Annotation-efficient training of medical image segmentation network based on scribble guidance in difficult areas

PURPOSE

The training of deep medical image segmentation networks usually requires a large amount of human-annotated data. To alleviate the burden of human labor, many semi- or non-supervised methods have been developed. However, due to the complexity of clinical scenario, insufficient training labels still causes inaccurate segmentation in some difficult local areas such as heterogeneous tumors and fuzzy boundaries.

METHODS

We propose an annotation-efficient training approach, which only requires scribble guidance in the difficult areas. A segmentation network is initially trained with a small amount of fully annotated data and then used to produce pseudo labels for more training data. Human supervisors draw scribbles in the areas of incorrect pseudo labels (i.e., difficult areas), and the scribbles are converted into pseudo label maps using a probability-modulated geodesic transform. To reduce the influence of the potential errors in the pseudo labels, a confidence map of the pseudo labels is generated by jointly considering the pixel-to-scribble geodesic distance and the network output probability. The pseudo labels and confidence maps are iteratively optimized with the update of the network, and the network training is promoted by the pseudo labels and the confidence maps in turn.

RESULTS

Cross-validation based on two data sets (brain tumor MRI and liver tumor CT) showed that our method significantly reduces the annotation time while maintains the segmentation accuracy of difficult areas (e.g., tumors). Using 90 scribble-annotated training images (annotated time: ~ 9 h), our method achieved the same performance as using 45 fully annotated images (annotation time: > 100 h) but required much shorter annotation time.

CONCLUSION

Compared to the conventional full annotation approaches, the proposed method significantly saves the annotation efforts by focusing the human supervisions on the most difficult regions. It provides an annotation-efficient way for training medical image segmentation networks in complex clinical scenario.

Cytomegalovirus Infection and Alzheimer's Disease: A Meta-Analysis

BACKGROUND

Evidence on the association of cytomegalovirus (CMV) infection with Alzheimer's disease (AD) is scarce and the results are inconsistent.

OBJECTIVE

To investigate the association of CMV infection with the risk of AD.

METHODS

Observational studies on the relationship between CMV infection and AD were identified from PubMed, Embase, Web of Science, and the Cochrane Library until September 30, 2022. The quality of included studies was assessed using the Newcastle-Ottawa Scale. Random-effect meta-analysis was performed using a generic inverse-variance method, followed by sensitivity analyses and subgroup analyses based on study designs, regions, adjustments, and population types.

RESULTS

Our search yielded 870 articles, of which 200 were duplicates and 663 did not meet the inclusion criteria, and finally yielded seven studies with 6,772 participants. No strong evidence was observed in the summary analysis for the association of CMV infection and risk of AD (odds ratio [OR] = 1.33; 95% confidence interval [CI]: 0.88, 2.03, I2 =69.9%). However, subgroup analysis showed that an increased risk of AD was detected in East Asians (OR = 2.39; 95% CI: 1.63, 3.50, I2 = 0.00%), cohort studies (OR = 1.99; 95% CI: 1.35, 2.94, I2 = 28.20%), and studies with confounder adjustment (OR = 2.05; 95% CI: 1.52, 2.77, I2 = 0.00%).

CONCLUSIONS

This meta-analysis provides evidence to support the heterogeneity of the associations between CMV infection and AD. Future studies with larger sample sizes and multi-ethnic populations are necessary.

Laparoscopic posterior pelvic exenteration is safe and feasible for locally advanced primary rectal cancer in female patients: a comparative study from China PelvEx collaborative

PURPOSE

Posterior pelvic exenteration (PPE) for locally advanced rectal cancer is a technical and challenging procedure. The safety and feasibility of laparoscopic PPE remain to be determined. This study aims to compare short-term and survival outcomes of laparoscopic PPE (LPPE) with open PPE (OPPE) in female patients.

METHOD

From January 2015 to December 2020, data from 105 female patients who underwent PPE at three institutions were retrospectively analyzed. The short-term and oncological outcomes between LPPE and OPPE were compared.

