swi1 and swi3 Perform Imprinting, Pausing, and Termination of DNA Replication in S. pombe

AbstractThe developmental program of cell-type switching of S. pombe requires a strand-specific imprinting event at the mating-type locus (mat1). Imprinting occurs only when mat1 is replicated in a specific direction and requires several trans- acting factors. This work shows (1) that the factors swi1p and swi3p act by pausing the replication fork at the imprinting site; and (2) that swi1p and swi3p are involved in termination at the mat1-proximal polar-terminator of replication (RTS1). A genetic screen to identify termination factors identified an allele that separated pausing/imprinting and termination functions of swi1p. These results suggest that swi1p and swi3p promote imprinting in novel ways both by pausing replication at mat1 and by terminating replication at RTS1

Mating behaviour in Lymnaea stagnalis pond snails is a maternally inherited, lateralized trait

Lateralization of the brain has traditionally been considered a specialization that is confined to the vertebrates, but recent studies have revealed that a range of invertebrates also have a brain that is structurally asymmetric and/or each side performs a different set of functions. Here, we show that the precopulatory mating behaviour of the pond snail Lymnaea stagnalis is lateralized. We present evidence that the asymmetry of the behaviour corresponds to the sinistral or dextral shell coil, or chirality, of the snail, and is apparently also controlled by a maternal effect locus. As sinistral snails also tend to have mirror image brains, these findings suggest that the lateralized sexual behaviour of L. stagnalis is set up early in development, and is a direct consequence of the asymmetry of the entire body

Why are some people left-handed? An evolutionary perspective

Since prehistoric times, left-handed individuals have been ubiquitous in human populations, exhibiting geographical frequency variations. Evolutionary explanations have been proposed for the persistence of the handedness polymorphism. Left-handedness could be favoured by negative frequency-dependent selection. Data have suggested that left-handedness, as the rare hand preference, could represent an important strategic advantage in fighting interactions. However, the fact that left-handedness occurs at a low frequency indicates that some evolutionary costs could be associated with left-handedness. Overall, the evolutionary dynamics of this polymorphism are not fully understood. Here, we review the abundant literature available regarding the possible mechanisms and consequences of left-handedness. We point out that hand preference is heritable, and report how hand preference is influenced by genetic, hormonal, developmental and cultural factors. We review the available information on potential fitness costs and benefits acting as selective forces on the proportion of left-handers. Thus, evolutionary perspectives on the persistence of this polymorphism in humans are gathered for the first time, highlighting the necessity for an assessment of fitness differences between right- and left-handers