Biomedical subjects

Donald A Fox

Publications and source records attributed to Donald A Fox.

6 recordsLinked to original sources

PubMed2006

Gene expression profiling in embryonic mouse lenses.

PURPOSE: In this study, we used laser capture microdissection (LCM) and microarray hybridization technology to compare the gene expression profiles of mouse embryonic days 10 and 12 lenses (E10 and E12). METHODS: Lens cells of C57/BL6 mouse embryos at E10 and E12 were harvested using the PixCell II LCM System. Total RNA was extracted, amplified, labeled, and hybridized to the 430 2.0 mouse chip (Affymetrix) according to the manufacturer's instructions. Data extracted from the images were analyzed using different software programs. Regulated expression of selected genes was confirmed by real-time PCR (RT-PCR). RESULTS: Analysis of the microarray data from E10 and E12 lenses identified 1,573 genes that showed a two fold or greater change in expression level. Among these 1,573 genes, 956 genes were downregulated and 617 were upregulated in E12 lenses. In addition to the upregulated expression of beta- and gamma-crystallin genes, genes that regulate the cell cycle showed significant changes of gene expression during the E10 (lens pit) to E12 (primary fiber cell induction) time period. Genes involved in insulin-like growth factor (IGF) signaling and Wnt (a family of secreted glycoproteins related to the Drosophila segment polarity gene, wingless, and to the proto-oncogene, int-1) signaling were also differentially regulated. In particular, positive regulators of Wnt signaling were downregulated and negative regulators were upregulated, indicating that modulation of Wnt signaling is important for normal lens morphogenesis. CONCLUSIONS: Our results provide new information about differential regulation of gene expression during early lens development. Analysis of global gene expression profiles in embryonic mouse lenses has allowed us to identify several molecular pathways that are differentially regulated during early lens development.

Animals↗

PubMed2004

The structure-function correlates of mammalian rod and cone photoreceptor mitochondria: observations and unanswered questions.

Our previous work suggests that cone photoreceptor inner segment (CIS) mitochondria demand and produce more ATP than rods. The CISs utilize two complimentary strategies to increase ATP production: increase the absolute number of mitochondria and their cristae surface membrane area. In this treatise, we ask: How are crista junctions formed and regulated? Once formed, are there physical mechanisms that constrain their diameter? How are the constrictions in cristae regulated and is this key for cytochrome c release during apoptosis? What are their differences in rod and cone susceptibility to apoptotic cell death during calcium overload and oxidative stress?

Journal Article↗

PubMed2003

Three-dimensional analysis of mouse rod and cone mitochondrial cristae architecture: bioenergetic and functional implications.

PURPOSE: Comparative studies of structure related to function offer a promising means of understanding the significance of differences in cytoarchitecture. Mitochondrial crista structure is linked tightly to mitochondrial function. Non-foveal cone photoreceptors of primates contain considerably more inner segment mitochondria and have higher oxidative enzyme activity than do rods. In addition, it is suggested that light-adapted cones have a higher aerobic ATP demand than light-adapted rods. Therefore, we investigated the oxidative metabolism and three-dimensional membrane architecture of mouse rod and cone inner segment mitochondria. METHODS: We determined the number, size, cytochrome c oxidase (CO) reactivity, and membrane architecture of rod and middle wavelength-sensitive (M) cone inner segment mitochondria from 21 day old light-adapted C57BL/6 mice using conventional electron microscopy and the three-dimensional approach of single- and double-tilt electron microscope tomography. Fourteen different measurements of mitochondrial substructures were analyzed. Photoreceptor oxygen consumption was determined in dark- and light-adapted retinas. RESULTS: Rod and cone mitochondria displayed an orthodox conformation. Cone inner segments, compared to rods, contained 2-fold more mitochondria and were more CO reactive. Rod and cone mitochondria had similar outer-inner membrane width, contact site width, diameter and density, crista width, number of cristae/volume, number of cristae segments/volume, and fraction of cristae with multiple segments. In contrast, cone mitochondria had narrower crista junctions, greater cristae connectivity, and approximately 3-fold more cristae membrane surface area compared to rods. The increased cristae membrane surface area in cones was accomplished by connecting more cristae segments together, rather than by creating more cristae. CONCLUSIONS: These results demonstrate that middle wavelength (M) cones have a different bioenergetic signature than do rods and suggest that the aerobic ATP demand and production is greater in light-adapted cones than in light-adapted rods. Cones utilize two complimentary strategies to increase their aerobic ATP production: increase the number of mitochondria and increase the cristae surface membrane area. The greater ATP generation by cones may also provide increased protection against metabolic insults and apoptosis compared to rods.

