Invasiveness of malignant ST/A mouse lung cells in vitro

ST/A mouse lung cells underwent apparently spontaneous malignant alteration in tissue culture. We have compared the capacity of these cells to form malignant tumours in syngeneic animals with their behaviour in vitro. ST-L1, ST-L22, and ST-L104 cells were malignant, whilst ST-L108 and ST-L109 cells were not. ST-L1 and ST-L22 cells showed anchorage-dependence of growth, whilst ST-L104, ST-L108 and ST-L109 cells did not. ST-L22, ST-L104, ST-L108 and ST-L109 performed directional migration from a spheroid explanted on glass. This capacity was lost in ST-L1 cells, which produced so-called round-cell transformants. All but ST-L108 cells produced type C viral particles. The tumorigenic cell lines ST-L1, ST-L22 and ST-L104 invaded fragments of embryonic chick heart in three-dimensional culture, whereas the non-tumorigenic ST-L108 and ST-L109 cells did not. Furthermore, the histology of ST-L cells invading in three-dimensional culture resembled that of the invasive sarcomas which they produced in vivo. The present observations with ST-L cells confirm that invasiveness in three-dimensional culture is a reliable criterion for malignant of tissue culture lines.     

Utilizing Custom-designed Galvanotaxis Chambers to Study Directional Migration of Prostate Cells

The physiological electric field serves specific biological functions, such as directing cell migration in embryo development, neuronal outgrowth and epithelial wound healing. Applying a direct current electric field to cultured cells in vitro induces directional cell migration, or galvanotaxis. The 2-dimensional galvanotaxis method we demonstrate here is modified with custom-made poly(vinyl chloride) (PVC) chambers, glass surface, platinum electrodes and the use of a motorized stage on which the cells are imaged. The PVC chambers and platinum electrodes exhibit low cytotoxicity and are affordable and re-useable. The glass surface and the motorized microscope stage improve quality of images and allow possible modifications to the glass surface and treatments to the cells. We filmed the galvanotaxis of two non-tumorigenic, SV40-immortalized prostate cell lines, pRNS-1-1 and PNT2. These two cell lines show similar migration speeds and both migrate toward the cathode, but they do show a different degree of directionality in galvanotaxis. The results obtained via this protocol suggest that the pRNS-1-1 and the PNT2 cell lines may have different intrinsic features that govern their directional migratory responses.     

Comparative studies of two types of "spontaneous" malignant alteration of ST/A mouse lung fibroblasts propagated in vitro.

Two types of apparently spontaneous malignant alterations of fibroblastlike ST/a mouse lung cells (ST-L cells) grown in vitro are described. One type is characterized by a high tumorigenic potential of the altered cells in nonconditioned syngeneic recipients, a fibroblastlike morphology with cell surface showing very few microvilli by scanning electron-microscopy (SEM), and a growth pattern typical of nontransformed cells. These cells were described as R- cells. The other type is characterized bya low tumorigenic potential in non-conditioned, immunocompetent syngeneic recipients, rounding up of the cells which by SEM showed numerous microvilli on the surface, and a growth pattern typical of transformed cells. These cells were described as round cells or R+ cells. In immunoincompetent mice, R+ cells readily produced sarcomas, which grew faster than those produced by R- cells. Both types of ST-L cells expressed murine leukemia virus (MuLV) when tested in a peroxidase anti-p30 plaque test. The concentration of murine leukemia virus envelope glycoprotein (gp70) has previously (5) been shown to be threefold higher in R+ cells compared to R- cells. Furthermore, round-cell transformation was accompanied by the development of crossreacting rejection antigens protective against a secondary shallenge with Ehrlich ascites tumor and with syngeneic dimethylbenzanthracene induced ST/a mouse leukemia (STABAL). A similar protection was obtained by preimmunization with a cloned embryonic feral mouse cell line (SC-1) infected with ST-L virus as well as with virus-free SC-1 cells, suggesting the presence of rejection antigens both of viral (gp70) and nonviral origin.     

