Determination Of Onset Time Of Antimicrobial Peptides Expression In Pelophylax Nigromaculatus Tadpoles

The embryo and tadpoles of amphibians are protected by a mucus barrier from challenges of environmental microbes.The protective mucus layer becomes weaker as development progresses.As compensation,the skin synthesizes antimicrobial peptides(AMPs)to inhibit accessing microbes.However,it is still unknown when the synthesis of AMPs starts.In order to answer the question,we investigated histological dynamics and expression of AMPs in the skin of black-spotted frog(Pelophylax nigromaculatus)tadpoles at different developmental stages.Results showed that the skin of the embryos and hatchlings were composed of 1-2 layers of cells among which giant mucosal cells and secretion cells produce mucus layer and fine pigment granules to the surface of skin.Epidermis continued to thicken as development progressed,and up to stage T3(corresponding to Gosner's stage 26),the spongy layer and compact layer were drastically thickened with primary mucus and granular glands being observable.It was this stage that AMPs were first detected.By stage T4(Gosner's stage 27 to 45)and juvenile frog,the skin tissue had developed structure similar to adult stage available for AMPs synthesis.These findings suggest that the shift of immunity barrier from physiological form to chemical form might be essential for tadpole's viability for landing,and factors influencing this process would affect its viability by disturbing the immunity.This provides a new insight into the mechanism of population dynamics under the ecological contexts of climate change and water pollution.