Nest building by lowland gorillas in the Lopé Reserve,Gabon: Environmental influences and implications for censusing

We analyzed data from 373 fresh nest-sites (containing 2435 nests) of lowland gorillas (Gorilla g. gorilla)during a 4-year period in the Lopé Reserve, Gabon, to determine whether the observed variability in nest building was due to environmental influences. We recognized and defined seven types of nest in terms of the degree of construction and the raw materials used. Overall, nests built on the ground from herbaceous plants are the most common type (40%), followed by tree nests (35%). Frequencies of the different nest-types vary significantly between eight habitat-types. In habitat-types with high densities of understory herbs, ground nests predominated, but when herbs were rare, the majority of nests were in trees. A general preference for sleeping in herbaceous ground nests is indicated since trees are abundant in all habitat-types, except savanna. The frequency of nesting in trees shows a significant positive correlation with rainfall, but effects of climate are confounded by seasonal variation in use of different habitat-types. When elephants were attracted to the same localized food sources as gorillas, many tree nests were built even when herbs were available. We conclude that different nest-types reflect a variety of solutions to maximize comfort, depending on available raw materials and the probability of rainfall or disturbance by elephants or both factors. Nests are a powerful tool for population censuses and demographic studies of great apes, but problems exist in interpreting data on lowland gorilla nests. Results from this analysis show that only a third of nest-sites accurately reflects group size (of weaned individuals) and that 26% of all gorilla nest-sites could be mistaken for those of chimpanzees, as all nests, or all those visible from a transect, were in trees. Gorilla nests at Lopé were nonrandomly distributed with respect to habitat-types, and nest construction varied seasonally, thereby introducing sources of bias to transect nest counts. We discuss these problems and ones related to assessing the decay rate of nest-sites and make recommendations relevant to census work.     

Cloning and characterization of a sialidase from the murine histocompatibility-2 complex: low levels of mRNA and a single amino acid mutation are responsible for reduced sialidase activity in mice carrying the Neula allele

The Neu1 locus, in the S region of the murine histocompatibility-2complex, regulates the sialic acid content of several liverlysosomal enzymes. Three alleles, Neu1^a, Neu1^b, and Neu1^c, havebeen described on the basis of differential sialylation of theenzyme liver acid phosphatase. The Neu1^a allele occurs in asmall number of mouse strains, e.g., SM/J and is associatedwith sialidase deficiency. We recently described G9, a sialidasegene in the human major histocompatibility complex (Milner etal. (1997) J. Biol. Chem., 272, 4549–4558), and we nowreport the characterization of the equivalent gene in mouse.The protein product of the murine G9 gene is 409 amino acidsin length and is 83% identical to its human orthologue. Expressionof the murine G9 protein in insect cells has confirmed thatit is a sialidase, with optimal activity at pH 5. To elucidatethe basis of sialidase deficiency in mouse strains carryingthe Neu1^a allele, we have sequenced the G9 coding regions frommice carrying the three Neu1 alleles and hence defined the aminoacid sequence characteristic of each allotype. Of particularinterest is a Leu-209 to Ile mutation that is unique to theNeu1^a allotype and is associated with reductions in sialidaseactivity of 68% and 88% compared to the Neu1^b and Neu1^c allotypes,respectively, when these three protein variants are expressedin insect cells. Additional factors, such as differential expression,may also influence the activities of the Nen1 allotypes in vivo.We have observed that the level of G9 mRNA is substantiallyreduced in mice carrying the Neu1^a allele compared to the Neu1^b(85–95% reduction) and Neu1^c (70% reduction) alleles. H2 complex MHC Neu1 sialidase     

Proteolytic activity of proteasome on myofibrillar structures

The physiologic function of proteasome remains unclear. Evidence suggests a role in degradation of ubiquitin-protein conjugates, MHC antigen presentation, and some specificity of substrate within certain cell types. To explore further the properties of proteasome we have examined its effect on a well defined structure, the myofibril. We find that despite its large size (20S) proteasome is able to degrade myofibrils and intact, permeabilized muscle fibrils. The proteins degraded showed some specificity because actin, myosin and desmin were degraded faster than -actinin, troponin T and tropomyosin. Changes in ultrastructure were slow and included a general loss of structure with Z and I bands effected before the M band and costameres.     

In vitro activity of minimised hammerhead ribozymes.

A number of minimised hammerhead ribozymes (minizymes) which lack stem II have been kinetically characterised. These minizymes display optimal cleavage activity at temperatures around 37 degrees C. The cleavage reactions of the minizymes are first order in hydroxide ion concentration up to around pH 9.3 above which the cleavage rate constants decline rapidly. The reactions show a biphasic dependence on magnesium-ion concentration; one of the interactions has an apparent dissociation constant of around 20 mM while the other appears to be very weak, showing no sign of saturation at 200 mM MgCl2. The minizymes are significantly less active than comparable, full-size ribozymes when cleaving short substrates. However, at a particular site in a transcribed TAT gene from HIV-1, minizymes are more effective than ribozymes.     

A comparison of the in vitro activity of DNA-armed and all-RNA hammerhead ribozymes.

Hammerhead ribozymes targeted against two unrelated RNA substrates have been prepared. For each substrate, four ribozymes, differing in their hybridising arm length and composition (DNA or RNA), have been synthesised and kinetically characterised. The presence of DNA in the hybridising arms had little effect on the overall cleavage rate when the cleavage step was rate determining. Shortening each of the hybridising arms of ribozymes from 10 to 6 nucleotides generally resulted in modest changes in rate constants for cleavage of the same 13mer substrate. In one case the presence of long RNA hybridising arms significantly impeded the cleavage reaction. Cleavage rates displayed first order dependence on hydroxide ion concentration at low pHs. At higher pH, some ribozymes deviated from this first order dependence because of a change in the rate-determining step, possibly due to a requirement for a conformation change in the ribozyme-substrate complex prior to cleavage. Ribozyme cleavage was strongly dependent on temperature in the range 5-45 degrees C, with an activation energy for the reaction of approximately 60 kJ mol-1. The ribozymes displayed biphasic dependence on magnesium ion concentration; evidence of strong apparent binding (Kd approximately 10 mM) as well as a looser interaction was observed for all ribozymes.     

Molecular basis and PCR-DNA typing of the Fya/fyb blood group polymorphism

Spondyloepiphyseal dysplasia tarda (SEDL) is an X-linked recessive disorder characterized in affected males by short stature resulting from a growth defect of the vertebral bodies. We have extended our earlier studies by analyzing 15 families with newly identified microsatellite DNA markers; analysis of recombination events with these markers indicates that the gene responsible for SEDL is located in Xp22 between DXS 16 and DXS 987 on an interval spanning approximately 2 Mb.     

Differential rates of loss of chromosomes aberrations in rat thyroids after X rays or neutrons

Rat thyroid glands were exposed in vivo to 5.5-Gy X rays or 2.75-Gy neutrons (14.7 MeV) and cell proliferation was stimulated by goitrogen treatment at various intervals up to 48 weeks postirradiation. The amount of chromosome damage in stimulated follicular cells declined much more slowly after neutron than X irradiation, suggesting differential repair. This observation may be relevant to the question of residual cellular damage and oncogenesis after X rays and neutrons.