A role for PP1/NIPP1 in steering migration of human cancer cells

Electrical gradients are present in many developing and regenerating tissues and around tumours. Mimicking endogenous electric fields in vitro has profound effects on the behaviour of many cell types. Intriguingly, specific cell types migrate cathodally, others anodally and some polarise with their long axis perpendicular to the electric vector. These striking phenomena are likely to have in vivo relevance since one of the determining factors during cancer metastasis is the ability to switch between attractive and repulsive migration in response to extracellular guidance stimuli. We present evidence that the cervical cancer cell line HeLa migrates cathodally in a direct current electric field of physiological intensity, while the strongly metastatic prostate cancer cell line PC-3-M migrates anodally. Notably, genetic disruption of protein serine/threonine phosphatase-1 (PP1) and its regulator NIPP1 decrease directional migration in these cell lines. Conversely, the inducible expression of NIPP1 switched the directional response of HeLa cells from cathodal to slightly anodal in a PP1-dependent manner. Remarkably, induction of a hyperactive PP1/NIPP1 holoenzyme, further shifted directional migration towards the anode. We show that PP1 association with NIPP1 upregulates signalling by the GTPase Cdc42 and demonstrate that pharmacological inhibition of Cdc42 in cells overexpressing NIPP1 recovered cathodal migration. Taken together, we provide the first evidence for regulation of directional cell migration by NIPP1. In addition, we identify PP1/NIPP1 as a novel molecular compass that controls directed cell migration via upregulation of Cdc42 signalling and suggest a way by which PP1/NIPP1 may contribute to the migratory properties of cancer cells.     

Real-Time Motion Analysis Reveals Cell Directionality as an Indicator of Breast Cancer Progression

Cancer cells alter their migratory properties during tumor progression to invade surrounding tissues and metastasize to distant sites. However, it remains unclear how migratory behaviors differ between tumor cells of different malignancy and whether these migratory behaviors can be utilized to assess the malignant potential of tumor cells. Here, we analyzed the migratory behaviors of cell lines representing different stages of breast cancer progression using conventional migration assays or time-lapse imaging and particle image velocimetry (PIV) to capture migration dynamics. We find that the number of migrating cells in transwell assays, and the distance and speed of migration in unconstrained 2D assays, show no correlation with malignant potential. However, the directionality of cell motion during 2D migration nicely distinguishes benign and tumorigenic cell lines, with tumorigenic cell lines harboring less directed, more random motion. Furthermore, the migratory behaviors of epithelial sheets observed under basal conditions and in response to stimulation with epidermal growth factor (EGF) or lysophosphatitic acid (LPA) are distinct for each cell line with regard to cell speed, directionality, and spatiotemporal motion patterns. Surprisingly, treatment with LPA promotes a more cohesive, directional sheet movement in lung colony forming MCF10CA1a cells compared to basal conditions or EGF stimulation, implying that the LPA signaling pathway may alter the invasive potential of MCF10CA1a cells. Together, our findings identify cell directionality as a promising indicator for assessing the tumorigenic potential of breast cancer cell lines and show that LPA induces more cohesive motility in a subset of metastatic breast cancer cells.     

Neural crest cell migration: requirements for exogenous fibronectin and high cell density

Cells of the neural crest participate in a major class of cell migratory events during embryonic development. From indirect evidence, it has been suggested that fibronectin (FN) might be involved in these events. We have directly tested the role of FN in neural crest cell adhesion and migration using several in vitro model systems. Avian trunk neural crest cells adhered readily to purified plasma FN substrates and to extracellular matrices containing cellular FN. Their adhesion was inhibited by antibodies to a cell-binding fragment of FN. In contrast, these cells did not adhere to glass, type I collagen, or to bovine serum albumin in the absence of FN. Neural crest cell adhesion to laminin (LN) was significantly less than to FN; however, culturing of crest cells under conditions producing an epithelioid phenotype resulted in cells that could bind equally as well to LN as to FN. The migration of neural crest cells appeared to depend on both the substrate and the extent of cell interactions. Cells migrated substantially more rapidly on FN than on LN or type I collagen substrates; if provided a choice between stripes of FN and glass or LN, cells migrated preferentially on the FN. Migration was inhibited by antibodies against the cell-binding region of FN, and the inhibition could be reversed by a subsequent addition of exogenous FN. However, the migration on FN was random and displayed little persistence of direction unless cells were at high densities that permitted frequent contacts. The in vitro rate of migration of cells on FN-containing matrices was 50 microns/h, similar to their migration rates along the narrow regions of FN-containing extracellular matrix in migratory pathways in vivo. These results indicate that FN is important for neural crest cell adhesion and migration and that the high cell densities of neural crest cells in the transient, narrow migratory pathways found in the embryo are necessary for effective directional migration.     

