Autotransplatation of immature third molars as substitutes for congenitally missing second premolars: an alternative solution in a young patient with oligodontia.

Auto transplantation of immature donor teeth can be a strategic therapeutic solution in young patients. It is preferable to choose this approach instead of prosthetic restorations because it offers a unique and definitive solution. Orthodontic space closure is not always deemed desirable, especially in non-extraction cases (53,54). Successful auto transplantations allow alveolar growth through eruption of donor teeth together with the adjacent dentition when skeletal and dental development is not yet completed. Auto transplantation of third molars is less well-recognised and less documented. The available literature shows promising success rates. Immature donor teeth are reportedly associated with better outcomes than mature donor teeth. Aim of this case report was to analyse the short-term outcomes of auto transplantation of immature maxillary third molars to replace the missing mandibular second premolars in a 17-year-old healthy female with oligodontia. The surgical procedure was performed as a single step. Left and right lower second deciduous molars (7.5-8.5), close to exfoliation, were extracted. Donor upper third molars with developing root were extracted as a traumatically as possible and immediately placed into the surgically modified recipient sites. They were stabilized by a sectional wire. One year after surgery, the survival of both transplanted teeth was achieved. They showed periodontal health, normal mobility and continuation of root development during the follow-up period. The upper left third molar responded to all success criteria, no signs of ankylosis, root resorption (infection or inflammatory), and pulp necrosis. The upper right third molar had long-standing evidence of not progressive cervical external inflammatory root resorption without any clinical signs. Further research is needed to determine their long-term survival and success rates.

Multiple and relapsing supernumerary teeth associated to dens invaginatus. Review of the literature and case report.

The aim of this paper is to show problems related to supernumerary teeth therapy according to their formation and mineralization. The clinical case of an 11-year old boy suffering from alteration of the eruptive sequence of the upper incisor teeth caused by 2 supernumerary teeth in the premaxilla, is reported. What is interesting about this case is that after the surgical removal of the supernumerary teeth, with a radiographic examination taken 6 months later, 2 other supernumerary teeth were observed. The authors point out that while the clinical approach can be the same for different situations it is not possible to have the same approach for the surgical therapy which may be different from case to case.

Sequence dependence of translational positioning of core nucleosomes.

The basis for the choice of translational position of a histone octamer on DNA is poorly understood. To gain further insights into this question we have studied the translational and rotational settings of core particles assembled on a simple repeating 20 bp positioning sequence. We show that the translational positions of the core particles assembled on this sequence are invariant with respect to the DNA sequence and occur at 20 bp intervals. Certain modifications of the original sequence reduce the spacing of possible dyads to 10 bp. At least one of these alters both the translational and rotational settings. We conclude that the translational position of a core particle is specified by sequence determinants additional to those specifying rotational positioning. The rotational settings on either side of the dyads of core particles assembled on the wild-type and a mutant sequence differ by +2 bp, corresponding to an overall helical periodicity of approximately 10.15 bp. The average helical periodicity of the central two to four turns is 10.5-11 bp whilst that of the flanking DNA is closer to 10 bp. The DNA immediately flanking the dyad is also characterised by a more extensive susceptibility to cleavage by hydroxyl radical.

Helical repeat of DNA in the nucleosome core particle.

Although the crystal structure of nucleosome core particle is essentially symmetrical in the vicinity of the dyad, the linker histone binds asymmetrically in this region to select a single high-affinity site from potentially two equivalent sites. To try to resolve this apparent paradox we mapped to base-pair resolution the dyads and rotational settings of nucleosome core particles reassembled on synthetic tandemly repeating 20 bp DNA sequences. In agreement with previous observations, we observed (1) that the helical repeat on each side of the dyad cluster is 10 bp maintaining register with the sequence repeat and (2) that this register changes by 2 bp in the vicinity of the dyad. The additional 2 bp required to effect the change in the rotational settings is accommodated by an adjustment immediately adjacent to the dyad. At the dyad the hydroxyl radical cleavage is asymmetric and we suggest that the inferred structural asymmetry could direct the binding of the linker histone to a single preferred site.

The role of histone H1 in chromatin condensation and transcriptional repression.

