Robert L. Davis

Expression of a single transfected cDNA converts fibroblasts to myoblasts

5-azacytidine treatment of mouse C3H10T1/2 embryonic fibroblasts converts them to myoblasts at a frequency suggesting alteration of one or only a few closely linked regulatory loci. Assuming such loci to be differentially expressed as poly(A)+ RNA in proliferating myoblasts, we prepared proliferating myoblast-specific, subtracted cDNA probes to screen a myocyte cDNA library. Based on a number of criteria, three cDNAs were selected and characterized. We show that expression of one of these cDNAs transfected into C3H10T1/2 fibroblasts, where it is not normally expressed, is sufficient to convert them to stable myoblasts. Myogenesis also occurs, but to a lesser extent, when this cDNA is expressed in a number of other cell lines. The major open reading frame encoded by this cDNA contains a short protein segment similar to a sequence present in the myc protein family.

The protein Id: A negative regulator of helix-loop-helix DNA binding proteins

We have isolated a cDNA clone encoding a novel helix-loop-helix (HLH) protein, Id. Id is missing the basic region adjacent to the HLH domain that is essential for specific DNA binding in another HLH protein, MyoD. An in vitro translation product of Id can associate specifically with at least three HLH proteins (MyoD, E12, and E47) and attenuate their ability to bind DNA as homodimeric or heterodimeric complexes. Id is expressed at varying levels in all cell lines tested. In three cell lines that can be induced to undergo terminal differentiation, Id RNA levels decrease upon induction. Transfection experiments indicate that over-expression of Id inhibits the trans-activation of the muscle creatine kinase enhancer by MyoD. Based on these findings, we propose that HLH proteins lacking a basic region may negatively regulate other HLH proteins through the formation of nonfunctional heterodimeric complexes.

The MyoD DNA binding domain contains a recognition code for muscle-specific gene activation

A 60 amino acid domain of the myogenic determination gene MyoD is necessary and sufficient for sequence-specific DNA binding in vitro and myogenic conversion of transfected C3H10T1/2 cells. We show that a highly basic region, immediately upstream of the helix-loop-helix (HLH) oligomerization motif, is required for MyoD DNA binding in vitro. Replacing helix1, helix2, or the loop of MyoD with the analogous sequence of the Drosophila T4 achaete-scute protein (required for peripheral neurogenesis) has no substantial effect on DNA binding in vitro or muscle-specific gene activation in transfected C3H10T1/2 cells. However, replacing the basic region of MyoD with the analogous sequence of other HLH proteins (the immunoglobulin enhancer binding E12 protein or T4 achaete scute protein) allows DNA binding in vitro, yet abolishes muscle-specific gene activation. These findings suggest that a recognition code that determines muscle-specific gene activation lies within the MyoD basic region and that the capacity for specific DNA binding is insufficient to activate the muscle program.

Positive autoregulation of the myogenic determination gene MyoD1

Transfection of cDNA expression vectors encoding either MyoD1 or myogenin into 10T1/2 cells converts them to myogenic cells. We show that transfection of 10T1/2 cells with the MyoD1 cDNA activates expression of endogenous MyoD1 mRNA, indicating that MyoD1 is subject to positive autoregulation. This activation of endogenous MyoD1 mRNA was also observed in Swiss 3T6 cells, but not in several other fibroblast or adipoblast cell lines transfected with the MyoD1 cDNA. In addition, transfection of the MyoD1 cDNA leads to activation of myogenin expression, and transfection of the myogenin cDNA leads to activation of MyoD1 expression. Thus, MyoD1 and myogenin appear to function in a positive autoregulatory loop that could either: account for or contribute to the stability of myogenic commitment; or amplify the level of expression of both MyoD1 and myogenin above a critical threshold that is required for activation of the myogenic program.

