Site-Specific Expression of Gelatinolytic Activity during Morphogenesis of the Secondary Palate in the Mouse Embryo

Morphogenesis of the secondary palate in mammalian embryos involves two major events: first, reorientation of the two vertically oriented palatal shelves into a horizontal position above the tongue, and second, fusion of the two shelves at the midline. Genetic evidence in humans and mice indicates the involvement of matrix metalloproteinases (MMPs). As MMP expression patterns might differ from sites of activity, we used a recently developed highly sensitive in situ zymography technique to map gelatinolytic MMP activity in the developing mouse palate. At embryonic day 14.5 (E14.5), we detected strong gelatinolytic activity around the lateral epithelial folds of the nasopharyngeal cavity, which is generated as a consequence of palatal shelf elevation. Activity was concentrated in the basement membrane of the epithelial fold but extended into the adjacent mesenchyme, and increased in intensity with lateral outgrowth of the cavity at E15.5. Gelatinolytic activity at this site was not the consequence of epithelial fold formation, as it was also observed in Bmp7-deficient embryos where shelf elevation is delayed. In this case, gelatinolytic activity appeared in vertical shelves at the exact position where the epithelial fold will form during elevation. Mmp2 and Mmp14 (MT1-MMP), but not Mmp9 and Mmp13, mRNAs were expressed in the mesenchyme around the epithelial folds of the elevated palatal shelves; this was confirmed by immunostaining for MMP-2 and MT1-MMP. Weak gelatinolytic activity was also found at the midline of E14.5 palatal shelves, which increased during fusion at E15.5. Whereas MMPs have been implicated in palatal fusion before, this is the first report showing that gelatinases might contribute to tissue remodeling during early stages of palatal shelf elevation and formation of the nasopharynx.

Detection of gelatinolytic activity in developing basement membranes of the mouse embryo head by combining sensitive in situ zymography with immunolabeling

Genetic evidence indicates that the major gelatinases MMP-2 and MMP-9 are involved in mammalian craniofacial development. Since these matrix metalloproteinases are secreted as proenzymes that require activation, their tissue distribution does not necessarily reflect the sites of enzymatic activity. Information regarding the spatial and temporal expression of gelatinolytic activity in the head of the mammalian embryo is sparse. Sensitive in situ zymography with dye-quenched gelatin (DQ-gelatin) has been introduced recently; gelatinolytic activity results in a local increase in fluorescence. Using frontal sections of wild-type mouse embryo heads from embryonic day 14.5-15.5, we optimized and validated a simple double-labeling in situ technique for combining DQ-gelatin zymography with immunofluorescence staining. MMP inhibitors were tested to confirm the specificity of the reaction in situ, and results were compared to standard SDS-gel zymography of tissue extracts. Double-labeling was used to show the spatial relationship in situ between gelatinolytic activity and immunostaining for gelatinases MMP-2 and MMP-9, collagenase 3 (MMP-13) and MT1-MMP (MMP-14), a major activator of pro-gelatinases. Strong gelatinolytic activity, which partially overlapped with MMP proteins, was confirmed for Meckel's cartilage and developing mandibular bone. In addition, we combined in situ zymography with immunostaining for extracellular matrix proteins that are potential gelatinase substrates. Interestingly, gelatinolytic activity colocalized precisely with laminin-positive basement membranes at specific sites around growing epithelia in the developing mouse head, such as the ducts of salivary glands or the epithelial fold between tongue and lower jaw region. Thus, this sensitive method allows to associate, with high spatial resolution, gelatinolytic activity with epithelial morphogenesis in the embryo.

Intraperitoneal murine Echinococcus multilocularis infection induces differentiation of TGF-beta-expressing DCs that remain immature