RESULTS

A total of 54 cases with LPPE and 51 cases with OPPE were enrolled. The operative time (240 vs. 295 min, p = 0.009), blood loss (100 vs. 300 ml, p < 0.001), surgical site infection (SSI) rate (20.4% vs. 58.8%, p = 0.003), urinary retention rate (3.7% vs. 17.6%, p = 0.020), and postoperative hospital stay (10 vs. 13 days, p = 0.009) were significantly lower in the LPPE group. The two groups showed no significant differences in the local recurrence rate (p = 0.296), 3-year overall survival (p = 0.129), or 3-year disease-free survival (p = 0.082). A higher CEA level (HR 1.02, p = 0.002), poor tumor differentiation (HR 3.05, p = 0.004), and (y)pT4b stage (HR 2.35, p = 0.035) were independent risk factors for disease-free survival.

CONCLUSION

LPPE is safe and feasible for locally advanced rectal cancers and shows lower operative time and blood loss, fewer SSI complications, and better preservation of bladder function without compromising oncological outcomes.

AnatomySketch: An Extensible Open-Source Software Platform for Medical Image Analysis Algorithm Development

The development of medical image analysis algorithm is a complex process including the multiple sub-steps of model training, data visualization, human-computer interaction and graphical user interface (GUI) construction. To accelerate the development process, algorithm developers need a software tool to assist with all the sub-steps so that they can focus on the core function implementation. Especially, for the development of deep learning (DL) algorithms, a software tool supporting training data annotation and GUI construction is highly desired. In this work, we constructed AnatomySketch, an extensible open-source software platform with a friendly GUI and a flexible plugin interface for integrating user-developed algorithm modules. Through the plugin interface, algorithm developers can quickly create a GUI-based software prototype for clinical validation. AnatomySketch supports image annotation using the stylus and multi-touch screen. It also provides efficient tools to facilitate the collaboration between human experts and artificial intelligent (AI) algorithms. We demonstrate four exemplar applications including customized MRI image diagnosis, interactive lung lobe segmentation, human-AI collaborated spine disc segmentation and Annotation-by-iterative-Deep-Learning (AID) for DL model training. Using AnatomySketch, the gap between laboratory prototyping and clinical testing is bridged and the development of MIA algorithms is accelerated. The software is opened at https://github.com/DlutMedimgGroup/AnatomySketch-Software .

MicroRNA-365 inhibits the progression of lung adenocarcinoma through targeting ETS1 and inactivating AKT/mTOR pathway

OBJECTIVE

MicroRNAs (miRNAs) act as important regulators in human cancers by regulating the gene expression. The dysregulation of miR-365 has been investigated in many cancers. However, the function of miR-365 remains unknown in lung adenocarcinoma. Therefore, the regulatory mechanism of miR-365 was explored in lung adenocarcinoma.

PATIENTS AND METHODS

The expression of miR-365 was detected in cell lines and 67 lung adenocarcinoma tissues using qRT-PCR. The Kaplan-Meier analysis was used to determine the association between miR-365 expressions and the survival rate in patients with lung adenocarcinoma. Transwell assay was then performed to investigate the effect of miR-365 on invasion and migration of lung adenocarcinoma cells.

RESULTS

Downregulation of miR-365 and upregulation of ETS1 were identified in lung adenocarcinoma. Furthermore, miR-365 reversely regulated ETS1 expression in lung adenocarcinoma. Functionally, the overexpression of miR-365 inhibited proliferation, migration, and invasion of lung adenocarcinoma cells. However, the upregulation of ETS1 lessened the inhibitory effect of miR-365 in lung adenocarcinoma. In addition, miR-365 inhibited EMT and inactivated AKT/mTOR pathway in lung adenocarcinoma.

CONCLUSIONS

MiR-365 inhibits the progression of lung adenocarcinoma by targeting ETS1 and inactivating the AKT/mTOR pathway.

HIV incidence is rapidly increasing with age among young men who have sex with men in China: a multicentre cross-sectional survey

OBJECTIVES

The HIV epidemic is worsening among men who have sex with men (MSM) in China, especially among those who are younger than 25 years old [younger MSM (YMSM)]. The aim of the study was to compare the prevalences of HIV incidence and recent HIV infection as well as factors associated with recent HIV infection in YMSM and older MSM (OMSM).

METHODS

A multicentre cross-sectional survey was conducted among 4496 MSM recruited from seven Chinese cities. YMSM were defined as those aged < 25 years. Data on demographics and sexual behaviours were collected using structural questionnaires. Blood samples were tested for recent HIV infection and other sexually transmitted infections.

