Effect of the G375C and G346E achondroplasia mutations on FGFR3 activation

Two mutations in FGFR3, G380R and G375C are known to cause achondroplasia, the most common form of human dwarfism. The G380R mutation accounts for 98% of the achondroplasia cases, and thus has been studied extensively. Here we study the effect of the G375C mutation on the phosphorylation and the cross-linking propensity of full-length FGFR3 in HEK 293 cells, and we compare the results to previously published results for the G380R mutant. We observe identical behavior of the two achondroplasia mutants in these experiments, a finding which supports a direct link between the severity of dwarfism phenotypes and the level and mechanism of FGFR3 over-activation. The mutations do not increase the cross-linking propensity of FGFR3, contrary to previous expectations that the achondroplasia mutations stabilize the FGFR3 dimers. Instead, the phosphorylation efficiency within un-liganded FGFR3 dimers is increased, and this increase is likely the underlying cause for pathogenesis in achondroplasia. We further investigate the G346E mutation, which has been reported to cause achondroplasia in one case. We find that this mutation does not increase FGFR3 phosphorylation and decreases FGFR3 cross-linking propensity, a finding which raises questions whether this mutation is indeed a genetic cause for human dwarfism.     

Chimeras of the native form or achondroplasia mutant (G375C) of human fibroblast growth factor receptor 3 induce ligand-dependent differentiation of PC12 cells.

Mutations in the gene for human fibroblast growth factor receptor 3 (hFGFR3) cause a variety of skeletal dysplasias, including the most common genetic form of dwarfism, achondroplasia (ACH). Evidence indicates that these phenotypes are not due to simple haploinsufficiency of FGFR3 but are more likely related to a role in negatively regulating skeletal growth. The effects of one of these mutations on FGFR3 signaling were examined by constructing chimeric receptors composed of the extracellular domain of human platelet-derived growth factor receptor beta (hPDGFR beta) and the transmembrane and intracellular domains of hFGFR3 or of an ACH (G375C) mutant. Following stable transfection in PC12 cells, which lack platelet-derived growth factor (PDGF) receptors, all clonal cell lines, with either type of chimera, showed strong neurite outgrowth in the presence of PDGF but not in its absence. Antiphosphotyrosine immunoblots showed ligand-dependent autophosphorylation, and both receptor types stimulated strong phosphorylation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase, an event associated with the differentiative response of these cells. In addition, ligand-dependent phosphorylation of phospholipase Cgamma and Shc was also observed. All of these responses were comparable to those observed from ligand activation, such as by nerve growth factor, of the native PC12 cells used to prepare the stable transfectants. The cells with the chimera bearing the ACH mutation were more rapidly responsive to ligand with less sustained MAPK activation, indicative of a preactivated or primed condition and consistent with the view that these mutations weaken ligand control of FGFR3 function. However, the full effect of the mutation likely depends in part on structural features of the extracellular domain. Although FGFR3 has been suggested to act as a negative regulator of long-bone growth in chrondrocytes, it produces differentiative signals similar to those of FGFR1, to which only positive effects have been ascribed, in PC12 cells. Therefore, its regulatory effects on bone growth likely result from cellular contexts and not the induction of a unique FGFR3 signaling pathway.     

An amino acid substitution determining G3m(g)

An allotypic G3m(g) marker-specific substitution was studied by sequence analysis of glycopeptides derived from myeloma proteins Ba (G3m(g+)) and Bu (G3m(g-)). The experimental results indicate that glutamic acid at position 295 is responsible for the specificity. Based on the results of chemical modification (Arg, Tyr, and Glu), this antigenic epitope is presumed to involve five sequential residues from Arg-292 to Tyr-296.     

Cytochrome a3 deficiency in human achondroplasia

Mitochondria prepared from tissue culture cells (skin fibroblasts) from normal subjects and subjects with homozygous achondroplasia were studied to determine the concentrations of cytochromes a and a3 in the preparations. Cytochrome a3 was markedly decreased (80%) in the achondroplastic preparations with cytochrome a present in normal amounts. Determination of total heme a (as the pyridine hemochromogen) in the normal and achondroplastic preparations demonstrated that the observed decrease in concentration of cytochrome a3 in the achondroplastic preparations was due to an absence of cytochrome a3 and not to a change in its absorbancy (extinction coefficient). The decreased concentrations of cytochrome a3 in the achondroplastic cells may decrease the reactivity or affinity of the mitochondrial oxidative systems for oxygen and result in the phenotypic expression of the disease.     

