Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and Their Application to COVID-19 Outbreaks.

Some infectious diseases, including COVID-19, can undergo airborne transmission. This may happen at close proximity, but as time indoors increases, infections can occur in shared room air despite distancing. We propose two indicators of infection risk for this situation, that is, relative risk parameter (Hr) and risk parameter (H). They combine the key factors that control airborne disease transmission indoors: virus-containing aerosol generation rate, breathing flow rate, masking and its quality, ventilation and aerosol-removal rates, number of occupants, and duration of exposure. COVID-19 outbreaks show a clear trend that is consistent with airborne infection and enable recommendations to minimize transmission risk. Transmission in typical prepandemic indoor spaces is highly sensitive to mitigation efforts. Previous outbreaks of measles, influenza, and tuberculosis were also assessed. Measles outbreaks occur at much lower risk parameter values than COVID-19, while tuberculosis outbreaks are observed at higher risk parameter values. Because both diseases are accepted as airborne, the fact that COVID-19 is less contagious than measles does not rule out airborne transmission. It is important that future outbreak reports include information on masking, ventilation and aerosol-removal rates, number of occupants, and duration of exposure, to investigate airborne transmission.

Vascular aging and cardiac maladaptation in growth-restricted preterm infants.

OBJECTIVE: To assess arterial morphology and mechanics in preterm infants with fetal growth restriction (FGR) compared with those appropriate for gestational age (AGA) in the early neonatal period. STUDY DESIGN: This observational study involved 20 preterm FGR infants (28 to 32 weeks) of gestational age (GA) and birth weight (BW) <10th centile and 20 preterm AGA infants. Vascular ultrasound was performed to measure aortic properties. RESULTS: GA and BW of FGR and AGA infants were 29.8±1.3 vs 30±0.9 weeks (P=0.78) and 923.4±168 vs 1403±237 g (P<0.001), respectively. At 10.5±1.3 (s.d.) days after birth, blood pressure (systolic 51±3 vs 46±4 mm Hg, P<0.001) and maximum aorta intima-media thickness (621±76 vs 479±54 µm; P<0.001) were significantly higher in FGR infants. Arterial wall stiffness and peripheral resistance were also increased in the FGR infants (2.36±0.24 vs 2.14±0.24, P=0.008 and 22.2±5 vs 13.7±2.3 mm Hg min ml-1, P<0.001), respectively. Significant correlations between vascular mechanics and cardiac function were observed (resistance vs E/E', r=0.7 and Tei index, r=0.79). CONCLUSION: Maladaptive arterial-ventricular coupling was noted. Early detection may aid in early therapeutic strategies such as afterload reduction.

Does growth restriction increase the vulnerability to acute ventilation-induced brain injury in newborn lambs? Implications for future health and disease.

Fetal growth restriction (FGR) and preterm birth are frequent co-morbidities, both are independent risks for brain injury. However, few studies have examined the mechanisms by which preterm FGR increases the risk of adverse neurological outcomes. We aimed to determine the effects of prematurity and mechanical ventilation (VENT) on the brain of FGR and appropriately grown (AG, control) lambs. We hypothesized that FGR preterm lambs are more vulnerable to ventilation-induced acute brain injury. FGR was surgically induced in fetal sheep (0.7 gestation) by ligation of a single umbilical artery. After 4 weeks, preterm lambs were euthanized at delivery or delivered and ventilated for 2 h before euthanasia. Brains and cerebrospinal fluid (CSF) were collected for analysis of molecular and structural indices of early brain injury. FGRVENT lambs had increased oxidative cell damage and brain injury marker S100B levels compared with all other groups. Mechanical ventilation increased inflammatory marker IL-8 within the brain of FGRVENT and AGVENT lambs. Abnormalities in the neurovascular unit and increased blood-brain barrier permeability were observed in FGRVENT lambs, as well as an altered density of vascular tight junctions markers. FGR and AG preterm lambs have different responses to acute injurious mechanical ventilation, changes which appear to have been developmentally programmed in utero.

Description of a method for inducing fetal growth restriction in the spiny mouse.