Adenosine Triphosphate↗

PubMed2003

Bcl-xL overexpression blocks bax-mediated mitochondrial contact site formation and apoptosis in rod photoreceptors of lead-exposed mice.

Photoreceptor apoptosis and resultant visual deficits occur in humans and animals with inherited and disease-, injury-, and chemical-induced retinal degeneration. A clinically relevant mouse model of progressive rod photoreceptor-selective apoptosis was produced by low-level developmental lead exposure and studied in combination with transgenic mice overexpressing Bcl-x(L) only in the photoreceptors. A multiparametric analysis of rod apoptosis and mitochondrial structure-function was performed. Mitochondrial cristae topography and connectivity, matrix volume, and contact sites were examined by using 3D electron tomography. Lead-induced rod-selective apoptosis was accompanied by rod Ca(2+) overload, rhodopsin loss, translocation of Bax from the cytosol to the mitochondria, decreased rod mitochondrial respiration and membrane potential, mitochondrial cytochrome c release, caspase-3 activation, and an increase in the number of mitochondrial contact sites. These effects occurred without mitochondrial matrix swelling, outer membrane rupture, caspase-8 activation, or Bid cleavage. Bcl-x(L) overexpression completely blocked all apoptotic events, except Ca(2+) overload, and maintained normal rod mitochondrial function throughout adulthood. This study presents images of mitochondrial contact sites in an in vivo apoptosis model and shows that Bcl-x(L) overexpression blocks increased contact sites and apoptosis. These findings extend our in vitro retinal studies with Pb(2+) and Ca(2+) and suggest that developmental lead exposure produced rod-selective apoptosis without mitochondrial swelling by translocating cytosolic Bax to the mitochondria, which likely sensitized the Pb(2+) and Ca(2+) overloaded rod mitochondria to release cytochrome c. These results have relevance for therapies in a wide variety of progressive retinal and neuronal degenerations where Ca(2+) overload, lead exposure, andor mitochondrial dysfunction occur.

Animals↗

PubMed2002

Increased ERG a- and b-wave amplitudes in 7- to 10-year-old children resulting from prenatal lead exposure.

PURPOSE: To determine the dose-response relationship between blood lead concentration ([PbB]) and scotopic ERG amplitude in 7- to 10-year-old children with lifetime lead exposure. METHODS: Full-field flash scotopic ERGs were recorded over a 4-log-unit range in 45 dark-adapted children with normal visual acuity. [PbB] was measured throughout pregnancy and postnatal development, and the subjects' [PbB] levels were grouped at each age by tertiles. RESULTS: The median [PbB] during pregnancy was, from lowest to highest tertile, 2.5 to 5.0, 7.5 to 9.0, and 14.0 to 16.5 microg/dL, and after birth was 4.0 to 8.0, 6.0 to 14.5, and 7.5 to 21.0 microg/dL. Only maternal [PbB] at 12 weeks of pregnancy showed a significant dose-response relationship with the ERG measures, so that with increasing [PbB] there were significant increases in leading-edge a-wave amplitude, peak a-wave amplitude, and b-wave amplitude and sensitivity, with no changes in implicit times. Data analyses showed that children whose mothers had [PbB] of 10.5 microg/dL or more at 12 weeks of pregnancy had relatively increased a- and b-waves. CONCLUSIONS: Lead exposure during the first trimester of pregnancy produces dose-dependent increases in scotopic a- and b-wave amplitudes in 7- to 10-year-old children. The results suggest that the increases in a- and b-wave amplitudes originate from rods; however, the increased b-wave amplitude and sensitivity may also originate in the inner retina. These alterations occurred at maternal [PbB] at or below currently accepted safe levels. These novel findings reveal that the developing retina is a sensitive target for lead and suggest that lead-exposed children be examined for possible future visual system deficits.

Child↗

PubMedDate not supplied

Carcinogenicity of saccharin in laboratory animals and humans: letter to Dr. Harry Conacher of Health Canada.

We appreciate this opportunity to provide input to the Health Protection Branch's (HPB's) review of the artificial sweetener saccharin. Concerns with regard to the safety of saccharin are of great public health significance and of great interest to the public because saccharin is consumed by tens of millions of people, including children and fetuses. Any evidence of carcinogenesis--and there is ample such evidence--of such a widely used chemical should spur health officials to minimize human exposure to it. It is worth noting that on October 31, 1997, the Board of Scientific Counselors of the National Toxicology Program, a unit of the National Institute of Environmental Health Sciences (NIEHS), voted not to delist saccharin from its Report on Carcinogens.

Animals↗