Active Low-Density Polyethylene-Based Films by Incorporating α-Tocopherol in the Free State and Loaded in PLA Nanoparticles: A Comparative Study.

In this work, alpha-tocopherol (α-TOC) was encapsulated in poly(lactic acid) nanoparticles (PLA NPs) and added to low-density polyethylene (LDPE) films with the aim of producing an active film for food packaging applications. PLA NPs loaded with α-TOC were produced through nanoprecipitation and dried using two methods (freeze-dryer and oven). LDPE-based films with final polymeric matrix concentrations of 10 and 20 g/kg were then produced through blow extrusion. The results showed that LDPE-based films loaded with α-TOC can be produced using blow extrusion, and a good distribution of PLA NPs can be obtained within the LDPE matrix as observed using scanning electron microscopy (SEM). The mechanical properties were affected by the incorporation of α-TOC and PLA NPs loaded with α-TOC, with the observation of a decrease in tensile strength and Young's Modulus values and an increase in elongation at break. Regarding water vapor permeability, the films showed a reduction in the values with the addition of α-TOC and PLA NPs loaded with α-TOC compared to the LDPE film (control). Films with α-TOC in the free state and loaded in PLA NPs showed antioxidant activity, but their behavior was affected by the encapsulation process.

Molecular epidemiology of HIV-1 among adult female sex workers at the Guatemala-Mexico border.

ABSTRACTSex workers have been demonstrated to have increased vulnerabilities to HIV and a high population prevalence of the disease. Despite their increased risk, sex workers have been underrepresented in molecular epidemiology studies assessing HIV in Mesoamerica. This study aims to describe the sociodemographic characteristics and phylogenetic profile of HIV-1 within a cohort of HIV-positive female sex workers (FSW) situated at the Guatemala-Mexico border. HIV viral sequences were collected from a cohort of FSW ≥18 years of age from San Marcos, Guatemala (n = 6) and compared to viral sequences collected as part of the Mesoamerican Drug Resistance Monitoring Programme to assess HIV viral diversity in Mexico and Guatemala (n = 3956). All of the FSW sampled were determined to have genetically unrelated HIV infections, suggesting multiple introductions of the virus and/or the potential existence of populations not captured by current surveillance efforts. Many reported numerous vulnerabilities that may have heightened their risk of acquiring and transmitting HIV through sex work activities. Our phylogenetic analysis indicated that national surveillance programmes may not fully capture the viral diversity among FSW and their clients within this region. Additional research is needed to fully capture HIV diversity and transmission in Mesoamerica, especially in the Guatemala-Mexico border region.

Imaging biofilms using fluorescence in situ hybridization: seeing is believing.

Biofilms are complex structures with an intricate relationship between the resident microorganisms, the extracellular matrix, and the surrounding environment. Interest in biofilms is growing exponentially given its ubiquity in so diverse fields such as healthcare, environmental and industry. Molecular techniques (e.g., next-generation sequencing, RNA-seq) have been used to study biofilm properties. However, these techniques disrupt the spatial structure of biofilms; therefore, they do not allow to observe the location/position of biofilm components (e.g., cells, genes, metabolites), which is particularly relevant to explore and study the interactions and functions of microorganisms. Fluorescence in situ hybridization (FISH) has been arguably the most widely used method for an in situ analysis of spatial distribution of biofilms. In this review, an overview on different FISH variants already applied on biofilm studies (e.g., CLASI-FISH, BONCAT-FISH, HiPR-FISH, seq-FISH) will be explored. In combination with confocal laser scanning microscopy, these variants emerged as a powerful approach to visualize, quantify and locate microorganisms, genes, and metabolites inside biofilms. Finally, we discuss new possible research directions for the development of robust and accurate FISH-based approaches that will allow to dig deeper into the biofilm structure and function.

Hoping for a Better Future during COVID-19: How Migration Plans Are Protective of Depressive Symptoms for Haitian Migrants Living in Chile.