ASK-1 (apoptosis signal-regulating kinase 1) is a direct E2F target gene

S1P (sphingosine 1-phosphate) receptor expression and the effects of S1P on migration were studied in one papillary (NPA), two follicular (ML-1, WRO) and two anaplastic (FRO, ARO) thyroid cancer cell lines, as well as in human thyroid cells in primary culture. Additionally, the effects of S1P on proliferation, adhesion and calcium signalling were addressed in ML-1 and FRO cells. All cell types expressed multiple S1P receptors. S1P evoked intracellular calcium signalling in primary cultures, ML-1 cells and FRO cells. Neither proliferation nor migration was affected in primary cultures, whereas S1P partly inhibited proliferation in ML-1 and FRO cells. Low nanomolar concentrations of S1P inhibited migration in FRO, WRO and ARO cells, but stimulated ML-1 cell migration. Consistently, S1P1 and S1P3, which mediate migratory responses, were strongly expressed in ML-1 cells, and S1P2, which inhibits migration, was the dominating receptor in the other cell lines. The migratory effect in ML-1 cells was mediated by G(i) and phosphatidylinositol 3-kinase. Both S1P and the S1P1-specific agonist SEW-2871 induced Akt phosphorylation at Ser473. However, SEW-2871 failed to stimulate migration, whereas the S1P1/S1P3 antagonist VPC 23019 inhibited S1P-induced migration. The results suggest that aberrant S1P receptor expression may enhance thyroid cancer cell migration and thus contribute to the metastatic behaviour of some thyroid tumours.     

Cellular Migration and Invasion Uncoupled: Increased Migration Is Not an Inexorable Consequence of Epithelial-to-Mesenchymal Transition

Metastatic dissemination requires carcinoma cells to detach from the primary tumor and invade through the basement membrane. To acquire these characteristics, epithelial tumor cells undergo epithelial-to-mesenchymal transitions (EMT), whereby cells lose polarity and E-cadherin-mediated cell-cell adhesion. Post-EMT cells have also been shown, or assumed, to be more migratory; however, there have been contradictory reports on an immortalized human mammary epithelial cell line (HMLE) that underwent EMT. In the context of carcinoma-associated EMT, it is not yet clear whether the change in migration and invasion must be positively correlated during EMT or whether enhanced migration is a necessary consequence of having undergone EMT. Here, we report that pre-EMT rat prostate cancer (PC) and HMLE cells are more migratory than their post-EMT counterparts. To determine a mechanism for increased epithelial cell migration, gene expression analysis was performed and revealed an increase in epidermal growth factor receptor (EGFR) expression in pre-EMT cells. Indeed, inhibition of EGFR in PC epithelial cells slowed migration. Importantly, while post-EMT PC and HMLE cell lines are less migratory, both remain invasive in vitro and, for PC cells, in vivo. Our study demonstrates that enhanced migration is not a phenotypic requirement of EMT, and migration and invasion can be uncoupled during carcinoma-associated EMT.     

Antigen‐responsive regulation of Cell motility and migration via the signalobodies based on c‐Fms and c‐Mpl

Since cell migration plays critical roles in development and homeostasis of the body, artificial control of cell migration would be promising for the treatment of various diseases related to migration. To this end, we previously developed single‐chain Fv (scFv)/receptor chimeras, named signalobodies, which can control cell fates via a specific antigen that is different from natural cytokines. Although a conventional chemotaxis chamber assay revealed that several signalobodies based on receptor tyrosine kinases transduced antigen‐dependent migration signals, we have never performed direct observation of the cells to obtain more information on overall properties of cell motility and migration. In this study, we utilized murine pro‐B Ba/F3 cells expressing either a scFv‐Fms or scFv‐Mpl signalobody, and compared their migratory characteristics. We employed a lipid–polyethylene glycol conjugate to softly immobilize the suspension cells on a slide, which facilitated direct observation of chemokinetic activity of the cells. Consequently, both cells markedly exhibited chemokinesis in response to a specific antigen. In addition, the cells were subjected to a stable antigen‐concentration gradient to observe horizontal directional cell migration in real time. The results showed that the cells expressing scFv‐Fms underwent directional migration toward a positive antigen‐concentration gradient. Taken together, we successfully demonstrated antigen‐responsive regulation of cell motility and migration via the signalobodies. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:411–417, 2014     

