the O. reevesii was affected by the tide for a long time and formed the tide memory.