Enamel Microstructure of Rodent Molars, Classification, and Parallelisms, with a Note on the Systematic Affiliation of the Enigmatic Eocene Rodent Protoptychus

To investigate the diversity of the enamel structures in rodent molars, the schmelzmuster of more than 270 genera from the various fossil and extant groups was investigated. Only three basic types of schmelzmuster were recognized. The most prominent one, the C-type, is characterized by a basal ring of lamellar enamel (BRLE) surrounding the molars at the base of the crown. It occurs in most murids (cricetids) and other Myodonta. It is shared by the Dipodidea, Eomyidae, Geomyidae, and Gliridae. The C-type schmelzmuster was not found in any of the other rodents groups (Sciuromorpha, Anomaluromorpha, Sciuravida, Hystricognathi, Bathyergomorphi, and Caviida). Despite the rare occurrence of the P-type schmelzmuster with radial enamel only, most of these rodents have thick Hunter–Schreger bands (HSB) in their molars (S-type schmelzmuster). Although the C-type schmelzmuster is strictly limited to the Myomorpha (sensu McKenna and Bell), the fossil record shows that this structure does not form a synapomorphy but developed in parallel mostly from the P-type, but in Gliridae from the S-type schmelzmuster. On the basis of molar and incisor enamel the systematic position of Protoptychus can be evaluated.     

New Studies of Enamel Microstructure in Mesozoic Mammals: A Review of Enamel Prisms as a Mammalian Synapomorphy

Characters from enamel microstructure have not been used in recent phylogenetic analyses of Mesozoic Mammalia. Reasons are that enamel characters have been perceived as (A) variable without regard to systematic position of taxa, (B) inconsistently reported within the literature, and (C) simply scored as either prismatic or not prismatic in earlier mammals. Our work on Mesozoic mammals such as Sinoconodon, Gobiconodon, Triconodontidae, Docodon, Laolestes, and others suggests that synapsid columnar enamel (SCE) structure was easily transformed into plesiomorphic prismatic enamel (PPE) and that PPE may be described with at least five independent character states. Two PPE characters—a flat, open prism sheath and a planar prism seam—were present in the cynodont Pachygenelus and in several Jurassic and Cretaceous mammals. We propose that appearance of a prism sheath transforms SCE into PPE and that reduction and loss of a prism sheath reverse PPE into SCE, in both phylogeny and ontogeny. We further propose that no amniote vertebrates other than the trithelodontid cynodont, Pachygenelus, plus Mammalia have ever evolved an ameloblastic Tomes process capable of secreting PPE and that the genetic potential to secrete PPE is a synapomorphy of Pachygenelus plus Mammalia, whether or not all lineages of the clade have expressed that potential.     

Enamel microstructure ofTribosphenomys (Mammalia,glires): Character analysis and systematic implications

Enamel distribution on the upper and lower incisors ofTribosphenomys minutus (from Late Paleocene-Early Eocene of Inner Mongolia of China) is typically rodent-like, i.e., primarily confined to the anterior surface throughout these transversely compressed, evergrowing teeth. AlthoughTribosphenomys incisor enamel is differentiated into two layers, it does not possess Hunter-Schreger bands (HSB). The incisor and molar enamels are radial in type, a condition regarded as either an autapomorph or a primtive retention forTribosphenomys. Character polarities concerning enamel thickness, enamel layer number, HSB, enamel types, and functional and phylogenetic implications of the enamel structures are discussed. Overall, enamel microstructural evolution at high taxonomic levels within Glires displays considerably more homoplasy than generally appreciated. A phylogenetic definition of Rodentia is proposed.Tribosphenomys is the sister-group of a taxon here named Rodentia, and thus is not itself a member of the order, from a systematic viewpoint.     