This paper explores the migration experiences, perceived COVID-19 impacts, and depression symptoms among Haitian migrants living in Santiago, Chile. Ninety-five participants from eight neighborhoods with a high density of Haitian migrants were recruited. Descriptive statistics, univariate analysis, and logistic regression analysis were conducted. Chi-squared tests were used to confirm univariate results. We found that 22% of participants had major depressive symptoms based on the CESD-R-20 scale, 87% reported major life changes due to COVID-19, and 78% said their migration plans had changed due to the pandemic. Factors associated with more depressive symptoms were being in debt (OR = 3.43) and experiencing discrimination (ORs: 0.60 to 6.19). Factors associated with less odds of depressive symptoms were social support (ORs: 0.06 to 0.25), change in migration plans due to COVID-19 (OR = 0.30), and planning to leave Chile (OR = 0.20). After accounting for relevant factors, planning to leave Chile is significantly predictive of fewer symptoms of depression. Haitian migrants living in Chile had a high prevalence of depression. Planning to leave Chile was a significant protector against depressive symptoms. Future studies should explore how nuanced experiences of uncertainty play out in migrants' lives, mental well-being, and planning for their future.

Active Flexible Films for Food Packaging: A Review.

Active food packaging is a dynamic area where the scientific community and industry have been trying to find new strategies to produce innovative packaging that is economically viable and compatible with conventional production processes. The materials used to develop active packaging can be organized into scavenging and emitting materials, and based on organic and inorganic materials. However, the incorporation of these materials in polymer-based flexible packaging is not always straightforward. The challenges to be faced are mainly related to active agents' sensitivity to high temperatures or difficulties in dispersing them in the high viscosity polymer matrix. This review provides an overview of methodologies and processes used in the production of active packaging, particularly for the production of active flexible films at the industrial level. The direct incorporation of active agents in polymer films is presented, focusing on the processing conditions and their effect on the active agent, and final application of the packaging material. Moreover, the incorporation of active agents by coating technologies and supercritical impregnation are presented. Finally, the use of carriers to help the incorporation of active agents and several methodologies is discussed. This review aims to guide academic and industrial researchers in the development of active flexible packaging, namely in the selection of the materials, methodologies, and process conditions.

Increasing the Reuse of Protein Non-Naïve Nonhuman Primates in Pharmaceutical Drug Discovery and Development: An Overview and Industry Position on the Challenges and Benefits.

The IQ Consortium NHP Reuse Working Group (WG) comprises members from 15 pharmaceutical and biotechnology companies. In 2020, the WG developed and distributed a detailed questionnaire on protein non-naïve NHP reuse to the WG member companies. The WG received responses from key stakeholders including principal investigators, facility managers, animal welfare officers and research scientists. This paper's content reflects the consolidated opinion of the WG members and the questionnaire responses on the subject of NHP reuse within nonclinical programs at all stages of research and development. Many of the pharmaceutical companies represented in the working group or participating in the questionnaire have already achieved some level of NHP reuse in their nonclinical programs, but the survey results suggested that there is significant potential to increase NHP reuse further and a need to understand the considerations involved in reuse more clearly. The WG has also focused carefully on the inherent concerns and risks of implementing protein non-naive NHP reuse and has evaluated the best methods of risk assessment and decision-making. This paper presents a discussion on the challenges and opportunities surrounding protein non-naïve NHP reuse and aims to stimulate further industry dialogue on the subject and provide guidance for pharmaceutical companies to establish roadmaps and decision trees enabling increased protein non-naïve NHP reuse. In addition, this paper represents a solid basis for collaborative engagement between pharmaceutical and biotechnology companies with contract research organizations (CROs) to discuss how the availability of protein non-naïve NHP within CROs can be better leveraged for their use within nonclinical studies.

Migration and Mobility: Correlates of Recent HIV Testing Among Substance Using Female Sex Workers at the Mexico-Guatemala Border.

The goal of this paper is to determine the association between traveling to engage in sex work in another country and recent access to HIV testing among substance-using female sex workers (FSWs) in the Mexico-Guatemala border region. From 2012 to 2015, through modified time-location sampling and peer referral, 255 FSWs were recruited at Mexico's southern border. Participants completed questionnaires on sociodemographics, migration and mobility experiences, work environment factors, and substance use. A conceptual framework, as depicted by a directed acyclic graph (DAG), guided our analysis. Crude and adjusted logistic regression models were used to evaluate the relationships between mobility experiences and HIV testing in the past year. Overall HIV testing was low (41%); after considering relevant covariates (i.e., interaction with health services and organizations, and sex work characteristics) traveling to engage in sex work in another country was found to be positively associated with HIV testing in the past year. Future efforts need to consider voluntary and non-stigmatizing prevention HIV services and focus on reaching out to less mobile women.