Comparative studies of two types of “spontaneous” malignant alteration of ST/A mouse lung fibroblasts propagated in vitro

Summary Two types of apparently spontaneous malignant alterations of fibroblastlike ST/a mouse lung cells (ST-L cells) grown in vitro are described. One type is characterized by a high tumorigenic potential of the altered cells in nonconditioned syngeneic recipients, a fibro-blastlike morphology with cell surface showing very few microvilli by scanning electron-microscopy (SEM), and a growth pattern typical of nontransformed cells. These cells were described as R⁻ cells. The other type is characterized by a low tumorigenic potential in nonconditioned, immunocompetent syngeneic recipients, rounding up of the cells which by SEM showed numerous microvilli on the surface, and a growth pattern typical of transformed cells. These cells were described as round cells or R⁺ cells. In immunoincompetent mice, R⁺ cells readily produced sarcomas, which grew faster than those produced by R⁻ cells. Both types of ST-L cells expressed murine leukemia virus (MuLV) when tested in a peroxidase anti-p30 plaque test. The concentration of murine leukemia virus envelope glycoprotein (gp70) has previously (5) been shown to be threefold higher in R⁺ cells compared to R⁻ cells. Furthermore, round-cell transformation was accompanied by the development of crossreacting rejection antigens protective against a secondary challenge with Ehrlich ascites tumor and with syngeneic dimethylbenzanthracene induced ST/a mouse leukemia (STABAL). A similar protection was obtained by preimmunization with a cloned embryonic feral mouse cell line (SC-1) infected with ST-L virus as well as with virus-free SC-1 cells, suggesting the presence of rejection antigens both of viral (gp70) and nonviral origin. Sponsored by the Danish Cancer Society. Supported by the Kankerfonds van de Algemene Spaar-en Lijfrentekas. The SC-1 cell line was originally provided by contract E-73-2001-N01 within the Special Virus-Cancer Program NIH, USPHS, through the courtesy of Walter A. Nelson-Rees, Naval Biomedical Research Laboratory, Oakland, California, and Wallace P. Rowe, Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland. The financial support of the Daell Foundation, the Schepler Foundation, the Jorgen Holm Foundation and the Danish National Research Foundation is gratefully acknowledged.     

Cadherin-11 Mediates Contact Inhibition of Locomotion during Xenopus Neural Crest Cell Migration

Collective cell migration is an essential feature both in embryonic development and cancer progression. The molecular mechanisms of these coordinated directional cell movements still need to be elucidated. The migration of cranial neural crest (CNC) cells during embryogenesis is an excellent model for collective cell migration in vivo. These highly motile and multipotent cells migrate directionally on defined routes throughout the embryo. Interestingly, local cell-cell interactions seem to be the key force for directionality. CNC cells can change their migration direction by a repulsive cell response called contact inhibition of locomotion (CIL). Cell protrusions collapse upon homotypic cell-cell contact and internal repolarization leads to formation of new protrusions toward cell-free regions. Wnt/PCP signaling was shown to mediate activation of small RhoGTPase RhoA and inhibition of cell protrusions at the contact side. However, the mechanism how a cell recognizes the contact is poorly understood. Here, we demonstrate that Xenopus cadherin-11 (Xcad-11) mediated cell-cell adhesion is necessary in CIL for directional and collective migration of CNC cells. Reduction of Xcad-11 adhesive function resulted in higher invasiveness of CNC due to loss of CIL. Additionally, transplantation analyses revealed that CNC migratory behaviour in vivo is non-directional and incomplete when Xcad-11 adhesive function is impaired. Blocking Wnt/PCP signaling led to similar results underlining the importance of Xcad-11 in the mechanism of CIL and directional migration of CNC.     