Microstructural Reinforcement in the Canine Enamel of the Hyaenid Crocuta crocuta, the FelidPuma concolorand the Late Miocene Canid Borophagus secundus

In bone-eating carnivores such as the hyena Crocuta crocuta, the tooth enamel contains a secondary vertical prism decussation phyletically derived from the wavelike horizontal decussation of primitive carnivores. The structure resists fracture under vertical, oblique, and horizontal tensile stresses, owing to the following modifications of the primitive structure. Positions of wave crests and of wave troughs are synchronized in the vertically successive layers of decussating prisms. Prisms in each successive layer run in a common direction at the crests and in a common but reversed direction at the troughs. Between the crests and troughs, prisms in obliquely slanting layers often retain their primitively reversed prism directions. Near the enamel–dentine junction (EDJ), irregular horizontal decussation is retained. In the upper canine of C. crocuta, a consumer of large bones, secondary vertical decussation is largely confined to the labial and anterior sides of the crown toward the tip where modeling of the static stresses predicts the tensile stresses to be highest and aligned vertically. In Puma concolor, which does not consume large bones, secondary vertical decussation is absent, indicating stress magnitude to be a critical factor in the selection for secondary vertical decussation. The canine enamel in Borophagus secundus, an extinct canid with derived aspects of skull and dental shape like those in hyenas, has dental structures similar to those in C. crocuta but which differ in several ways. The wavelike shapes of the decussation planes are better developed in transverse sections in B. secundus than in C. crocuta, suggesting either the folds are less modified or they dip at a steeper angle. Secondary vertical decussation in B. secundus is more extensive around the circumference of the canine than in C. crocuta, related to a difference in cross-sectional shape of the tooth. Vertical prism decussation may have been more frequently attained in carnivorous mammals than in ungulates because of the more random orientation of dental stresses which creates a selective advantage for wavy decussation planes—a structural transition to vertical decussation.     

On the systematic position ofChaetomys subspinosus (Rodentia: Caviomorpha) based on evidence from the incisor enamel microstructure

We have studied the incisor enamel microstructure ofChaetomys subspinosus and other possibly closely related caviomorph rodents.Chaetomys subspinosus lacks the important synapomorphy of the Octodontoidea, reactangular plate-like interprismatic matrix (IPM) in the portio interna (PI) of the incisor Schmelzmuster. Therefore its transfer from the Erethizontidae to the Echimyidae, as proposed by Patterson and Wood (Bull. Mus. Comp. Zool. 149, 371–543, 1982) based on retention of dP4, is contested. The parallel to acute angular IPM in the PI ofChaetomys and the Erethizontidae is a symplesiomorphy and does not indicate close relationship. Contrary to previous claims, a posterior carotid foramen is also retained inChaetomys. Chaetomys is characterized by an unusual thin enamel which is considered primitive after outgroup comparison. Therefore, it is proposed to leaveChaetomys in the monospecific erethizontid subfamily Chaetomyinae, until additional information on the species is available.     

Enamel thickness,microstructure and development in Afropithecus turkanensis

Afropithecus turkanensis, a 17-17.5 million year old large-bodied hominoid from Kenya, has previously been reported to be the oldest known thick-enamelled Miocene ape. Most investigations of enamel thickness in Miocene apes have been limited to opportunistic or destructive studies of small samples. Recently, more comprehensive studies of enamel thickness and microstructure in Proconsul, Lufengpithecus, and Dryopithecus, as well as extant apes and fossil humans, have provided information on rates and patterns of dental development, including crown formation time, and have begun to provide a comparative context for interpretation of the evolution of these characters throughout the past 20 million years of hominoid evolution. In this study, enamel thickness and aspects of the enamel microstructure in two A. turkanensis second molars were quantified and provide insight into rates of enamel apposition, numbers of cells actively secreting enamel, and the time required to form regions of the crown. The average value for relative enamel thickness in the two molars is 21.4, which is a lower value than a previous analysis of this species, but which is still relatively thick compared to extant apes. This value is similar to those of several Miocene hominoids, a fossil hominid, and modern humans. Certain aspects of the enamel microstructure are similar to Proconsul nyanzae, Dryopithecus laietanus, Lufengpithecus lufengensis, Graecopithecus freybergi and Pongo pygmaeus, while other features differ from extant and fossil hominoids. Crown formation times for the two teeth are 2.4-2.6 years and 2.9-3.1 years respectively. These times are similar to a number of extant and fossil hominoids, some of which appear to show additional developmental similarities, including thick enamel. Although thick enamel may be formed through several developmental pathways, most Miocene hominoids and fossil hominids with relatively thick enamel are characterized by a relatively long period of cuspal enamel formation and a rapid rate of enamel secretion throughout the whole cusp, but a shorter total crown formation time than thinner-enamelled extant apes.     

