From segment to somite: segmentation to epithelialization analyzed within quantitative frameworks.

One of the most visually striking patterns in the early developing embryo is somite segmentation. Somites form as repeated, periodic structures in pairs along nearly the entire caudal vertebrate axis. The morphological process involves short- and long-range signals that drive cell rearrangements and cell shaping to create discrete, epithelialized segments. Key to developing novel strategies to prevent somite birth defects that involve axial bone and skeletal muscle development is understanding how the molecular choreography is coordinated across multiple spatial scales and in a repeating temporal manner. Mathematical models have emerged as useful tools to integrate spatiotemporal data and simulate model mechanisms to provide unique insights into somite pattern formation. In this short review, we present two quantitative frameworks that address the morphogenesis from segment to somite and discuss recent data of segmentation and epithelialization.     

Summary of complementation groups of UV-sensitive CHO cell mutants isolated by large-scale screening

A summary is given for the lineage and complementation groupassignments of 153 UV-sensitive mutants of the CHO AA8 cellline. The distribution of mutants among six complementationgroups was highly non-random, with the great majority of theisolates belonging to groups 1 and 2. This asymmetry is consistentwith the known hemizygosity of these two linked loci in CHOcells. The relative numbers of mutants induced in group 2 wasfound to depend greatly on the type of mutagen used. Mutagenesiswith UV radiation, ethyl methanesulfonate (EMS), N-methyl-N'-nitro-N-nitroso-guanidine and 7-bromomethylbenz[a]anthraceneproduced high frequencies of group 2 mutants. In contrast, ICR170and ICR191, which are thought to produce mostly frameshift mutations,yielded very few mutants in group 2. These results are of particularimportance in light of the recent finding that the human ERCC2gene, which corrects group 2 mutants, has very strong homologywith the yeast gene RAD3. RAD3 is an essential gene for viabilityin yeast, and the low recovery of group 2 mutants using theframeshift agents strongly suggests that frameshift mutationstend to be lethal in the hamster ERCC2 locus. Several mutagen-sensitivedouble mutants were isolated in two-step selections from EMS-,mitomycin C- or UV-sensitive parental cells, including the lineUVU1, the first mammalian line with two mutations that affectUV sensitivity. The first mutation inactivated excision repair,and the second mutation appears to have affected some otherrecovery process. UVU1 should be useful for studying recoveryprocesses that are separate from nucleotide excision repair. ¹To whom correspondence should be addressed     

Cells of the central nervous system as targets and reservoirs of the human immunodeficiency virus

The availability of highly active antiretroviral therapies (HAART) has not eliminated HIV-1 infection of the central nervous system (CNS) or the occurrence of HIV-associated neurological problems. Thus, the neurobiology of HIV-1 is still an important issue. Here, we review key features of HIV-1-cell interactions in the CNS and their contributions to persistence and pathogenicity of HIV-1 in the CNS. HIV-1 invades the brain very soon after systemic infection. Various mechanisms have been proposed for HIV-1 entry into the CNS. The most favored hypothesis is the migration of infected cells across the blood-brain barrier ("Trojan horse" hypothesis). Virus production in the CNS is not apparent before the onset of AIDS, indicating that HIV-1 replication in the CNS is successfully controlled in pre-AIDS. Brain macrophages and microglia cells are the chief producers of HIV-1 in brains of individuals with AIDS. HIV-1 enters these cells by the CD4 receptor and mainly the CCR5 coreceptor. Various in vivo and cell culture studies indicate that cells of neuroectodermal origin, particularly astrocytes, may also be infected by HIV-1. These cells restrict virus production and serve as reservoirs for HIV-1. A limited number of studies suggest restricted infection of oligodendrocytes and neurons, although infection of these cells is still controversial. Entry of HIV-1 into neuroectodermal cells is independent of the CD4 receptor, and a number of different cell-surface molecules have been implicated as alternate receptors of HIV-1. HIV-1-associated injury of the CNS is believed to be caused by numerous soluble factors released by glial cells as a consequence of HIV-1 infection. These include both viral and cellular factors. Some of these factors can directly induce neuronal injury and death by interacting with receptors on neuronal membranes (neurotoxic factors). Others can activate uninfected cells to produce inflammatory and neurotoxic factors and/or promote infiltration of monocytes and T-lymphocytes, thus amplifying the deleterious effects of HIV-1 infection. CNS responses to HIV-1 infection also include mechanisms that enhance neuronal survival and strengthen crucial neuronal support functions. Future challenges will be to develop strategies to prevent HIV-1 spread in the brain, bolster intrinsic defense mechanisms of the brain and to elucidate the impact of long-term persistence of HIV-1 on CNS functions in individuals without AIDS.     

