Efficient cell electrotransfection can be achieved using combinations of high-voltage (HV; 800 V/cm, 100 micros) and low-voltage (LV; 80 V/cm, 100 ms) pulses. We have developed equipment allowing the generation of various HV and LV combinations with precise control of the lag between the HV and LV pulses. We injected luciferase-encoding DNA in skeletal muscle, before or after pulse delivery, and measured luciferase expression after various pulse combinations. In parallel, we determined permeabilization levels using uptake of (51)Cr-labeled EDTA. High voltage alone resulted in a high level of muscle permeabilization for 300 seconds, but very low DNA transfer. Combinations of one HV pulse followed by one or four LV pulses did not prolong the high permeabilization level, but resulted in a large increase in DNA transfer for lags up to 100 seconds in the case of one HV + one LV and up to 3000 seconds in the case of one HV + four LV. DNA expression also reached similar levels when we injected the DNA between the HV and LV pulses. We conclude that the role of the HV pulse is limited to muscle cell permeabilization and that the LV pulses have a direct effect on DNA. In vivo DNA electrotransfer is thus a multistep process that includes DNA distribution, muscle permeabilization, and DNA electrophoresis.

The semaphorin family is a large group of proteins controlling cell migration and axonal growth cone guidance. These proteins are bi-functional signals capable of growth promotion or growth inhibition. Initially described in the nervous system, the majority of studies related to semaphorins and semaphorin signalling are nowadays performed in model systems outside the nervous system. Here, we provide an exhaustive review of the many faces of semaphorins both during developmental, regulatory and pathological processes. Indeed, because of their crucial fundamental roles, the semaphorins and their receptors represent important targets for the development of drugs directed at a variety of diseases.