Formation of sperm cells inGalium mollugo (Rubiaceae),Trichodiadema setuliferum (Aizoaceae), andAvena sativa (Poaceae)

The formation of sperm cells has been examined ultrastructurally in the tricellular pollen grains ofGalium mollugo L. (Rubiaceae).Trichodiadema setuliferum Schwantes (Aizoaceae), andAvena sativa L. (Poaceae). After detachement from the intine the generative cell of all three species lies free within the vegetative cytoplasm. The two sperm cells are built inTrichodiadema andAvena by a single separating wall, while inGalium mollugo two independent walls are formed. However, both mechanisms separate the two male gametes completely.     

Synthesis and characterization of a radiolabelled derivative of the phencyclidine/N-methyl-D-aspartate receptor ligand (+) MK-801 with high specific radioactivity

A [3H]-labelled derivative of the drug (+)MK-801 with a high specific radioactivity was synthesized by first preparing a tribromo derivative of (+)MK-801 followed by catalytic reduction in the presence of [3H]-gas and subsequent purification of the radioactive product by reversed-phase high performance liquid chromatography (RP-HPLC). This resulted in pure (+) [3H]MK-801 with a specific radioactivity of 97 Ci/mmol. The (+) [3H]MK-801 was shown to interact with high affinity and selectivity with the phencyclidine (PCP) receptor in guinea pig brain membrane suspensions. The PCP receptor is associated with a cation channel that is chemically gated by glutamate and N-methyl-D-aspartate (NMDA). Drugs that interact with the PCP receptor block this channel. The (+) [3H]MK-801 described here will be useful to investigate the biochemistry of PCP/NMDA receptors in experiments where a high specific radioactivity is essential.     

Host range differentiation of spore-positive and spore-negative strain types of Frankia in stands of Alnus glutinosa and Alnus incana in Finland

Host compatibility of different spore-positive (Sp⁺)and spore-negative (Sp^?) strain types of Frankia from alder stands in Finland was studied in Modulation tests with hydrocultures of Alnus glutinosa (L.) Gaertner, A. incana (L.) Moench and A. nitida Endl. Root nodules and soil samples from stands of A. incana (Lammi forest and Hämeenlinna forest) were dominated by Sp ⁺ types of Frankia (coded AiSp⁺ and AiSp⁺ H. respectively), which caused effective root nodules in test plants of A. incana, but failed to induce nodules in A. nitida. In A. glutinosa Frankia strain types AiSp ⁺ and AiSp ⁺ H caused small, ineffective root nodules with sporangia (coded Ineff ^?), which were recognized by the absence or near absence of vesicles in the nodule tissue. Ineffective nodules without sporangia (coded Ineff ^?) were induced on A. glutinosa with soil samples collected at Lammi swamp. The spore-negative strain type of Frankia was common in root nodules of A. glutinosa in Finland (Lammi swamp) and caused effective Sp^? type root nodules (coded AgSp ^?) in hydrocultures of A. incana, A. glutinosa and A. nitida. A different Sp ⁺ strain type of Frankia. coded AgSp⁺ Finland, was occasionally found in stands of A. glutinosa. It was clearly distinguished from strain type AiSp ⁺ by the ability to produce effective nodules on both A. glutinosa and A. incana. The nodulation capacities of soil and nodule samples were calculated from the nodulation response in hydrocutlure and served as a measure for the population density of infective Frankia particles. Sp ⁺ nodules from both strain types had equal and high nodulation capacities with compatible host species. The nodulation capacities of Sp type root nodules from A. glutinosa were consistently low. High frequencies of Frankia AiSp⁺ and AiSp⁺ H were found in the soil environment of dominant AiSp ⁺ nodule populations on A. incana. The numbers of infective particles of this strain type were insignificant in the soil environment of nearby Sp ^? nodule populations on A. glutinosa and in the former field at Hämeen-linna near the Sp⁺ nodule area in Hämeenlinna forest. Strain type AgSp^? had low undulation capacity in the soil environment of both A. incana and A. glutinosa stands, Explanations for the strong associations between Frankia strain types AiSp⁺ and AiSp ^? H and A. incana and between strain type AgSp^? and A. glutinosa are discussed in the light of host specificity and of some characteristics of population dynamics of both strain types. The possible need to adapt the concept of Frankia strain types Sp ⁺ and Sp ^? to strains with some variation in spore development was stressed by the low potentials of strain type AiSp ⁺ H to develop spores in symbioses with hydrocultures of A. incnna.     

Primary structure of a Plasmodium falciparum malaria antigen located at the merozoite surface and within the parasitophorous vacuole

DNA encoding an antigen of 101,000 apparent molecular weight from the human malaria parasite Plasmodium falciparum was cloned and sequenced. Genomic DNA from the Camp strain covering the complete coding region along with cDNA from the FCR3 strain covering 81% of the coding region were obtained. The cloned DNA specified a full-length protein of 743 amino acids which included two tandemly repeated regions, one near the amino terminus containing eight hexapeptide repeats of sequence TVNDEDED, and the second near the carboxyl terminus containing primarily KE and KEE repeats. The latter repeated region is encoded by a 174-base stretch of mRNA containing only a single pyrimidine. Except for a putative leader sequence located at the amino terminus of the protein, the protein is hydrophilic and highly charged with a calculated isoelectric point of 5.6. Sequences from the Camp and FCR3 strains are very close and are also nearly identical to the partial cDNA sequence of the acidic basic repeated antigen (ABRA) protein from the FC27 strain (Stahl, H.D., Bianco, A.E., Crewther, R.F., Anders, R.F., Kyne, A.P., Coppel, R. L., Mitchell, G.F., Kemp, D.J., and Brown, G.V. (1986) Mol. Biol. Med. 3, 351-368). ABRA was previously shown to be located at the merozoite surface and in the parasitophorous vacuole. Because of its location and because it becomes complexed to merozoites when schizonts rupture in the presence of immune serum, ABRA is a candidate component of a malaria vaccine.     

