Germline Transformation of Drosophila Virilis with the Transposable Element Mariner

An important goal in molecular genetics has been to identify a transposable element that might serve as an efficient transformation vector in diverse species of insects. The transposable element mariner occurs naturally in a wide variety of insects. Although virtually all mariner elements are nonfunctional, the Mos1 element isolated from Drosophila mauritiana is functional. Mos1 was injected into the pole-cell region of embryos of D. virilis, which last shared a common ancestor with D. mauritiana 40 million years ago. Mos1 PCR fragments were detected in several pools of DNA from progeny of injected animals, and backcross lines were established. Because G(0) lines were pooled, possibly only one transformation event was actually obtained, yielding a minimum frequency of 4%. Mos1 segregated in a Mendelian fashion, demonstrating chromosomal integration. The copy number increased by spontaneous mobilization. In situ hybridization confirmed multiple polymorphic locations of Mos1. Integration results in a characteristic 2-bp TA duplication. One Mos1 element integrated into a tandem array of 370-bp repeats. Some copies may have integrated into heterochromatin, as evidenced by their ability to support PCR amplification despite absence of a signal in Southern and in situ hybridizations.