The finding that spermatozoa of virtually all animal species can spontaneously bind exogenous
DNA molecules and deliver it to oocytes at fertilisation first suggested that these cells can be used as vectors
for introducing new genetic and phenotypic traits in animals. That has led to the development of a novel
approach to animal transgenesis, namely Sperm Mediated Gene Transfer (SMGT). Here we review findings
obtained using this experimental approach. A critical examination of published evidence indicates that the
alternative between direct binding to the plasma membrane of sperm cells, or its bypass, represents a crucial
parameter for the fate of exogenous nucleic acid molecules: in the former case, episomal structures are
mainly generated; in the latter, integration in the host genome is more frequent. The original protocol was
based on the direct interaction between sperm cells and foreign DNA. Several alternative variants have been
developed thereafter to improve the efficacy of the method. Improved protocols include the combination of
SMGT with: i) ICSI (intracytoplasmic sperm injection) technology, ii) restriction enzymes favoring DNA
integration (REMI), or iii) linker-based (LB), in which the DNA binding is mediated by an antibody
recognizing a membrane antigen. In another approach, the aim is to produce “transgenic spermatozoa”: for
example, in testis-mediated gene transfer (TMGT) the foreign DNA is microinjected directly into testis; in
virus-mediated transgenesis, new genes are delivered to spermatogonal stem cells by viral vectors. The
recent finding that mature spermatozoa are the source of non-integrated, transcriptionally competent
retrogenes also suggests a potential use of SMGT for embryonic gene therapy.
Keywords: SMGT, Transgenesis, Episomal structures, DNA integration, RNA-mediated transgenesis,
ICSI, REMI, TMGT, Non-Mendelian characters, Sperm-mediated gene therapy.
