Characterization of the targeting signal of the Arabidopsis 22-kD integral peroxisomal membrane protein

Using a combination of in vivo and in vitro assays, we characterized the sorting pathway and molecular targeting signal for the Arabidopsis 22-kD peroxisome membrane protein (PMP22), an integral component of the membrane of all peroxisomes in the mature plant. We show that nascent PMP22 is sorted directly from the cytosol to peroxisomes and that it is inserted into the peroxisomal boundary membrane with its N- and C-termini facing the cytosol. This direct sorting of PMP22 to peroxisomes contrasts with the indirect sorting reported previously for cottonseed (Gossypium hirsutum) ascorbate peroxidase, an integral PMP that sorts to peroxisomes via a subdomain of the endoplasmic reticulum. Thus, at least two different sorting pathways for PMPs exist in plant cells. At least four distinct regions within the N-terminal one-half of PMP22, including a positively charged domain present in most peroxisomal integral membrane-destined proteins, functions in a cooperative manner in efficient peroxisomal targeting and insertion. In addition, targeting with high fidelity to peroxisomes requires all four membrane-spanning domains in PMP22. Together, these results illustrate that the PMP22 membrane peroxisomal targeting signal is complex and that different elements within the signal may be responsible for mediating unique aspects of PMP22 biogenesis, including maintaining the solubility before membrane insertion, targeting to peroxisomes, and ensuring proper assembly in the peroxisomal boundary membrane.     

Enamel thickness and microstructure in pitheciin primates, with comments on dietary adaptations of the middle Miocene hominoid Kenyapithecus

Many living primates that feed on hard food have been observed to have thick-enameled molars. Among platyrrhine primates, members of the tribe Pitheciini (Cacajao, Chiropotes, and Pithecia) are the most specialized seed and nut predators, and Cebus apella also includes exceptionally hard foods in its diet. To examine the hypothesized relationship between thick enamel and hard-object feeding, we sectioned small samples of molars from the platyrrhine primates Aotus trivergatus, Ateles paniscus, Callicebus moloch, Cebus apella, Cacajao calvus, Chiropotes satanas, Pithecia monachus, and Pithecia pithecia. We measured relative enamel thickness and examined enamel microstructure, paying special attention to the development of prism decussation and its optical manifestation, Hunter-Schreger Bands (HSB). Cebus apella has thick enamel with well-defined but sinuous HSB overlain by a substantial layer of radial prisms. Aotus and Callicebus have thin enamel consisting primarily of radial enamel with no HSB, Ateles has thin enamel with moderately developed HSB and an outer layer of radial prisms, and the thin enamel of the pitheciins (Cacajao, Chiropotes, and Pithecia) has extremely well-defined HSB. Among platyrrhines, two groups that feed on hard objects process these hard foods in different ways. Cebus apella masticates hard and brittle seeds with its thick-enameled cheek teeth. Pitheciin sclerocarpic foragers open hard husks with their canines but chew relatively soft and pliable seeds with their molars. These results reveal that thick enamel per se is not a prerequisite for hard object feeding. The Miocene hominoid Kenyapithecus may have included hard objects in its diet, but its thick-enameled molars indicate that its feeding adaptations differed from those of the pitheciins. The morphology of both the anterior and posterior dentition, including enamel thickness and microstructure, should be taken into consideration when inferring the dietary regime of fossil species.     

Pathogenicity of Haemoproteus danilewskyi,Kruse, 1890, in blue jays (Cyanocitta cristata)

Although the impact of blood parasite infections on passerine birds is potentially great, little is known of their pathologic effects. We studied Haemoproteus danilewskyi in experimentally infected captive and naturally infected free-ranging blue jays (Cyanocitta cristata) to determine patterns of infection and examine the pathologic effects of the parasite on the host. Physiologic changes, such as elevated numbers of lymphocytes, heterophils, basophils, eosinophils, and monocytes and decreased packed cell volume in the peripheral blood were associated with the erythrocytic phase of experimental infections of captive juvenile jays. Sublethal pathologic changes associated with the pre-erythrocytic phase of infections were observed in the liver, lung, and spleen. Schizonts were observed in the pulmonary capillaries of a 1 yr old jay necropsied 31 days post-inoculation, but not in 20 juvenile jays necropsied 57 days post-inoculation. In free-ranging naturally infected jays plasma protein concentration increased with density of natural infections.     

Mesd encodes an LRP5/6 chaperone essential for specification of mouse embryonic polarity

Specification of embryonic polarity and pattern formation in multicellular organisms requires inductive signals from neighboring cells. One approach toward understanding these interactions is to study mutations that disrupt development. Here, we demonstrate that mesd, a gene identified in the mesoderm development (mesd) deletion interval on mouse chromosome 7, is essential for specification of embryonic polarity and mesoderm induction. MESD functions in the endoplasmic reticulum as a specific chaperone for LRP5 and LRP6, which in conjunction with Frizzled, are coreceptors for canonical WNT signal transduction. Disruption of embryonic polarity and mesoderm differentiation in mesd-deficient embryos likely results from a primary defect in WNT signaling. However, phenotypic differences between mesd-deficient and wnt3(-)(/)(-) embryos suggest that MESD may function on related members of the low-density lipoprotein receptor (LDLR) family, whose members mediate diverse cellular processes ranging from cargo transport to signaling.     