Intrauterine or fetal growth restriction (IUGR) is a major complication of pregnancy and leads to significant perinatal morbidities and mortality. Typically, induction of IUGR in animals involves the complete occlusion or ablation of vessels to the uterus or placenta, acutely impairing blood flow and fetal growth, usually with high fetal loss. We aimed to produce a model of reduced fetal growth in the spiny mouse with minimal fetal loss. At 27 days gestational age (term is 38-39 days), a piece of silastic tubing was placed around the left uterine artery to prevent the further increase of uterine blood flow with advancing gestation to induce IUGR (occluded). Controls were generated from sham surgeries without placement of the tubing. Dams were humanely euthanized at 37 days gestational age and all fetuses and placentas were weighed and collected. Of the 17 dams that underwent surgery, 15 carried their pregnancies to 37 days gestational age and 95% of fetuses survived to this time. The difference in fetal body weight between occluded and control was ~21% for fetuses in the left uterus side: there were no differences for fetuses in the right uterus side. Offspring from the occluded group had significantly lower brain, liver, lung, kidney and carcass weights compared with shams. Preventing the gestation-related increase of uterine blood flow induced significant growth restriction in the fetal spiny mouse, with minimal fetal loss. This technique could be readily adapted for other small animal.

Microbial analyses of airborne dust collected from dormitory rooms predict the sex of occupants.

We have long known that human occupants are a major source of microbes in the built environment, thus raising the question: How much can we learn about the occupants of a building by analyzing the microbial communities found in indoor air? We investigated bacterial and fungal diversity found in airborne dust collected onto heating, ventilation, and air-conditioning (HVAC) air filters and settling plates from 91 rooms within a university dormitory. The sex of the room occupants had the most significant effect on the bacterial communities, while the room occupants had no significant effect on fungal communities. By examining the abundances of bacterial genera, we could predict the sex of room occupants with 79% accuracy, a finding that demonstrates the potential forensic applications of studying indoor air microbiology. We also identified which bacterial taxa were indicators of female and male rooms, and found that those taxa often identified as members of the vaginal microbiome were more common in female-occupied rooms while taxa associated with human skin or the male urogenital microbiota were more common in male-occupied rooms.

High temporal variability in airborne bacterial diversity and abundance inside single-family residences.

Our homes are microbial habitats, and although the amounts and types of bacteria in indoor air have been shown to vary substantially across residences, temporal variability within homes has rarely been characterized. Here, we sought to quantify the temporal variability in the amounts and types of airborne bacteria in homes, and what factors drive this variability. We collected filter samples of indoor and outdoor air in 15 homes over 1 year (approximately eight time points per home, two per season), and we used culture-independent DNA sequencing approaches to characterize bacterial community composition. Significant differences in indoor air community composition were observed both between homes and within each home over time. Indoor and outdoor air community compositions were not significantly correlated, suggesting that indoor and outdoor air communities are decoupled. Indoor air communities from the same home were often just as different at adjacent time points as they were across larger temporal distances, and temporal variation correlated with changes in environmental conditions, including temperature and relative humidity. Although all homes had highly variable indoor air communities, homes with the most temporally variable communities had more stable, lower average microbial loads than homes with less variable communities.

Identification of SNPs located on BTA 6 and BTA 20 significantly associated with bovine respiratory disease in crossbred cattle.

The objective of the present study was to evaluate single nucleotide polymorphisms (SNPs) located in two quantitative trait locus (QTL) regions (BTA 6 and BTA 20) that are associated with bovine respiratory disease (BRD). A population of 323 crossbred steers sired by five purebred sire breeds during 2010-2013 (Angus, Braford, Braunvieh, Charolais, and Simmental) were evaluated for BRD susceptibility during the finishing process at a commercial feedlot. A total of 21 animals representing all sire breeds were affected with BRD at some time during the finishing process over the 4-year period. Although multiple sire breeds were evaluated in the present study, no sire breed effects were detected. A total of 82 SNPs were evaluated (58 on BTA 6 and 24 on BTA 20) in the present study for potential associations with BRD incidence. When evaluating the previously described QTL regions on BTA 6, three SNPs (rs42968895, rs42823614, and rs43448463) were significantly (P < 0.05) associated with BRD incidence. Another three SNPs (rs42477340, rs42512588, and rs42524468) were identified as significantly associated with BRD on the previously described BTA 6 QTL region. For both of these regions, animals inheriting different genotypes differed in BRD incidence during the finishing period. Although multiple SNPs were identified as being significantly associated with BRD incidence in the present study, these SNP associations should be validated in larger and more diverse populations.

Role of mechanical ventilation in the airborne transmission of infectious agents in buildings.

