Pollen stigma interactions: so near yet so far

Getting a firm grip on the 'S' (incompatibility)-loci, which encourage outbreeding in many flowering plants, continues to be a frustrating exercise. Only last year it seemed that all the male and female S-locus factors that regulate self-incompatibility in a key group of plants - Brassica - had at last been characterized. However, it now appears that the first S-locus product to be identified, does not, after all, play a part in determining S-specificity.     

The mitochondrial genome: so simple yet so complex.

Mitochondria possess a small set of genes that are essential for respiratory function. This review highlights recent advances in our understanding of mitochondrial gene organization and expression. These studies illustrate a remarkable diversity among eukaryotic lineages and an impressive complexity of events needed to achieve nuclear-mitochondrial harmony.     

TRAIL- and TNF-induced signaling complexes—so similar yet so different

TNF receptor-1 (TNFR1) and TRAIL death receptors preferentially induce pro-inflammatory or cytotoxic signaling, respectively, via distinct plasma membrane and cytosolic complexes. New studies identifying the pro-inflammatory factors TRAF2, RIP, and LUBAC in TRAIL death receptor complexes suggest that the latter are more “TNFR1-like” than anticipated and argue for revision of prevailing models of spatio-hierarchical TRAIL-induced signaling complex assembly.     

Drosophila Melanogaster, Drosophila Simulans: so Similar yet so Different

During the last two decades, the two cosmopolitan species Drosophila melanogaster and Drosophila simulans have been compared with regard to numerous characteristics, ranging from their geographic distribution and ecology to their DNA polymorphism. Various traits have been compared, including morphology, physiology, sexual behavior, allozymes and other proteins, chromosomal inversions, mitochondrial and nuclear DNA, transposable elements, wolbachia etc. Such comparisons reveal similarities and differences between the two species, depending on the trait considered. In most cases, the between-population variability of D. simulans is lower than that of D. melanogaster, but the two species exhibit similar levels of within-population variability. One of the main exceptions is the nucleotide polymorphism of several nuclear regions. Although several hypotheses have been proposed to explain these observations, the evolutionary dynamics of these two species are far from being understood. How have two species sharing a common ancestor in the recent past accumulated so many differences? A brief history of comparisons of the two species, from the first in 1919 by A.H. Sturtevant, and a summary of the hypotheses proposed to explain the similarities and the differences between these species are presented and discussed.     

Podosome-type adhesions and focal adhesions, so alike yet so different

Cell-matrix adhesions are essential for cell migration, tissue organization and differentiation, therefore playing central roles in embryonic development, remodeling and homeostasis of tissues and organs. Matrix adhesion-dependent signals cooperate with other pathways to regulate biological functions such as cell survival, cell proliferation, wound healing, and tumorigenesis. Cell migration and invasion are integrated processes requiring the continuous, coordinated assembly and disassembly of integrin-mediated adhesions. An understanding of how integrins regulate cell migration and invasiveness through the dynamic regulation of adhesions is fundamental to both physiological and pathological situations. A variety of cell-matrix adhesions has been identified, namely, focal complexes, focal adhesions, fibrillar adhesions, podosomes, and invadopodia (podosome-type adhesions). These adhesion sites contain integrin clusters able to develop specialized structures, which are different in their architecture and dynamics although they share almost the same proteins. Here we compare recent advances and developments in the elucidation of the organization and dynamics of focal adhesions and podosome-type adhesions, in order to understand how such subcellular sites - though closely related in their composition - can be structurally and functionally different. The underlying question is how their respective physiological or pathological roles are related to their distinct organization.