Fgf10 mutant newts regenerate normal hindlimbs despite severe developmental defects.

In amniote limbs, Fibroblast Growth Factor 10 (FGF10) is essential for limb development, but whether this function is broadly conserved in tetrapods and/or involved in adult limb regeneration remains unknown. To tackle this question, we established Fgf10 mutant lines in the newt Pleurodeles waltl which has amazing regenerative ability. While Fgf10 mutant forelimbs develop normally, the hindlimbs fail to develop and downregulate FGF target genes. Despite these developmental defects, Fgf10 mutants were able to regenerate normal hindlimbs rather than recapitulating the embryonic phenotype. Together, our results demonstrate an important role for FGF10 in hindlimb formation, but little or no function in regeneration, suggesting that different mechanisms operate during limb regeneration versus development.

Siliceous scales in the centrohelid heliozoan Raphidocystis contractilis facilitate settlement to the substratum.

The centrohelid heliozoan Raphidocystis contractilis has hundreds of small scales on the surface of the cell body. To understand the biological functions of the scales, comparative examinations were conducted between wild-type and scale-deficient strains that has naturally lost scales after long-term cultivation. The scale-deficient strain exhibited decreased adhesion to the substratum and had a lower sedimentation rate in water than the wild-type strain, suggesting that the scale may have the ability to attach quickly and strongly to the substratum. Percoll density gradient centrifugation showed that the scale-deficient strain had a lower density than that of the wild-type strain. In the wild-type strain, more scaled cells were observed in the higher specific gravity fractions. During the long-term culture of cells, only the cells suspended in the upper area of the flask were transferred to fresh medium. By repeating this procedure, we may have selected only cells that did not possess normal scales. In the natural environment, centrohelid heliozoans are easily flushed away if they cannot adhere strongly to the bottom. These results suggest that they use scales to ensure effective adhesion to the substratum.

A novel capsid protein network allows the characteristic internal membrane structure of Marseilleviridae giant viruses.

Marseilleviridae is a family of giant viruses, showing a characteristic internal membrane with extrusions underneath the icosahedral vertices. However, such large objects, with a maximum diameter of 250 nm are technically difficult to examine at sub-nanometre resolution by cryo-electron microscopy. Here, we tested the utility of 1 MV high-voltage cryo-EM (cryo-HVEM) for single particle structural analysis (SPA) of giant viruses using tokyovirus, a species of Marseilleviridae, and revealed the capsid structure at 7.7 Å resolution. The capsid enclosing the viral DNA consisted primarily of four layers: (1) major capsid proteins (MCPs) and penton proteins, (2) minor capsid proteins (mCPs), (3) scaffold protein components (ScPCs), and (4) internal membrane. The mCPs showed a novel capsid lattice consisting of eight protein components. ScPCs connecting the icosahedral vertices supported the formation of the membrane extrusions, and possibly act like tape measure proteins reported in other giant viruses. The density on top of the MCP trimer was suggested to include glycoproteins. This is the first attempt at cryo-HVEM SPA. We found the primary limitations to be the lack of automated data acquisition and software support for collection and processing and thus achievable resolution. However, the results pave the way for using cryo-HVEM for structural analysis of larger biological specimens.