Infectious disease outbreaks and epidemics such as those due to SARS, influenza, measles, tuberculosis, and Middle East respiratory syndrome coronavirus have raised concern about the airborne transmission of pathogens in indoor environments. Significant gaps in knowledge still exist regarding the role of mechanical ventilation in airborne pathogen transmission. This review, prepared by a multidisciplinary group of researchers, focuses on summarizing the strengths and limitations of epidemiologic studies that specifically addressed the association of at least one heating, ventilating and/or air-conditioning (HVAC) system-related parameter with airborne disease transmission in buildings. The purpose of this literature review was to assess the quality and quantity of available data and to identify research needs. This review suggests that there is a need for well-designed observational and intervention studies in buildings with better HVAC system characterization and measurements of both airborne exposures and disease outcomes. Studies should also be designed so that they may be used in future quantitative meta-analyses.

Contribution of human-related sources to indoor volatile organic compounds in a university classroom.

Although significant progress has been made in understanding the sources and chemistry of indoor volatile organic compounds (VOCs) during the past decades, much is unknown about the role of humans in indoor air chemistry. In the spring of 2014, we conducted continuous measurements of VOCs using a proton transfer reaction mass spectrometer (PTR-MS) in a university classroom. Positive matrix factorization (PMF) of the measured VOCs revealed a 'human influence' component, which likely represented VOCs produced from human breath and ozonolysis of human skin lipids. The concentration of the human influence component increased with the number of occupants and decreased with ventilation rate in a similar way to CO2 , with an average contribution of 40% to the measured daytime VOC concentration. In addition, the human skin lipid ozonolysis products were observed to correlate with CO2 and anticorrelate with O3 , suggesting that reactions on human surfaces may be important sources of indoor VOCs and sinks for indoor O3 . Our study suggests that humans can substantially affect VOC composition and oxidative capacity in indoor environments.

Dopamine treatment during acute hypoxia is neuroprotective in the developing sheep brain.

Dopamine is often used to treat hypotension in preterm infants; these infants are at risk of developing brain injury due to impaired autoregulation and cerebral hypoperfusion. However the effects of dopamine on the immature brain under conditions of cerebral hypoxia are not known. We hypothesized that pretreatment with dopamine would protect the immature brain from injury caused by cerebral hypoxia. Preterm fetal sheep were used to determine the effects of intravenous dopamine on hypoxia-induced brain injury. In 16 pregnant sheep at 90days of gestation (0.6 of term, term=147days) catheters were implanted aseptically into the fetal carotid artery and jugular vein; an inflatable occluder was placed loosely around the umbilical cord for later induction of fetal hypoxemia. At 5days after surgery, dopamine (10µg/kg/min, n=7 fetuses) or saline (n=9 fetuses) was infused for 74h. Two hours after commencing the dopamine/saline infusion, we induced umbilical cord occlusion (UCO) for up to 25min to produce fetal asphyxia. Fetuses were allowed to recover, and brains were collected 72h later for assessment of neuropathology. Un-operated twin fetuses were used as age-matched non-UCO controls (n=8). In UCO+saline fetuses, microglial and apoptotic cell density in the subcortical and periventricular white matter, caudate nucleus and hippocampus was greater than that in age-matched controls; oxidative stress was elevated in the subcortical and periventricular white matter and caudate nucleus compared to that in age-matched controls. In UCO+dopamine fetuses microglial density and oxidative stress in the cerebral white matter and caudate nucleus were not different to that of age-matched controls. Apoptotic cell death was decreased in the cerebral white matter of UCO+dopamine brains, relative to UCO+saline brains. We conclude that pretreatment with dopamine does not exacerbate hypoxia-induced injury in the immature brain and may be neuroprotective because it led to decreased apoptosis, oxidative stress and neuroinflammation in the cerebral white matter and decreased neuroinflammation in the caudate nucleus.

The effect of suspended sediment on fertilization success in the urchin Evechinus chloroticus: analysis of experimental data using hierarchical Bayesian methods.

Terrestrial sediments are a significant stressor on coastal ecosystems, with both suspended and deposited sediment having adverse effects on aquatic organisms. However, information on the effect of suspended sediments on fertilization success for urchin species is lacking. Using sediment levels similar to those encountered in situ, a controlled experiment was conducted to test whether suspended sediment affects fertilization success in the urchin Evechinus chloroticus. Analyses used generalized linear mixed models (GLMMs) and hierarchical Bayesian (HB) regression. Both approaches showed a significant decrease in fertilization success with increased suspended sediment levels. Uncertainties in estimates were narrower for HB models, suggesting that this approach has advantages over GLMMs for sparse data problems sometimes encountered in laboratory experiments. Given future global change scenarios, this work is important for predicting the effects of stressors such as sedimentation that may ultimately impact marine populations.