RESUMEN: El objetivo de este artículo es determinar la asociación entre viajar a otro país para ejercer el comercio sexual y el acceso a una prueba reciente de VIH, en una población de mujeres trabajadoras sexuales en la frontera de México con Guatemala. Entre el 2012 y 2015, utilizando un muestreo por conveniencia y por referencia de pares, se invitó a 255 mujeres trabajadoras sexuales en la frontera sur de México a participar en este proyecto de investigación. Las participantes completaron una encuesta que comprendió preguntas sociodemográficas así como experiencias de migración y movilidad, características del trabajo sexual, y patrones de uso de sustancia. Utilizamos un marco conceptual que se ilustra en una Gráfica Acíclica Dirigida (DAG) el cual sirvió para guiar nuestro análisis. Realizamos análisis de regresión logística cruda y ajustada para evaluar la asociación entre experiencias de movilidad y haber recibido una prueba de VIH en el último año. En general, el porcentaje de haber recibido una prueba de VIH en el último año fue bajo (41%); después de considerar covariables relevantes; (ej., interacción con organizaciones y servicios de salud, características del trabajo sexual) encontramos que viajar a otro país para ejercer el comercio sexual está asociado con haber recibido una prueba de VIH en el último año. Es importante que, en el futuro, se concentren esfuerzos en servicios de prevención del VIH que sean voluntarios, no estigmatizantes, y que se enfoquen en mujeres trabajadoras sexuales menos móviles.

Intercepted journeys: Associations between migration and mobility experiences and depressive symptoms among substance using migrants at the Mexico-Guatemala border.

Substance use and depressive psychiatric symptoms have been associated with migration and mobility. The Mexico-Guatemala border is a key transit point for internal, regional, and international migration flows. However, there is limited knowledge of the role of substance use, migration, and mobility on mental health among migrants at this border. Our paper explores the association of migration and mobility patterns with possible major depressive symptoms among migrants at this key geographic region. We recruited 392 substance-using migrants using modified time-location sampling. Crude and adjusted logistic regression models were developed. We found that 12% of the sample had possible major depressive symptoms. After adjusting for relevant covariates, including gender, income, and perceived homelessness, we found that recent rural-urban and short-term migrants had higher odds of possible major depressive symptoms, whereas international migrants had lower odds. Findings of this paper suggest that although migrants experience hardship and uncertainty, they may respond with complex and nuanced forms of coping and planning.

Mutations in DISC1 alter IP3R and voltage-gated Ca2+ channel functioning, implications for major mental illness.

Disrupted in Schizophrenia 1 (DISC1) participates in a wide variety of developmental processes of central neurons. It also serves critical roles that underlie cognitive functioning in adult central neurons. Here we summarize DISC1's general properties and discuss its use as a model system for understanding major mental illnesses (MMIs). We then discuss the cellular actions of DISC1 that involve or regulate Ca2+ signaling in adult central neurons. In particular, we focus on the tethering role DISC1 plays in transporting RNA particles containing Ca2+ channel subunit RNAs, including IP3R1, CACNA1C and CACNA2D1, and in transporting mitochondria into dendritic and axonal processes. We also review DISC1's role in modulating IP3R1 activity within mitochondria-associated ER membrane (MAM). Finally, we discuss DISC1-glycogen synthase kinase 3ß (GSK3ß) signaling that regulates functional expression of voltage-gated Ca2+ channels (VGCCs) at central synapses. In each case, DISC1 regulates the movement of molecules that impact Ca2+ signaling in neurons.

Assessing Scientific Soundness and Translational Value of Animal Studies on DPP4 Inhibitors for Treating Type 2 Diabetes Mellitus.