RESULTS

Among the participants, 1313 were YMSM and 3183 were OMSM. Compared with OMSM, YMSM had a higher prevalence of recent HIV infection [5.4% (71 of 1313) for YMSM vs. 3.6% (115 of 3175) for OMSM; P = 0.006] and a higher HIV incidence [11.8 per 100 person-years (PY) (95% confidence interval (CI) 9.0-14.5) for YMSM vs. 7.6 per 100 PY (95% CI 6.3-9.0) for OMSM]. The incidence increased with age among YMSM, especially between the ages of 16 and 21 years. In contrast, the incidence declined with age among OMSM. Anal bleeding, recreational drug use, syphilis and herpes simplex virus 2 (HSV-2) infection were independent risk factors for recent HIV infection among YMSM. The prevalence of all these risk factors increased with age between the ages of 16 and 21 years. Anal bleeding (19.8%) and recreational drug use (19.5%) had the highest adjusted population attributable fractions (aPAFs) among YMSM. The highest aPAFs of anal bleeding (27.4%) and syphilis infection (25.5%) were found between the ages of 19 and 21 years.

CONCLUSIONS

The HIV incidence in Chinese YMSM was significantly higher than that in OMSM. YMSM aged 16-21 years had an extremely high risk of recent HIV infection.

[Effects of transthyretin on biological behavior of retinal pigment epithelial cells and retinal microvascular epithelial cells]

Objective: To explore the effects of transthyretin (TTR) on biological behavior of retinal pigment epithelial cells (RPECs) and retinal microvascular epithelial cells (RMVECs). Methods: RPECs were cultured with exogenous TTR to explore the effect of TTR on the proliferation of RPECs. The expression of TTR of RPECs was silenced by TTR specific small interfering RNA and the expression of TTR was detected by using Western blotting to identify the efficacy of TTR silence. The level of vascular endothelial growth factor (VEGF) massage RNA was detected by using RT-PCR to identify the interaction between VEGF and TTR. The different proliferation and migration abilities of RMVECs with different expressions of TTR were measured by transwell system. Results: MTT assay showed that RPECs with 0 μmol/L TTR glowed faster than with 4 μmol/L TTR (t=18.08, P<0.0001). The expression level of TTR was decreased in the small interfering RNA group as compared with the negative control group (P<0.05). RT-PCR assay showed no differential expression of VEGF after the silencing of TTR (P>0.05). The transwell assay showed RMVECs with the silence of TTR proliferated more slowly than RMVECs without the treatment (t=4.901, P=0.0012), and also migrated more slowly (t=4.213, P=0.0029). Conclusions: TTR can inhibit the proliferation of RPECs and promote the proliferation and migration of RMVECs without the help of VEGF, the mechanism of which may be worth further study. (Chin J Ophthalmol, 2016, 52: 856-860).

Genetic analysis of floral organ size in broccoli × cabbage via a mixed inheritance model of a major gene plus polygene

Broccoli and cabbage are important vegetable crops that produce hybrid seeds after insect pollination; the size of floral organs is crucial for this process. To investigate the genetic characteristics of floral organ sizes (corolla width, petal length and width, and lengths of stamen, anther, style, and stigma) and to improve the flower size and breeding efficiency of broccoli, we used multi-generation analysis of a major gene plus polygene model. Six populations obtained from a broccoli inbred line 93219 (small floral organs) and cabbage inbred line 195 (large floral organs) were used for the analysis. Corolla and petal width and stamen and anther length were controlled by the additive-dominance-epistasis polygene model. The heritability of these traits in BC1, BC2, and F2 generations was high (72.80-93.76%). Petal and stigma length were governed by the two major genes of additive-dominance-epistasis effects plus additive-dominance polygene model; the major gene heritability in the F2 generation were 79.17 and 65.77%, respectively. Style length was controlled by one major gene of additive-dominance effects plus additive-dominance-epistasis polygene model; the major gene heritability in BC1, BC2, and F2 were 40.60, 10.35, and 38.44%, respectively; the polygene heritability varied from 41.85 to 68.44%. Our results provide important genetic information for breeding, which could guide improvement of flower-related traits and lay the foundation for quantitative trait loci mapping of the flower-size traits in Brassica.

Reirradiation of nasopharyngeal carcinoma focusing on volumetric modulated arcs with flattening filter-free beams

OBJECTIVE

The goal of this study was to assess the role of flattening filter-free (FFF) beams in volumetric modulated arc radiotherapy for patients with recurrent nasopharyngeal carcinoma (rNPC).

