Biomedical subjects

Hilde Janssens

Publications and source records attributed to Hilde Janssens.

6 recordsLinked to original sources

PubMed2006

A role for Phospholipase D in Drosophila embryonic cellularization.

BACKGROUND: Cellularization of the Drosophila embryo is an unusually synchronous form of cytokinesis in which polarized membrane extension proceeds in part through incorporation of new membrane via fusion of apically-translocated Golgi-derived vesicles. RESULTS: We describe here involvement of the signaling enzyme Phospholipase D (Pld) in regulation of this developmental step. Functional analysis using gene targeting revealed that cellularization is hindered by the loss of Pld, resulting frequently in early embryonic developmental arrest. Mechanistically, chronic Pld deficiency causes abnormal Golgi structure and secretory vesicle trafficking. CONCLUSION: Our results suggest that Pld functions to promote trafficking of Golgi-derived fusion-competent vesicles during cellularization.

Animals↗

PubMed2006

Quantitative and predictive model of transcriptional control of the Drosophila melanogaster even skipped gene.

Here we present a quantitative and predictive model of the transcriptional readout of the proximal 1.7 kb of the control region of the Drosophila melanogaster gene even skipped (eve). The model is based on the positions and sequence of individual binding sites on the DNA and quantitative, time-resolved expression data at cellular resolution. These data demonstrated new expression features, first reported here. The model correctly predicts the expression patterns of mutations in trans, as well as point mutations, insertions and deletions in cis. It also shows that the nonclassical expression of stripe 7 driven by this fragment is activated by the protein Caudal (Cad), and repressed by the proteins Tailless (Tll) and Giant (Gt).

Animals↗

PubMed2006

Results of compensatory extraocular muscle surgery after macular translocation.

PURPOSE: Macular translocation is an optional surgical treatment for age-related macular degeneration. However, this technique induces postoperative torsional complaints and surgical counterrotation of the globe is mandatory. The purpose of this study is to report the effect of compensatory extraocular muscle surgery upon the torsional complaints in patients who underwent a macular translocation procedure. DESIGN: The pre- and postoperative data on the first 35 patients in our department who underwent a counterrotation procedure after macular translocation surgery are reviewed. METHODS: From November 2001 to January 2005, 35 patients underwent a macular translocation procedure, with subsequent extraocular muscle surgery to counterrotate the eye. Three types of rectus muscle transposition procedures were used: full-tendon transposition of two opposite rectus muscles, "crossed" half-tendon transposition of all rectus muscles ('split & cross' procedure), and "uncrossed" half-tendon transposition of all rectus muscles ('split & neighbor cross' procedure). In the majority of patients these procedures were associated with oblique muscle surgery. RESULTS: With the selected procedures, retinal excyclodeviations are easier to correct then retinal incyclodeviations. In our hands, full-tendon transposition of two opposite rectus muscles with or without associated oblique muscle surgery, never corrects more than 30 degrees. 'Split & cross' procedures combined with oblique muscle surgery are sufficient for retinal excyclodeviations of 30-45 degrees and for incyclodeviations of up to 30 degrees; 'split & neighbor cross' procedures combined with oblique muscle surgery are sufficient for retinal excyclodeviations of 45-65 degrees and for incyclodeviations of up to 40 degrees . CONCLUSIONS: The effect of the various procedures appears to be predictable. It is possible to select a surgical procedure as a function of the amount of retinal cyclodeviation.

Adult↗

PubMed2005

Regulation of phototransduction responsiveness and retinal degeneration by a phospholipase D-generated signaling lipid.

Drosophila melanogaster phototransduction proceeds via a phospholipase C (PLC)-triggered cascade of phosphatidylinositol (PI) lipid modifications, many steps of which remain undefined. We describe the involvement of the lipid phosphatidic acid and the enzyme that generates it, phospholipase D (Pld), in this process. Pld(null) flies exhibit decreased light sensitivity as well as a heightened susceptibility to retinal degeneration. Pld overexpression rescues flies lacking PLC from light-induced, metarhodopsin-mediated degeneration and restores visual signaling in flies lacking the PI transfer protein, which is a key player in the replenishment of the PI 4,5-bisphosphate (PIP2) substrate used by PLC to transduce light stimuli into neurological signals. Altogether, these findings suggest that Pld facilitates phototransduction by maintaining adequate levels of PIP2 and by protecting the visual system from metarhodopsin-induced, low light degeneration.

Animals↗

PubMed2005

A high-throughput method for quantifying gene expression data from early Drosophila embryos.

We describe an automated high-throughput method to measure protein levels in single nuclei in blastoderm embryos of Drosophila melanogaster by means of immunofluorescence. The method consists of a chain of specific algorithms assembled into an image processing pipeline. This pipeline transforms a confocal scan of an embryo stained with fluorescently tagged antibodies into a text file. This text file contains a numerical identifier for each nucleus, the coordinates of its centroid, and the average concentrations of three proteins in that nucleus. The central algorithmic component of the method is the automatic identification of nuclei by edge detection with the use of watersheds as an error-correction step. This method provides high-throughput quantification at cellular resolution.

Algorithms↗

PubMed2004

Dynamic control of positional information in the early Drosophila embryo.

Morphogen gradients contribute to pattern formation by determining positional information in morphogenetic fields. Interpretation of positional information is thought to rely on direct, concentration-threshold-dependent mechanisms for establishing multiple differential domains of target gene expression. In Drosophila, maternal gradients establish the initial position of boundaries for zygotic gap gene expression, which in turn convey positional information to pair-rule and segment-polarity genes, the latter forming a segmental pre-pattern by the onset of gastrulation. Here we report, on the basis of quantitative gene expression data, substantial anterior shifts in the position of gap domains after their initial establishment. Using a data-driven mathematical modelling approach, we show that these shifts are based on a regulatory mechanism that relies on asymmetric gap-gap cross-repression and does not require the diffusion of gap proteins. Our analysis implies that the threshold-dependent interpretation of maternal morphogen concentration is not sufficient to determine shifting gap domain boundary positions, and suggests that establishing and interpreting positional information are not independent processes in the Drosophila blastoderm.

Animals↗