New primate hind limb elements from the middle Eocene of China

The continued washing, sorting, and identification of middle Eocene (45 Mya) primates from the Shanghuang fissure-fillings (Jiangsu Province, China) have produced additional hind limb elements. All are isolated elements. The strepsirhine hind limb elements include a first metatarsal and a talus, which are appropriate in size and morphology to pertain to Adapoides troglodytes. Adapoides is interpreted as a quadrupedal-climbing (nonleaping) primate with similarities to living lorises and the fossil primate Adapis. The haplorhine hind limb elements are estimated to span a range of adult body sizes from tiny (17 g) to small (200 g). Included among the new sample of haplorhine hind limb specimens is the smallest primate talus reported thus far. These new postcranial specimens expand our understanding of early haplorhine hind limb anatomy and demonstrate additional similarities between Shanghuang eosimiids and other anthropoids.     

Margaretbarromyces dictyosporus gen. sp. nov.: a permineralized corticolous ascomycete from the Eocene of Vancouver Island, British Columbia

A single, permineralized ascoma resembling a pseudothecium assignable to the Pleosporales is described from the Eocene Appian Way fossil locality on Vancouver Island, British Columbia. The ascoma is globose, ostiolate, and erumpent on a fragment of the bark from an unidentified seed plant. Basally arranged asci contain large, multicelled, obovate ascospores within a single cavity or locule enclosed by a two-layered pseudoparenchymatous tissue that ostensibly represents ascostroma. Given this interpretation of the specimen's morphological features, Margaretbarromyces dictyosporus gen. sp. nov. represents the first report of a corticolous pleosporalean ascoma in the fossil record.     

Additional materials of Myanmarpithecus yarshensis (Amphipithecidae, Primates) from the middle Eocene Pondaung Formation

Myanmarpithecus yarshensis is an amphipithecid primate from the middle Eocene Pondaung Formation in Myanmar. It was previously known based on maxillary fragments with P⁴–M³ and mandibular fragments with C–P₃ and M_2–3. This study reports new materials for the genus, including a humeral head fragment, a lingual fragment of the right M², a lingual fragment of the right M³, and a left I¹. These new materials were collected from approximately the same point, and likely belonged to the same individual. The upper molar morphology and size of the new materials show similarity to those of the type specimen, indicating that the new materials can be assigned to M. yarshensis. The humeral head is the first postcranial element that is associated with dental materials for amphipithecids. The morphological similarity between the previously reported larger humerus and this specimen confirms the assignment of the former specimen to Amphipithecidae and suggests common locomotor adaptations in the family. The upper central incisor is large relative to the molar fragments, but is within the variation among extant platyrrhines. The tooth is spatulate-shaped and high crowned, and lacks the mesial process, indicating similarity to I¹ of haplorhines and clear differences from that of adapoids. It has been suggested that amphipithecids, including Myanmarpithecus, have affinities with notharctine adapoids, but the morphology of I¹ does not support the notharctine hypothesis of the Amphipithecidae.     

The first described Arsinoitherium from the upper Eocene Aydim Formation of Oman: Biogeographic implications

A new fossiliferous locality is discovered from the upper Eocene Aydim Formation, in Dhofar, Southern Sultanate of Oman. A left ulna of Arsinoitherium is described, and cranial and postcranial specimens found in close proximity are referred to the same taxon. The locality is promising for the recovery of additional fossil specimens. Moreover, the presence of Arsinoitherium in Oman is of biogeographic significance; as the Red Sea did not exist during the late Eocene, these large-bodied animals were able to freely travel between what is now the Arabian Peninsula and continental Africa.     

