Assessment of dentofacial widths in adults with anterior open bite.

CONTEXT: Anterior open bite is a complex condition involving a combination of various dental and skeletal components in three dimensions. The data on the differences and changes in the transverse relation in individuals with anterior open bite are limited. AIMS: To assess the dental arch widths in individuals with anterior open bite using study casts and facial widths using frontal cephalogram and to compare these widths with that of individuals without anterior open bite. MATERIALS AND METHODS: Eighty adults [40 with and 40 without anterior open bite, mean (standard deviation) age = 20.68 years] were selected. The study group was divided into skeletal (n = 19) and dental (n = 21) open bite groups according to Jarabak's ratio. Posteroanterior cephalograms and study casts were analyzed. RESULTS: The mean width of zygomatic arch (112.18 mm) and condylar region (100.55 mm) in the control group was significantly higher (P < 0.05). The mean gonial width in the skeletal open bite group (81.143 mm) was significantly (P < 0.05) lesser than the dental open bite group (84.842). The maxillary intercanine width for the skeletal open bite group (36.48 mm) was significantly (P < 0.01) higher than that of the dental open bite group (34.26 mm). CONCLUSION: A transverse deficiency was seen in in the zygomatic and condylar regions in adults with anterior open bite. Individuals with a skeletal open bite showed a narrow gonial and wider maxillary intercanine width compared with individuals with dental open bite.

Reciprocal expression of the Eph receptor Cek5 and its ligand(s) in the early retina.

Recent evidence suggests that Eph receptor tyrosine kinases and their ligands provide positional information in the developing visual system. We previously found that the Eph receptor Cek5 is more highly expressed in the ventral than dorsal chicken embryonic retina. We now report the identification of a chicken ligand for Cek5 (cCek5-L) that is 75% identical to the ligand LERK2. In situ hybridization experiments do not reveal a dorsoventral gradient of cCek5-L transcripts in the optic tectum at Embryonic Day 8, suggesting that this ligand is not involved in guiding Cek5-expressing axons in the tectum. Surprisingly, it is in the retina that high levels of cCek5-L mRNA are present. In the early retina, cCek5-L is more highly expressed in the dorsal than the ventral aspect. Similarly, a Cek5 Ig chimera labels dorsal but not ventral retina, indicating that even if several Cek5 ligands are present, their overall distribution is complementary to that of Cek5. Hence, Cek5 and cCek5-L may both contribute to define anatomical compartments within the early retina. In contrast, in the 11-day embryonic retina the distributions of Cek5 and its ligand(s) show considerable overlap, suggesting changing functions as development progresses. In dissociated cultures of dorsal or ventral retinal cells seeded on plates coated with either receptor or ligand Ig chimeras, the interaction between Cek5 and its ligand(s) or cCek5-L and its receptor(s) is sufficient to mediate cell adhesion and allows neurite outgrowth.

Developmental expression and distinctive tyrosine phosphorylation of the Eph-related receptor tyrosine kinase Cek9.

Cek9 is a receptor tyrosine kinase of the Eph subfamily for which only a partial cDNA sequence was known (Sajjadi, F.G., and E.B. Pasquale. 1993. Oncogene. 8:1807-1813). We have obtained the entire cDNA sequence and identified a variant form of Cek9 that lacks a signal peptide. We subsequently examined the spatio-temporal expression and tyrosine phosphorylation of Cek9 in the chicken embryo by using specific antibodies. At embryonic day 2, Cek9 immunoreactivity is concentrated in the eye, the brain, the posterior region of the neural tube, and the most recently formed somites. Later in development, Cek9 expression is widespread but particularly prominent in neural tissues. In the developing visual system, Cek9 is highly concentrated in areas containing retinal ganglion cell axons, suggesting a role in regulating their outgrowth to the optic tectum. Unlike other Eph-related receptors, Cek9 is substantially phosphorylated on tyrosine in many tissues at various developmental stages. Since autophosphorylation of receptor protein-tyrosine kinases typically correlates with increased enzymatic activity, this suggests that Cek9 plays an active role in embryonic signal transduction pathways.