Intraperitoneal larval infection (alveolar echinococcosis, AE) with Echinococcus multilocularis in mice impairs host immunity. Metacestode metabolites may modulate immunity putatively via dendritic cells. During murine AE, a relative increase of peritoneal DCs (pe-DCs) in infected mice (AE-pe-DCs; 4% of total peritoneal cells) as compared to control mice (naive pe-DCs; 2%) became apparent in our study. The differentiation of AE-pe-DCs into TGF-beta-expressing cells and the higher level of IL-4 than IFN-gamma/IL-2 mRNA expression in AE-CD4+pe-T cells indicated a Th2 orientation. Analysis of major accessory molecule expression on pe-DCs from AE-infected mice revealed that CD80 and CD86 were down-regulated on AE-pe-DCs, while ICAM-1(CD54) remained practically unchanged. Moreover, AE-pe-DCs had a weaker surface expression of MHC class II (Ia) molecules as compared to naive pe-DCs. The gene expression level of molecules involved in MHC class II (Ia) synthesis and formation of MHC class II (Ia)-peptide complexes were down-regulated. In addition, metacestodes excreted/secreted (E/S) or vesicle-fluid (V/F) antigens were found to alter MHC class II molecule expression on the surface of BMDCs. Finally, conversely to naive pe-DCs, an increasing number of AE-pe-DCs down-regulated Con A-induced proliferation of naive CD4+pe-T cells. These findings altogether suggested that TGF-beta-expressing immature AE-pe-DCs might play a significant role in the generation of a regulatory immune response within the peritoneal cavity of AE-infected mice.

Migration of immature mouse DC across resting endothelium is mediated by ICAM-2 but independent of beta2-integrins and murine DC-SIGN homologues

Immature dendritic cells (DC) reside in tissues where they initiate immune responses by taking up foreign antigens. Since DC have a limited tissue half-life, the DC pool in tissues has to be replenished constantly. This implies that precursor/immature DC must be able to cross non-activated endothelium using as yet unknown mechanisms. Here we show that immature, but not mature bone marrow-derived murine DC migrate across resting endothelial monolayers in vitro. We find that endothelial intercellular adhesion molecule-2 (ICAM-2) is a major player in transendothelial migration (TEM) of immature DC, accounting for at least 41% of TEM. Surprisingly, the ICAM-2-mediated TEM was independent of beta2-integrins, the known ICAM-2 ligands, since neither blocking of beta2-integrins with antibodies nor the use of CD18-deficient DC affected the ICAM-2-specific TEM. In humans, the C-type lectin DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN) was shown to interact with ICAM-2, suggesting a similar role in mice. However, we find that none of the murine DC-SIGN homologues mDC-SIGN, murine DC-SIGN-related molecule-1 (mSIGN-R1) and mSIGN-R3 is expressed on the surface of bone marrow-derived mouse DC. Taken together, this study shows that ICAM-2 strongly supports transmigration of immature DC across resting endothelium by interacting with ligands that are distinct from beta2-integrins and DC-SIGN homologues.

Targeting survivin via PI3K but not c-akt/PKB by anticancer drugs in immature neutrophils

Myelosuppression is the most common unwanted side effect associated with the administration of anticancer drugs, and infections remain a common cause of death in chemotherapy-treated patients. Several mechanisms of the cytotoxicity of these drugs have been proposed and may synergistically operate in a given cell. Survivin expression has been associated with cancer, but recent reports suggest that this molecule is also expressed in several immature and mature hematopoietic cells. Here, we provide evidence that treatment of immature neutrophils with anticancer drugs reduced endogenous survivin levels causing apoptosis. The anticancer drugs did not directly target survivin, instead they blocked the activity of phosphatidylinositol-3-OH kinase, which regulated survivin expression and apoptosis in these cells. Strikingly, and in contrast to other cells, this pathway did not involve the serine/threonine kinase c-akt/PKB. Moreover, in combination with anticancer drug therapy, rapamycin did not induce increased myelosuppression in an experimental lymphoma mouse model. These data suggest that drugs that block either c-akt/PKB or signaling molecules located distal to c-akt/PKB may preferentially induce apoptosis of cancer cells as they exhibit no cytotoxicity for immature neutrophils.

Epithelial transformations in the establishment of the blood-gas barrier in the developing chick embryo lung

The tall epithelium of the developing chick embryo lung is converted to a squamous one, which participates in formation of the thin blood-gas barrier. We show that this conversion occurred through processes resembling exocrine secretion. Initially, cells formed intraluminal protrusions (aposomes), and then transcellular double membranes were established. Gaps between the membranes opened, thus, severing the aposome from the cell. Alternatively, aposomes were squeezed out by adjacent cells or were spontaneously constricted and extruded. As a third mechanism, formation and fusion of severed vesicles or vacuoles below the aposome and their fusion with the apicolateral plasma membrane resulted in severing of the aposome. The atria started to form by progressive epithelial attenuation and subsequent invasion of the surrounding mesenchyme at regions delineated by subepithelial alpha-smooth muscle actin-positive cells. Further epithelial attenuation was achieved by vacuolation; rupture of such vacuoles with resultant numerous microfolds and microvilli, which were abscised to accomplish a smooth squamous epithelium just before hatching.