Integrins alpha5beta1, alphavbeta1, and alphavbeta6 collaborate in squamous carcinoma cell spreading and migration on fibronectin

The expression of alphavbeta6 fibronectin/tenascin receptor integrin is induced in malignant transformation of oral epithelium. In this study, we demonstrate the contribution of alphavbeta6 as well as other fibronectin receptor integrins in squamous cell carcinoma (SCC) cell adhesion and migration. Of 11 SCC cell lines isolated from the head and neck area, 8 (73%) expressed alphavbeta6 integrin on the cell surface. Three cell lines were chosen for further functional experiments: 1 with relatively high, 1 with moderate, and 1 with minimal surface expression of alphavbeta6 integrin. In addition to alphavbeta6, all 3 cell lines expressed alpha5beta1 and alphavbeta1 fibronectin receptor integrins. Function-blocking experiments with inhibitory anti-integrin antibodies showed that all these three integrins were functional in SCC cell spreading on fibronectin. Integrin alphavbeta6, however, was not used as a primary but as an alternative fibronectin receptor by SCC cells, as the inhibitory anti-beta6 integrin antibody alone had no effect on spreading. In migration, however, alphavbeta6, alpha5beta1, and alphavbeta1 integrins were all used in cooperation. The presence of alphavbeta1 integrin in SCC cells is a novel finding as is its contribution to SCC cell migration. When one or two of these three receptors were blocked, the cells demonstrated an adaptive ability to remain migratory using integrins that were not targeted by antibodies. Utilization of a combination of receptors of different affinities may be beneficial for SCC cell migration versatility.     

Hepatocellular carcinoma model cell lines with two distinct migration modes

Migration is an essential feature of metastatic cancer cells. To understand how motility is regulated in hepatocellular carcinoma, we analyzed gene expression profiles of mouse model cell lines we established from transgenic mice carrying SV40 large T antigen. A non-motile HC9 cell line was isolated from mouse liver tumors, and two additional cell lines, HCM1 and HCM4, were derived from HC9 cells. We found that both HCM1 and HCM4 cells were substantially more migratory than HC9, and that HCM1 generated tumor nodules in nude mice. In contrast to HCM4 cells that exhibited mesenchymal cell-type gene expression similar to HC9 cells, HCM1 cells appeared to have undergone a mesenchymal-amoeboidal transition. Thus, HCM1 and HCM4 cells have distinct migration and gene expression patterns, and together with HC9 cells, they can serve as model cell lines for understanding how migration is acquired and controlled in hepatocellular carcinoma.     

Induction of pancreatic cancer cell migration by an autocrine epidermal growth factor receptor activation

Pancreatic cancer is characterized by aggressive local invasion and early metastasis formation. Active migration of the pancreatic cancer cells is essential for these processes. We have shown previously that the pancreatic cancer cells lines CFPAC1 and IMIM-PC2 show high migratory activity, and we have investigated herein the reason for this observation. Cell migration was assessed using a three-dimensional, collagen-based assay and computer-assisted cell tracking. The expression of receptor tyrosine kinases was determined by flow-cytometry and cytokine release was measured by an enzyme-linked immunoassay. Receptor function was blocked by antibodies or pharmacological enzyme inhibitors. Both cells lines express the epidermal growth factor receptor (EGFR) as well as its family-member ErbB2 and the platelet-derived growth factor receptor (PDGFR)α, whereas only weak expression was detected for ErbB3 and no expression of PDGFRβ. Pharmacological inhibition of the EGFR or ErbB2 significantly reduced the migratory activity in both cell lines, as did an anti-EGFR antibody. Interestingly, combination of the latter with an anti-PDGFR antibody led to an even more pronounced reduction. Both cell lines release detectable amounts of EGF. Thus, the high migratory activity of the investigated pancreatic cancer cell lines is due to autocrine EGFR activation and possibly of other receptor tyrosine kinases.     

