Tetrapod phylogeny inferred from 18S and 28S ribosomal RNA sequences and a review of the evidence for amniote relationships [published erratum appears in Mol Biol Evol 1991 May;8(3):398]

The 18S ribosomal RNAs of 21 tetrapods were sequenced and aligned with five published tetrapod sequences. When the coelacanth was used as an outgroup, Lissamphibia (living amphibians) and Amniota (amniotes) were found to be statistically significant monophyletic groups. Although little resolution was obtained among the lissamphibian taxa, the amniote sequences support a sister-group relationship between birds and mammals. Portions of the 28S ribosomal RNA (rRNA) molecule in 11 tetrapods also were sequenced, although the phylogenetic results were inconclusive. In contrast to previous studies, deletion or down- weighting of base-paired sites were found to have little effect on phylogenetic relationships. Molecular evidence for amniote relationships is reviewed, showing that three genes (beta-hemoglobin, myoglobin, and 18S rRNA) unambiguously support a bird-mammal relationship, compared with one gene (histone H2B) that favors a bird- crocodilian clade. Separate analyses of four other genes (alpha- crystallin A, alpha-hemoglobin, insulin, and 28S rRNA) and a combined analysis of all sequence data are inconclusive, in that different groups are defined in different analyses and none are strongly supported. It is suggested that until sequences become available from a broader array of taxa, the molecular evidence is best evaluated at the level of individual genes, with emphasis placed on those studies with the greatest number of taxa and sites. When this is done, a bird-mammal relationship is most strongly supported. When regarded in combination with the morphological evidence for this association, it must be considered at least as plausible as a bird-crocodilian relationship.      

The role of synapse elimination in the establishment of neuromuscular compartments

To investigate the specificity of development of initial neuromuscular connections, we examined the compartmental distribution of synapses in neonatal rat lateral gastrocnemius (LG) muscle. Initial neuromuscular connections might be restricted to the compartmental territories present in adults; alternatively, synapse elimination could establish the compartments from a less precise pattern of innervation. We examined 46 pups of ages 0 to 14 postnatal days using a variety of techniques. The principle method was evoked electromyographic (EMG) activity in response to nerve stimulation. The nerve branch to one neuromuscular compartment was cut and the remainder of the nerve was stimulated. The presence of EMG activity was used to identify the areas of muscle contracting in response to nerve stimulation. After cutting a particular branch, EMG activity generally could not be recorded from the denervated compartment. These results indicate that the pattern of innervation at birth is essentially compartment-specific, and that neuromuscular compartments are not shaped from some less precise pattern by postnatal synapse elimination. The factors which operate prenatally to determine this high degree of specificity in neuromuscular connectivity seen at the time of birth, however, remain unknown.     

The methionine initiator tRNA genes of yeast

We have isolated three distinct tRNAimet genes from a yeast DNA clone bank. The complete sequence of two shows that these genes are colinear with the mature tRNAimet and supports the RNA sequence of tRNAimet. Southern analysis of yeast genomic DNA indicates the presence of four copies of tRNAimet gene per haploid genome.     

Activity of enzymes regulating glycogen metabolism in perfused muscle-cuticle sections of Ascaris suum (Nematoda)

A new perfusion system has been developed in which muscle-cuticle sections of Ascaris suum were perfused, enabling study of enzymes in vitro. Using this technique the activity of the regulatory enzymes glycogen synthase and glycogen phosphorylase was determined, and the level of glycogen in the muscle was assessed. During starvation, 98% of glycogen synthase was in the inactive D-form, and 80% of the glycogen phosphorylase activity was in the active a-form. When the ascarid muscle section was perfused with 27 mM glucose, 13.1% of the glycogen synthase was in the active I-form, whereas phosphorylase a-levels dropped to 46% and glycogen was synthesized at a linear rate of 12 mg/g/hr or 1.23 mumoles/min/g muscle-cuticle. ATP levels (3.71 +/- 0.32 mM) remained unchanged over a 4-hr perfusion period with an adenylate energy charge of 0.82. Fructose supported glycogen synthesis, though not as well as glucose. Galactose, mannose, and trehalose did not support glycogen synthesis. The new perfusion system should be useful in future, similar studies on Ascaris.     

Dopamine production in the caudate putamen restores feeding in dopamine-deficient mice.

Dopamine-deficient (DD) mice cannot synthesize dopamine (DA) in dopaminergic neurons due to selective inactivation of the tyrosine hydroxylase gene in those neurons. These mice become hypoactive and hypophagic and die of starvation by 4 weeks of age. We used gene therapy to ascertain where DA replacement in the brain restores feeding and other behaviors in DD mice. Restoration of DA production within the caudate putamen restores feeding on regular chow and nest-building behavior, whereas restoration of DA production in the nucleus accumbens restores exploratory behavior. Replacement of DA to either region restores preference for sucrose or a palatable diet without fully rescuing coordination or initiation of movement. These data suggest that a fundamental difference exists between feeding for sustenance and the ability to prefer rewarding substances.     

Nanoindentation of human meniscal surfaces

Menisci are crescent shaped fibrocartilaginous structures which support load distribution of the knee. The menisci are specifically designed to fit the contour of the femoral condyles, aiding to disperse the stresses on the tibial plateau and in turn safeguarding the underlying articular cartilage. The importance of the meniscal superficial layer has not been fully revealed and it is suspected that this layer plays a pivotal role for meniscal function. In this study, both femoral (proximal) and tibial (distal) contacting meniscal surfaces were mechanically examined on the nano-level among three distinct regions (anterior, central and posterior) of the lateral and medial menisci. Nanoindentation testing showed no significant differences among regions, surfaces or anatomical locations, possibly elucidating on the homogeneity of the meniscal superficial zone structure (E(instantaneous): 3.17-4.12MPa, E(steady-state): 1.47-1.69MPa). Nanomechanical moduli values were approximately an order of magnitude greater than micro-scale testing derived moduli values. These findings validate the structural homogeneity of the meniscal superficial zone, showing that material properties are statistically similar regardless of meniscal surface and region. Understanding the mechanical behavior of meniscal surfaces is imperative to properly design an effective meniscal replacement.     

Centralized mouse repositories

Because the mouse is used so widely for biomedical research and the number of mouse models being generated is increasing rapidly, centralized repositories are essential if the valuable mouse strains and models that have been developed are to be securely preserved and fully exploited. Ensuring the ongoing availability of these mouse strains preserves the investment made in creating and characterizing them and creates a global resource of enormous value. The establishment of centralized mouse repositories around the world for distributing and archiving these resources has provided critical access to and preservation of these strains. This article describes the common and specialized activities provided by major mouse repositories around the world.