An uncommon oyster breeding system in a Late Tertiary Patagonian species

Iribarne, O. O., Pascual, M. S. & Zampatti, E. A. 1990 04 15: An uncommon oyster breeding system in a Late Tertiary Patagonian species. Lethaia , Vol. 23 , pp. 153–156. Oslo. ISSN 0024–1164.
The brooding extant species Ostrea puelchana has a breeding system that is unique among living oysters. Females larger than 55 mm often carry small epidictic males (up to 30 mm) on the anterior edge of the concave shell. These are strongly attached when small, but become relatively less strongly attached as they grow larger. Field experiments show that their growth is retarded as a result of the influence of the carrier. Advantages of this mating system are reflected in the success of fertilization; sperm transfer is facilitated safely during long periods of the oyster's life. A similar attachment pattern was found in a fossil oyster, Ostrea aluarezi , from a Patagonian deppsit. The finding suggests that this particular reproductive strategy had already evolved among late Tertiary ostreids. * Epibiotic. breeding system, fossil , Ostrea alvarezi, oyster, Tertiary .     

Mortality in babies with achondroplasia: Revisited

BACKGROUND: Natural history studies performed 30 years ago identifying higher mortality among children born with achondroplasia, a genetic dwarfing condition, resulted in clinical recommendations aimed at improving mortality in childhood. The objective of this study was to determine if mortality rates have changed over the past few decades. METHODS: Children born with achondroplasia during 1996 to 2003 were ascertained from the Texas Birth Defects Registry and matched with death certificate data from the Bureau of Vital Statistics through 2007. Infant and overall mortality rates, both crude and standardized to the 2005 (SMR₂₀₀₅) and 1975 (SMR₁₉₇₅) U.S. populations, were calculated. RESULTS: 106 children born with achondroplasia were identified. Four deaths were reported, with all occurring in the first year of life (mortality rate: 41.4 /1000 live‐births). Infant mortality was higher when standardized to the 2005 U.S. population (SMR₂₀₀₅:6.02, 95% CI:1.64–15.42) than the 1975 population (SMR₁₉₇₅:2.58, 95% CI:0.70–6.61). CONCLUSION: The higher SMR₂₀₀₅ compared with SMR₁₉₇₅, along with the fact that SMR₁₉₇₅ was nearly half that of a previous cohort reported 25 years ago (rate ratio: 0.53, 95% CI: 0.11–2.25), reflect a discrepancy in the changes in mortality in the overall population and in our cohort. Although an overall improvement in mortality, especially after the first year of life, is observed in our cohort, children with achondroplasia are still at a much higher risk of death compared with the general population. A longer follow‐up is needed to elucidate whether evaluation/intervention changes have resulted in significant improvement in long‐term survival among these patients. Birth Defects Research (Part A) 100:247–249, 2014. © 2014 Wiley Periodicals, Inc.     

A mouse kidney cell line with a G:C --> C:G transversion mutator phenotype

We report the identification of a mouse kidney epithelial cell line (K435) in which G:C-->C:G transversion mutations occur at an elevated rate and are the predominant spontaneous events observed at the selectable Aprt locus. Of three genotoxins tested, ultraviolet radiation (UV), ionizing radiation, and hydrogen peroxide, only UV exposure was able to alter the spectrum of small mutational events. To determine if the G:C-->C:G mutator phenotype was due to a deficiency in the mismatch repair pathway, the K435 cells were tested for resistance to 6-thioguanine, cisplatin, and MNNG. Although the K435 cells were as resistant to 6-thioguanine and cisplatin as Pms2 and Mlh1 null kidney cells, they were hypersensitive to MNNG. Moreover, the K435 cells do not exhibit microsatellite instability, a hallmark of mismatch repair deficiency. These results suggest that a novel mechanism, which does not include a classical deficiency in mismatch repair, accounts for the G:C-->C:G mutator phenotype.     

An uncommon phenotypical variant in the Shereshevsky-Turner syndrome

Summary Three young girls of short stature and with somatic anomalies typical for the Shereshevsky-Turner syndrome are described. Signs of sexual maturation and menarche appeared on time. Later on, menstrual periods came to resemble juvenile bleedings. Karyotypes determined in lymphocyte culture were 45,X/46,XX/47,XXX; 45,X/46,XXp-; and 46,XXp-, respectively. A possibility of spontaneous sexual maturation in patients with the Shereshevsky-Turner syndrome is discussed.     