Linker histones are a major determinant of chromatin condensation. We discuss here the nature and position of the interaction of the globular domain of histone H5 with the core nucleosome and the relevance of this positioning to chromatin structure and the regulation of transcription of the Xenopus borealis 5S rRNA genes.

Differential nucleosome positioning on Xenopus oocyte and somatic 5 S RNA genes determines both TFIIIA and H1 binding: a mechanism for selective H1 repression.

In Xenopus somatic cells histone H1 effects the transcriptional repression of oocyte type 5 S RNA genes, without altering the transcription of the somatic type 5 S RNA genes. Using an unambiguous nucleosome mapping method we find substantial differences between the multiple in vitro nucleosome positions on the two types of genes. These nucleosome positions determine both transcription factor and H1 binding, allowing TFIIIA to bind more efficiently to nucleosomes containing the somatic 5 S RNA gene than to nucleosomes on the oocyte 5 S RNA gene. Significantly, in a binding competition between TFIIIA and H1, TFIIIA preferentially binds to the somatic nucleosome whereas H1 preferentially binds to the oocyte nucleosome, excluding TFIIIA binding. These results strongly suggest that nucleosome positioning plays a key role in the regulation of transcription of 5 S RNA genes and provide a molecular mechanism for the selective repression of the oocyte 5 S RNA genes by H1.

The exocyclic groups of DNA modulate the affinity and positioning of the histone octamer.

To investigate the nature of the chemical determinants in DNA required for nonspecific binding and bending by proteins we have created a novel DNA in which inosine-5-methylcytosine and 2, 6-diaminopurine-uracil base pairs are substituted for normal base pairs in a defined DNA sequence. This procedure completely switches the patterns of the base pair H bonding and attachment of exocyclic groups. We show that this DNA binds a histone octamer more tightly than normal DNA but, surprisingly, does not alter the orientation of the sequence on the surface of the protein. However, in general, the addition or removal of DNA exocyclic groups reduces or increases, respectively, the affinity for the histone octamer. The average incremental change in binding energy for a single exocyclic group is approximately 40 J/mol. The orientation of the DNA in core nucleosomes also is sensitive to the number and nature of the exocyclic groups present. Notably, substitution with the naturally occurring cytosine analogue, 5-methylcytosine, shifts the preferred rotational position by 3 bp, whereas incorporating 2,6-diaminopurine shifts it 2 bp in the opposite direction. These manipulations potentially would alter the accessibility of a protein recognition sequence on the surface of the histone octamer. We propose that exocyclic groups impose steric constraints on protein-induced DNA wrapping and are also important in determining the orientation of DNA on a protein surface. In addition, we consider the implications of the selection of A-T and G-C base pairs in natural DNA.

Mutational analysis of the transcription start site of the yeast tRNA(Leu3) gene.

In addition to the well-known internal promoter elements of tRNA genes, 5' flanking sequences can also influence the efficiency of transcription by Saccharomyces cerevisiae extracts in vitro. A consensus sequence of yeast tRNA genes in the vicinity of the transcriptional start site can be derived. To determine whether the activity of this region can be attributed to particular sequence features we studied in vitro mutants of the start site region. We found that the start site can be shifted, but only to a limited extent, by moving the conserved sequence element. We found that both a pyrimidine-purine motif (with transcription initiating at the purine) and a small T:A base pair block upstream are important for efficient transcription in vitro. Thus the sequence surrounding the start site of transcription of the yeast tRNA(Leu3) gene does play a role in determining transcription efficiency and fixing the precise site of initiation by RNA polymerase III.

Induction of the neoplastic phenotype of EBV-established B lymphocytes by the human Ha-ras oncogene.

We report on the use of human B lymphocytes immortalized by the Epstein-Barr virus (EBV) as targets for transformation by the c-Ha-ras oncogene of bladder carcinoma cells T24. Several stably transformed cell lines were obtained and their in vivo and in vitro growth properties as well as levels of expression of the ras gene were studied. The transformed phenotype in these cells was correlated to ras oncoprotein expression level; only the cell lines which overproduce p21 ras, by at least six-fold, were tumorigenic in nude mice. In this regard, our ras transformed cells behave as lymphoblastoid cells transformed by the c-myc oncogene, suggesting that c-myc and c-Ha-ras might act on the same regulatory level.