Adaptive architecture and mechanoresponse of epithelial cells on a torus

Curvature is a geometric feature widely observed in the epithelia and critical to the performance of fundamental biological functions. Understanding curvature-related biophysical phenomena remains challenging partly owing to the difficulty of quantitatively tuning and measuring curvatures of interfacing individual cells. In this study, we prepared confluent wild-type Madin-Darby canine kidney cells on a torus structure presenting positive, zero, and negative Gaussian curvatures with a tubule diameter of 2-7 cells and quantified the mechanobiological characteristics of individual cells. Cells on the torus surface exhibited topological sensing ability both as an individual cell and collective cell organization. Both cell bodies and nuclei, adapted on the torus, exhibited local Gaussian curvature-dependent preferential orientation. The cells on the torus demonstrated significant adjustment in the nuclear area and exhibited asymmetric nuclear position depending on the local Gaussian curvature. Moreover, cells on top of the torus, where local Gaussian curvature is near zero, exhibited more sensitive morphological adaptations than the nuclei depending on the Gaussian curvature gradient. Furthermore, the spatial heterogeneity of intermediate filament proteins related to mechanoresponsive expression of the cell body and nucleus, vimentin, keratin and lamin A, revealed local Gaussian curvature as a key factor of cellular adaptation on curved surfaces.

A French collaborative survey of 272 fetuses with 22q11.2 deletion: ultrasound findings, fetal autopsies and pregnancy outcomes

OBJECTIVE

The 22q11.2 deletion (del22q11.2) is one of the most common microdeletions. We performed a collaborative, retrospective analysis in France of prenatal diagnoses and outcomes of fetuses carrying the del22q11.2.

METHODS

A total of 272 fetuses were included. Data on prenatal diagnosis, ultrasound findings, pathological features, outcomes and inheritance were analyzed.

RESULTS

The mean time of prenatal diagnosis was 25.6 ± 6 weeks of gestation. Most of the diagnoses (86.8%) were prompted by abnormal ultrasound findings [heart defects (HDs), in 83.8% of cases]. On fetal autopsy, HDs were again the most common disease feature, but thymus, kidney abnormalities and facial dysmorphism were also described. The deletion was inherited in 27% of cases. Termination of pregnancy (TOP) occurred in 68.9% of cases and did not appear to depend on the inheritance status. However, early diagnosis was associated with a higher TOP rate.

CONCLUSION

This is the largest cohort of prenatal del22q11.2 diagnoses. As in postnatally diagnosed cases, HDs were the most frequently observed abnormalities. However, thymus and kidney abnormalities and polyhydramnios should also be screened for in the prenatal diagnosis of del22q11.2. Only the time of diagnosis appeared to be strongly associated with the pregnancy outcome: the earlier the diagnosis, the higher the TOP rate.

Currarino Syndrome and HPE Microform Associated with a 2.7-Mb Deletion in 7q36.3 Excluding SHH Gene

Holoprosencephaly (HPE) is the most common forebrain defect in humans. It results from incomplete midline cleavage of the prosencephalon and can be caused by environmental and genetic factors. HPE is usually described as a continuum of brain malformations from the most severe alobar HPE to the middle interhemispheric fusion variant or syntelencephaly. A microform of HPE is limited to craniofacial features such as congenital nasal pyriform aperture stenosis and single central maxillary incisor, without brain malformation. Among the heterogeneous causes of HPE, point mutations and deletions in the SHH gene at 7q36 have been identified as well as extremely rare chromosomal rearrangements in the long-range enhancers of this gene. Here, we report a boy with an HPE microform associated with a Currarino syndrome. Array CGH detected a de novo 2.7-Mb deletion in the 7q36.3 region including the MNX1 gene, usually responsible for the Currarino triad but excluding SHH, which is just outside the deletion. This new case provides further evidence of the importance of the SHH long-range enhancers in the HPE spectrum.