Although there is a wide range of animal models of type 2 diabetes mellitus (T2DM) used in research; we have limited evidence on their translation value. This paper provides a) a comparison of preclinical animal and clinical results on the effect of five dipeptidyl peptidase-4 (DPP4) inhibitors by comparing the pharmaceutical caused glucose changes, and b) an evaluation of methodological and reporting standards in T2DM preclinical animal studies. DPP4 inhibitors play an important role in the clinical management of T2DM: if metformin alone is not sufficient enough to control the blood sugar levels, DPP4 inhibitors are often used as second-line therapy; additionally, DPP-4 inhibitors are also used in triple therapies with metformin and sodium-glucose co-transporter-2 (SGLT-2) inhibitors or with metformin and insulin. In our analysis of 124 preclinical studies and 47 clinical trials, (1) we found no evidence of species differences in glucose change response to DPP4 inhibitors, which may suggest that, for this drug class, studies in mice and rats may be equally predictive of how well a drug will work in humans; and (2) there is good reporting of group size, sex, age, euthanasia method and self-reported compliance with animal welfare regulations in animal studies but poor reporting of justification of group size, along with a strong bias towards the use of male animals and young animals. Instead of the common non-transparent model selection, we call for a reflective and evidenced-based assessment of predictive validity of the animal models currently available.

HIV Infection and Risk Heightened Among Female Sex Workers Who Entered the Sex Trade as Adolescents in Guatemala.

A dearth of empirical research exists on female sex workers in Central America who begin selling sex under age 18. Data were collected from adult female sex workers (N = 1216) sampled using census and modified time-location sampling in three urban centers of Guatemala. In adjusted analyses, female sex workers who entered the sex trade under age 16 years were more likely to be HIV positive (AOR = 4.6, 95% CI 1.6, 13.2), have not received HIV education in their first year of sex trade (AOR = 2.8, 95% CI 1.5, 5.5), have experienced violence to force commercial sex (AOR = 4.6, 95% CI 2.2, 9.8) and have not used condoms in their first month (AOR = 2.8, 95% CI 1.3, 6.1) , relative to those who entered as adults. An interaction between age at entry and foreign migration at entry was found for HIV risk. Efforts to prevent adolescent sex trade entry are needed and may also help to reduce HIV rates in Guatemala.

Voltage-induced Ca2+ release by ryanodine receptors causes neuropeptide secretion from nerve terminals.

Depolarisation-secretion coupling is assumed to be dependent only on extracellular calcium ([Ca2+ ]o ). Ryanodine receptor (RyR)-sensitive stores in hypothalamic neurohypophysial system (HNS) terminals produce sparks of intracellular calcium ([Ca2+ ]i ) that are voltage-dependent. We hypothesised that voltage-elicited increases in intraterminal calcium are crucial for neuropeptide secretion from presynaptic terminals, whether from influx through voltage-gated calcium channels and/or from such voltage-sensitive ryanodine-mediated calcium stores. Increases in [Ca2+ ]i upon depolarisation in the presence of voltage-gated calcium channel blockers, or in the absence of [Ca2+ ]o , still give rise to neuropeptide secretion from HNS terminals. Even in 0 [Ca2+ ]o , there was nonetheless an increase in capacitance suggesting exocytosis upon depolarisation. This was blocked by antagonist concentrations of ryanodine, as was peptide secretion elicited by high K+ in 0 [Ca2+ ]o . Furthermore, such depolarisations lead to increases in [Ca2+ ]i . Pre-incubation with BAPTA-AM resulted in > 50% inhibition of peptide secretion elicited by high K+ in 0 [Ca2+ ]o . Nifedipine but not nicardipine inhibited both the high K+ response for neuropeptide secretion and intraterminal calcium, suggesting the involvement of CaV1.1 type channels as sensors in voltage-induced calcium release. Importantly, RyR antagonists also modulate neuropeptide release under normal physiological conditions. In conclusion, our results indicate that depolarisation-induced neuropeptide secretion is present in the absence of external calcium, and calcium release from ryanodine-sensitive internal stores is a significant physiological contributor to neuropeptide secretion from HNS terminals.

Selected Uterine Immune Events Associated With the Establishment of Pregnancy in the Dog.