METHODS

13 patients with rNPC were replanned for FFF RapidArc(®) (RA-FFF) and conventional RapidArc (RA) (Varian Medical Systems, Palo Alto, CA). Quantitative evaluation was performed for the planning target volume (PTV) and organs at risk (OARs). Phantom dose verifications, treatment delivery time and monitor units (MUs) were also assessed.

RESULTS

Each technique delivered similar doses to the PTV. RA-FFF had a better sparing effect on the brain stem and normal tissue when compared with RA, whereas RA provided lower mean doses to the skin. No significant difference between the two techniques could be established for other OAR parameters. Both techniques showed equally good gamma scores in dosimetric verification. RA-FFF required more MUs than RA, whereas the delivery time for RA-FFF was slightly shorter than for RA.

CONCLUSION

Both treatment plans met the planning objectives. Dose measurements also showed good agreement with computed doses. In addition to slightly faster delivery times, RA-FFF produced better sparing of brain stem and normal tissue with uncompromised target coverage compared with RA.

ADVANCES IN KNOWLEDGE

FFF beams have recently been assembled for clinical use. Our findings show RA-FFF is useful in the salvage treatment of rNPC owing to better brain stem and normal tissue sparing with uncompromised target coverage compared with RA. This may be beneficial in the case of tumour invasion close to the brain stem.

Submandibular gland sparing in intensity-modulated radiotherapy for N0-stage nasopharyngeal carcinoma

OBJECTIVE

This study evaluated and quantified the feasibility of submandibular gland (SMG) sparing in intensity-modulated radiotherapy (IMRT) for N0-stage nasopharyngeal carcinoma (NPC).

METHODS

Ten patients with N0-stage NPC were enrolled in the study. Four IMRT plans were produced for each, with different limiting conditions. In plan A, SMG sparing was ignored; in plans B, C and D, the mean dose to SMGs was restricted to 39 Gy. In addition, at least 95% of planning target volume (PTV)-IIa (PTV of clinical target volume involving level IIa lymph node) in plan C and 90% of PTV-IIa in plan D were required to have a 60 Gy covering.

RESULTS

The average mean dose to SMGs was 54.6 ± 3.6 Gy in plan A and was lower 39.3 ± 0.3, 49.3 ± 1.9 and 46.7 ± 2.8 Gy in plans B, C and D, respectively. The volume of PTV-IIa covered by 60 Gy was 98.9%, 81.6%, 95.2% and 90.8% in plans A, B, C and D, respectively, and showed a parallel association between dose reduction to SMGs and the covering deficit of PTV-IIa.

CONCLUSION

Reducing the mean dose received by SMG to 39 Gy or less in IMRT for N0-stage NPC is feasible.

Correlation between dihydropyrimidine dehydrogenase and efficacy and toxicity of fluoropyrimidine drugs

At present, fluoropyrimidine, based on 5-fluorouracil (5-FU), remains one of the most frequently prescribed chemotherapeutics drugs for the treatment of cancer. Dihydropyrimidine dehydrogenase (DPD) is the rate-limiting enzyme in the catabolism of 5-FU, and DPD enzymatic activities are usually varied dramatically from individual to individual, including both the intrapatient differences and the interpatient variability. There is a certain correlation between the DPD activity and efficacy and toxicity following the administration of fluoropyrimidine drugs. Partial or complete loss of DPD activity can lead to serious or even lethal toxicity. In this article, we review the relationship between DPD activity and efficacy and toxicity following the administration of fluoropyrimidine drugs, and also the structure, function, and characteristics of DPD. We report here that measurement of DPD activity may become a strategy and be paid much attention to predict the efficacy and toxicity prior to starting a fluoropyrimidine-based therapy.

Clinical analysis of prophylactic central neck dissection for papillary thyroid carcinoma

Purpose

The need of prophylactic central neck dissection (PCND) in patients with papillary thyroid carcinoma (PTC) is still controversial. The major restriction of PCND is the potential complications. We undertook a retrospective study to discuss its necessity in PTC patients.

Methods

A total of 188 patients with PTC who underwent total thyroidectomy and PCND were involved. In all of these, central lymph nodes were pathologic examined. Univariate and multivariate analyses were performed based on tumor location and size, etc.