Ordered stacking of F-actin layers and mixed lipid bilayers: a columnar liquid crystal

In this Letter, we show how the grooved helical structure of actin microfilaments (F-actin) interacting with mixed fluid lipid bilayers leads to handedness-independent 1D lipid bilayer undulations coupled to longitudinal in-plane ordering of the microfilaments. This longitudinal ordering is forced by the emerging in-plane compression and curvature energy terms of the straight 1D bilayer undulation wave fronts. Thereby, adjacent helices are set into registry along their long axis in their monolayer and π shifted between adjacent monolayers. An ordered composite multilamellar structure emerges by alternate stacking of these lipid bilayers and monolayers of F-actin. This two-dimensionally ordered system has the symmetries of a centered rectangular columnar liquid crystal, the straight 1D wave fronts playing the role of the classical molecular columns.

Orientation and polarity in collectively migrating cell structures: statics and dynamics

Collective cell migration is often characterized by the spontaneous onset of multicellular protrusions (known as fingers) led by a single leader cell. Working with epithelial Madin-Darby canine kidney monolayers we show that cells within the fingers, as compared with the epithelium, are well oriented and polarized along the main finger direction, which suggests that these cells actively migrate. The cell orientation and polarity decrease continuously from the tip toward the epithelium over a penetration distance of typically two finger lengths. Furthermore, laser photoablation experiments at various locations along these fingers demonstrate that the cells in the fingers are submitted to a tensile stress whose value is larger close to the tip. From a dynamical point of view, cells entering a finger gradually polarize on timescales that depend upon their particular initial position. Selective laser nanosurgery of the leader lamellipodium shows not only that these structures need a leader to progress, but that this leader itself is the consequence of a prior self-organization of the cells forming the finger. These results highlight the complex interplay between the collective orientation within the fingers and the mechanical action of the leader.

Fine mapping of re-arranged Y chromosome in three infertile patients with non-obstructive azoospermia/cryptozoospermia

BACKGROUND

Cytogenetically detectable aberrations of the Y chromosome, such as isodicentrics, rings or translocations are sometimes associated with male non-obstructive infertility. This report presents a detailed analysis of the clinical, cytogenetic and molecular data in three patients with a re-arranged Y chromosome.

METHODS

Patients A and B were azoospermic, whereas patient C was cryptozoospermic. All had a somatic mosaic karyotype including a population of 45,X cells and a cell line with a re-arranged Y chromosome. A molecular and FISH analysis of their re-arranged Y was undertaken, which specifically focussed on the presence of the AZFa, b and c regions.

RESULTS

The AZFa region was present in all the three patients. The AZFb and AZFc regions were absent in patients A and B, whereas, in patient C, the distal part of AZFb and the whole AZFc region were deleted. Moreover, in this patient, the AZF FISH analysis revealed a mosaicism for the size of the AZF deletion within the re-arranged Y, suggesting a progressive enlargement of the deletion during cell mitotic divisions.

CONCLUSIONS

This investigation allowed not only a more precise description of the abnormal Y, but also shed light on how this re-arrangement could be involved in the infertility phenotype.

Prenatal diagnosis of DMD in a female foetus affected by Turner syndrome

OBJECTIVES

We report on a prenatal diagnosis of DMD complicated by a 45,X karyotype that was revealed only in the chorionic villus long-term culture.

METHODS

Cytogenetic investigations were performed on both short-term (STC) and long-term cultures (LTC) of the chorionic villus sample. Familial segregation was performed using a panel of intragenic polymorphic markers, and multiplex PCR was used to characterize exonic deletion.

RESULTS

Investigations performed for sex determination after STC of the chorionic villus sample showed a normal karyotype 46,XX, while the karyotype performed after LTC revealed a homogeneous monosomy X. Cytogenetic analysis performed on amniotic fluid cells showed 45,X/46,XX mosaicism. Familial segregation analysis for DMD showed loss of heterozygosity for the STR49 marker in the DNA of the proband, her mother and the foetus. Dystrophin gene analysis on the 45,X cells led to the identification of a deletion of exon 50.

CONCLUSIONS

The report described a rare situation of monosomy X associated with a DMD genotype. The data confirmed the DMD carrier status of the proband and her mother and indicated that the foetus had a high risk to combine a Turner phenotype and DMD. This study illustrated the potential risk of using short-term culture of villi as the only source of biological material for prenatal diagnosis.