Incidence of fibroblast growth factor receptor 3 gene (FGFR3) A248C, S249C, G372C, and T375C mutations in bladder cancer

Bladder cancer is the most frequent cancer of the urinary system. Fibroblast growth factor receptors (FGFR) belong to the tyrosine kinase family and have important roles in cell differentiation and proliferation and embryogenesis. FGFR3 is located on chromosome 4p16.3, and missense mutations of FGFR3 are associated with autosomal dominant human skeletal disorders and have some oncogenic effects. We examined the incidence of FGFR3 thanatophoric dysplasia mutations located in exon 7, A248C and S249C, and in exon 10, G372C and T375C, and their correlation with clinical-pathological parameters in bladder carcinoma patients. Fifty-six paraffin-embedded specimens of transitional cell carcinoma of the urinary bladder were included in this study. Analysis of FGFR3 thanatophoric dysplasia mutations located in exon 7, A248C and S249C, and in exon 10, G372C and T375C, was performed by PCR-restriction fragment length polymorphism (RFLP) analysis and DNA sequencing. FGFR3 thanatophoric dysplasia mutations located in exon 7, A248C and S249C, and in exon 10, G372C and T375C, were detected in 33 of the 56 patients (heterozygous mutant). Among the 56 transitional cell carcinomas, missense point mutations were detected in seven of them at codon A248C, 28 of them at codon S249C, and three of them at codon T375C, similar to data from previous reports. When the results of the FGFR3 thanatophoric dysplasia mutations located in exon 7, A248C and S249C and in exon 10, G372C and T375C, were analyzed one by one or as a group, despite the findings of previous research reports, our data suggest that these mutations are detected homogenously regardless of the tumor classification and tumor grade.     

An uncommon form of thymidine kinase in breast cancers

An unusual form of thymidine kinase has been found in cytosols from breast cancers. It differs from the adult and fetal isoenzymes of thymidine kinase in so far as its activity could not be isolated from that of thymidylate kinase. Following sucrose density gradients, electrofocusing, ion exchange chromatography or molecular sieving, both activities appeared as a single peak. These facts suggest that they could be attributed to a single multifunctional protein.     

Thermodynamics of RNA duplexes with tandem mismatches containing a uracil-uracil pair flanked by C.G/G.C or G.C/A.U closing base pairs

The thermodynamics governing the denaturation of RNA duplexes containing 8 bp and a central tandem mismatch or 10 bp were evaluated using UV absorbance melting curves. Each of the eight tandem mismatches that were examined had one U-U pair adjacent to another noncanonical base pair. They were examined in two different RNA duplex environments, one with the tandem mismatch closed by G.C base pairs and the other with G.C and A.U closing base pairs. The free energy increments (Delta Gdegrees(loop)) of the 2 x 2 loops were positive, and showed relatively small differences between the two closing base pair environments. Assuming temperature-independent enthalpy changes for the transitions, (Delta Gdegrees(loop)) for the 2 x 2 loops varied from 0.9 to 1.9 kcal/mol in 1 M Na(+) at 37 degrees C. Most values were within 0.8 kcal/mol of previously estimated values; however, a few sequences differed by 1.2-2.0 kcal/mol. Single strands employed to form the RNA duplexes exhibited small noncooperative absorbance increases with temperature or transitions indicative of partial self-complementary duplexes. One strand formed a partial self-complementary duplex that was more stable than the tandem mismatch duplexes it formed. Transitions of the RNA duplexes were analyzed using equations that included the coupled equilibrium of self-complementary duplex and non-self-complementary duplex denaturation. The average heat capacity change (DeltaC(p)) associated with the transitions of two RNA duplexes was estimated by plotting DeltaH degrees and DeltaS degrees evaluated at different strand concentrations as a function of T(m) and ln T(m), respectively. The average DeltaC(p) was 70 +/- 5 cal K(-)(1) (mol of base pairs)(-)(1). Consideration of this heat capacity change reduced the free energy of formation at 37 degrees C of the 10 bp control RNA duplexes by 0.3-0.6 kcal/mol, which may increase Delta Gdegrees(loop) values by similar amounts.