Differential regulation of endochondral bone growth and joint development by FGFR1 and FGFR3 tyrosine kinase domains.

Fibroblast growth factor receptors (FGFR) 1 and 3 have distinct mitogenic activities in vitro. In several cultured cell lines, FGFR1 transmits a potent mitogenic signal, whereas FGFR3 has little or no mitogenic activity. However, in other in vitro assays the FGFR3 intracellular domain is comparable with that of FGFR1. In vivo, FGFR3 negatively regulates chondrocyte proliferation and differentiation, and activating mutations are the molecular etiology of achondroplasia. By contrast, FGFR1 transmits a proliferative signal in various cell types in vivo. These observations suggest that inhibition of the proliferating chondrocyte could be a unique property of FGFR3 or, alternatively, a unique property of the proliferating chondrocyte. To test this hypothesis, FGFR1 signaling was activated in the growth plate in cells that normally express FGFR3. Comparison of transgenic mice with an activated FGFR1 signaling pathway with an achondroplasia-like mouse that expresses a similarly activated FGFR3 signaling pathway demonstrated that both transgenes result in a similar achondroplasia-like dwarfism. These data demonstrate that suppression of mitogenic activity by FGFR signaling is a property that is unique to growth plate chondrocytes. Surprisingly, we observed that in transgenic mice expressing an activated FGFR, some synovial joints failed to develop and were replaced by cartilage. The defects in the digit joints phenocopied the symphalangism that occurs in Apert syndrome and the number of affected joints was dependent on transgene dose. In contrast to the phenotype in the growth plate, the joint phenotype was more severe in transgenic mice with an activated FGFR1 signaling pathway. The failure of joint development resulted from expanded chondrification in the presumptive joint space, suggesting a crucial role for FGF signaling in regulating the transition of condensed mesenchyme to cartilage and in defining the boundary of skeletal elements.

Male-to-female sex reversal in mice lacking fibroblast growth factor 9.

Fgfs direct embryogenesis of several organs, including the lung, limb, and anterior pituitary. Here we report male-to-female sex reversal in mice lacking Fibroblast growth factor 9 (Fgf9), demonstrating a novel role for FGF signaling in testicular embryogenesis. Fgf9(-/-) mice also exhibit lung hypoplasia and die at birth. Reproductive system phenotypes range from testicular hypoplasia to complete sex reversal, with most Fgf9(-/-) XY reproductive systems appearing grossly female at birth. Fgf9 appears to act downstream of Sry to stimulate mesenchymal proliferation, mesonephric cell migration, and Sertoli cell differentiation in the embryonic testis. While Sry is found only in some mammals, Fgfs are highly conserved. Thus, Fgfs may function in sex determination and reproductive system development in many species.

Fibroblast growth factor receptor 3 gene transcription is suppressed by cyclic adenosine 3',5'-monophosphate. Identification of a chondrocytic regulatory element.

Signaling through fibroblast growth factor receptors (FGFRs) is critical for the development and patterning of the vertebrate skeleton. Gain-of-function alleles of fgfr2 and fgfr3 have been linked to several dominant skeletal disorders in humans, while null mutations in fgfr3 result in the overgrowth of long bones in a mouse model system. Interestingly, the expression pattern of fgfr3 in growth plate chondrocytes overlaps that of the parathyroid hormone (PTH)-related peptide (PTHrP) receptor, a signaling molecule that also regulates endochondral ossification. The coincident expression of these two receptors suggests that their signaling pathways may also interact. To gain insight into the regulatory mechanism(s) that govern the expression of the fgfr3 gene in chondrocytes, we have identified a cell-specific transcriptional regulatory element (CSRh) by measuring the activity of various promoter fragments in FGFR3-expressing (CFK2) and nonexpressing (RCJ) chondrocyte-like cell lines. Furthermore, we demonstrate that activation of PTH/PTHrP receptors, either by stimulation with PTH or through the introduction of activating mutations, represses CSRh-mediated transcriptional activity. Finally, the transcriptional repression of the CSRh element was mimicked by treatment with forskolin, 8-bromo-cAMP, and 3-isobutyl-1-methylxanthine or by overexpression of the catalytic subunit of protein kinase A. Together, these data suggest that protein kinase A activity is a critical factor that regulates fgfr3 gene expression in the proliferative or prehypertrophic compartment of the epiphyseal growth plate. Furthermore, these results provide a possible link between PTHrP signaling and fgfr3 gene expression during the process of endochondral ossification.

Retinal detachment in U.S. Air Force flyers.