French multi-centric study of 2000 amniotic fluid interphase FISH analyses from high-risk pregnancies and review of the literature

This prospective and multi-centric study confirms the accuracy and the limitations of interphase FISH and shows that any cytogenetics laboratory can perform this technique. With regard to the technical approach, we think that slides must be examined by two investigators, because the scoring may be subjective. The main problem with the AneuVysion kit concerns the alpha satellite probes, and especially the chromosome 18 probe, which is sometimes very difficult to interpret because of the high variability of the size of the spots, and this may lead to false negative and uninformative cases. The best solution would be to replace these probes by locus-specific probes. Concerning clinical management, we offer interphase FISH only in very high-risk pregnancies or/and at late gestational age because of the cost of the test. We think that an aberrant FISH result can be used for a clinical decision when it is associated with a corresponding abnormal ultrasound scan. In other cases, most of the time, we prefer to wait for the standard karyotype.

Combined scanning optical coherence and two-photon-excited fluorescence microscopy

We demonstrate simultaneous imaging by optical coherence microscopy (OCM) and two-photon-excited (TPE) fluorescence microscopy. A mode-locked Ti:sapphire laser is focused and scanned in three dimensions through a fixed sample, generating both backscattered light and fluorescence light, which are independently detected. Both imaging modes provide rapid en-face imaging with submicrometer resolution. High-power delivery into the sample yields an OCM sensitivity in excess of 130 dB at 100-kHz pixel rates. Simultaneous imaging of cell nuclei with OCM and TPE is demonstrated in live drosophila embryos.

Surface-induced polymerization of actin

Living cells contain a very large amount of membrane surface area, which potentially influences the direction, the kinetics, and the localization of biochemical reactions. This paper quantitatively evaluates the possibility that a lipid monolayer can adsorb actin from a nonpolymerizing solution, induce its polymerization, and form a 2D network of individual actin filaments, in conditions that forbid bulk polymerization. G- and F-actin solutions were studied beneath saturated Langmuir monolayers containing phosphatidylcholine (PC, neutral) and stearylamine (SA, a positively charged surfactant) at PC:SA = 3:1 molar ratio. Ellipsometry, tensiometry, shear elastic measurements, electron microscopy, and dark-field light microscopy were used to characterize the adsorption kinetics and the interfacial polymerization of actin. In all cases studied, actin follows a monoexponential reaction-limited adsorption with similar time constants (approximately 10(3) s). At a longer time scale the shear elasticity of the monomeric actin adsorbate increases only in the presence of lipids, to a 2D shear elastic modulus of mu approximately 30 mN/m, indicating the formation of a structure coupled to the monolayer. Electron microscopy shows the formation of a 2D network of actin filaments at the PC:SA surface, and several arguments strongly suggest that this network is indeed causing the observed elasticity. Adsorption of F-actin to PC:SA leads more quickly to a slightly more rigid interface with a modulus of mu approximately 50 mN/m.

Population screening for aneuploidy using maternal age and ultrasound

The coexistence of an epidemiological register and a multidisciplinary centre for prenatal diagnosis promoted us to report data collected during six years (1990-1995) in Isère county on prenatally detected chromosomal aberrations. During the whole study period prenatal diagnosis strategy towards chromosome aberrations was based solely on maternal age and ultrasound examination. Results showed a respective contribution of one-third/two-thirds for the two detection modes (maternal age/ultrasound signs). From 1990 to 1995 a significant increase in the proportion of prenatally detected autosomal aneuploidy was observed, from 52 per cent to 75 per cent (P < 0.001). This significant variation was mainly due to an increase in the proportion of prenatally detected trisomy 21 cases, and to an increase in the proportion of aberrations which were detected through first trimester ultrasound examination. The highest positive predictive values were observed for polymalformation, cardiac anomalies and cystic hygroma ultrasound signs (51 per cent, 21 per cent and 26 per cent, respectively). Our results for trisomy 21 are close to those obtained in other studies, even when prenatal strategies are different. Their interest lies in the fact that they can be considered as a reference level of prenatal diagnosis efficiency due to a strategy based on maternal age and ultrasound signs, a level which has to be taken into account when evaluating the benefits of additional serum screening policies in other studies.

