The ossification centers in the lower end of tibiotarsus in domestic fowl.

The morphogenesis of lower end of tibia in chick is studied commonly but the process of ossification of the same has received very little attention so far. The present study is directed to throw some light on the appearance of ossification centers in the lower end of tibiotarsus of chick. The histology of lower end of tibiotarsus was studied by procuring developing tibiotarsi from chick embryos (20) of 6th day incubation till hatching and 3 post hatched chicks. The transparancies of chick embryos at different incubation periods and post hatched chicks were prepared by Dawson's Alizarin staining method. Three cartilage center (tibial, fibulare and intermedium) appeared in 6...9 days of incubation period in the tarsal region. These gradually fused with the lower end of tibia. Three ossification centres developed in the lower end of tibiotarsus. One for intermedium appeared on 16th day and two fotibial and fibulare on 20th day. All these three centres could be located in the transparancies of the chick embryos in tarsal region. The present study proves that the three cartilages centres maintain their individuality during the ossification process even though those fuse completely with the lower end of tibia in chick. The centers for tibial and fibulare are similar to epiphyseal centres of mammals in histological details.     

Genetic studies on species composition and population structure of sand eels (Genera: Ammodytes, Hyperoplus and Gymnammodytes) in Norwegian waters

Five species of sand eels (Ammodytidae) are regularly found in the north-east Atlantic. Some of these species (i.e. Ammodytes tobianus L. and A. marinus Raitt) are difficult to identify by morphological criteria. The aims of the study reported were (a) to reveal unambiguous genetic traits for species classification and (b) to study possible population structure of the more common species in Norwegian waters. In total more than 900 specimens were analysed for inter- and intraspecific allozyme variation. Reference samples were obtained from Scotland and Denmark. By combining the patterns at different loci, all five species could be unambiguously defined. In Norwegian waters A. marinus was found together with minor numbers of Hyperoplus lanceolatus (Le Sauvage). As expected, Gymnammodytes semisquamatus (Jourdain) and H. immaculatus (Corbin) were not found, but not finding A. tobianus in these waters was unexpected. Distribution of alleles at three polymorphic loci did not indicate any structure of A. marinus in Norwegian waters.     

Wnt-7a in feather morphogenesis: involvement of anterior-posterior asymmetry and proximal-distal elongation demonstrated with an in vitro reconstitution model.

How do vertebrate epithelial appendages form from the flat epithelia? Following the formation of feather placodes, the previously radially symmetrical primordia become anterior-posterior (A-P) asymmetrical and develop a proximo-distal (P-D) axis. Analysis of the molecular heterogeneity revealed a surprising parallel of molecular profiles in the A-P feather buds and the ventral-dorsal (V-D) Drosophila appendage imaginal discs. The functional significance was tested with an in vitro feather reconstitution model. Wnt-7a expression initiated all over the feather tract epithelium, intensifying as it became restricted first to the primordia domain, then to an accentuated ring pattern within the primordia border, and finally to the posterior bud. In contrast, sonic hedgehog expression was induced later as a dot within the primordia. RCAS was used to overexpress Wnt-7a in reconstituted feather explants derived from stage 29 dorsal skin to further test its function in feather formation. Control skin formed normal elongated, slender buds with A-P orientation, but Wnt-7a overexpression led to plateau-like skin appendages lacking an A-P axis. Feathers in the Wnt-7a overexpressing skin also had inhibited elongation of the P-D axes. This was not due to a lack of cell proliferation, which actually was increased although randomly distributed. While morphogenesis was perturbed, differentiation proceeded as indicated by the formation of barb ridges. Wnt-7a buds have reduced expression of anterior (Tenascin) bud markers. Middle (Notch-1) and posterior bud markers including Delta-1 and Serrate-1 were diffusely expressed. The results showed that ectopic Wnt-7a expression enhanced properties characteristic of the middle and posterior feather buds and suggest that P-D elongation of vertebrate skin appendages requires balanced interactions between the anterior and posterior buds.     

The cost of mutualism in a fly-fungus interaction

The movement ability of individuals has become increasingly important to a variety of ecological questions. In this study, I investigate how plant structure and changes in body size through development affect the movement ability of a predaceous stinkbug, Podisus maculiventris, on three species of goldenrod (Solidago spp.) representing a wide range of surface complexities. I adapt existing techniques for quantifying movement in two dimensions to the study of movement on natural plant structures in three dimensions. These experiments indicate that plant structure and insect size are significant factors affecting the movement ability of P. maculiventris. Changes in movement ability due to factors of ontogeny and different habitat structures suggest that the scale of an individual’s ambit or ecological sphere of influence may vary within its lifespan. Considering the influence of ontogeny and habitat structure on movement ability may be useful to investigations of population dynamics, foraging behavior, and pest management. Received: 14 July 1999 / Accepted: 23 March 2000     

Stereoselectivity of the membrane potential-generating citrate and malate transporters of lactic acid bacteria.

The citrate transporter of Leuconostoc mesenteroides (CitP) and the malate transporter of Lactococcus lactis (MleP) are homologous proteins that catalyze citrate-lactate and malate-lactate exchange, respectively. Both transporters transport a range of substrates that contain the 2-hydroxycarboxylate motif, HO-CR(2)-COO(-) [Bandell, M., et al. (1997) J. Biol. Chem. 272, 18140-18146]. In this study, we have analyzed binding and translocation properties of CitP and MleP for a wide variety of substrates and substrate analogues. Modification of the OH or the COO(-) groups of the 2-hydroxycarboxylate motif drastically reduced the affinity of the transporters for the substrates, indicating their relevance in substrate recognition. Both CitP and MleP were strictly stereoselective when the R group contained a second carboxylate group; the S-enantiomers were efficiently bound and translocated, while the transporters had no affinity for the R-enantiomers. The affinity of the S-enantiomers, and of citrate, was at least 1 order of magnitude higher than for lactate and other substrates with uncharged R groups, indicating a specific interaction between the second carboxylate group and the protein that is responsible for high-affinity binding. MleP was not stereoselective in binding when the R groups are hydrophobic and as large as a benzyl group. However, only the S-enantiomers were translocated by MleP. CitP had a strong preference for binding and translocating the R-enantiomers of substrates with large hydrophobic R groups. These differences between CitP and MleP explain why citrate is a substrate of CitP and not of MleP. The results are discussed in the context of a model for the interaction between sites on the protein and functional groups on the substrates in the binding pockets of the two proteins.