Retinal detachment is a serious ocular condition, even though 85% can be repaired permanently. Long-term complications include decreased or loss of vision, redetachment, visual field changes, and proliferative vitreoretinpathy. To assess the effect of retinal detachment on flying careers, we reviewed the records of all aviators with a rhegmatogenous retinal detachment who were examined by the Ophthalmology Branch of the Aerospace Medicine Directorate at the Armstrong Laboratory (formerly the USAF School of Aerospace Medicine) from 1967-1986. Of the 19 flyers, 12 were returned to flying duties; only 2 were disqualified for ocular reasons alone. In 10 flyers, the detachments were previously undiagnosed. Associated vitreoretinal pathology was common in both eyes (42%). All received some type of treatment. Redetachment occurred in 4 flyers, but the overall final reattachment rate was 95%. Final posttreatment visual acuities were 20/20 or better in 16 flyers. Treatment-induced myopia was common. Many flyers enjoyed long flying careers after detachment repairs.

Experimental investigation of vector phase conjugation in Nd(3+):YAG.

We present a study of vector phase conjugation based on degenerate four-wave mixing in inverted Nd:YAG. The results demonstrate polarization correction for weak probe strength, with near-unity fidelity for polarization compensation of the returning conjugate. As the probe strength is increased, the fidelity of the polarization state of the conjugate is seen to deteriorate to an average value of 92% when the probe is strongly saturating and is several times stronger than the pump beams. We also show that, for strong probe strengths, an individual transmission grating or reflection grating is more efficient than when both gratings are present.

A survey of U.S. Air Force flyers regarding their use of extended wear contact lenses.

We reviewed the USAF Tactical Air Command's (TAC) contact lens database for the period July 1989 through June 1991. An anonymous survey was mailed to 396 TAC aircrew members in February 1992 to assess their experiences using extended wear soft contact lenses (EWSCL). Analysis was performed on those responses to compare differences between aviators who currently wear (CW), those who discontinued wear (DCW), and flyers who wore EWSCL while deployed to S.W. Asia for Desert Shield/Desert Storm. Of the 396 surveyed, 284 (72%) returned the survey and demonstrated that the daily use of EWSCL to be logistically practical and physiologically safe. No ocular malady was reported that would preclude continued use by aircrews. Desert Shield/Storm experiences documented that the use of EWSCL by USAF aircrews in a desert environment was possible. Logistical difficulties for the small number who either deployed with inadequate supplies or required replacement lenses were shown to be the primary challenge to the wear of EWSCL during Desert Shield/Storm. Subjectively, aircrews expressed strong beliefs that EWSCL contributed to their abilities as combat aviators.

Retinal vein occlusions: case reviews of USAF aviators.

Retinal vein occlusions are primarily a disease of the elderly, frequently with permanent visual abnormalities. However, both branch and central retinal vein occlusions occur rarely in young individuals. Reported here are a series of retinal vein occlusions in USAF aviators. Seven cases were identified from records of the USAF Armstrong Laboratory Aeromedical Consultation Service from 1976-91. Four cases of central retinal vein occlusions and three cases of branch occlusions are summarized. Initial visual acuity ranged from 20/15 to 20/400. All seven aviators recovered 20/15 vision and returned to flying status. Hyperlipidemia was found in four of the seven aviators, and hypertension was diagnosed in two aviators. Included is a discussion of current concepts in the natural history, associated systemic conditions, treatment options, and aeromedical implications of retinal vein occlusions.

A physical comparison of chromosome III in six strains of Saccharomyces cerevisiae.

We have tested the clones used in the European Yeast Chromosome III Sequencing Programme for possible artefacts that might have been introduced during cloning or passage through Escherichia coli. Southern analysis was performed to compare the BamHI, EcoRI, HindIII and PstI restriction pattern for each clone with that of the corresponding locus on chromosome III in the parental yeast strain. In addition, further enzymes were used to compare the restriction maps of most clones with the map predicted by the nucleotide sequence (Oliver et al., 1992). Only four of 506 6-bp restriction sites predicted by the sequence were not observed experimentally. No significant cloning artefacts appear to disrupt the published sequence of chromosome III. The restriction patterns of six yeast strains have also been compared. In addition to two previously identified sites of Ty integration on chromosome III (Warmington et al., 1986; Stucka et al., 1989; Newlon et al., 1991), a new polymorphic site involving Ty retrotransposition (the Far Right-Arm transposition Hot-Spot, FRAHS) has been identified close to CRY1. On the basis of simple restriction polymorphisms, the strains S288C, AB972 and W303-1b are closely related, while XJ24-24a and J178 are more distant relatives of S288C. A polyploid distillery yeast is heterozygous for many polymorphisms, particularly on the right arm of the chromosome.