Expression patterns of neurexin-1 and neuroligins in brain and retina of the chick embryo: Neuroligin-3 is absent in retina

Neuroligins (NLs) constitute a family of cell-surface proteins that interact with neurexins (beta-Nxs), another class of neuronal cell-surface proteins, one of each class functioning together in synapse formation. The localization of the various neurexins and neuroligins, however, has not yet been clarified in chicken. Therefore, we studied the expression patterns of neurexin-1 (Nx-1) and neuroligin-1 and -3 during embryonic development of the chick retina and brain by reverse-transcriptase polymerase chain reaction (RT-PCR) and in situ hybridization (ISH). While neurexin-1 increased continuously in both brain and retina, the expression of both neuroligins was more variable. As shown by ISH, Nx-1 is expressed in the inner half retina along with differentiation of ganglion and amacrine cells. Transcripts of NL-1 were detected as early as day 4 and increased with the maturation of the different brain regions. In different brain regions, NL-1 showed a different time regulation. Remarkably, neuroligin-3 was entirely absent in retina. This study indicates that synaptogenetic processes in brain and retina use different molecular machineries, whereby the neuroligins might represent the more distinctly regulated part of the neurexin-neuroligin complexes. Noticeably, NL-3 does not seem to be involved in the making of retinal synapses.

Adiponectin as a marker of success in intracytoplasmic sperm injection/embryo transfer cycles

Adiponectin (Acrp30) is an adipose tissue-derived protein whose serum concentrations, in contrast to leptin, are reported to be negatively correlated to body mass. In spite of the comparatively high circulating adiponectin concentrations, this protein has not been studied in the context of assisted reproduction to date. The aim of this preliminary project was thus to examine the potential of adiponectin to serve as a marker for fertility. We compared adiponectin levels in serum before and after controlled ovarian hyperstimulation, as well as in follicular fluid (FF), between two groups: those with successful outcome (clinical pregnancies) and those with implantation failure. In the former, adiponectin concentrations were higher than in the negative outcome group; this difference was statistically significant (p < 0.05) in serum on the day of oocyte pick-up (OPU) as well as two or three days before OPU, but not in FF or in serum at the beginning of the stimulation phase. This finding adds a new perspective to the suggested but still controversial reduction in FF leptin concentrations in the positive outcome group, and may become a useful tool for early prediction of success of in vitro fertilization treatment for a given patient.

Microvascular endowment in the developing chicken embryo lung

In the current study, the contribution of the major angiogenic mechanisms, sprouting and intussusception, to vascular development in the avian lung has been demonstrated. Sprouting guides the emerging vessels to form the primordial vascular plexus, which successively surrounds and encloses the parabronchi. Intussusceptive angiogenesis has an upsurge from embryonic day 15 (E15) and contributes to the remarkably rapid expansion of the capillary plexus. Increased blood flow stimulates formation of pillars (the archetype of intussusception) in rows, their subsequent fusion and concomitant delineation of slender, solitary vascular entities from the disorganized meshwork, thus crafting the organ-specific angioarchitecture. Morphometric investigations revealed that sprouting is preponderant in the early period of development with a peak at E15 but is subsequently supplanted by intussusceptive angiogenesis by the time of hatching. Quantitative RT-PCR revealed that moderate levels of basic FGF (bFGF) and VEGF-A were maintained during the sprouting phase while PDGF-B remained minimal. All three factors were elevated during the intussusceptive phase. Immunohistoreactivity for VEGF was mainly in the epithelial cells, whereas bFGF was confined to the stromal compartment. Temporospatial interplay between sprouting and intussusceptive angiogenesis fabricates a unique vascular angioarchitecture that contributes to the establishment of a highly efficient gas exchange system characteristic of the avian lung.