Cadherin-2 Controls Directional Chain Migration of Cerebellar Granule Neurons

Long distance migration of differentiating granule cells from the cerebellar upper rhombic lip has been reported in many vertebrates. However, the knowledge about the subcellular dynamics and molecular mechanisms regulating directional neuronal migration in vivo is just beginning to emerge. Here we show by time-lapse imaging in live zebrafish (Danio rerio) embryos that cerebellar granule cells migrate in chain-like structures in a homotypic glia-independent manner. Temporal rescue of zebrafish Cadherin-2 mutants reveals a direct role for this adhesion molecule in mediating chain formation and coherent migratory behavior of granule cells. In addition, Cadherin-2 maintains the orientation of cell polarization in direction of migration, whereas in Cadherin-2 mutant granule cells the site of leading edge formation and centrosome positioning is randomized. Thus, the lack of adhesion leads to impaired directional migration with a mispositioning of Cadherin-2 deficient granule cells as a consequence. Furthermore, these cells fail to differentiate properly into mature granule neurons. In vivo imaging of Cadherin-2 localization revealed the dynamics of this adhesion molecule during cell locomotion. Cadherin-2 concentrates transiently at the front of granule cells during the initiation of individual migratory steps by intramembraneous transport. The presence of Cadherin-2 in the leading edge corresponds to the observed centrosome orientation in direction of migration. Our results indicate that Cadherin-2 plays a key role during zebrafish granule cell migration by continuously coordinating cell-cell contacts and cell polarity through the remodeling of adherens junctions. As Cadherin-containing adherens junctions have been shown to be connected via microtubule fibers with the centrosome, our results offer an explanation for the mechanism of leading edge and centrosome positioning during nucleokinetic migration of many vertebrate neuronal populations.     

Cyclic AMP-dependent protein kinase A plays a role in the directed migration of human keratinocytes in a DC electric field.

Skin wound healing requires epithelial cell migration for re-epithelialization, wound closure, and re-establishment of normal function. We believe that one of the earliest signals to initiate wound healing is the lateral electric field generated by the wound current. Normal human epidermal keratinocytes migrate towards the negative pole, representing the center of the wound, in direct currents of a physiological strength, 100 mV/mm. Virtually nothing is known about the signal transduction mechanisms used by these cells to sense the endogenous electric field. To elucidate possible protein kinase (PK) involvement in the process, PK inhibitors were utilized. Two important findings have been described. Firstly, addition of 50 nM KT5720, an inhibitor of PKA, resulted in a 53% percent reduction in the directional response of keratinocytes in the electric field, while not significantly affecting general cell motility. The reduction was dose-dependent, there was a gradual decrease in the directional response from 5 to 50 nM. Secondly, addition of 1 microM ML-7, a myosin light chain kinase inhibitor, resulted in an approximate 31% decrease in the distance the cells migrated without affecting directional migration. The PKC inhibitors GF109203X at 4 microM and H-7 at 20 microM and W-7, a CaM kinase inhibitor, did not significantly alter either directed migration or cell migration, although they all resulted in a slight reduction in directional migration. D-erythro-sphingosine at 15 microM, a PKC inhibitor, had virtually no effect on either migration distance or directed migration. These findings demonstrate that divergent kinase signaling pathways regulate general cell motility and sustained directional migration and highlight the complexity of the signal transduction mechanisms involved. The inhibitor studies described in this paper implicate a role for PKA in the regulation of the directional migratory response to applied electric fields, galvanotaxis.     

Lamellipodia-based migrations of larval epithelial cells are required for normal closure of the adult epidermis of Drosophila

Cell migrations are an important feature of animal development. They are, furthermore, essential to wound healing and tumour progression. Despite recent progress, it is still mysterious how cell migration is spatially and temporally regulated during morphogenesis and how cell migration is coordinated with other cellular behaviours to shape tissues and organs. The formation of the abdominal epithelium of Drosophila during metamorphosis provides an attractive system to study morphogenesis. Here, the diploid adult histoblasts replace the polyploid larval epithelial cells (LECs). Using in vivo 4D microscopy, I show that, besides apical constriction and apoptosis, the LECs undergo extensive coordinated migrations. The migrations follow a transition from a stationary (epithelial) to a migratory mode. The migratory behaviour is stimulated by autocrine Dpp signalling. Directed apical lamellipodia-like protrusions propel the cells. Initially, planar cell polarity determines the orientation of LEC migration. While LECs are migrating they also constrict apically, and changes in activity of the small GTPase Rho1 can favour one behaviour over the other. This study shows that the LECs play a more active role in morphogenesis than previously thought, with their migrations contributing to abdominal closure. It furthermore provides insights into how the migratory behaviour of cells is regulated during morphogenesis.     