Reflectivity and oscillation conditions of a gain medium in a self-conjugating loop geometry.

The intensity-dependent reflectivity of a gain medium in a self-phase-conjugating loop geometry is numerically modeled by use of exact integration equations without restriction on the degree of gain saturation. High conjugate reflectivity and high energy extraction efficiency of the gain medium are predicted. A weak saturation analysis is also presented to derive useful expressions for the threshold input intensity for oscillation of the backward conjugate mode and the resonant oscillation frequencies.

Holographic laser resonators in Nd:YAG.

We report the operation of Nd:YAG ring laser resonators formed by diffractive coupling from a gain volume hologram written in a Nd:YAG amplifier. Stable diffraction-limited output in a TEM(00) mode is demonstrated in a Nd:YAG system with thermal lensing and without the requirement of spatial mode control.

Chimeric-transgenic mice represent a powerful tool for studying how the proliferation and differentiation programs of intestinal epithelial cell lineages are regulated.

An in vivo system has been developed for examining the effects of wild-type or mutant proteins on cell fate determination in the mouse intestinal epithelium or on the proliferation and differentiation programs of its component epithelial lineages. This system takes advantage of the fact that at the conclusion of gut morphogenesis, each intestinal crypt is composed of a monoclonal population of cells descended from a single active multipotent stem cell, each villus is supplied by several monoclonal crypts, and the four principal cell types of the intestinal epithelium differentiate during a rapid, geographically well-organized migration along the crypt-to-villus axis. Embryonic stem (ES) cells (129/Sv origin) are initially transfected with recombinant DNAs consisting of a reporter of interest linked to transcriptional regulatory elements that control the cell lineage-specific, differentiation-dependent, and axial patterns of expression of fatty acid binding protein genes in the gut. Stably transfected ES cells are subsequently introduced into host C57BL/6 blastocysts to generate chimeric-transgenic mice. At the borders of ES cell-derived and host blastocyst-derived epithelium, intestinal villi are found that are supplied by both ES cell- and host blastocyst-derived crypts. These villi can be rapidly identified in fixed whole-mount preparations of intestine using the alpha-L-fucose-specific Ulex europaeus agglutinin type I (UEA-I) lectin. They appear striped because UEA-I recognizes a cell-surface carbohydrate polymorphism between the inbred strains used to generate the chimeric animals. The strength of this system derives from the fact that two gut epithelial populations can be compared and contrasted that occupy virtually identical positions along the crypt-to-villus and duodenal-to-colonic axes within the same animal and differ only by the presence or absence of a single gene product. The band of blastocyst-derived epithelium in these striped, polyclonal villi can be used as an internal control to assess the biological effect of the transfected gene product produced in the adjacent stripe of ES-derived cells. The system can be used for either gain-of-function or loss-of-function experiments.

The pigmentary dispersion disorder in USAF aviators.

The pigmentary dispersion syndrome (PDS) can have serious ocular consequences. Visual changes due to glaucoma and the treatment required can threaten the high level of visual function necessary in military aviation. We reviewed the records of 50 aviators with PDS who were evaluated at the Aeromedical Consultation Service (formerly the USAF School of Aerospace Medicine) over the past 10 years. At last evaluation, 48 were still qualified to fly. Only two aviators were permanently removed from flying duties due to glaucoma. Initial intraocular pressures, cup-to-disc ratios, and refractions were not statistically correlated with progression to glaucoma, but sample sizes were small. At final evaluation, 20 of the 34 aviators with follow-up had glaucoma and required medication. Thirteen eyes underwent laser trabeculoplasty. With appropriate management, the majority of aviators with PDS were able to safely continue their flying careers.

Cataract surgery and intraocular lenses in military aviators.

We reviewed the medical records of 23 military aviators who were evaluated by the United States Air Force School of Aerospace Medicine (USAFSAM) after cataract extraction with intraocular lens implantation between 1979 and 1990. The 23 subjects were male Caucasians, with a mean age of 43 years. Of the subjects, 21 were pilots, and, of these, 8 were qualified in high-performance aircraft. There were a total of 28 operated eyes, 24 of which had received extracapsular cataract extractions (ECCE) with posterior chamber lenses. The best-corrected, postoperative vision was 20/20 or better in all eyes. Posterior capsule opacification occurred in 14 (60%) of the ECCE eyes, with five requiring Nd:YAG (Yttrium-Aluminum-Garnet) laser capsulotomies. One aviator was disqualified from flying duties because of ocular deficiencies, for a visually-qualified-to-fly rate of 96%. Eight aviators have actually flown since surgery. Although follow-up was short, the initial results are encouraging.