Sequence elements essential for the rapid turnover of <Emphasis Type="Italic">Crithidia fasciculata</Emphasis> ornithine decarboxylase

Summary. Ornithine decarboxylase (ODC) has a very fast turnover in mammalian cells, but is a stable enzyme in T. brucei and other trypanosmatid parasites like Leishmania donovani. However, Crithidia fasciculata, which is a phylogenetically closely related trypanosomatid to L. donovani, has an ODC with a rapid turnover. Interestingly, C. fasciculata ODC, but not L. donovani ODC, is rapidly degraded also in mammalian systems. In order to obtain information on what sequences are important for the rapid degradation of C. fasciculata ODC, we produced a variety of C. fasciculata/L. donovani ODC hybrid proteins and characterized their turnover using two different mammalian expression systems. The results obtained indicate that C. fasciculata ODC contains several sequence elements essential for the rapid turnover of the protein and that these regions are mainly located in the central part of the enzyme. Present address: Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin – Trinity College, Dublin, Ireland Authors’ address: Lo Persson, Department of Experimental Medical Science, Lund University, BMC D-12, S-221 84 Lund, Sweden     

Evolutionary relationships of a new genus and three new species of Omomyid primates (Willwood Formation, Lower Eocene, Bighorn Basin, Wyoming)

Studies of new finds of omomyid primates from the lower Eocene Willwood Formation of northwest Wyoming reveal the presence of a new genus and two new species of anaptomorphines and a new species of omomyine. All were apparently short-lived immigrants into the Bighorn Basin. The new genus and speciesTatmanius szalayi is typified by a diminutive single-rooted p3 and a bilobed-rooted p4 with a crown smaller than ml. These traits were probably derived fromPseudotetonius and parallel similar conditions inTrogolemur andNannopithex. The new speciesArapahovius advena is the first occurrence ofArapahovius outside the Washakie Basin, where it appears to have also been a vagrant species.Steinius annectens, sp. nov., is larger than the olderSteinius vespertinus and strengthens the alliance between this genus and BridgerianOmomys carteri, although which species ofSteinius is closer toOmomys is not yet clear. The available evidence suggests a derivation ofOmomys (Omomyini) fromSteinius and all Washakiini from the anaptomorphineTeilhardina, which would indicate that Omomyinae were at least diphyletic. Preliminary evidence suggests that the geographic distributions of at least some Willwood omomyids correlate with paleosol distributions.     

On the Adaptive Nature of the Dissociation Process in Bacillus thuringiensis

The process of dissociation into variants that differ in colony morphology occurring in batch cloned cultures of two Bacillus thuringiensis strains belonging to different subspecies was studied at optimal and elevated temperatures. An increase in the cultivation temperature to 40°C resulted in an increase in the fraction of R variants to 100% after 72 h of cultivation of either of the strains. This increase was not due to the selection of forms with greater resistance to elevated temperature. The level of resistance to elevated temperature was determined by the strain genotype and did not correlate with morphological characteristics of the colonies.     

Transgenic tobacco plants overexpressing the Met25 gene of Saccharomyces cerevisiae exhibit enhanced levels of cysteine and glutathione and increased tolerance to oxidative stress

Summary. The cysteine biosynthesis pathway differs between plants and the yeast Saccharomyces cerevisiae. The yeast MET25 gene encoded to O-acetylhomoserine sulfhydrylase (AHS) catalyzed the reaction that form homocysteine, which later can be converted into cystiene. In vitro studies show that this enzyme possesses also the activity of O-acetyl(thiol)lyase (OASTL) that catalyzes synthesis of cysteine in plants. In this study, we generated transgenic tobacco plants expressing the yeast MET25 gene under the control of a constitutive promoter and targeted the yeast protein to the cytosol or to the chloroplasts. Both sets of transgenic plants were taller and greener than wild-type plants. Addition of SO₂, the substrate of the yeast enzyme caused a significant elevation of the glutathione content in representative plants from each of the two sets of transgenic plants expressing the yeast gene. Determination of non-protein thiol content indicated up to four-folds higher cysteine and 2.5-fold glutathione levels in these plants. In addition, the leaf discs of the transgenic plants were more tolerant to toxic levels of sulphite, and to paraquat, an herbicide generating active oxygen species.     

