On the optimal growth of the alimentary tract in avian postembryonic development

It was shown in the mathematical model described elsewhere that when growth rate of the chicks is maximized and not constrained by the food availability, the optimal relationship between body mass and alimentary tract mass should conform to a single straight line, or two-, or three-segmented straight lines. Here, we present the data on growth of 11 bird species, and we test the model using the mass of intestines as an indicator of growth of the alimentary tract. The results support the predictions of the model for altricial species and contradict them for precocials. Since precocial species examined here were not food-limited, we suggest that the lack of optimal growth of their alimentary tract is inherent to their mode of development. This may account for their lower growth rate, as compared to altricials. The existence of the optimal growth of the alimentary tract in altricial nestlings suggests that under natural conditions the food is much more abundant than it is generally assumed.     

Isolation and regional localization of a large collection (2,000) of single-copy DNA fragments on human chromosome 3 for mapping and cloning tumor suppressor genes

Summary A collection of 2,000 lambda phage-carrying human single-copy inserts (> 700 bp) were isolated from two chromosome-3 flow-sorted libraries. The single-copy DNA fragments were first sorted into 3p and 3q locations and about 700 3p fragments were regionally mapped using a deletion mapping panel comprised of two humanhamster and two-human-mouse cell hybrids, each containing a chromosome 3 with different deletions in the short arm. The hybrids were extensively mapped with a set of standard 3p markers physically localized or ordered by linkage. The deletion mapping panel divided the short arm into five distinct subregions (A-E). The 3p fragments were distributed on 3p regions as follows: region A, 26%; B, 31%; C, 4%; D, 4% and E, 35%. We screened 300 single-copy DNA fragments from the distal part of 3p (regions A and B) with ten restriction endonucleases for their ability to detect restriction fragment length polymorphisms (RFLPs). Of these fragments 110 (36%) were found to detect useful RFLPs: 35% detected polymorphisms with frequency of heterozygosity of 40% or higher, and 25% with frequency of 30% or higher. All polymorphisms originated from single loci and most of them were of the base pair substitution type. These RFLP markers make it possible to construct a fine linkage map that will span the distal part of chromosome 3p and encompasses the von Hippel-Lindau disease locus. The large number of single-copy fragments (2,000) spaced every 100–150 kb on chromosome 3 will make a significant contribution to mapping and sequencing the entire chromosome 3. The 300 conserved chromosome 3 probes will increase the existing knowledge of man-mouse homologies.     

Site-site interactions in EF-hand calcium-binding proteins. Laser-excited europium luminescence studies of 9-kDa calbindin, the pig intestinal calcium-binding protein

Europium(III) binding to 9-kDa calbindin from pig intestines was studied by direct excitation of the 7Fo----5Do transition of the ion and by near-ultraviolet circular dichroic spectroscopy. Europium(III) binding is clearly biphasic. As with other lanthanides the C-terminal metal-binding site (site II) is filled first. The europium ion in this site gives an excitation spectrum with a single peak at 579.1 nm (peak 2). The occupation of the N-terminal site (site I) by europium gives excitation spectra that are pH-dependent and show a peak at 579.4 nm (peak 1a) at pH 5 which shifts to 578.7 nm (peak 1b) over the pH range 5-7. At pH 8.07 the fluorescence from europium in site I largely disappears because of weak binding, whereas that from site II is quenched by about 75% in spite of full occupancy of the site as shown by circular dichroic titration. There is a strong interaction between the two sites in spite of the very different affinities. The fluorescence from site II increases stoichiometrically with the addition not only of the first equivalent of europium, but also concomitantly with the fluorescence from site I upon addition of the second equivalent. Furthermore, when Eu1-calbindin is titrated with calcium the fluorescence at 579.1 nm is quenched by about 30% during the addition of one equivalent of calcium which fills site I. Subsequent titration with large excesses of calcium displaces europium from site II. The affinity of site II for europium is about 100 times that of calcium under these conditions.     

Mapping the idiotopes of a monoclonal anti-myoglobin antibody with syngeneic monoclonal anti-idiotypic antibodies: detection of a common idiotope

A panel of syngeneic monoclonal anti-idiotypic antibodies was prepared by immunizing A.SW mice with keyhole limpet hemocyanin-coupled A.SW monoclonal anti-myoglobin (HAL 19, IgG1) and screening the cloned hybridomas for production of IgG2 binding to idiotype but not to certain other anti-myoglobin antibodies of the same subclass in an ELISA. With these antibodies, we identified three nonoverlapping idiotopes, based on three clusters of monoclonal anti-idiotopes that mutually inhibit within each cluster, but not between clusters (Cluster I: S2, S6, S8; Cluster II: S5, S7; Cluster III: S9). Only Cluster II antibodies block the binding of myoglobin to HAL 19 and so identify a binding site-related idiotope(s). Binding of both Cluster II monoclonals (S5 and S7) to Hal 19 is inhibited by a rabbit anti-idiotype that we previously reported detects a common cross-reactive anti-myoglobin idiotope in immune sera. However, only one of these, S7, and not S5, identifies an idiotope that is present on 20 to 30% of A.SW anti-myoglobin antibodies in immune sera and ascites. The panel of syngeneic monoclonal anti-idiotype antibodies also detects new idiotopes not detected by the rabbit anti-idiotype. The development of a panel of syngeneic monoclonal anti-idiotypic antibodies to different clusters of idiotopes on the same antibody molecule, including one that identifies a major common idiotope in immune sera, should allow the analysis of possible idiotype network regulation in vivo and in vitro in a completely syngeneic system.     