The medical acceptability of soft contact lens wear by USAF tactical aircrews.

Seventy-two Tactical Air Command (TAC) aircrew members completed one full year of soft contact lens (SCL) wear. A daily-wear regimen, using extended-wear lenses, was used to minimize corneal stress. Baseline measurements of visual acuity with SCLs and with spectacles after SCL removal and ocular indicator gradings were compared to measurements at 5-d, 10-d, 1-month, 3-month, 6-month, and 12-month examinations. Visual acuity did not decrease during the test. No aircrew member developed corneal ulcers or other serious complications requiring elimination from the test. Two aircrew members lost a total of 9 "duties not to include flying" (DNIF) days: one flyer was grounded for 1 d with a corneal abrasion and another for 8 d with epithelial microcysts. The TAC SCL Test, as designed, was generally successful. The conservative approach to SCL wear during the test and the meticulous follow-up care by United States Air Force eye care professionals most likely contributed to the low ocular complication rate.

Prescribing spectacles for aviators: USAF experience.

This special report was written for USAF vision specialists to use as a guide when prescribing spectacles for military aviators and to extend to the civilian sector the knowledge gained from the USAF experience. Visual correction in aviators presents some unique problems, especially for presbyopes. The demands of each individual aircraft environment need to be well understood. Ophthalmologists and optometrists must consider all pertinent aeromedical factors before prescribing spectacles for ametropic aviators.

The mouse intestinal fatty acid binding protein gene: nucleotide sequence, pattern of developmental and regional expression, and proposed structure of its protein product.

The rat intestinal fatty acid binding protein (I-FABP) gene has been used as a model to study temporal and spatial differentiation of the gut epithelium while its protein product has been used as a model for examining the atomic details of noncovalent fatty acid-protein interactions. We have isolated the mouse I-FABP gene (Fabpi) and determined its nucleotide sequence. Comparisons of the orthologous mouse, rat, and human I-FABP genes revealed three conserved domains in their otherwise divergent 5' nontranscribed sequences. RNA blot hybridization and multilabel immunocytochemical methods were used to compare the developmental stage-specific patterns of activation of the rat and mouse genes. In addition, Fabpi expression in enterocytes was examined as a function of their differentiation along the crypto-to-villus and duodenal-to-colonic axes of the small intestine. Based on the similar temporal and geographic patterns of mouse and rat I-FABP expression described here and the results of our earlier studies of transgenic mice containing rat Fabpi/human growth hormone fusion genes, we propose that one of the conserved domains, spanning nucleotides -500 to -419 in mouse Fabpi, and/or a 14-bp element, are necessary for establishing and maintaining its region-specific expression along the duodenal-to-colonic axis of the perpetually renewing gut epithelium. Finally, predictions of the structure of mouse I-FABP using the refined 2.0 A model of rat I-FABP, suggest that a proline found at position 69 of the mouse, but not rat, protein may affect its ligand binding properties.

Investigation of multipass geometries for efficient degenerate four-wave mixing in Nd:YAG.

Degenerate four-wave mixing in the saturable gain of a flash-lamp-pumped Nd:YAG amplifier has been investigated. Three different geometries are examined in which the probe beam experiences (a) one pass, (b) two passes, and (c) four passes of the four-wave interaction region. It is found that multipassing the gain medium has a dramatic effect on the efficiency of the process, with a phase-conjugate reflectivity of 2500 and a conjugate energy extraction efficiency of greater than 200% demonstrated.

The career impact of keratoconus on Air Force aviators.

Keratoconus causes progressive blurring and distortion of vision, which threatens the career of a military aviator. To assess the impact of keratoconus on flying careers, we reviewed the records of all aviators with keratoconus who have been examined at the United States Air Force School of Aerospace Medicine over the past 23 years. Of the 22 aviators observed for more than three years, 18 were still qualified to fly at their most recent examination. The remaining four aviators were permanently removed from flying duties because of visual dysfunction caused by keratoconus. Of the 22 aviators examined, 15 required hard contact lenses for optimal correction of vision. No aircraft accidents or incidents, attributable to visual factors, were documented. We concluded that the majority of aviators with keratoconus are able to continue their flying careers safely with the aid of spectacles or contact lenses.