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MAP kinases (MAPK) are involved in the regulation of cellular processes such as reproduction and growth. In parasites, the role of MAPK has been scarcely studied. Here, we describe the participation of an ERK-like protein in estrogen-dependent reproduction of the helminth parasite Taenia crassiceps. Our results show that 17beta-estradiol induces a concentration-dependent increase in the bud number of in vitro cultured cysticerci. If parasites are also incubated in presence of an ERK-inhibitor, the stimulatory effect of estrogen is blocked. The expression of ERK-like mRNA and its corresponding protein was detected in the parasite. The ERK-like protein was over-expressed by all treatments. Nevertheless, a strong induction of phosphorylation of this protein was observed only in response to 17beta-estradiol. Cross-contamination by host cells was discarded by flow cytometry analysis. Parasite cells expressing the ERK-like protein were exclusively located at the subtegument tissue by confocal microscopy. Finally, the ERK-like protein was separated by bidimensional electrophoresis and then sequenced, showing the conserved TEY activation motif, typical of all known ERK 1/2 proteins. Our results show that an ERK-like protein is involved in the molecular signalling during the interaction between the host and T. crassiceps, and may be considered as target for anti-helminth drugs design.

Taenia crassiceps cysticerci (cysts) reproduce by budding. The cysts' production of buds was measured in vitro to explore parasite and environmental-related factors involved in the extreme individual variation in parasite loads of inbred mice. Cysts were placed in in vitro culture for 10 days at initial parasite densities of 1, 5, 10 cysts/well in 1 ml of RPMI Medium 1640 without serum. Results showed that there is considerable intrinsic initial variation among inoculated cysts in their production of buds and that increasing parasite density (crowding) stimulates the overall production of buds and recruit into budding most of the cysts. Identical cultures were then subjected to various treatments such as heating and exposure to peroxide to induce stress, or to 17beta-estradiol, insulin, glucose, or insulin+glucose to supplement putatively limiting hormonal and energy resources. All treatments increased budding but the parasites' strong budding response to crowding alone overshadows the other treatments.