Collaborative study of mosaic tetrasomy 12p or Pallister-Killian syndrome (nineteen fetuses or children)

The difficulties in the diagnosis of Pallister-Killian syndrome are illustrated in this study of nineteen fetuses and children. Diagnosis based on clinical appearance alone is often difficult due to the broad spectrum of clinical anomalies not specific to this syndrome. Due to mosaicism, it is altogether necessary to examine several tissues for the presence of tetrasomy 12p, including circulating lymphocytes in which mosaicism can be as low as 1-3%, amniocytes, chorionic cells and skin fibro-blasts in which mosaicism ranges from 6-100%. When highly suspected on ultrasound examination, the diagnosis recommends prenatal cytogenetic studies because survivors are severely mentally retarded. All the cases are sporadic with only a single preliminary report of recurrence. The cytogenetic diagnosis is therefore helpful in order to reassure family members in regard to genetic counseling.

Molecular analysis of antigen-independent adhesion forces between T and B lymphocytes

The low-affinity interactions underlying antigen recognition by T-cell receptors (TCRs) are thought to involve antigen-independent adhesion mechanisms. Using a hydrodynamic approach, we found that antigen-independent adhesion occurred between human B cells and resting T cells in a transient and temperature-dependent fashion. The mean cell-cell adhesion force was 0.32 x 10(-9) N and was generated by similar contributions (0.16 x 10(-9) N) of the LFA-1- and CD2-dependent adhesion pathways. After T-cell stimulation with a phorbol ester, the force contributed by LFA-1 was drastically increased, while that of CD2 was unaffected. We propose that weak receptor-mediated adhesion initiates antigen-independent intercellular contacts required for antigen recognition by the TCR and is upregulated following TCR engagement. The method used permits adhesion forces between living cells to be resolved at the molecular level and should prove valuable for the rapid assessment of interaction forces between various types of cells and cell-sized particles.

Physical mapping by FISH of the DiGeorge critical region (DGCR): involvement of the region in familial cases

We describe the relative ordering, by fluorescence in situ hybridization, of cosmid loci and translocation breakpoints in the DiGeorge syndrome (DGS) critical region of chromosome 22. This physical map enables us to define a large region, commonly deleted in a majority of affected patients, and the smallest deleted region which, when lost, is sufficient to produce DGS. In four instances, a similar large deleted region is observed in a familial context. In these pedigrees, the deletion is encountered in one parent with mild features of the disease.

New chamber for flow cytometric analysis over an extended range of stream velocity and application to cell adhesion measurements

When analyzed in a flow cytometer, particles are suddenly accelerated to high velocities (1-10 m.s-1) over very short distances. This feature is essential to obtain high analysis rates and low coincidence levels, but translates into very strong velocity gradients (greater than 10(5) s-1): particles experience strong hydrodynamic stresses that elongate them and tend to dissociate weakly associated complexes. In order to analyze fragile conjugates formed by heterotypic adhesion between two cell types, a flow cytometer was modified to make hydrodynamic stress not only much weaker but also adjustable. A new and easily adaptable flow cell was designed for the instruments of the FACS series; it provided satisfactory hydrodynamic conditions on a wide continuous range of flow rates. Accompanying electronic adaptations permitted standard analysis between 0.01 and 10 m.s-1. At 0.01 m.s-1, the velocity gradient roughly amounts to 50 s-1. Conjugates formed by the adhesion between human B and resting T lymphocytes, disrupted in conventional flow cytometers, could be detected and precisely quantified provided analysis velocity was kept below 0.1 m.s-1. We conclude that low velocity flow cytometry makes possible the quantification of weak intercellular adhesion phenomena, and is potentially useful for the future development of new biomechanical techniques and other applications.

Interaction of CD4 with HLA class II antigens and HIV gp120

We have developed a cellular adhesion assay in which B lymphocytes expressing HLA class II antigens form rosettes with COS cells expressing high levels of cell surface CD4 upon transient transfection with a CDM8-CD4 plasmid construct. The assay is specific, quantitative, and overcomes the difficulties encountered with a previously described system using an SV40 viral vector. Rosette formation was inhibited by a series of CD4- and HLA-DR-specific antibodies, as well as by human immunodeficiency virus (HIV) gp 120, and a synthetic peptide derived from part of its binding site for CD4 (amino acid residues 414-434), but not by a variety of other effectors, including several soluble CD4 derivatives. The comparison of this pattern of inhibition with those observed in other systems further emphasizes the great similarity, but incomplete identity, in the CD4 binding sites for HLA class II antigens and HIV gp120, and supports a model in which CD4 is considered as an allosteric servomodulator of T-cell adhesion and function which probably is induced to interact with HLA class II antigens when associated with the Tcr/CD3 complex.

