Structure/function relationships in the minicollagen of Hydra nematocysts

The minicollagens found in the inner layer of the Hydra nematocyst walls are the smallest collagens known with 12-16 Gly-X-Y repeats. Minicollagen-1, the best characterized member of this protein family so far, consists of a central collagen triple helix of 12 nm in length flanked at both ends by a polyproline stretch and a conserved cysteine-rich domain. The cysteine-rich tails are proposed to function in the assembly of soluble minicollagen trimers to high molecular structures by a switch of the disulfide linkage from intramolecular to intermolecular bonds. In this study, we investigate the trimeric nature of minicollagen-1 and its capacity to form disulfide-linked polymers in vitro. A fusion protein of minicollagen-1 with maltose-binding protein is secreted as a soluble trimer with only intrachain and no interchain disulfide bridges as confirmed by melting the collagen triple helix under reducing and non-reducing conditions. The conversion of minicollagen-1 trimers to monomers takes place between 40 and 55 degrees C with the melting point being approximately 45 degrees C. Oxidative reshuffling of the minicollagen-1 trimers leads to the formation of high molecular aggregates, which upon reduction show distinct polytrimeric states. Minicollagen trimers in isolated nematocyst capsules proved to be sensitive to SDS and were engaged in polymeric structures with additional cross-links that were resistant to reducing agent.     

Isoprenoids influence expression of Ras and Ras-related proteins

Mevalonate depletion by inhibition of hydroxymethylglutaryl coenzyme A reductase impairs post-translational processing of Ras and Ras-related proteins. We have previously shown that this mevalonate depletion also leads to the upregulation of Ras, Rap1a, RhoA, and RhoB. This upregulation may result from global inhibition of isoprenylation or depletion of key regulatory isoprenoid species. Studies utilizing specific isoprenoid pyrophosphates in mevalonate-depleted cells reveal that farnesyl pyrophosphate (FPP) restores Ras processing and prevents RhoB upregulation while geranylgeranyl pyrophosphate (GGPP) restores Rap1a processing and prevents RhoA and RhoB upregulation. Either FPP or GGPP completely prevents lovastatin-induced upregulation of RhoB mRNA. Inhibition of FPP or squalene synthase allowed for the further identification of the putative regulatory species. Studies involving the specific isoprenyl transferase inhibitors FTI-277 and GGTI-286 demonstrate that selective inhibition of protein isoprenylation does not mimic lovastatin's ability to increase Ras and RhoA synthesis, decrease Ras and RhoA degradation, increase RhoB mRNA, or increase total levels of Ras, Rap1a, RhoA, and RhoB. In aggregate, these findings reveal a novel role and mechanism for isoprenoids to influence levels of Ras and Ras-related proteins.     

Maintenance of ancestral complexity and non-metazoan genes in two basal cnidarians

Cnidarians are among the simplest extant animals; however EST analyses reveal that they have a remarkably high level of genetic complexity. In this article, we show that the full diversity of metazoan signaling pathways is represented in this phylum, as are antagonists previously known only in chordates. Many of the cnidarian ESTs match genes previously known only in non-animal kingdoms. At least some of these represent ancient genes lost by all bilaterians examined so far, rather than genes gained by recent lateral gene transfer.     

Boundary cells of endodermal origin define the mouth of Hydra vulgaris (Cnidaria)

We investigated morphology, dynamics and origin of cells surrounding the mouth of Hydra vulgaris using the monoclonal antibody L96. This antibody recognises a one cell-thick ring of endodermal epithelial cells exactly at the boundary between endoderm (gastrodermis) and ectoderm (epidermis). L96⁺ cells can stretch considerably without any cell rupture during mouth opening. Thus, our data prove the existence of a distinct cell population defining hydra's mouth. A model for mouth opening is proposed and the significance of L96⁺ cells for boundary formation between ectoderm and endoderm is discussed.     

Targeted disruption of the Insl3 gene causes bilateral cryptorchidism.