Systemic Corticosteroids in Infant Bronchiolitis: A Meta-analysis

Objective. To determine whether corticosteroids are efficacious in treating bronchiolitis in hospitalized infants. Methods. Online bibliographic databases (Medline, Embase, and Cochrane Clinical Trials Registry) were searched for: 1) bronchiolitis or respiratory syncytial virus, and 2) corticosteroid or glucocorticoid or steroidal antiinflammatory agents or adrenal cortex hormones. Reference lists from all selected articles were also examined. Randomized, placebo-controlled trials of systemic corticosteroids in treatment of infants hospitalized with bronchiolitis were selected by 2 investigators. Of 12 relevant publications identified in the literature search, 6 met the selection criteria and had relevant data available. Investigators independently extracted data for 3 outcomes: length of stay (LOS), duration of symptoms (DOS), and clinical scores. Results. In the pooled analysis, infants who received corticosteroids had a mean LOS or DOS that was .43 days less than those who received the placebo treatment (95% confidence interval: −.81 to −.05 days). The effect size for mean clinical score was −1.60 (95% confidence interval: −1.92 to −1.28), favoring treatment. Secondary analyses of mean LOS or DOS were performed on 5 trials that had clearly identified methods of randomization, 5 trials that measured LOS, and 4 trials that clearly excluded infants with previous wheezing. The estimates of effect were similar to the primary analysis but were not statistically significant. Conclusions. Combined, published reports of the effect of systemic corticosteroids on the course of bronchiolitis suggest a statistically significant improvement in clinical symptoms, LOS, and DOS.

Acute Lung Injury in Isolated Traumatic Brain Injury

OBJECTIVEnTo determine the incidence of acute lung injury (ALI) in comatose patients after isolated traumatic brain injury, to determine whether specific brain lesions diagnosed by cranial computed tomographic scans are associated with ALI, and to determine the outcome of patients with head injuries who developed ALI.nnnMETHODSnDescriptive epidemiology and a case-control study using the Traumatic Coma Data Bank was performed to evaluate clinical features and brain lesions associated with ALI in patients with isolated head trauma. Patients with ALI were defined as those who demonstrated a ratio of partial pressure of arterial oxygen to fractional expired oxygen of 300 or less.nnnRESULTSnTwenty of 100 comatose patients developed ALI. Patients with ALI were almost three times more likely to die or survive in a vegetative state (odds ratio, 2.8; 95% confidence interval, 1.6-4.9). Specific anatomic brain lesions diagnosed by cranial computed tomographic scans were not associated with ALI. However, patients with more severe injuries, i.e., large nonevacuated mass lesions, and those with midline shift demonstrated a 10- and 5-fold increased risk of ALI (odds ratio, 9.9; 95% confidence interval, 1.2-217.1; and odds ratio, 5.5; 95% confidence interval, 1.5-20.0).nnnCONCLUSIONSnALI was common in comatose victims with an isolated traumatic brain injury and was associated with an increased risk of death or a severe neurological morbidity. ALI was associated with the global severity of head injury but not with specific anatomic lesions diagnosed by cranial computed tomographic scans.

Is condom use habit forming?: Condom use at sexual debut and subsequent condom use.

Objective: The objective of this study was to assess whether using a condom at adolescent sexual debut is associated with an increased likelihood of subsequent condom use. Study Design: A nationally representative sample was used, including 4024 sexually active adolescents (12–18 years) from the National Longitudinal Study of Adolescent Health. Logistic regression was used to model the association of condom use at sexual debut on condom use at most recent sex (mean interval, 23 months). Results: Condom use at adolescent sexual debut was associated with a twofold increased likelihood of condom use during most recent sex (odds ratio, 2.28; 95% confidence interval, 1.91–2.73). Conclusions: Among adolescents, early condom use is associated with an increased likelihood of subsequent condom use.

Cranial Computed Tomography Scans in Children After Minimal Head Injury With Loss of Consciousness

STUDY OBJECTIVEnTo assess the need for cranial computed tomography (CT) in the emergency department evaluation of children with Glasgow Coma Scale (GCS) score of 15 after mild head injury with loss of consciousness.nnnDESIGNnRetrospective case series of children aged 2 to 17 years with documented loss of consciousness after head injury from January 1, 1988, to July 31, 1992. All had a GCS score of 15 on initial ED evaluation and were further categorized according to physical examination findings, neurologic status, and whether the head injury was isolated or nonisolated. Recursive partitioning was used to identify variables predictive of the presence and absence of intracranial hemorrhage.nnnSETTINGnED in two settings: a regional tertiary care trauma center and a community childrens hospital.nnnRESULTSnOf the 185 patients who met study criteria, 17 had evidence of depressed or basilar skull fractures on physical examination or had a ventriculoperitoneal shunt in place before head injury. In the remaining 168 patients, recursive partitioning identified two variables (neurologic status and head injury type) associated with intracranial hemorrhage. Overall, 12 of 168 patients (7%) had intracranial bleeding. However, none of the 49 neurologically normal children with isolated head injury had intracranial hemorrhage (95% confidence interval, 0.0 to 6.0).nnnCONCLUSIONnThe prevalence of intracranial hemorrhage in children with mild closed-head injury appears to vary with the presence of neurologic abnormalities and other noncranial injuries. After isolated head injury with loss of consciousness, children older than 2 years who are neurologically normal and without signs of depressed or basilar skull fracture may be discharged home from the ED without a cranial CT scan after careful physical examination alone.