Mismatch Repair Genes on Chromosomes 2p and 3p Account for a Major Share of Hereditary Nonpolyposis Colorectal Cancer Families Evaluable by Linkage

Two susceptibility loci for hereditary nonpolyposis colo-rectal cancer (HNPCC) have been identified, and each contains a mismatch repair gene: MSH2 on chromosome 2p and MLH1 on chromosome 3p. We studied the involvement of these loci in 13 large HNPCC kindreds originating from three different continents. Six families showed close linkage to the 2p locus, and a heritable mutation of the MSH2 gene was subsequently found in four. The 2p-linked kindreds included a family characterized by the lack of extracolonic manifestations (Lynch I syndrome), as well as two families with cutaneous manifestations typical of the Muir-Torre syndrome. Four families showed evidence for linkage to the 3p locus, and a heritable mutation of the MLH1 gene was later detected in three. One 3p-linked kindred was of Amerindian origin. Of the remaining three families studied for linkage, one showed lod scores compatible with exclusion of both MSH2 and MLH1, while lod scores obtained in the other two families suggested exclusion of one HNPCC locus (MSH2 or MLH1) but were uninformative for markers flanking the other locus. Our results suggest that mismatch repair genes on 2p and 3p account for a major share of HNPCC in kindreds that can be evaluated by linkage analysis.     

Changes in diatom assemblages in the profundal sediments of two large oligohumic lakes in eastern Finland

Sedimentary diatom assemblages in two large oligotrophic clear-water lakes were analysed, to assess their present ecological state and possible eutrophication due to diffuse nutrient loading. The lakes Pyhäjärvi and Puruvesi (Finnish lake district) are proportionally large for their catchment areas which accounts for their long retention times (ca 7 and 11 yr) and oligohumic character. Pyhäjärvi was studied by pairwise comparison of surface sediment diatom assemblages collected in 1985 and 1990 at 12 sites from different parts of the lake. In Puruvesi, the stratigraphy of diatoms was analysed in two short cores from 8 m and 32 m depths.The diatom assemblages of the two lakes are rather similar, and quite distinct from the assemblages of the mesohumic large lakes of the area. Cyclotella kuetzingiana is the most common planktonic dia- tom, but Aulacoseira ambigua abounds in Pyhäjärvi at sites with local sources of eutrophication. A diverse assemblage of benthic forms, especially Fragilaria and Achnanthes spp. characterizes the shallow bottoms in both lakes.There was little change within the short-core diatom profiles of Puruvesi, but the floral composition of the 8-m and 32-m sites differed markedly. The 8-m site, with 60–70% of benthic forms, represents illuminated bottom, on which much of the buried algae have lived in situ, while the deeper site is true profundal, dominated by sedimented planktonic algae.In Pyhäjärvi there was a slight increase in the benthic diatoms from 1985 to 1990, coinciding with increased phosphorus and chlorophyll concentrations as well as Secchi depth lowering. We interprete this observation as a very early step of eutrophication, of which first the sessile algal communities of the illuminated bottom areas have benefited.     

Expression and properties of acetylcholine receptors in several clones of mouse neuroblastoma X L cell somatic hybrids

Three clones of somatic cell hybrids between neuroblastoma and L cells, NL-1F, NL-308 and NL-309 (3), have been studied for their electrical excitability and chemosensitivity to acetylcholine (Ach) applied by iontophoresis. Parental and hybrid lines were all treated and tested in media containing mM db-cAMP. The percentage of excitable N X L hybrid cells was as high or higher than that of their neuroblastoma parents. The percentage of cells sensitive to Ach was several-fold higher for the three N X L clones than for the neuroblastoma or L cell parents. While the neuroblastoma parents gave only depolarizing cholinergic responses, the N X L hybrid cells displayed slow hyperpolarizing (H) responses which resembled the H-cholinergic response obtained from L cells. The H-response of the N X L hybrids has properties which indicate the involvement of a muscarinic receptor. A correlation between expression of muscarinic receptors and excitability to electrical current (i.e., action potential ionophores), not found in the neuroblastoma parents, was present in the hybrids. However, a few N X L hybrid cells expressed muscarinic receptors independently from electrical excitability, as is the case for the L cell parent. The three N X L clones are discussed as potentially useful models to study interaction of Ach with muscarinic receptors.