The evolution of insect germline specification strategies

• Germline determination modes are evolutionarily labile.
• Cricket germline determination bears similarity to mammals.
• oskar is the crucial molecule for organizing insect germ plasm.
• oskar is heavily involved in transitions between germline determination modes.

The establishment of the germline is essential for sexually reproducing organisms. In animals, there are two major strategies to specify the germline: maternal provision and zygotic induction. The molecular basis of the maternal provision mode has been well characterized in several model organisms (fly, frog, fish, and nematode), while that of the zygotic induction mode has mainly been studied in mammalian models such as the mouse. Shifts in germline determination modes occur unexpectedly frequently and many such shifts have occurred several times among insects. Given their general tractability and rapidly increasing genomic and genetic tools applicable to many species, the insects present a uniquely powerful model system for understanding major transitions in reproductive strategies, and developmental processes in general.