Housing and husbandry of Xenopus for oocyte production

Despite their importance as a research model, particularly in developmental toxicology investigations, there are few established standards for maintaining Xenopus spp. frogs in the laboratory. The authors review the literature on handling, housing, nutrition, and breeding of Xenopus spp. for optimal oocyte production.     

Dynamics of bacterial and fungal communities on decaying salt marsh grass

Both bacteria and fungi play critical roles in decomposition processes in many natural environments, yet only rarely have they been studied as an integrated microbial community. Here we describe the bacterial and fungal assemblages associated with two decomposition stages of Spartina alterniflora detritus in a productive southeastern U.S. salt marsh. 16S rRNA genes and 18S-to-28S internal transcribed spacer (ITS) regions were used to target the bacterial and ascomycete fungal communities, respectively, based on DNA sequence analysis of isolates and environmental clones and by using community fingerprinting based on terminal restriction fragment length polymorphism (T-RFLP) analysis. Seven major bacterial taxa (six affiliated with the alpha-Proteobacteria and one with the Cytophagales) and four major fungal taxa were identified over five sample dates spanning 13 months. Fungal terminal restriction fragments (T-RFs) were informative at the species level; however, bacterial T-RFs frequently comprised a number of related genera. Amplicon abundances indicated that the salt marsh saprophyte communities have little-to-moderate variability spatially or with decomposition stage, but considerable variability temporally. However, the temporal variability could not be readily explained by either successional shifts or simple relationships with environmental factors. Significant correlations in abundance (both positive and negative) were found among dominant fungal and bacterial taxa that possibly indicate ecological interactions between decomposer organisms. Most associations involved one of four microbial taxa: two groups of bacteria affiliated with the alpha-Proteobacteria and two ascomycete fungi (Phaeosphaeria spartinicola and environmental isolate "4clt").     

Prevalence of bacteria of division TM7 in human subgingival plaque and their association with disease

Members of the uncultivated bacterial division TM7 have been detected in the human mouth, but little information is available regarding their prevalence and diversity at this site. Human subgingival plaque samples from healthy sites and sites exhibiting various stages of periodontal disease were analyzed for the presence of TM7 bacteria. TM7 ribosomal DNA (rDNA) was found in 96% of the samples, and it accounted for approximately 0.3%, on average, of all bacterial rDNA in the samples as determined by real-time quantitative PCR. Two new phylotypes of this division were identified, and members of the division were found to exhibit filamentous morphology by fluorescence in situ hybridization. The abundance of TM7 rDNA relative to total bacterial rDNA was higher in sites with mild periodontitis (0.54% +/- 0.1%) than in either healthy sites (0.21% +/- 0.05%, P < 0.01) or sites with severe periodontitis (0.29% +/- 0.06%, P < 0.05). One division subgroup, the I025 phylotype, was detected in 1 of 18 healthy samples and 38 of 58 disease samples. These data suggest that this phylotype, and the TM7 bacterial division in general, may play a role in the multifactorial process leading to periodontitis.     

Harmonic analysis of perfusion pumps

The controversy over the use of nonpulsatile versus pulsatile pumps for maintenance of normal organ function during ex vivo perfusion has continued for many years, but resolution has been limited by lack of a congruent mathematical definition of pulsatility. We hypothesized that the waveform frequency and amplitude, as well as the underlying mean distending pressure are all key parameters controlling vascular function. Using discrete Fourier Analysis, our data demonstrate the complexity of the pulmonary arterial pressure waveform in vivo and the failure of commonly available perfusion pumps to mimic in vivo dynamics. In addition, our data show that the key harmonic signatures are intrinsic to the perfusion pumps, are similar for flow and pressure waveforms, and are unchanged by characteristics of the downstream perfusion circuit or perfusate viscosity.     

Population Reduction and Social Disorganization in Alouatta pigra Following a Hurricane

The opportunity to study the effects of a powerful hurricane on monkey populations, diet, and behavior via pre- and post-hurricane data was presented when hurricane Iris virtually destroyed the forest along Monkey River in southern Belize on October 8, 2001, including a 52-ha area where black howlers have been subjects since 1999. Before the hurricane, 8 social groups, averaging 6.37 members, had been stable in both group composition and range for q 2 years. The hurricane, which levelled much of the forest, resulted in the complete loss of the forest canopy. The trees that remained standing lost most or all branches and were 100% defoliated. The monkey population in the study area was reduced by 42% and survivers experienced a period of extended social disorganization involving transient individuals, high numbers of solitary monkeys, and small fragmentary social groups. The period of disorganization lasted 12 weeks, after which the number of solitaries reduced and stability of the large groups increased. Within the study area, 5 social groups have been more or less stable since ca. week 15; however, home ranges had yet to stabilize at week 35. The social and ranging effects are similar to what has been described for translocated primates. Post-hurricane diet was limited to fruit and leaves remaining in the deadfall for the first 2 weeks and to new leaves and leaf buds for many weeks after that. Normal fruit consumption in April and May was prevented by the failure of surviving trees to produce fruit. With the loss of forest canopy there has been increased use of low foliage and ground travel, and with the reduction in population density there has been a reduction in vocalization frequency.