Cell adhesion molecule in the hexactinellid Aphrocallistes vastus

Abstract. The Hexactinellida sponge Aphrocallistes vastus contains a soluble aggregation factor (AF) whose purification has been described in this communication. It is characterized by a S°_20.w value of 37 and a buoyant density of 1.45 g/cm³. The AF is a glycoporteinaceous particle composed of three major protein species; no core structure could be visualized. In the presence of Ca²⁺, the AF causes secondary aggregation of single cells. The aggregation process is temperature, pH, and ionic strength independent within a broad range. Evidence is presented indicating that two (or more) AF molecules are required for the establishment of a stable cell: cell interaction. In contrast to the AFs from demosponges, the hexactinellid AF functions species-unspecifically.     

Ribonuclease III: new sense from nuisance.

RNases play an important role in the processing of precursor RNAs, creating the mature, functional RNAs. The ribonuclease III family currently is one of the most interesting families of endoribonucleases. Surprisingly, RNase III is involved in the maturation of almost every class of prokaryotic and eukaryotic RNA. We present an overview of the various substrates and their processing. RNase III contains one of the most prominent protein domains used in RNA-protein recognition, the double-stranded RNA binding domain (dsRBD). Progress in the understanding of this domain is summarized. Furthermore, RNase III only recently emerged as a key player in the new exciting biological field of RNA silencing, or RNA interference. The eukaryotic RNase III homologues which are likely involved in this process are compared with the other members of the RNase III family.     

Delimitation of morphologically similar sponge crab species of the genus Pseudodromia (Crustacea, Decapoda, Dromiidae) from South Africa

Stewart, B. A., Gouws, G., Daniels, S. R. & Matthee, C. A. (2004). Delimitation of morphologically similar sponge crab species of the genus Pseudodromia (Crustacea, Decapoda, Dromiidae) from South Africa. — Zoologica Scripta , 33 , 45–55.
Presently, three Pseudodromia sponge crab species are recognized, all of which are endemic to the continental shelf off the coast of South Africa. Two of these differ only in the morphology of their rostral teeth, making them difficult to distinguish, and can thus be considered as cryptic species. In addition they have very similar distribution ranges, thus raising doubts as to their specific status. Discriminant function analysis of morphometric data, differentiation at 10 allozyme loci, and sequence data derived from the 12S rRNA mitochondrial gene were used to test whether specimens identified as P. latens and P. rotunda are morphological forms of a single, widespread species, or represent two, distinct, reproductively isolated species, and to establish whether these two taxa are sister species, and thus form a monophyletic entity. The presence of fixed allele differences at three, and strong genetic heterogeneity at five other allozyme loci, indicating no gene flow occurring between sympatric populations, as well as the relatively high degree of 12S rRNA and allozyme genetic differentiation observed, supported the recognition of P. latens and P. rotunda as separate species. The 12S rRNA topology suggested that the genus Pseudodromia , as presently constituted, is paraphyletic, thus inferring that the morphological characters used to define this taxon might not be useful for phylogenetic inferences. It was concluded that in view of the uncertainties raised regarding the designation and composition of certain genera within the family Dromiidae, further rigorous analyses of morphological and genetic data are needed to further our understanding of the taxonomy of the sponge crabs.     

Formation of a 55 000-weight cross-linked beta crystallin dimer in the Ca2+-treated lens. A model for cataract

Incubation of lens in Ca2+-containing media, considered by several investigators to be a useful model of cataract formation, gave rise to significant alterations in the covalent structures of various proteins. In rabbit lens, when sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used after reduction of disulfides in urea, the most readily observable changes were (i) disappearance of 210K, 95K, and 60K proteins, (ii) modifications of alpha crystallin subunits, (iii) alterations of beta H crystallins, and (iv) de novo production of 55K and higher molecular weight polymers. The addition of leupeptin inhibited the disappearances of 210K, 95K, and 60K proteins and the alteration of alpha crystallins, suggesting that all these were caused by a Ca2+-activated protease. The proteolytically sensitive 60K species was identified as vimentin, a component of intermediate filaments. Formation of the 55K material and of higher molecular weight polymers during Ca2+ treatment of the lens could be prevented by histamine, a compound known to inhibit the transglutaminase-mediated cross-linking of proteins by epsilon-(gamma-glutamyl)lysine peptide bonds in other biological systems. It could also be shown by immunoblotting that an antibody raised against the 55K material reacted selectively with beta crystallins of normal lens. This indicates that the 55K product is in all likelihood an essential intermediate toward higher polymers and that the 55K product is a cross-linked dimer of certain polypeptides of beta crystallin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intracellular chloride activity and pH during polar lobe formation and cytokinesis in eggs and embryos of Ilyanassa obsoleta

The objectives of this study were to compare membrane potential, intracellular chloride activity, and intracellular pH in unfertilized and fertilized eggs of Ilyanassa obsoleta throughout polar lobe formation and cytokinesis. Membrane potential, psi m, was measured with single- and double-barrel microelectrodes containing 3 M KCl. Chloride activity, (Cl)c, was measured with single-barrel, chloride-sensitive microelectrodes. Intracellular pH, pHc, was measured with double-barrel microelectrodes, utilizing an antimony-filled barrel to monitor pHc. Unfertilized eggs having a psi m of -13.7 mV displayed an average (Cl)c of 29.9 mM, whereas at electrochemical equilibrium, (Cl)ce, it would be 155.7 mM. This suggests that Cl is pumped out of the cell in eggs that are not fertilized. Fertilized eggs had a psi m of -78.2 mV and a (Cl)c of 18.6 mM. At electrochemical equilibrium, (Cl)ce would be 12.1 mM, thus suggesting that Cl is pumped into the cell in fertilized eggs. Double-barrel microelectrodes measured a psi m of -69.0 mV and a pHc of 7.3 in fertilized eggs. The psi m, (Cl)c, and pHc remained stable as fertilized eggs underwent the cellular shape changes involved in forming first, second, and third polar lobes and first cleavage.     

Brood size and the cost of provisioning nestlings: interpreting Lack's hypothesis

A recent model of parental provisioning (the tradeoff model) suggests that the maximum delivery rate of food to nestlings represents a tradeoff between parental residual reproductive value and nestling survival. In contrast, Lack's hypothesis suggests that maximum provisioning rate determines brood size and therefore delivery rates are limited by shortages of food or foraging time, not by tradeoffs of parental investment. Several authors have examined the shape of the per-nestling feeding curves to test the tradeoff model against Lack's hypothesis. We show that Lack's hypothesis can produce per-nestling feeding curves consistent with the tradeoff model. Therefore, the shape of the per-nestling feeding curve cannot be used to distinguish between the models.     

Example of a system which is computation universal but not effectively programmable

The incorporation of a chaotic component in a computing system is incompatible with its being effectively programmable. The example presented shows that concepts of programming suitable for biological systems may differ from those which have grown out of our experience with present day digital computers.