Results

Overall, node metastases were found in 44.1 % (83/188) of patients. Tumor size was the independent positive predictor for lymph node metastasis, while gender, age, tumor multifocality, tumor location, and capsular infiltration were not independent predictors of central lymph node metastases. Postoperative complications happened in 5.3 % (10/188) of patients, which 4.8 % (9/188) had temporary hypocalcemia and 0 % (0/188) had permanent hypocalcemia. Rates of temporary and permanent recurrent laryngeal nerve injury were 0.5 % (1/188) and 0 % (0/188), respectively.

Conclusions

PCND is recommended in all patients with PTC.

MCM-41 Supported Cu−Mn Catalysts for Catalytic Oxidation of Toluene at Low Temperatures

Complete catalytic oxidation of toluene was investigated on Cu-Mn doped mesoporous and microporous catalysts, i.e., Cu-Mn/MCM-41, Cu-Mn/beta-zeolite, Cu-Mn/ZSM-5 (where SiO2/Al2O3 is either 25 or 38), and Cu-Mn/porous silica, in the presence of excess oxygen. The result shows that mesoporous catalysts have exhibited the highest catalytic activity among these catalysts above. The less amount of coke formation due to the unique mesoporous structures could play a key role in the high activity on the mesoporous catalyst. In addition, the bimetallic Cu-Mn-MCM-41 supported catalyst shows higher oxidation activity than either single metal catalyst, i.e., Cu-MCM-41 and Mn-MCM-41. The highly dispersed Cu-Mn mixed oxides on mesoporous structures probably provide active sites for the complete oxidation of toluene on these mesoporous catalysts.

Oligomerization triggers binding of a Bacillus thuringiensis Cry1Ab pore-forming toxin to aminopeptidase N receptor leading to insertion into membrane microdomains

Bacillus thuringiensis Cry1A toxins, in contrast to other pore-forming toxins, bind two putative receptor molecules, aminopeptidase N (APN) and cadherin-like proteins. Here we show that Cry1Ab toxin binding to these two receptors depends on the toxins' oligomeric structure. Toxin monomeric structure binds to Bt-R1, a cadherin-like protein, that induces proteolytic processing and oligomerization of the toxin (Gomez, I., Sanchez, J., Miranda, R., Bravo A., Soberon, M., FEBS Lett. (2002) 513, 242-246), while the oligomeric structure binds APN, which drives the toxin into the detergent-resistant membrane (DRM) microdomains causing pore formation. Cleavage of APN by phospholipase C prevented the location of Cry1Ab oligomer and Bt-R1 in the DRM microdomains and also attenuates toxin insertion into membranes despite the presence of Bt-R1. Immunoprecipitation experiments demonstrated that initial Cry1Ab toxin binding to Bt-R1 is followed by binding to APN. Also, immunoprecipitation of Cry1Ab toxin-binding proteins using pure oligomeric or monomeric structures showed that APN was more efficiently detected in samples immunoprecipitated with the oligomeric structure, while Bt-R1 was preferentially detected in samples immunoprecipitated with the monomeric Cry1Ab. These data agrees with the 200-fold higher apparent affinity of the oligomer than that of the monomer to an APN enriched protein extract. Our data suggest that the two receptors interact sequentially with different structural species of the toxin leading to its efficient membrane insertion.

Self consistent direct dynamics studies of interfaces

To reach the goal of prediction of electrochemical behavior from first principles, it appears increasingly evident that an intermediate stage, between ab initio calculation and Monte Carlo or classical molecular dynamics, will be required. Here we report progress on the development of such an intermediate computational method, using a self consistent tight binding approach, and report some preliminary results on the structure and dynamics of water on the 110 face of rutile titanium dioxide.

Crystallization and preliminary X-ray analysis of cardiotoxic phospholipase A2 from Ophiophagus hannah (king cobra)

An acidic phospholipase A2 exhibiting cardiotoxicity, myotoxicity and anti-platelet activity was isolated from Ophiophagus hannah (king cobra) from Guangxi, China. It contains an unusual 'pancreatic loop'. The enzyme was purified to homogeneity and crystallized using polyethylene glycol and ethylene glycol as precipitants. The crystal belongs to space group C2, with unit-cell parameters a = 117.92, b = 62.94, c = 57.16 A, beta = 100.93 degrees. Diffraction data were collected to 2.6 A.