In the dog, implantation takes place at approximately 17 days of embryonal life and, while exposed to relatively high circulating progesterone concentrations, embryos presence is required for the formation of decidua. Furthermore, a balance between pro- and anti-inflammatory responses in conceptus-maternal communication is crucial for the onset of pregnancy. Strikingly, the understanding of such immune mechanisms in canine reproduction is still elusive. Here, canine uterine samples from pre-implantation (day 10-12, E+) and corresponding non-pregnant controls (E-), implantation (day 17, Imp) and post-implantation (day 18-25, Post-Imp) stages of pregnancy were used to investigate the expression and localization of several immune-related factors. The most important findings indicate increased availability of CD4, MHCII, NCR1, IDO1, AIF1, CD25, CCR7, and IL6 in response to embryo presence (E+), while FoxP3 and CCL3 were more abundant in E- samples. Implantation was characterized by upregulated levels of FoxP3, IL12a, ENG, and CDH1, whereas CD4, CCR7, IL8, and -10 were less represented. Following implantation, decreased transcript levels of TNFR1, MHCII, NCR1, TLR4, CD206, FoxP3, and IL12a were observed concomitantly with the highest expression of IL6 and IL1ß. MHCII, CD86, CD206, CD163, TNFα, IDO1, and AIF1 were immunolocalized in macrophages, CD4 and Nkp46 in lymphocytes, and some signals of IDO1, AIF1, and TNF-receptors could also be identified in endothelial cells and/or uterine glands. Cumulatively, new insights regarding uterine immunity in the peri-implantation period are provided, with apparent moderated pro-inflammatory signals prevailing during pre-implantation, while implantation and early trophoblast invasion appear to be associated with immunomodulatory and rather anti-inflammatory conditions.

Communication Strategies To Enhance HIV/STI Prevention, Sexual and Reproductive Health, and Safety Among Migrant Sex Workers at the Mexico-Guatemala Border.

Communication-based interventions have been linked to improved health and social outcomes among underserved populations. Migrant women in sex work face serious health and social inequities, including risks of HIV and other sexually transmitted infections (STIs) and violence. Given gaps in evidence about health communication among migrant sex workers and the potential for communication-based interventions to promote health and safety, this qualitative study investigates experiences with accessing and sharing information regarding HIV/STI prevention, sexual and reproductive health, and physical safety among migrant sex workers at the Mexico-Guatemala border. Findings suggest that participatory peer-based, workplace, and m-health communication interventions could facilitate access to HIV/STI prevention, and to sexual and reproductive health/safety resources for migrant women involved in sex work, while strengthening peer support networks and social cohesion. To have long-lasting results, such interventions must be complemented by broader structural changes, including sex work and migration law reforms, increased community mobilization, and improved working conditions.

The influence of migration in substance use practices and HIV/STI-related risks of female sex workers at a dynamic border crossing.

We explored the association of international migration with substance use and HIV/STI risk factors among female sex workers (FSW). Using modified time-location sampling, we recruited 266 FSW at the Mexico-Guatemala border. Crude and adjusted logistic regression models were used to evaluate the relationships. HIV risks, such as frequent hard drug use and drug use in another country, were greater for migrant compared to nonmigrant FSW. However, more migrant versus nonmigrant FSW reported consistent condom use with clients and having a health card. Our study highlights regional patterns of substance use among FSW and risk or protective behaviors related to migration status.

Struggling bodies at the border: migration, violence and HIV vulnerability in the Mexico/Guatemala border region.

The Mexico-Guatemala border is the site of significant movement of people whose principal destination is the USA. The first step, to cross Mexico, is considered as one of the most dangerous routes in the world for undocumented migrants. For some male migrants and displaced persons from Honduras, El Salvador and Guatemala, initiating sex work in the Mexican border city of Tapachula has become a way to earn money to survive during the trip northward - providing funds to keep traveling and decrease the danger of being killed or kidnaped by organized crime groups. Non-injected drug use during sex work with men and/or women is a common praxis for this purpose, and is linked to HIV risk activities such as unprotected sex. Our study is based on ethnographic fieldwork with observation and interviews and within a relational approach understanding the processes subject/structure, sociopolitical/cultural and global/local, not as oppositions, rather as linkages visible through actors' points of view and praxis. The productions of politics and cultures related to structural vulnerability to HIV infection are embedded in local and global borderization processes where legal and illegal transnational forces, states' frameworks and social groups play a linked role. The economies of structural, symbolic and direct violence affect migratory patterns, institutional interactions and social and cultural relations with the local population. In this context, social representations and praxis about unprotected sex and drug use are the locus of struggling bodies at the border.

Acute phase proteins and biomarkers of oxidative status in feline spontaneous malignant mammary tumours.