Spinal cord hypothermia without systemic hypothermia.

BACKGROUND AND PURPOSE: Hypothermia has been shown to be beneficial in the setting of acute SCI. However, widespread use has been hindered by the need for systemic hypothermia as the vehicle for achieving spinal cord hypothermia. This study demonstrates that localized spinal cord hypothermia can be achieved via a percutaneous approach while maintaining systemic normothermia. MATERIALS AND METHODS: Five Yucatan swine underwent catheterization of the subarachnoid space and infusion of room temperature, chilled, and iced PL solutions into the cervical spinal canal, with drainage from the lumbar canal. Thermocouples were placed within the spinal cord and in the subarachnoid space and recorded during infusions and recovery from hypothermia. RESULTS: Results demonstrated that hypothermia as low as 16.8°C is feasible in the spinal cord with retention of systemic normothermia, with strong (r = 0.95) correlation between the spinal cord temperature and the CSF temperature. Degrees of cooling varied with flow rates and with infusate temperature. CONCLUSIONS: While the data are preliminary in a small group of animals, the ability to rapidly create a wide range of controlled spinal cord hypothermia while preserving normal body temperature warrants wider exploration. The study also indicates that further investigation of the hypothesis that CSF temperature monitoring may be an acceptable surrogate for direct spinal cord temperature monitoring should be pursued.

Glucocorticoid treatment does not alter early cardiac adaptations to growth restriction in preterm sheep fetuses.

OBJECTIVE: To study the consequences of glucocorticoid treatment in fetal growth restriction (FGR) on cardiac function. SETTING: Laboratory. SAMPLE: Sheep. METHODS: Growth restriction was induced in sheep fetuses using single umbilical artery ligation (SUAL) on days 105-110 of gestation (term 147). Control fetuses were not ligated. Betamethasone (BM) (11.4 mg intramuscularly) or saline was administered to ewes on days 5 and 6 after surgery. Ewes were anaesthetised on day 7, the fetuses were removed, and their hearts were mounted on a Langendorff apparatus. Balloon catheters were inserted into the right and left ventricles. OUTCOME MEASURES: Ventricular contractile function and infarct area following ischaemia/reperfusion. RESULTS: The SUAL resulted in FGR (body weight 77% of control). The FGR was associated with increases in basal left ventricular pressure development and rates of contraction and relaxation. Right ventricular contraction was unaffected. Following brief ischaemia/reperfusion, the infarct area in FGR hearts was increased four-fold compared with controls. Antenatal BM resulted in a proportional increase in heart size and coronary flow, especially in FGR fetuses, and left ventricular pressure and heart rate responses to ß-adrenoceptor activation were increased. CONCLUSIONS: Fetal hearts rapidly adapt to FGR to maintain substrate delivery to the brain and heart. The FGR greatly enhanced the area of ischaemia, with implications for susceptibility in postnatal life. Antenatal BM treatment does not interfere with these cardiac changes but appears to increase left ventricle ß-adrenoceptor responsiveness, which may render the offspring vulnerable to subsequent cardiac dysfunction.

Antioxidant therapies: a potential role in perinatal medicine.

Pregnancies complicated by impaired placentation, acute severe reductions in oxygen supply to the fetus, or intrauterine infection are associated with oxidative stress to the mother and developing baby. Such oxidative stress is characterized as an upregulation in the production of oxidative or nitrative free radicals and a concomitant decrease in the availability of antioxidant species, thereby creating a state of fetoplacental oxidative imbalance. Recently, there has been a good deal of interest in the potential for the use of antioxidant therapies in the perinatal period to protect the fetus, particularly the developing brain, against oxidative stress in complications of pregnancy and birth. This review will examine why the immature brain is particularly susceptible to oxidative imbalance and will provide discussion on antioxidant treatments currently receiving attention in the adult and perinatal literature - allopurinol, melatonin, α-lipoic acid, and vitamins C and E. In addition, we aim to address the interaction between oxidative stress and the fetal inflammatory response, an interaction that may be vital when proposing antioxidant or other neuroprotective strategies.

Supplementation of fibrin gels with sodium chloride enhances physical properties and ensuing osteogenic response.