Perinatal Risk Factors for Infant Hospitalization With Viral Gastroenteritis

Context.u2003 A tetravalent vaccine against rotavirus, the most commonly identified etiologic agent of viral gastroenteritis (GE), has recently been licensed for use in the United States. Objective.u2003 To evaluate whether specific groups of infants might be at sufficiently high risk to warrant a focused rotavirus vaccine policy, we investigated perinatal risk factors for hospitalization with viral GE and rotavirus in the first year of life. Design.u2003 Population-based, case–control study. Setting.u2003 Washington State linked birth certificate and hospital discharge abstracts from 1987 through 1995. Patients.u2003 Infants, 1 through 11 months of age, hospitalized for viral GE (N = 1606) were patients in this study. Control subjects were 8084 nonhospitalized infants, frequency-matched to patients on year of birth. Primary Outcome Measure.u2003 Maternal and infant characteristics associated with infant hospitalization for viral GE. Results.u2003 We found a significant association between birth weight and the risk for hospitalization. Very low birth weight infants (<1500 g) were at the highest risk (odds ratio [OR] 2.6; 95% confidence interval [CI]: 1.6,4.1);, low birth weight infants (1500–2499 g), at intermediate risk (OR 1.6; 95% CI: 1.3,2.1); and large infants (>4000 g), at reduced risk (OR 0.8; 95% CI: 0.6,0.9). Other characteristics associated with GE hospitalization were male gender (OR 1.4; 95% CI: 1.3,1.6); maternal smoking (OR 1.2; 95% CI: 1.1,1.4); unmarried mother (OR 1.2; 95% CI: 1.1,1.4); Medicaid insurance (OR 1.4; 95% CI: 1.3,1.7); and maternal age <20 years (OR 1.2; 95% CI: 1.0,1.5). Infants born October through December were at decreased risk for hospitalization (OR 0.8; 95% CI: 0.7,0.9), as were infants born to Asian mothers (OR 0.5; 95% CI: 0.3,0.7), and infants born to mothers >34 years of age (OR 0.7; 95% CI: 0.6,0.9). Using these factors, the area under a receiver operating characteristic curve was 0.63. Therefore, to achieve a sensitivity of 90% in identifying high-risk infants, specificity would fall to 10%. Subanalyses of children admitted for viral GE during the peak of the Northwest rotavirus season (January to March) and children with confirmed rotavirus infection demonstrated similar risk factors and receiver operating characteristic curves. Conclusion.u2003 We conclude that a focused rotavirus vaccination policy using readily identifiable potential high-risk groups would be unlikely to prevent most infant hospitalizations associated with rotavirus infection. However, the safety of rotavirus vaccine in low birth weight and premature infants must be established, because these children appear to be at greater risk for hospitalization with viral GE and rotavirus.

Prone sleep position and the sudden infant death syndrome in King County, Washington: A case-control study*

OBJECTIVEnTo determine whether the prone sleep position was associated with an increased risk of the sudden infant death syndrome (SIDS).nnnSTUDY DESIGNnPopulation-based case-control study.nnnPARTICIPANTSnCase subjects were infants who died of SIDS in King County, Washington. Control subjects were randomly selected infants born in King County. Up to four control subjects were matched on date of birth to each case subject.nnnMETHODSnDuring the study period, November 1992 through October 1994, sleep-position data were collected on infants who died of SIDS by the King Count Medical Examiners Office during their investigation of the deaths. Parents of infants chosen as control subjects were contacted by telephone, and sleep position information was obtained. Infants who usually slept on their abdomen were classified as sleeping prone; those who usually slept on the side or back were categorized as sleeping nonprone. The adjusted odds ratio for prone sleep position as a risk factor for SIDS was calculated with conditional logistic regression after control for race, birth weight, maternal age, maternal marital status, household income, and maternal cigarette smoking during pregnancy.nnnRESULTSnSleep position data were collected on 47 infants with SIDS (77% of eligible infants) and 142 matched control subjects; 57.4% of infants who died of SIDS usually slept prone versus 24.6% of control subjects (p < 0.00001). The unadjusted odds ratio for prone sleep position as a risk factor for SIDS was 4.69 (95% confidence interval: 2.17, 10.17). After control for potentially confounding variables, the adjusted odds ratio for prone sleep position was 3.12 (95% confidence interval: 1.08, 9.03).nnnCONCLUSIONnProne sleep position was significantly associated with an increased risk of SIDS among a group of American infants.