Some notes on uncertainty; Federal policy and innovation

The legislative background and current responsibilities of the new National Center for Health Care Technology (NCHCT) are discussed. The NCHCT's charge is to consider the stage of development, the actual or potential risks, costs and rate of use of health care technology. The role of Government in supporting new technologies, stimulating innovation and encouraging application of research products is considered. These issues are discussed in the context of the uncertainty inherent in planning and the formulation of public policy.     

Assessment of Self-Reward Strategies for Maintenance of Breast Self-Examination

This study examined the relative impact of different self-reward strategies on maintenance of breast self-examination (BSE) practice among 1649 women trained to do BSE. Training groups were randomized into four conditions: (a) self-reward instructions and materials delivered at the end of the BSE training session; (b) self-reward suggestions delivered through the mail each month, contingent upon the BSE performance; (c) external monetary rewards and self-reward suggestions delivered through the mail each month on an intermittent schedule, contingent upon BSE practice; and (d) a no-reward control condition. Follow-up assessments 12 months following training revealed a pattern of evidence in support of the benefits of external monetary rewards and self-reward prompts on BSE frequency and quality; however, it is likely that the value of that condition lies in the external reward component.     

Hydrogen peroxide induces DNA single strand breaks in respiratory epithelial cells

The respiratory epithelium is often exposed to oxidant gases, including ozone from photochemical smog and toxic oxygen metabolites released from neutrophils recruited in conditions of airway inflammation. We evaluated DNA single strand break formation by alkaline elution as a measure of oxidant-induced DNA damage to bronchial epithelial cells. Human AdenoSV-40-transformed bronchial epithelial cells (BEAS), subclone R1.4 or nonhuman primate bronchial epithelial cells were cultured in growth factor supplemented Ham's F12 medium on polycarbonate filters. DNA was labeled by incubation with [³H]thymidine. Cells were incubated for 1 h in HBSS or HBSS and increasing concentrations of hydrogen peroxide (H₂O₂). Cells incubated in H₂O₂ demonstrated dose-dependent increases in strand break formation, and BEAS cells were more sensitive to H₂O₂-induced injury than primary bronchial epithelial cells. The addition of catalase or preincubation of cells with the iron chelator desferoxamine prevented H₂O₂-induced strand breakage. DNA strand break formation may be an important mechanism of oxidant injury in respiratory epithelial cells.This work was supported by NIEHS grant ES-00628 and California Primate Research Center Base grant. Portions of this work were presented at the American Thoracic Society annual meeting, May 1992, Miami, Florida.     

Duchenne muscular dystrophy and idiopathic hyperCKemia segregating in a family

A 7-month-old boy with gross motor delay and failure to thrive presented with rhabdomyolysis following an acute asthmatic episode. During hospitalization an electrocardiographic conversion to a Wolff-Parkinson-White type 1 (WPW) pattern took place. Duchenne muscular dystrophy (DMD) was suspected based on elevated creatine kinase (CK) serum levels, muscle biopsy, and family history. The diagnosis was confirmed by molecular analysis, which documented a deletion corresponding to cDNA probe 1-2a in the dystrophin gene, in the propositus and in an affected male cousin of his mother. “Idiopathic” hyperCKemia was found in the propositus, his father, and 5 of his relatives. We suggest that the unusually early and severe manifestations of DMD in this patient may be related to the coincidental inheritance of the maternal DMD gene and of a paternal gene, causing hyperCKemia. © 1995 Wiley-Liss, Inc.