Retinoic acid in the anteroposterior patterning of the zebrafish trunk

Retinoic acid has been linked to pattern formation in the vertebrate anteroposterior axis. This report describes the spatial and temporal distributions of both endogenous retinoic acid and retinoic acid synthase activity along the anteroposterior axis of neurulating zebrafish embryos, as detected by a transient transgenic assay and by a zymography bioassay. Both retinoic acid levels and synthase activity were found to be highest in anterior regions of the trunk at all of the stages which were analysed. The drug disulfiram inhibited retinoic acid synthase activity in the zebrafish trunk both in vitro and in vivo, and reduced retinoic acid levels in vivo. Disulfiram treatment of neurulating embryos resulted in larvae with hypertrophic wavy notochords, shortened spinal cords and deformed pectoral fins. The results support the hypothesis that retinoic acid plays a role in the coordination of axial patterning at the developing node/zone of involution, as well as in the subsequent development of anterior trunk structures such as the fins.     

Asymmetrical retinoic acid synthesis in the dorsoventral axis of the retina.

An aldehyde dehydrogenase present at high levels in the dorsal retina of the embryonic and adult mouse was identified as the isoform AHD-2 known to oxidize retinaldehyde to retinoic acid. Comparative estimates of retinoic acid levels with a reporter cell line placed the retinas among the richest tissues in the entire body of the early embryo; levels in ventral retina, however, exceeded dorsal levels. Retinoic acid synthesis from retinaldehyde in the dorsal pathway was less effective than the ventral pathway at low substrate levels and more effective at high levels. The dorsal pathway was preferentially inhibited by disulfiram, while ventral synthesis was preferentially inhibited by p-hydroxymercuribenzoate. When protein fractions separated by isoelectric focusing were analyzed for retinoic acid synthesizing capacity by a zymography-bioassay, most of the synthesis in dorsal retina was found to be mediated by AHD-2, and ventral synthesis was mediated by dehydrogenase activities distinct in charge from AHD-2. Postnatally, levels of highest retinoic acid synthesis shifted from ventral to dorsal retina. In the adult retina, the dorsal pathway persisted, but the preferential ventral pathway was no longer detectable. Our observations raise the possibility that retinoic acid plays a role in the determination and maintenance of the dorsoventral axis of the retina, and that the morphogenetically significant asymmetry here lies in the spatial arrangement of synthetic pathways.     

A novel use of passive integrated transponder (PIT) tags as nest markers

ABSTRACT.   Double-observer methodology requires independent collection of data to accurately estimate population parameters. Use of visual nest markers to facilitate matching, relocating, and monitoring nests as part of a double-observer study violates this assumption, but few reliable alternatives exist, especially when working with cryptic nests and high nest densities in homogeneous habitat. We used passive integrated transponder (PIT) tags to nonvisually mark the nests of ground-nesting birds at the Yukon Delta National Wildlife Refuge in western Alaska in a double-observer study of nest density. We marked 70 nests with PIT tags and naïve observers subsequently detected tags at 44 of 50 re-scanned nests (88% correct identification). Failed detections were likely due to either suboptimal tag orientation or tags falling through nest material, and such failures may be an inherent, but uncommon, feature of this nest-marking technique. PIT tags facilitated nest monitoring among independent observers, uniquely and reliably marked nests, provided a minimum of cues to potential nest predators, and allowed us to estimate densities in a double-observer framework while not violating assumptions. These tags should be useful in other studies of nesting birds where nonvisual, reliable nest markers are needed, and they provide a new tool for double-observer studies.     

Screening Global Positioning System Location Data for Errors Using Animal Movement Characteristics

Abstract: Animal locations estimated by Global Positioning System (GPS) inherently contain errors. Screening procedures used to remove large positional errors often trade data accuracy for data loss. We developed a simple screening method that identifies locations arising from unrealistic movement patterns. When applied to a large data set of moose (Alces alces) locations, our method identified virtually all known errors with minimal loss of data. Thus, our method for screening GPS data improves the quality of data sets and increases the value of such data for research and management.     

Isolation and partial characterization of the luminal plasmalemma of microvascular endothelium from rat lungs.

This paper describes a procedure for isolating in high yield and at a high degree of purity the endothelial luminal plasmalemma from the microvasculature of the rat lung. The procedure relies on the modification of the density of the luminal plasmalemma obtained by coating it by perfusion in situ first, with cationized colloidal silica and then with Na polyacrylate. These steps generate a strongly adhering coat to the luminal plasmalemma that resists tissue homogenization to yield, upon repeated centrifugation through Nycodenz density gradients, a nearly homogeneous fraction of coated luminal plasmalemmal fragments still carrying their associated plasmalemmal vesicles. The fraction is enriched in the luminal plasmalemmal antigen, angiotensin converting enzyme, contains gp60, an antigen expected to occur on both plasmalemmal domains, is not enriched in either alkaline phosphatase or 5'-nucleotidase activity and is free of the mitochondrial and endoplasmic reticulum antigens so far tested. This procedure, that can be extended--in principle--to any vascular bed, obviates the use of cultured cells for studying the biochemistry of the endothelium, at least as far as the luminal endothelial plasmalemma is concerned.     

Host‐plant genotype mediates supply and demand of animal food in an omnivorous insect

1. Omnivorous predators can protect plants from herbivores, but may also consume plant material themselves. Omnivores and their purely herbivorous prey have previously been thought to respond similarly to host‐plant quality. However, different responses of omnivores and herbivores to their shared host plants may influence the fitness, trophic identity, and population dynamics of the omnivores. 2. The aim of the present study was to show that an omnivorous heteropteran (Anthocoris nemorum L.) and two strictly herbivorous prey species respond differently to different genotypes of their shared host plant, Salix. Some plant genotypes were sub‐optimal for the omnivore, although suitable for the herbivores, and vice versa. 3. The contrasting patterns of plant suitability for the omnivore and the herbivores highlight an interaction between plant genotype and omnivores' access to animal food. Plant genotypes that were sub‐optimal for the omnivore when herbivores were experimentally excluded became the best host plants when herbivores were present, as in the latter situation additional prey became available. By contrast, the quality of plant genotypes that were intrinsically suitable for omnivores, did not improve when herbivores were present as these plant genotypes were intrinsically sub‐optimal for herbivores, thus providing omnivores with almost no additional animal food. 4. The differential responses of omnivores and their prey to the same host‐plant genotypes should allow omnivores to colonise sub‐optimal host plants in their capacity as predators, and to colonise more suitable host plants in their capacity as herbivores. It may thus be difficult for Salix to escape herbivory entirely, as it will rarely be unsuitable for both omnivores and pure herbivores at the same time.