Acute phase proteins (APP) and biomarkers of oxidative status change in human and canine mammary tumours, however, they have not been studied in feline mammary tumours. The aims of this study were to investigate the APP and antioxidant responses in feline malignant mammary tumours, to evaluate their relation with tumour features, and to assess their prognostic value. Serum amyloid A (SAA), haptoglobin (Hp), albumin, butyrylcholinesterase (BChE), insulin-like growth factor1 (IGF1), paraoxonase1 (PON1), total serum thiols (Thiol), glutathione peroxidase (GPox) and total antioxidant capacity determined by different assays, including trolox equivalent antioxidant capacity assessed by two different methodologies (TEAC1/2), ferric reducing ability of plasma (FRAP), and cupric reducing antioxidant capacity (CUPRAC), were determined in serum of 50 queens with spontaneous mammary carcinomas and of 12 healthy female cats. At diagnosis, diseased queens presented significantly higher SAA and Hp, and lower albumin, BChE, GPox, TEAC1, TEAC2 and CUPRAC than controls. Different tumour features influenced concentrations of APP and antioxidants. Increases in serum Hp, and decreases in albumin, Thiol and FRAP were significantly associated with neoplastic vascular emboli, metastasis in regional lymph nodes and/or in distant organs. Distant metastasis development during the course of the disease was associated with increases in SAA and TEAC1. At diagnosis, decreased albumin was associated with a longer survival, and BChE <1.15 µmoL/mL.minute was associated with a shorter survival time on multivariate analysis. Feline malignant mammary tumours are associated with an APP response and oxidative stress, and different tumour features influence the inflammatory response and the oxidative damage. Furthermore, some of these analytes proved to have prognostic value.

Factors associated with HIV testing among men who have sex with men in Guatemala City.

Although men who have sex with men (MSM) have the highest human immunodeficiency virus (HIV) prevalence in Guatemala, prevention efforts have been focused on other vulnerable populations. Respondent-driven sampling was used to recruit 444 MSM in Guatemala City to explore factors related to HIV testing among MSM. About 56% of participants reported HIV testing in the past 12 months, which was associated with a public MSM status (adjusted odds ratio (AOR) 2.08; 95% CI 1.02-4.26), participating in peer HIV prevention intervention (AOR 3.71; 95% CI 1.86-7.43), having at least one casual male partner (AOR 2.16; 95% CI 1.11-4.20), and practicing only insertive anal sex (AOR 3.35; 95% CI 1.59-7.09). Men with comprehensive HIV knowledge (AOR 2.63; 95% CI 1.38-5.02) were also more likely to have been tested. Further interventions in Guatemala targeting the most hidden MSM are needed.

Making the Link: A Pilot Health Navigation Intervention to Improve Timely Linkage to Care for Men Who have Sex with Men and Transgender Women Recently Diagnosed with HIV in Guatemala City.

We piloted a health navigation strategy to promote timely linkage to care among men who have sex with men (MSM) and transgender women (TW) recently diagnosed with HIV in Guatemala City. We used a mixed-methods approach, integrating quantitative data collected during clinic visits and qualitative data from in-depth interviews, to characterize acceptability of navigation and time to linkage, defined as having the first clinical care visit. Out of 54 participants who enrolled in the pilot (n = 52 MSM; n = 2 TW), 50 (92.6%) accepted navigation and all were linked to care. Median time to linkage was 3 days (Interquartile Range 2-5 days). In qualitative interviews, participants expressed feeling scared and alone following their diagnosis and appreciated the support of a navigator, especially when they did not feel they could access their existing support networks. Future research and evaluation should continue to assess how to best use health navigation to support key populations recently diagnosed with HIV.

Differential expression of zinc transporters accompanies the differentiation of C2C12 myoblasts.

Zinc transporters facilitate metal mobilization and compartmentalization, playing a key role in cellular development. Little is known about the mechanisms and pathways of Zn movement between Zn transporters and metalloproteins during myoblast differentiation. We analyzed the differential expression of ZIP and ZnT transporters during C2C12 myoblast differentiation. Zn transporters account for a transient decrease of intracellular Zn upon myogenesis induction followed by a gradual increase of Zn in myotubes. Considering the subcellular localization and function of each of the Zn transporters, our findings indicate that a fine regulation is necessary to maintain correct metal concentrations in the cytosol and subcellular compartments to avoid toxicity, maintain homeostasis, and for loading metalloproteins needed during myogenesis. This study advances our basic understanding of the complex Zn transport network during muscle differentiation.