Recently, we showed that generation of tumours in syngeneic mice by cells devoid of mitochondrial (mt) DNA (ρ0 cells) is linked to the acquisition of the host mtDNA. However, the mechanism of mtDNA movement between cells remains unresolved. To determine whether the transfer of mtDNA involves whole mitochondria, we injected B16ρ0 mouse melanoma cells into syngeneic C57BL/6Nsu9-DsRed2 mice that express red fluorescent protein in their mitochondria. We document that mtDNA is acquired by transfer of whole mitochondria from the host animal, leading to normalisation of mitochondrial respiration. Additionally, knockdown of key mitochondrial complex I (NDUFV1) and complex II (SDHC) subunits by shRNA in B16ρ0 cells abolished or significantly retarded their ability to form tumours. Collectively, these results show that intact mitochondria with their mtDNA payload are transferred in the developing tumour, and provide functional evidence for an essential role of oxidative phosphorylation in cancer.DOI: http://dx.doi.org/10.7554/eLife.22187.001

Laser microdissection was used for the preparation of whole chromosome painting probes in Silurana (Xenopus) tropicalis. Subsequent cross-species fluorescence in situ hybridization (Zoo-FISH) on its tetraploid relative Xenopus laevis revealed persistence of chromosomal quartets even after 50-65 million years of separate evolution. Their arrangement is in a partial concordance with previous experiments based on similarity of a high-resolution replication banding pattern. Further support for an allotetraploid origin of X. laevis was given by hybridization with a probe derived from the smallest X. tropicalis chromosome (Xt10). Here, pericentric areas of both arms of Xl 14 and 18 were stained, indicating intrachromosomal rearrangements. The positions of signals were not in agreement with the chromosomal quartets revealed by painting probes Xt 8 and 9 (Xl 11 + 14 and Xl 15 + 18, respectively). This suggests that both X. tropicalis chromosomes underwent non-reciprocal translocation of Xt10 separately in at least two different ancient ancestors. In addition, the observed translocation events could explain the origin of individuals with 18 chromosomes in diploid karyotypes, probably extinct after the genesis of the allotetraploid X. laevis (2n = 36).

Three major cytoskeletal proteins, actin, tubulin and spectrin, are present in the head of mammalian spermatozoa. Although cytoskeletal proteins are implicated in the regulation of capacitation and the acrosome reaction (AR), their exact role remains poorly understood. The aim of this study was to compare the distribution of the sperm head cytoskeleton before and after the AR in spermatozoa representing a range of acrosome size and shape. Spermatozoa from the human and three rodents (rat, hamster and grey squirrel) were fixed before and after the AR in appropriate medium in vitro. Indirect immunofluorescent localization of cytoskeletal proteins was undertaken with antibodies recognizing actin, spectrin and a-tubulin. Preparations were counterstained with propidium iodide and examined by epifluorescent and confocal microscopy. Our results clearly demonstrated changes in localization of cytoskeleton during the AR, mainly in the apical acrosome with further changes to the equatorial segment and post-acrosomal regions. The pattern of cytoskeletal proteins in the sperm head of all the species was similar in respect to various sub-compartments. These observations indicated that the sperm head cortical cytoskeleton exhibits significant changes during the AR and, therefore, support the image of cytoskeletal proteins as highly dynamic structures participating actively in processes prior to fertilization.

The mechanism of gamete fusion remains largely unknown on a molecular level despite its indisputable significance. Only a few of the molecules required for membrane interaction are known, among them IZUMO1, which is present on sperm, tetraspanin CD9, which is present on the egg, and the newly found oolema protein named Juno. A concept of a large multiprotein complex on both membranes forming fusion machinery has recently emerged. The Juno and IZUMO1, up to present, is the only known extracellular receptor pair in the process of fertilization, thus, facilitating the essential binding of gametes. However, neither IZUMO1 nor Juno appears to be the fusogenic protein. At the same time, the tetraspanin is expected to play a role in organizing the egg membrane order and to interact laterally with other factors. This review summarizes, to present, the known molecules involved in the process of sperm-egg fusion. The complexity and expected redundancy of the involved factors makes the process an intricate and still poorly understood mechanism, which is difficult to comprehend in its full distinction.