Characterization of the expression of the Cek8 receptor-type tyrosine kinase during development and in tumor cell lines.

Cek8 is a receptor-type tyrosine kinase gene that was identified by screening a 10 day chicken embryo library with a DNA probe corresponding to the related kinase Cek4 (Sajjadi & Pasquale, 1993). Here we report the characterization of the Cek8 protein and its expression in embryonic tissues and tumor cell lines. The 120 kd Cek8 protein is detected early in embryogenesis, is developmentally regulated and preferentially, but not exclusively, expressed in neural tissues. In the stage 24 chick embryo, Cek8 immunoreactivity is prominent in the spinal cord and spinal nerves. At embryonic day 6, Cek8 expression becomes concentrated to the ventral portion of the spinal nerves, suggesting a role in axonogenesis of specific subsets of neurons. Cek8 is expressed in nearly all of the tumor cell lines examined, including cell lines derived from tumors of the central nervous system. Although the phosphorylation on tyrosine of Cek8 during development is moderate or undetectable, Cek8 is substantially phosphorylated on tyrosine (and thus presumably activated) in many of the transformed cell lines. Because of its high frequency of expression in tumor cell lines, Cek8 differs from previously investigated Eph-related kinases. However, as we show, Cek8 is not unique among the Eph-related kinases: another member of the Eph subclass, Cek5, has similar patterns of expression and phosphorylation in tumor cells. Based on its binding to a variety of lectin columns, Cek8 contains complex N-linked oligosaccharides. Cross-linking of Cek8 molecules on the cell surface with wheat germ agglutinin caused their rapid phosphorylation on tyrosine. Autophosphorylation on tyrosine is typically the first step in the activation of a receptor tyrosine kinase by a ligand.

Studies of ligand binding to Escherichia coli adenylosuccinate synthetase.

Dissociation constants of Escherichia coli adenylosuccinate synthetase with IMP, GTP, adenylosuccinate, and AMP (a competitive inhibitor for IMP) were determined by measuring the extent of quenching of the intrinsic tryptophan fluorescence of the enzyme. The enzyme has one binding site for each of these ligands. Aspartate and GDP did not quench the fluorescence to any great extent, and their dissociation constants could not be determined. These ligand binding studies were generally supportive of the kinetic mechanism proposed earlier for the enzyme. Cys291 was modified with the fluorescent chromophores N-(iodoacetylaminoethyl)-5-naphthylamine-1-sulfonate and tetramethylrhodamine maleimide in order to measure enzyme conformational changes attending ligand binding. The excitation and emission spectra of these fluorophores are not altered by the addition of active site binding ligands. TbGTP and TbGDP were used as native reporter groups, and changes in their fluorescence on complexing with the enzyme and various ligands made it possible to detect conformational changes occurring at the active site. Evidence is presented for abortive complexes of the type: enzyme-TbGTP-adenylosuccinate and enzyme-TbGTP-adenylosuccinate-aspartate. These results suggest that the IMP and aspartate binding sites are spatially separated.

Identification of different classes of nonessential sulfhydryl groups in Escherichia coli adenylosuccinate synthetase.

Reaction of Escherichia coli adenylosuccinate synthetase with the thiol reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) or N-ethylmaleimide (NEM) leads to modification of one cysteine residue per enzyme monomer without significant loss of enzyme activity. Modification of a second cysteine residue occurs under mild denaturing conditions (3.5 M urea), and derivatization of this thiol followed by dialysis results in complete loss of enzyme activity. The remaining two cysteine residues react with DTNB only after treatment with 8 M urea. The location of the various cysteine residues in the enzyme was established by using [14C]NEM followed by tryptic digestion and radiopeptide isolation. The reactive cysteine has been identified as Cys291, and the thiol exposed with 3.5 M urea is Cys344. When Cys344 was replaced by either serine or alanine, the mutant enzymes were found to be as active as the wild-type enzyme. These findings point to the nonessential role of Cys344 in adenylosuccinate synthetase.