The fine structure of the dorsal ocelli in the male bibionid fly

The dorsal ocelli of bibionid flies, details of which have not previously been described, were examined in males of Dilophus febrilis. The three ocelli are combined within an elevated chitin capsule, in a medial position between the enlarged dorsal compound eyes. The biconvex lenses show a multiple layering of up to 150 regularly spaced, clear and dense cuticle zones (100 nm spacing) which probably provide some spectral filtering, suggested by in vivo observations with an epifluorescence microscope. The corneagenous cells and the retina with 100-200 photoreceptor cells are adjoined proximally. A distal retina zone comprises the rhabdoms, which are laterally connected in an hexagonal network. The rhabdoms are between 4 and 15 mum in length; they decrease gradually from the dorsal to the ventral retina region. A middle retina zone comprises the receptor somata, a proximal zone, their axons. Synaptic contacts between axons and interneuron dendrites, feedback synapses to axons, and axo-axonic synapses are found, showing varying pre-synaptic structures. A possible functional role of the ocelli is discussed.     

Prochlorococcus marinus nov. gen. nov. sp.: an oxyphototrophic marine prokaryote containing divinyl chlorophyll a and b

Several years ago, prochlorophyte picoplankton were discovered in the N. Atlantic. They have since been found to be abundant within the euphotic zone of the world's tropical and temperate oceans. The cells are extremely small, lack phycobiliproteins, and contain divinyl chlorophyll a and b as their primary photosynthetic pigments. Phylogenies constructed from DNA sequence data indicate that these cells are more closely related to a cluster of marine cyanobacteria than to their prochlorophyte relatives Prochlorothrix and Prochloron. Several strains of this organism have recently been brought into culture, and herewith are given the name Prochlorococcus marinus.     

Isolation and mapping of polymorphic cosmid clones used for sublocalization of the multiple endocrine neoplasia type 1 (MEN1) locus

Summary Multiple endocrine neoplasia type 1 (MEN1) is characterized by neoplasia of the parathyroids, the pancreas, and the pituitary. Tumorigenesis involves unmasking of a recessive mutation at the MEN1 locus, which has been mapped to the centromeric part of chromosomal region 11q. In order to localize the MEN1 gene further and to make its isolation possible, a number of new markers were isolated. Two radiation-reduced somatic cell hybrids were identified that only contained markers close to and flanking the MEN1 region. DNA from these hybrids was used for the construction of a cosmid library, and clones containing human inserts were isolated. In addition, cosmid clones were isolated for locus expansion of 7 other markers that were mapped to the 11q12–13.2 region. The 33 newly isolated clones together with 25 previously published markers from this region were analyzed in a panel of radiation-reduced somatic cell hybrids. From the hybridization pattern, the region was divided into 11 parts. New restriction fragment length polymorphisms were identified in 7 of the newly isolated cosmid clones and in one plasmid. These were then used to sublocalize meiotic cross-overs more precisely in two MEN1 families, thus refining the mapping of the disease gene.     

Expert systems in histopathology. IV. The management of uncertainty.

Expert systems deal with data that are categorical and conceptual, that represent elements of fuzzy sets and that often, by themselves, do not allow an unequivocal decision. The management of uncertainty in expert systems thus becomes a crucial issue. It involves defining measures of uncertainty and procedures for combining accumulating evidence in a manner that properly considers the dependence structure of diagnostic clues. Probability theory offers valuable procedures for uncertainty assessment; however, their practical application in the domain of quantitative histopathology and histopathologic diagnosis can be problematic.     

Survey of human and rat microsatellites

Length variations in simple sequence tandem repeats (microsatellite DNA polymorphisms) are finding increasing usage in mammalian genetics. Although every variety of short tandem repeat that has been tested has been shown to exhibit length polymorphisms, little information on the relative abundance of the different repeat motifs has been collected. In this report, summaries of GenBank searches for all possible human and rat microsatellites ranging from mononucleotide to tetranucleotide repeats are presented. In humans, the five most abundant microsatellites with total lengths for the runs of repeats of greater than or equal to 20 nucleotides contained repeat sequences of A, AC, AAAN, AAN, and AG, in order of decreasing abundance, where N is C, G, or T. These five groups comprised about 76% of all microsatellites. Many other human simple sequence repeats were found at low frequency. In the 745 kb of human genomic DNA surveyed, one microsatellite of greater than or equal to 20 nucleotides in length was found, on average, every 6 kb. Only 12% of the human microsatellites had total lengths greater than or equal to 40 nucleotides. Roughly 80% of the A, AAN, and AAAN microsatellites and 50% of the AT microsatellites, but few of the other human microsatellites, were found to be associated with interspersed, repetitive Alu elements. In rats, the five most abundant microsatellites contained AC, AG, A, AAAN, and AAGG sequences, respectively. Rat microsatellites were generally longer than human microsatellites, with 43% of the rat sequences greater than or equal to 40 nucleotides.