Autocrine action of IL-10 suppresses proinflammatory mediators and inflammation in the HSV-1-infected cornea

We investigated whether IL-10 produced endogenously would influence the development of HSV-1-induced acute corneal disease. Murine corneal epithelial cells and fibroblasts cultured in vitro expressed IL-10 mRNA and protein constitutively and also IL-10 receptors. Inclusion of IL-10 neutralizing antibody in the culture medium significantly (p<0.05) enhanced TNF-alpha-induced IL-6 and MIP-2 production by both corneal cell types. Endogenous IL-10 synthesis, which also occurred in vivo, was not modulated by Herpes virus infection or by depletion of neutrophils or natural killer cells. Antibody to IL-10 given locally at the time of HSV-1 intracorneal infection was associated with significantly (p<0.05) enhanced production of IL-6, MIP-2, and MIP-1alpha, increased neutrophil infiltration, and more extensive corneal disease. Similarly, mice with a disrupted IL-10 gene developed more severe corneal disease than wild-type controls. Collectively, these observations suggest that locally produced IL-10 can act in an autocrine/paracrine fashion to down-regulate the production of proinflammatory mediators and thus limit corneal inflammation.

The Arabidopsis Information Resource (TAIR): a comprehensive database and web-based information retrieval, analysis, and visualization system for a model plant

Arabidopsis thaliana, a small annual plant belonging to the mustard family, is the subject of study by an estimated 7000 researchers around the world. In addition to the large body of genetic, physiological and biochemical data gathered for this plant, it will be the first higher plant genome to be completely sequenced, with completion expected at the end of the year 2000. The sequencing effort has been coordinated by an international collaboration, the Arabidopsis Genome Initiative (AGI). The rationale for intensive investigation of Arabidopsis is that it is an excellent model for higher plants. In order to maximize use of the knowledge gained about this plant, there is a need for a comprehensive database and information retrieval and analysis system that will provide user-friendly access to Arabidopsis information. This paper describes the initial steps we have taken toward realizing these goals in a project called The Arabidopsis Information Resource (TAIR) (www.arabidopsis.org).

ISYS: a decentralized, component-based approach to the integration of heterogeneous bioinformatics resources

MOTIVATION

Heterogeneity of databases and software resources continues to hamper the integration of biological information. Top-down solutions are not feasible for the full-scale problem of integration across biological species and data types. Bottom-up solutions so far have not integrated, in a maximally flexible way, dynamic and interactive graphical-user-interface components with data repositories and analysis tools.

RESULTS

We present a component-based approach that relies on a generalized platform for component integration. The platform enables independently-developed components to synchronize their behavior and exchange services, without direct knowledge of one another. An interface-based data model allows the exchange of information with minimal component interdependency. From these interactions an integrated system results, which we call ISYSf1.gif" BORDER="0">. By allowing services to be discovered dynamically based on selected objects, ISYS encourages a kind of exploratory navigation that we believe to be well-suited for applications in genomic research.

Differential regulation of two period genes in the Xenopus eye

The recent identification and analysis of mammalian homologues of the well characterized Drosophila circadian clock gene, Period (Per), has led to the idea that key features of vertebrate circadian rhythmicity are conserved at the molecular level. The Xenopus laevis retina contains a circadian clock mechanism that can be studied in vitro. To study the rhythmic expression of Per in the Xenopus retina, we used a degenerate RT-PCR strategy to obtain cDNA clones covering the entire 1427 amino acid coding region of a Xenopus homologue of Per2 and a partial cDNA sequence for a Xenopus homologue of Per1. Northern blot analysis shows that xPer1 and xPer2 transcripts are expressed most abundantly in the eye and the brain. However, rhythmic expression of xPer2 transcripts in the retina and retinal pigment epithelium (RPE) is light dependent and occurs only under 12 h light/12 h dark (LD) conditions, not in constant dark (DD). In contrast, xPer1 mRNA accumulation is rhythmic under both LD and DD conditions. Light dependent regulation of xPer2 mRNA and circadian regulation of xPer1 mRNA in the Xenopus retina differs from that in Drosophila and mammals. Light dependence of xPer2 mRNA levels and the offset phase relationship of the xPer2 rhythm to that for xPer1 suggests a role for xPer2 in circadian entrainment.