The DIX domain targets dishevelled to actin stress fibres and vesicular membranes

Colorectal cancer results from mutations in components of the Wnt pathway that regulate beta-catenin levels. Dishevelled (Dvl or Dsh) signals downstream of Wnt receptors and stabilizes beta-catenin during cell proliferation and embryonic axis formation. Moreover, Dvl contributes to cytoskeletal reorganization during gastrulation and mitotic spindle orientation during asymmetric cell division. Dvl belongs to a family of eukaryotic signalling proteins that contain a conserved 85-residue module of unknown structure and biological function called the DIX domain. Here we show that the DIX domain mediates targeting to actin stress fibres and cytoplasmic vesicles in vivo. Neighbouring interaction sites for actin and phospholipid are identified between two helices by nuclear magnetic resonance spectroscopy (NMR). Mutation of the actin-binding motif abolishes the cytoskeletal localization of Dvl, but enhances Wnt/beta-catenin signalling and axis induction in Xenopus. By contrast, mutation of the phospholipid interaction site disrupts vesicular association of Dvl, Dvl phosphorylation, and Wnt/beta-catenin pathway activation. We propose that partitioning of Dvl into cytoskeletal and vesicular pools by the DIX domain represents a point of divergence in Wnt signalling.     

A revision of the Patagonian predaceous midges of the subgenus Acanthohelea of Stilobezzia excluding the S. (A.) edwardsi group (Diptera: Ceratopogonidae)

In this revision of the Patagonian predaceous midges of Stilobezzia (Acanthohelea) (Diptera: Ceratopogonidae), the seven previously known species, Stilobezzia bicinctipes Ingram and Macfie, S. hirsuta I. and M, S. ornaticrus I. and M, S. patagonica I. and M, S. rava I. and M, S. succinea I. and M. and S. varia I. and M. are redescribed, illustrated and their distributions are expanded. Diagnoses are provided for Stilobezzia curvistyla Cazorla and Spinelli, S. longisternalis Cazorla and Spinelli and S. nigerrima I. and M, and the male of S. bicinctipes and the female of S. ornaticrus are described for the first time. Seven new species are described with photographs: S. estepae, S. mapuche, S. megatheca, S. monomorphica, S. pabloi, S. spinosa and S. tridentis. The species are illustrated by photographs, and a key to males and females is provided as well as distributional maps for all species.

http://zoobank.org/urn:lsid:zoobank.org:pub:CCEB2CB7-2FB3-4ABF-BCD4-75021AD6C338     

Fluctuating asymmetry in populations of the South American frog Physalaemus cuvieri (Leptodactylidae) in areas with different degrees of disturbance

Methods to measure and monitor wild populations are important conservation tools in areas affected by anthropogenic disturbances. We compared three populations of the South American frog Physalaemus cuvieri Fitzinger, 1826 (Leptodactylidae) from areas with different degrees of anthropogenic disturbance in regard to their degrees of fluctuating asymmetry (FA). We selected four morphological characters (radio-ulna, femur, tibia-fibula and digit length) and compared two populations from relatively pristine areas with one population located in a highly urbanised and disturbed area. We found a significantly higher level of FA for the digit length, p < 0.05, in the population suffering the highest level of anthropogenic disturbance in relation to the two populations located in the pristine areas. There are no significant differences in the three populations in regard to FA for the radio-ulna, femur and tibia-fibula. The absence of FA in these three measurements might indicate a negative effect of limb asymmetry on this species survivorship. Our study provides a good example of the use of FA as indicator of environmental stress. However, this result must be viewed with some caution, since we observed FA in only one morphological character.     

Control of leaf morphogenesis by microRNAs

Plants with altered microRNA metabolism have pleiotropic developmental defects, but direct evidence for microRNAs regulating specific aspects of plant morphogenesis has been lacking. In a genetic screen, we identified the JAW locus, which produces a microRNA that can guide messenger RNA cleavage of several TCP genes controlling leaf development. MicroRNA-guided cleavage of TCP4 mRNA is necessary to prevent aberrant activity of the TCP4 gene expressed from its native promoter. In addition, overexpression of wild-type and microRNA-resistant TCP variants demonstrates that mRNA cleavage is largely sufficient to restrict TCP function to its normal domain of activity. TCP genes with microRNA target sequences are found in a wide range of species, indicating that microRNA-mediated control of leaf morphogenesis is conserved in plants with very different leaf forms.