Transitional forms between the three domains of life and evolutionary implications

The question as to the origin and relationship between the three domains of life is lodged in a phylogenetic impasse. The dominant paradigm is to see the three domains as separated. However, the recently characterized bacterial species have suggested continuity between the three domains. Here, we review the evidence in support of this hypothesis and evaluate the implications for and against the models of the origin of the three domains of life. The existence of intermediate steps between the three domains discards the need for fusion to explain eukaryogenesis and suggests that the last universal common ancestor was complex. We propose a scenario in which the ancestor of the current bacterial Planctomycetes, Verrucomicrobiae and Chlamydiae superphylum was related to the last archaeal and eukaryotic common ancestor, thus providing a way out of the phylogenetic impasse.     

Sex estimation using the first cervical vertebra

The articular surfaces and vertebral foramen area of the first cervical vertebra are sexually dimorphic and can be used to sex complete or fragmentary specimens. Eight measurements were taken from the articular regions (superior and inferior) of 100 first cervical vertebrae from Terry collection specimens housed at the Smithsonian Institution. Seven regression and seven discriminant function equations were created that predict sex with 77–85% and 75–85% accuracy, respectively. In separate control tests, measurements from 100 first cervical vertebrae from Hamann-Todd collection individuals (Cleveland Museum of Natural History) and from 34 archaeological specimens were used with the Terry equations. The control samples were sexed with 60—85% accuracy. © 1995 Wiley-Liss, Inc.     

Synchondroseal growth in the first cervical vertebra of the rat

Growth and remodelling of the first cervical vertebra were studied in the rat by means of biometry, vital staining (alizarin red S and oxytetracycline), and histology. The measurements showed a change in the ratio of the dorso-ventral to the transversal diameter in the lumen after obliteration of the dorsal synchondrosis. The pattern of labelling between the three segments of the vertebrae joined by synchondroses in the young animals indicated that expansion of the vertebral lumen took the form of a displacement of all three parts making up the bony ring. After closure of the dorsal synchondrosis the two ventral ones were still active and the lumen size increased more in the dorso-ventral direction than transversally. Alizarin red S and oxytetracycline tended to persist in the ventral part of the vertebra, while the staining almost disappeared from the dorso-lateral segment. Resting lines were found laterally to the ventral synchondroses in haematoxylin and eosin stained sections, but not in the ventral segment between the cartilages. The growth of the rat atlas is the result of an early rapid cartilage-mediated expansion of the vertebral lumen in conjunction with the growth of the spinal cord and, at a later age, mainly of a displacement of the ventral vertebral segment, leading to the final form of the vertebra and its lumen.     

Sclerotomal origin of the ribs

The somites of vertebrate embryos give rise to sclerotomes and dermomyotomes. The sclerotomes form the axial skeleton, whereas the dermomyotomes give rise to all trunk muscles and the dermis of the back. The ribs were thought to be ventral processes of the axial skeleton and therefore to be derived from the sclerotomes; however, recently a dermomyotomal origin of the distal rib (the costal shaft) was suggested, with only the proximal parts (head and neck of the rib) being of sclerotomal origin. We have re-investigated the development of the ribs in quail-chick chimeras and carried out three experimental series. (1) Single dermomyotomes and (2) single sclerotomes were grafted homotopically, and (3) the ectoderm overlying the unsegmented paraxial mesoderm was removed in the prospective thoracic region. We found that the cells of the dermomyotome gave rise to epaxial and hypaxial trunk muscles, dermis of the back and endothelial cells, but not to ribs. Cells of the sclerotome formed the axial skeleton and all parts of the ribs. Ablation of the ectoderm, which affects dermomyotome development, results in severe malformations of the ribs, probably due to disturbed interactions between dermomyotome and sclerotome. Our results strongly confirm the traditional view of the sclerotomal origin of the ribs.     

Ultrastructure of the L forms of meningococcus]

The authors carried out an electron microscope study of the ultrastructure of the L-form of meningococcus. Several types of cells differing by shape, size, and electron density were revealed. Sharply angular cells closely adjacent to one another prevailed in the culture. Structureless material, possibly representing material of cellular wall was not infrequently revealed around the cells. Elemental bodies and membranous structures of the lamellar type were revealed within the cells.     

Population differences in the morphology of the first cervical vertebra.

Cephalometric radiographs from 180 healthy Caucasian females, 90 of whom lived in the north of Finland and 90 in the south, were analysed with respect to the morphology of the atlas vertebra. The main findings were a smaller dorsal arch height and a larger ventral arch height in those from the north, including a longer atlas vertebra. These results are interpreted as evidence of morphogenetic reactions to changes in function, in this case a raised head posture attributable to climatic conditions.     

Multiple forms of pig somatotropin]

The multiple forms of pig somatotropin were investigated. Four monomer hormone variants were isolated and some of their physico-chemical characteristics were determined. It is shown that they differ in their molecular mass, N-terminal amino acid residues and amino acid composition. The results of work permit supposing that the identified somatotropin forms are controlled by two different genes. The age dependence of spectrum of somatotropin monomer forms is demonstrated.     

Spectrophotometric characteristics of the coccoid forms of actinomycetes]

IR spectra of thw whole cells of the coccoid forms (Mycococcus and Micrococcus) isolated from lithophilous lichen were compared with IR spectra of the collection cultures of Micrococcus and Arthrobacter. Generic spectral characteristics of Mycococcus and Micrococcus are presented. Spectral heterogeneity within the genus Arthrobacter complicates the diagnosis. The cultures of the Mycococcus genus were divided into three groups according to their spectral characteristics. Spectral scans of the studied coccoid forms differ from the scans of the mycelial actinomycetes, and their intensities within the range of 900-1200 cm-1 (lipids) decrease in the series Mycococcus, Arthrobacter, Micrococcus.     

Molecular forms of acid proteinases of the brain]

Molecular forms of cathepsin D bound with subcellular structures were studied in the grey matter of the large hemispheres. Free and bound forms of the enzymes exposed to solubilization with detergent triton X-100 were fractionated by passage through a Sephadex G-100 column. Gel chromatographic analysis demonstrated three peaks of acid proteinase activity. Different areas of solubilization curves of acid proteinases corresponded to different molecular forms of cathepsins. The initial S-shape areas of solubilization curve corresponded to the first high molecular weight peak of the enzyme activity in the grey matter, whereas the subsequent linear ones -- to the second peak; the activity of free forms of the enzyme corresponded to the third peak.     

Mammalian valyl-tRNA synthetase forms a complex with the first elongation factor

The high-molecular-mass form of valyl-tRNA synthetase is associated with the first elongation factor activity. It includes two polypeptides of about 50 kDa and two others of 40 and 30 kDa, identified as alpha, beta, gamma and delta subunits of eEF-1H. The complex of valyl-tRNA synthetase with eEF-1H is suggested to be a novel form of the first elongation factor.