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PubMed1996

Effects of electroporation on the tubulin cytoskeleton and directed migration of corneal fibroblasts cultured within collagen matrices.

Electroporation provides a useful method for loading fibroblasts with fluorescent probes for the cytoskeleton, but the possible deleterious effects of this loading technique on cell motility are unknown. We have used conventional and confocal microscopy of living cells and immunohistochemistry to examine the migration and cytoskeleton of chick embryo corneal fibroblasts electroporated while cultured within collagen gels. Fibroblasts cultured in collagen (1 mg/ml) are successfully electroloaded (0.5-1.0 kVcm-1/960 microF in DMEM/F12/20 mM Hepes, pH 7.2) with dextran (4-150 kDa) and immunoglobulin, but subsequently display uncoordinated pseudopodia and hence are unable to migrate effectively in any one direction. The lack of directed movement is due to depolymerization of microtubules and/or a perinuclear collapse of vimentin filaments, seemingly caused by millimolar levels of Ca2+ ions derived from culture medium following electroporation. Fibroblasts loaded in a buffer which resembles intracellular fluid (< or = 10 microM Ca2+) maintain their cytoskeleton and continue to migrate, when returned to culture medium within 10 min. Using this novel approach, we have loaded fibroblasts migrating through extracellular matrix (ECM) with rhodamine phalloidin and monitored the behavior of the labeled actin cortex by confocal microscopy. During migration phalloidin-actin accumulates near the base of pseudopodia and at the rear of the cell where it is subsequently left behind. We conclude that electroporation is a valuable technique for loading fibroblasts to study migration within ECM, provided that the conditions used support stability of the tubulin cytoskeleton.

Actins↗
PubMed1980

Probabilistic income-maximizing behavior in regional migration: an empirical test.

"This paper provides an empirical test of the hypothesis that migrants consider income risk in their evaluation of the returns to migration in that higher levels of income risk for a given region reduce the rate of net migration into that region." Theoretical approaches to the incorporation of income risk in migration models are first considered, and alternative approaches are then tested using data on white and nonwhite net migration in the United States between 1960 and 1970. The results indicate support for the hypothesis that the extent of net migration is inversely affected by income risk.

Americas↗
PubMed1995

Problems and policies regarding the socio-economic integration of returnees and foreign workers in Greece.

"The integration of repatriating Greek migrants, ethnic Greeks and foreign workers has individual and macroeconomic aspects, both of which must be addressed within a dynamic perspective.... This article analyses the problems involved, and the policies and programmes adopted (or the lack of policies), for the integration of incoming workers to the Greek economy. Wherever possible, the suitability and effectiveness of measures taken are evaluated against the experience gained.... It may be concluded from this analysis that policies adopted for the integration of various migrant groups to Greece (i.e. Greek migrant returnees, ethnic-Greek foreigners and illegal migrants) lack a central aim, orientation and strategy, as well as a long-term perspective." (SUMMARY IN FRE AND SPA)

Acculturation↗
PubMed1988

Socio-economic stratification generated by international migration loops.

This paper analyzes the migration phenomenon within a framework that treats migration movements as continuous loops, from the country of origin to the destination and back. Significant social-psychological factors at each step of the loop process contribute to the development of migration streams along a predictable pattern. The general model of the loop process shows that the migration stream is 1st sparked when labor is recruited from less developed countries for work in developed industrialized countries. Once the social process of migration has begun, it tends to acquire a self-feeding character. Social and economic change in sending and receiving societies brought about by migration make further migration more likely. The case of the Mexico-US-Mexico loop process is analyzed. This case illustrates the effects of socioeconomic stratification that occurs in communities where the migration loop process reaches a certain level of maturity. The majority of a town's population may become committed to migration as a way of life. Eventually, wealth becomes concentrated in the hands of those that are most able to migrate. Thus, migrants may become a new elite segment of rural populations that were once relatively homogenous societies. Further research of the migration loop process should be conducted. At least in the case of Mexico, the socioeconomic stratification in the villages and towns acting as sources of migration loops with destinations in the US have significant internal economic, social, and political implications.

Americas↗
PubMed1997

Skilled Hong Kong immigrants' intention to repatriate.