The sexual dimorphic position of the gonads in mammals is dependent on differential development of two ligaments, the cranial suspensory ligament (CSL) and the gubernaculum. During male embryogenesis, outgrowth of the gubernaculum and regression of the CSL result in transabdominal descent of the testes, whereas in the female, development of the CSL in conjunction with failure of the gubernaculum development holds the ovaries in a position lateral to the kidneys. Several lines of evidence suggest that regression of the CSL and induction of gubernaculum development are mediated by testosterone and a yet unidentified testicular factor, respectively. The Insl3 gene (originally designated Ley I-L), a member of the insulin-like superfamily, is specifically expressed in Leydig cells of the fetal and postnatal testis and in theca cells of the postnatal ovary. Here we show that male mice homozygous for a targeted deletion of the Insl3 locus exhibit bilateral cryptorchidism with free moving testes and genital ducts. These malformations are due to failure of gubernaculum development during embryogenesis. In double-mutant male mice for Insl3 and androgen receptor genes, testes are positioned adjacent to the kidneys and steadied in the abdomen by the CSL. These findings demonstrate, that the Insl3 induces gubernaculum development in an androgen-independent way, while androgen-mediated regression of the CSL occurs independently from Insl3.     

Permeation of ions across the potassium channel: brownian dynamics studies

The physical mechanisms underlying the transport of ions across a model potassium channel are described. The shape of the model channel corresponds closely to that deduced from crystallography. From electrostatic calculations, we show that an ion permeating the channel, in the absence of any residual charges, encounters an insurmountable energy barrier arising from induced surface charges. Carbonyl groups along the selectivity filter, helix dipoles near the oval chamber, and mouth dipoles near the channel entrances together transform the energy barrier into a deep energy well. Two ions are attracted to this well, and their presence in the channel permits ions to diffuse across it under the influence of an electric field. Using Brownian dynamics simulations, we determine the magnitude of currents flowing across the channel under various conditions. The conductance increases with increasing dipole strength and reaches its maximum rapidly; a further increase in dipole strength causes a steady decrease in the channel conductance. The current also decreases systematically when the effective dielectric constant of the channel is lowered. The conductance with the optimal choice of dipoles reproduces the experimental value when the dielectric constant of the channel is assumed to be 60. The current-voltage relationship obtained with symmetrical solutions is linear when the applied potential is less than approximately 100 mV but deviates from Ohm's law at a higher applied potential. The reversal potentials obtained with asymmetrical solutions are in agreement with those predicted by the Nernst equation. The conductance exhibits the saturation property observed experimentally. We discuss the implications of these findings for the transport of ions across the potassium channels and membrane channels in general.     

香菇的学名及其在当代真菌分类中的位置

本文综述了香菇(Lentinula edodes)的分类历史,确认其在蘑菇目(Agaricales)Tricholomataceae科下的分类地位,并证实了它与多孔菌目(Poriales)Lentinaceae科的Lentinus属没有联系。根据《真菌、地衣汉语学名命名法规》,作者讨论了译为“香菇属”的Lentinus和“小香菇属”的Lentinellus两属的汉语学名问题,提出Lentinus的汉语学名应订正为“韧伞属”,Lentinellus为“螺壳菌属”。香菇所在的Lentinula属的汉语学名建议为“木菇属”。     

Maize endosperm ADP-glucose pyrophosphorylase SHRUNKEN2 and BRITTLE2 subunit interactions

ADP-glucose pyrophosphorylase (AGP) represents a key regulatory step in polysaccharide synthesis in organisms ranging from bacteria to plants. Higher plant AGPs are complex in nature and are heterotetramers consisting of two similar but distinct subunits. How the subunits are assembled into enzymatically active polymers is not yet understood. Here, we address this issue by using naturally occurring null mutants of the Shrunken2 (Sh2) and Brittle2 (Bt2) loci of maize as well as the yeast two-hybrid expression system. In the absence of the maize endosperm large AGP subunit (SH2), the BT2 subunit remains as a monomer in the developing endosperm. In contrast, the SH2 protein, in the absence of BT2, is found in a complex of 100 kD. A direct interaction between SH2 and BT2 was proven when they were both expressed in yeast. Several motifs are essential for SH2:BT2 interaction because truncations removing the N or C terminus of either subunit eliminate SH2:BT2 interactions. Analysis of subunit interaction mutants (sim) also identified motifs essential for protein interactions.     

Morphology of the “spindle-shaped body” in the developing tail of human spermatids

Summary At the beginning of the late cap phase of the normal differentiation of human spermatids, a unique structure, the spindle shaped body, occupies part of the future middlepiece. This spindle-shaped body was followed throughout its development, and its functional relationship to the formation of the fibrous sheath is discussed. The spindle-shaped body disappears when the fibrous sheath is completed and the annulus moves down, giving rise to the middle-piece.Supported by Grants from the Deutsche Forschungsgemeinschaft.