Modifying the relative concentrations of fibrinogen and thrombin can control the physical properties of fibrin gels, while the viability of associated cells has been linked to the gel's final network structure. It was hypothesized that increasing the gel ionic strength during fabrication through supplementation with sodium chloride (NaCl) would provide an improved approach for tailoring the physical properties of fibrin gels and maintaining the viability and osteogenic potential of entrapped cells. Fibrin gels were formed by mixing fibrinogen, thrombin and calcium chloride with varying masses of NaCl (0-4.40% w/v), and the osteogenic potential of entrapped human mesenchymal stem cells (MSC) was examined over 14 days. Physical properties including gelation time, compressive modulus and fiber diameter were dependent upon NaCl content, with gels containing 2.60% NaCl possessing compressive moduli threefold higher than gels without NaCl. Alkaline phosphatase activity was highest for MSC entrapped in gels containing 2.15-2.60% NaCl after 14 days, and all gels exhibited increased calcium incorporation over the culture period. These data confirm that varying the salt concentration of the pre-gel solution can modulate the material properties of fibrin constructs without additional fibrinogen or thrombin, thereby offering a new approach for generating improved cell transplantation vehicles for use in bone tissue regeneration.

The Denver Aerosol Sources and Health (DASH) Study: Overview and Early Findings.

Improved understanding of the sources of air pollution that are most harmful could aid in developing more effective measures for protecting human health. The Denver Aerosol Sources and Health (DASH) study was designed to identify the sources of ambient fine particulate matter (PM(2.5)) that are most responsible for the adverse health effects of short-term exposure to PM (2.5). Daily 24-hour PM(2.5) sampling began in July 2002 at a residential monitoring site in Denver, Colorado, using both Teflon and quartz filter samplers. Sampling is planned to continue through 2008. Chemical speciation is being carried out for mass, inorganic ionic compounds (sulfate, nitrate and ammonium), and carbonaceous components, including elemental carbon, organic carbon, temperature-resolved organic carbon fractions and a large array of organic compounds. In addition, water soluble metals were measured daily for 12 months in 2003. A receptor-based source apportionment approach utilizing positive matrix factorization (PMF) will be used to identify PM (2.5) source contributions for each 24-hour period. Based on a preliminary assessment using synthetic data, the proposed source apportionment should be able to identify many important sources on a daily basis, including secondary ammonium nitrate and ammonium sulfate, diesel vehicle exhaust, road dust, wood combustion and vegetative debris. Meat cooking, gasoline vehicle exhaust and natural gas combustion were more challenging for PMF to accurately identify due to high detection limits for certain organic molecular marker compounds. Measurements of these compounds are being improved and supplemented with additional organic molecular marker compounds. The health study will investigate associations between daily source contributions and an array of health endpoints, including daily mortality and hospitalizations and measures of asthma control in asthmatic children. Findings from the DASH study, in addition to being of interest to policymakers, by identifying harmful PM(2.5) sources may provide insights into mechanisms of PM effect.

The danger of weight loss in the elderly.

Aging is generally accompanied by weight loss made up of both fat mass and fat-free mass. As more people, including elderly, are overweight or obese, weight loss is recommended to improve health. Health risks are decreased in overweight children and adults by dieting and exercise, but the health benefits of weight loss in elderly, particularly by calorie restriction, are uncertain. Rapid unintentional weight loss in elderly is usually indicative of underlying disease and accelerates the muscle loss which normally occurs with aging. Intentional weight loss, even when excess fat mass is targeted also includes accelerated muscle loss which has been shown in older persons to correlate negatively with functional capacity for independent living. Sarcopenic obesity, the coexistence of diminished lean mass and increased fat mass, characterizes a population particularly at risk for functional impairment since both sarcopenia (relative deficiency of skeletal muscle mass and strength) and obesity have been shown to predict disability. However, indices of overweight and obesity such as body mass index (BMI) do not correlate as strongly with adverse health outcomes such as cardiovascular disease in elderly as compared to younger individuals. Further, weight loss and low BMI in older persons are associated with mortality in some studies. On the other hand, studies have shown improvement in risk factors after weight loss in overweight/obese elderly. The recent focus on pro-inflammatory factors related to adiposity suggest that fat loss could ameliorate some catabolic conditions of aging since some cytokines may directly impact muscle protein synthesis and breakdown. Simply decreasing weight may also ease mechanical burden on weak joints and muscle, thus improving mobility. However, until a strategy is proven whereby further loss of muscle mass can be prevented, weight loss by caloric restriction in individuals with sarcopenic obesity should likely be avoided.