"An emphasis on skills in Australian immigration policy in the past decade has led to the increase of highly skilled Hong Kong immigrants. However, Australia has not been able to retain all of them.... This paper reports the results of an in-depth study on intention to repatriate and work in Hong Kong, conducted in Australia with 111 professional and managerial Hong Kong immigrants. Correlational and loglinear analyses on prediction of such an intention are presented. Research findings on the career-family dilemma experienced by a number of immigrants are likewise discussed."

Asia↗
PubMed1999

Turnover rates at regulatory phosphorylation sites on myosin II in endothelial cells.

Assembly and motor activity of non-muscle myosin II can be regulated by phosphorylation. Because myosin II-containing structures undergo continuous assembly, disassembly, and remodeling in living cells, especially during cell migration, myosin II should undergo frequent phosphorylation and dephosphorylation. This study examines the turnover of phosphate on myosin II in stationary and migrating endothelial cells. Cultured bovine aortic endothelial cells were metabolically labeled with (32)P-phosphate, and the incorporation of phosphate into myosin II was assessed by quantitative phosphor imaging of electrophoretic gels of myosin II immunoadsorbed from cell lysates. Likewise, phosphate turnover was measured upon chasing the (32)P with unlabeled phosphate. Phosphate incorporated very slowly into heavy chains, taking >8 h to plateau, and turned over at </=12.7% per hour. Regulatory light chains became completely labeled in </=4 h, and turnover occurred at two rates: 49% turned over at 20% per hour, the remainder at 67% per hour. Peptide mapping showed light chain phosphorylation at serine 19 and threonine 18, but phosphate turnover was the same in mono- and diphosphorylated lights chains, indicating that rates are not different at the two sites. When cells were stimulated to migrate by wounding a confluent monolayer, the rate of light chain dephosphorylation increased and the rate of phosphate incorporation decreased causing a net 10% dephosphorylation of light chains. This process persisted during migration and returned to baseline when the wound was closed. There was no effect on heavy chain phosphates. Light chain dephosphorylation may facilitate migration by mobilizing myosin II during cytoskeletal remodeling.

Animals↗
PubMed2005

Nocturnal life of young songbirds well before migration.

In songbirds, nocturnal activity is believed to be a characteristic feature of migration. However, unlike experimental conditions where the onset of nocturnal restlessness is defined as a shift of activity leading up to the dark period, this behaviour has, until now, not been observed in natural conditions. Here we studied the nocturnal behaviour of radio-tagged juvenile Eurasian reed warblers (Acrocephalus scirpaceus) during the pre-migratory period. The birds started nocturnal flights at the age of 38 days, whereas migration did not commence until they were at least 50 days old. The birds left their natal site by nocturnal flights and repeatedly returned to it. Such shuttle movements suggest the existence of a previously unknown period of nocturnal activity. Motivation to perform such night flights gradually increases with age. We relate the function of these nocturnal pre-migratory flights to the development of a stellar compass, necessary for detecting the compass direction towards winter quarters and for the formation of a navigational target, which will be used during return (spring) migration.

Age Factors↗
PubMedDate not supplied

[Elderly Turkish male and female migrants in the later stage of employment and in retirement].

Older Turkish migrant workers who came to the Federal Republic of Germany in the 1960s and 1970s to establish a financial basis for a better life after returning to Turkey have remained longer than initially intended. For many of them, the question has arisen of whether the actual goal of their migration--a return to the native country--can be realized. Based on the results of nonstandardized interviews, conflicts and problems of aging Turkish migrant workers are described and discussed. Central aspects are the cultural identity and the longing for their native country, as well as the social rootedness of their children in the FRG. The latter may well stand in the way of a return to Turkey. Furthermore, financial, legal, and health aspects play an important role in the future of aging Turkish migrants.

Aged↗
PubMed2005

The migratory experiences of people with HIV/AIDS (PWHA) in Wilmington, North Carolina.

People with a serious illness such as HIV/AIDS may migrate in order to receive support from family and friends and/or better health care. In this paper, I examine the experiences of people with HIV/AIDS (PWHA) that are initial and return migrants to Wilmington, North Carolina. For the study this paper is based upon, I conducted 63 interviews of service providers, PWHA and community members in Wilmington, North Carolina. Qualitative data analysis reveals that for return migrants, migration networks made the move and getting 'into the system' easier while initial migrants struggled through the relocation process and often moved for reasons unrelated to family or friends in the area.

Emigration and Immigration↗