Mutations in the D strand of the human CD4 V1 domain affect CD4 interactions with the human immunodeficiency virus envelope glycoprotein gp120 and HLA class II antigens similarly

CD4, a cell surface glycoprotein expressed primarily by T lymphocytes and monocytes, interacts with HLA class II antigens to regulate the immune response. In AIDS, CD4 is the receptor for the human immunodeficiency virus, which binds to CD4 through envelope glycoprotein gp120. Delineation of the ligand-binding sites of CD4 is necessary for the development of immunomodulators and antiviral agents. Although the gp120 binding site has been characterized in detail, much less is known about the class II binding site, and it is as yet uncertain whether they partially or fully overlap. To investigate CD4 binding sites, a cellular adhesion assay between COS cells transiently transfected with CD4 and B lymphocytes expressing HLA class II antigens has been developed that is strictly dependent on the CD4--class II interaction, quantitative, and highly reproducible. Mutants of CD4 expressing amino acids with distinct physicochemical properties at positions Arg-54, Ala-55, Asp-56, and Ser-57 in V1, the first extracellular immunoglobulin-like domain, have been generated and studied qualitatively and quantitatively for interaction with HLA class II antigens, for membrane expression, for the integrity of CD4 epitopes recognized by a panel of monoclonal antibodies, and for gp120 binding. The results obtained show that the mutations in this tetrapeptide, which forms the core of a synthetic peptide previously shown to have immunosuppressive properties, affect the two binding functions of CD4 similarly, lending support to the hypothesis that the human immunodeficiency virus mimicks HLA class II binding to CD4.

Regulation of T helper-B lymphocyte adhesion through CD4-HLA class II interaction

Antigen-independent adhesion of CD4+ T lymphocytes to Epstein-Barr virus (EBV)-transformed B cells is mediated by CD2/lymphocyte function-associated antigen (LFA)-3 and LFA-1/intracellular adhesion molecule (ICAM)-1. Although some anti-CD4 antibodies block the antigen-independent adhesion of CD4+ T lymphocytes, the CD4-HLA class II interaction does not appear to significantly contribute to the forces of cell adhesion since CD4+ T cells equally bind HLA class II+ and HLA class II- mutant B cells. In addition, conjugates formed between CD4+ T cells and HLA class II- B cells remain stable for at least 1 h while CD4+T/HLA class II+ B cell conjugate percentages promptly drop off. Down-regulation of CD4 or spontaneous low expression of CD4 also results in a persistance of conjugates formed with B cells. The role of the CD4-HLA class II interaction has been further studied by investigating the inhibitory effect of synthetic 12-mer peptides analogous to HLA class II and containing the Arg-Phe-Asp-Ser sequence conserved in the beta 1 domain. These peptides were previously found to inhibit HLA class II-restricted T cell responses, this sequence being thought to be involved in CD4-HLA class II interaction. These peptides block conjugate formation of CD4+ resting T cells or clones but not of CD8+ T cells, by interacting with the T cells as shown by preincubation experiments. Down-regulation of CD4 or spontaneous low expression results in the loss of the inhibitory activity. The peptide-mediated inhibition is neutralized by a soluble dimeric CD4 molecule. Alteration within the Arg-Phe-Asp-Ser sequence results in a significant loss of inhibition. It is thus proposed that the CD4-HLA class II interaction negatively regulates antigen-independent adhesion of T cells, this interaction involving the highly conserved Arg-Phe-Asp-Ser sequence in the HLA class II beta 1 sequence as a CD4-binding site.

A 140-kilodalton protein is released from cultured astrocytes by phosphatidylinositol phospholipase C

Astrocytes in culture synthesize a 140-kilodalton (140-kD) protein (protein 140) that is released into the medium on incubation with phosphatidylinositol phospholipase C. This molecule therefore belongs to the class of proteins anchored to the external side of the cell membrane through a glycolipid moiety. Protein 140 is present in astrocyte cultures derived from two different regions of the brain and is not expressed by neurons in vitro. It differs from neuronal cell adhesion molecule 120 or 140 and is probably identical to a protein of 140 kD present in C6 glioma cells.