Genetic Structure and Low-genetic Diversity Suggesting the Necessity for Conservation of the Chinese Longsnout Catfish, Leiocassis longirostris (Pisces: Bagriidae)

Synopsis Genetic variation and phylogenetic relationship of Leiocassis longirostris populations from the Yangtze River were investigated at mitochondrial DNA level. The samples were collected from the upstream and mid-downstream of the Yangtze River. Three mitochondrial DNA fragments, ND5/6, cytochrome b (Cyt b) and control region (D-loop), were amplified and then digested by 10 restriction endonucleases. Twenty-three D-loop fragments randomly selected were sequenced. Digestion patterns of ND5/6 by AluI and HaeIII, D-loop by HinfI and RsaI, and Cyt b by HaeIII were polymorphic. Ten and eighteen haplotypes were obtained from RFLP data and sequence data, respectively. The individuals from upstream and mid-downstream of the Yangtze River were apparently divided into two groups. The average genetic distance was 0.008 and 0.010 according to the two data. Low diversities and decreasing abundance indicated that Leiocassis longirostris may be in severe danger and reasonable measures of fishery management should be taken.     

Purification of branched-chain amino acid aminotransferase from <Emphasis Type=Italic>Helicobacter pylori</Emphasis> NCTC 11637

Summary. Branched-chain amino acid aminotransferase was purified by several column chromatographies from Helicobacter pylori NCTC 11637, and the N-terminal amino acid sequence was analyzed. The enzyme gene was sequenced based on a putative branched-chain amino acid aminotransferase gene, ilvE of H. pylori 26695, and the whole amino acid sequence was deduced from the nucleotide sequence. The enzyme existed in a homodimer with a calculated subunit molecular weight (MW) of 37,539 and an isoelectric point (pI) of 6.47. The enzyme showed high affinity to 2-oxoglutarate (K _m = 0.085 mM) and L-isoleucine (K _m = 0.34 mM), and V _max was 27.3 μmol/min/mg. The best substrate was found to be L-isoleucine followed by L-leucine and L-valine. No activity was shown toward the D-enantiomers of these amino acids. The optimal pH and temperature were pH 8.0 and 37 °C, respectively.     

Potent isozyme-selective inhibition of human glutathione S-transferase A1-1 by a novel glutathione S-conjugate

Summary. Elevated levels of glutathione S-transferases (GSTs) are among the factors associated with an increased resistance of tumors to a variety of antineoplastic drugs. Hence a major advancement to overcome GST-mediated detoxification of antineoplastic drugs is the development of GST inhibitors. Two such agents have been synthesized and tested on the human Alpha, Mu and Pi GST classes, which are the most representative targets for inhibitor design. The novel fluorescent glutathione S-conjugate L-γ-glutamyl-(S-9-fluorenylmethyl)-L-cysteinyl-glycine (4) has been found to be a highly potent inhibitor of human GSTA1-1 in vitro (IC₅₀=0.11±0.01 μM). The peptide is also able to inhibit GSTP1-1 and GSTM2-2 isoenzymes efficiently. The backbone-modified analog L-γ-(γ-oxa)glutamyl-(S-9-fluorenylmethyl)-L-cysteinyl-glycine (6), containing an urethanic junction as isosteric replacement of the γ-glutamyl-cysteine peptide bond, has been developed as γ-glutamyl transpeptidase-resistant mimic of 4 and evaluated in the same inhibition tests. The pseudopeptide 6 was shown to inhibit the GSTA1-1 protein, albeit to a lesser extent than the lead compound, with no effect on the activity of the isoenzymes belonging to the Mu and Pi classes. The comparative loss in biological activity consequent to the isosteric change confirms that the γ-glutamyl moiety plays an important role in modulating the affinity of the ligands addressed to interact with GSH-dependent proteins. The new specific inhibitors may have a potential in counteracting tumor-protective effects depending upon GSTA1-1 activity.