Nucleo-kinetoplast interactions and variability in the Kinetoplastida

Summary A detailed electron microscope study of epimastigotes of some Trypanosoma cruzi strains and of Leishmania spp. promastigotes has revealed in these not only a close spatial proximity between the nucleus and kinetoplast but also a direct contact between these two compartments and even their occasional tight joining. These contacts are seen to evolve in parallel with trypanosomatid development, even within the limits of one stage of the life cycle, and to become more obvious during the parasitic cell differentiation into invasive form. A possibility of exchange between genetically important molecules at the contact of two different DNAcontaining cell structures is discussed in terms of the role of kinetoplast DNA minicircles as a source of genotypic diversity and transposable genetic elements. Moreover, these events are regarded as being presumably involved in the specific mechanism of variability characteristic of the agamic protozoa of the order Kinetoplastida.