Hippocampal activation in adults with mild cognitive impairment predicts subsequent cognitive decline.

OBJECTIVE: To use functional MRI (fMRI) to investigate whether hippocampal activation during a memory task can predict cognitive decline in individuals with mild cognitive impairment (MCI). METHODS: 25 older individuals with MCI performed a visual scene encoding task during fMRI scanning, and were followed clinically for at least 4 years after scanning. A hypothesis driven analysis of fMRI data was performed. First, fMRI data were analysed at the group level to identify the regions of the hippocampal formation that were engaged by this memory task. Parameter estimates of each subject's memory related hippocampal activation (% signal change) were extracted and were analysed with a linear regression model to determine whether hippocampal activation predicted the degree or rate of cognitive decline, as measured by change in Clinical Dementia Rating Sum-of-Boxes (CDR-SB). RESULTS: Over 5.9 (1.2) years of follow-up after scanning, subjects varied widely in degree and rate of cognitive decline (change in CDR-SB ranged from 0 to 6, and the rate ranged from 0 to 1 CDR-SB unit/year). Greater hippocampal activation predicted greater degree and rate of subsequent cognitive decline (p<0.05). This finding was present even after controlling for baseline degree of impairment (CDR-SB), age, education and hippocampal volume, as well as gender and apolipoprotein E status. In addition, an exploratory whole brain analysis produced convergent results, demonstrating that the hippocampal formation was the only brain region where activation predicted cognitive decline. CONCLUSIONS: In individuals with MCI, greater memory task related hippocampal activation is predictive of a greater degree and rate of cognitive decline subsequent to scanning. fMRI may provide a physiological imaging biomarker useful for identifying the subgroup of MCI individuals at highest risk of cognitive decline for potential inclusion in disease modifying clinical trials.

Prefrontal-hippocampal-fusiform activity during encoding predicts intraindividual differences in free recall ability: an event-related functional-anatomic MRI study.

The ability to spontaneously recall recently learned information is a fundamental mnemonic activity of daily life, but has received little study using functional neuroimaging. We developed a functional MRI (fMRI) paradigm to study regional brain activity during encoding that predicts free recall. In this event-related fMRI study, ten lists of fourteen pictures of common objects were shown to healthy young individuals and regional brain activity during encoding was analyzed based on subsequent free recall performance. Free recall of items was predicted by activity during encoding in hippocampal, fusiform, and inferior prefrontal cortical regions. Within-subject variance in free recall performance for the ten lists was predicted by a linear combination of condition-specific inferior prefrontal, hippocampal, and fusiform activity. Recall performance was better for lists in which prefrontal activity was greater for all items of the list and hippocampal and fusiform activity were greater specifically for items that were recalled from the list. Thus, the activity of medial temporal, fusiform, and prefrontal brain regions during the learning of new information is important for the subsequent free recall of this information. These fronto-temporal brain regions act together as a large-scale memory-related network, the components of which make distinct yet interacting contributions during encoding that predict subsequent successful free recall performance.

Nek3 kinase regulates prolactin-mediated cytoskeletal reorganization and motility of breast cancer cells.

Prolactin (PRL) stimulates the cytoskeletal re-organization and motility of breast cancer cells. During PRL receptor signaling, Vav2 becomes phosphorylated and activated, an event regulated by the serine/threonine kinase Nek3. Given the regulatory role of Vav2, the function of Nek3 in PRL-mediated motility and invasion was examined. Overexpression of Nek3 in Chinese hamster ovary transfectants potentiated cytoskeletal re-organization in response to PRL. In contrast, downregulation of Nek3 expression by small-interfering RNA (siRNA) attenuated PRL-mediated cytoskeletal reorganization, activation of GTPase Rac1, cell migration and invasion of T47D cells. In addition, PRL stimulation induced an interaction between Nek3 and paxillin and significantly increased paxillin serine phosphorylation, whereas Nek3 siRNA-transfected cells showed a marked reduction in paxillin phosphorylation. Analysis of breast tissue microarrays also demonstrated a significant up-regulation of Nek3 expression in malignant versus normal specimens. These data suggest that Nek3 contributes to PRL-mediated breast cancer motility through mechanisms involving Rac1 activation and paxillin phosphorylation.