Cellular and molecular mechanisms of cerebellar granule cell migration

The real-time observation of cell movement in brain slice preparations reveals that in the developing brain, postmitotic neurons alter their shape concomitantly with changes in the mode, direction, tempo, and rate of migration as they traverse different cortical layers. Although it has been hypothesized that orchestrated activities of multiple external cues and cell-cell contact are essential for controlling the cortical-layer-specific changes in cell migration, signaling mechanisms and external guidance cues related to the alteration of neuronal cell migration remain to be determined. In this article, we will first review recent studies on position-specific changes in granule cell behavior through different migratory terrains of the developing cerebellar cortex. We will then present possible roles for the coordinated activity of Ca2+ channels, NMDA type of glutamate receptors, and intracellular Ca2+ fluctuations in controlling cerebellar granule cell movement. Furthermore, we will discuss the crucial roles of brain-derived neurotrophic factor (BDNF), neuregulin (NRG), stromal cell-derived factor 1alpha (SDF-1alpha), ephrin-B2, and EphB2 receptor in providing directional cues promoting granule cell migration from the external granular layer (EGL) to the internal granular layer (IGL). Finally, we will demonstrate that endogenous somatostatin controls the migration of granule cells in a cortical layer-specific manner: Endogenous somatostatin accelerates granule cell movement near the birthplace within the EGL, but significantly slows down the movement near their final destination within the IGL.     

Evolutionary genetics of partial migration – the threshold model of migration revis(it)ed

Partial migration is a common and widespread phenomenon in animal populations. Even though the ecological causes for the evolution and maintenance of partial migration have been widely discussed, the consequences of the genetics underlying differences in migration patterns have been little acknowledged. Here, I revise current ideas on the genetics of partial migration and identify open questions, focussing on migration in birds. The threshold model of migration describing the inheritance and phenotypic expression of migratory behaviour is strongly supported by experimental results. As a consequence of migration being a threshold trait, high levels of genetic variation can be preserved, even under strong directional selection. This is partly due to strong environmental canalization. This cryptic genetic variation may explain rapid de novo evolution of migratory behaviour in resident populations and the high prevalence of partial migration in animal populations. To date the threshold model of migration has been tested only under laboratory conditions. For obtaining a more realistic representation of migratory behaviour in the wild, the simple threshold model needs to be extended by considering that the threshold of migration or the liability may be modified by environmental effects. This environmental threshold model is valid for both facultative and obligate migration movements, and identifies genetic accommodation as an important process underlying evolutionary change in migration status. Future research should aim at identifying the major environmental variables modifying migration propensity and at determining reaction norms of the threshold and liability across variation in these variables.     

Cell cycle of neural crest cells in the early migratory stage in vivo

Abstract. The fact that directional migration of neural crest cells (NCC) in vivo occurs in narrow pathways at high cell density, together with our preliminary results showing their high proliferative behaviour, supports the view that a 'population pressure' could be an important factor in the mechanism of early dispersion of NCC.
The purpose of this work was to establish the cranial proliferative pattern of chick embryo NCC during their early migratory stage in vivo . Growth rates and parameters of cell cycle were obtained from cell populations at several cephalic levels by means of autoradiography after labelling with [³H]dT. The labelled cell index of NCC (Forebrain, 0.288; Midbrain, 0.206; and Hindbrain, 0.134) was significantly greater than in other cells populations (e.g. for the neural tube cells: 0.085, 0.030, and 0.031, respectively). The cell generation time was the shortest in NCC (16 h), compared to ectoderm (33 h), mesoderm (58 h) and endoderm (72 h). The duration of the cell cycle phases for NCC were: M, 0.29 h; G₁, 11.23 h; S, 3.40 h; and G₂, 1.02 h.
These quantitative results show that NCC have the greatest proliferative rate in young chick embryos. In relation to cranial regions, the data are consistent with the idea that, in the early migratory phase of this cell population in vivo , migration is in part driven by population pressure.