Melastatin subfamily Transient Receptor Potential channels support spermatogenesis in planarian flatworms

ABSTRACTThe Transient Receptor Potential superfamily of proteins (TRPs) form cation channels that are abundant in animal sensory systems. Amongst TRPs, the Melastatin-related subfamily (TRPMs) is composed of members that respond to temperature, pH, sex hormones, and various other stimuli. Some TRPMs exhibit enriched expression in gonads of vertebrate and invertebrate species, but their contributions to germline development remain to be determined. We identified twenty-one potential TRPMs in the planarian flatwormSchmidtea mediterraneaand analyzed their anatomical distribution of expression by whole-mountin situhybridization. Enriched expression of two TRPMs (Smed-TRPM-candSmed-TRPM-l) was detected in testis, whereas eight TRPM genes had detectable expression in patterns representative of neuronal and/or sensory cell types. Functional analysis of TRPM homologs by RNA-interference (RNAi) revealed that disruption ofSmed-TRPM-cexpression results in reduced sperm development, indicating a role for this receptor in supporting spermatogenesis.Smed-TRPM-lRNAi did not result in a detectable phenotype, but it increased sperm development deficiencies when combined withSmed-TRPM-cRNAi. Fluorescencein situhybridization revealed expression ofSmed-TRPM-cin early spermatogenic cells within testes, suggesting cell-autonomous regulatory functions in germ cells for this gene. In addition,Smed-TRPM-cRNAi resulted in reduced numbers of presumptive germline stem cell clusters in asexual planarians, suggesting thatSmed-TRPM-csupports establishment, maintenance, and/or expansion of spermatogonial germline stem cells. While further research is needed to identify the factors that trigger Smed-TRPM-c activity, these findings reveal one of few known examples for TRPM function in direct regulation of sperm development.