Faculty Bibliography

Tudor domains are found in many organisms and have been implicated in protein-protein interactions in which methylated protein substrates bind to these domains. Here, we present evidence for the involvement of specific Tudor domains in germline development. Drosophila Tudor, the founder of the Tudor domain family, contains 11 Tudor domains and is a component of polar granules and nuage, electron-dense organelles characteristic of the germline in many organisms, including mammals. In this study, we investigated whether the 11 Tudor domains fulfil specific functions for polar granule assembly, germ cell formation and abdomen formation. We find that even a small number of non-overlapping Tudor domains or a substantial reduction in overall Tudor protein is sufficient for abdomen development. In stark contrast, we find a requirement for specific Tudor domains in germ cell formation, Tudor localization and polar granule architecture. Combining genetic analysis with structural modeling of specific Tudor domains, we propose that these domains serve as ;docking platforms' for polar granule assembly

The ability of organs such as the liver or the lymphoid system to maintain their original size or regain it after injury is well documented. However, little is known about how these organs sense that equilibrium is breached, and how they cease changing when homeostasis is reached. Similarly, it remains unclear how, during normal development, different cell types within an organ coordinate their growth. Here we show that during gonad development in the fruitfly Drosophila melanogaster the proliferation of primordial germ cells (PGCs) and survival of the somatic intermingled cells (ICs) that contact them are coordinated by means of a feedback mechanism composed of a positive signal and a negative signal. PGCs express the EGF receptor (EGFR) ligand Spitz, which is required for IC survival. In turn, ICs inhibit PGC proliferation. Thus, homeostasis and coordination of growth between soma and germ line in the larval ovary is achieved by using a sensor of PGC numbers (EGFR-mediated survival of ICs) coupled to a correction mechanism inhibiting PGC proliferation. This feedback loop ensures that sufficient numbers of PGCs exist to fill all the stem-cell niches that form at the end of larval development. We propose that similar feedback mechanisms might be generally used for coordinated growth, regeneration and homeostasis

OBJECTIVE: Clinical scales evaluating arm function after stroke are weak at detecting quality of movement. Therefore a new scale, the Motor Evaluation Scale for Upper Extremity in Stroke Patients (MESUPES), was developed, comprising 22 items pertaining to arm and hand performance. The scale was investigated for validity and unidimensionality using the Rasch measurement model, and for inter-rater reliability. SETTING: Twelve hospitals and rehabilitation centres in Belgium, Germany and Switzerland. PATIENTS: There were 396 patients (average age 63.38+/-12.89 years) in the Rasch study and 56 patients (average age 65.68+/-12.75 years) in the reliability study. MAIN MEASURES: The scale was examined on its fit to the Rasch model, thereby evaluating the scale's unidimensionality and validity. Differential item functioning was performed to test the stability of item hierarchy on several variables. Inter-rater reliability was examined with kappa values, weighted percentage agreement and intraclass correlation coefficients (ICC). RESULTS: Based on Rasch analysis, five items were removed. The MESUPES was divided in two tests: the MESUPES-arm test (8 items) and MESUPES-hand test (9 items). Both scales fitted the Rasch model. All items were stable among the subgroups of the sample. ICCs were 0.95 (95% confidence interval (CI) 0.91 -0.97) and 0.97 (95% CI 0.95-0.98) for the total score on arm and hand test respectively. The scale was also reliable at item level (weighted kappa 0.62 -0.79, weighted percentage agreement 85.71 -98.21). CONCLUSION: The MESUPES-arm and MESUPES-hand meet the statistical properties of reliability, validity and unidimensionality. Both tests provide a useful clinical and research tool to qualitatively evaluate arm and hand function during recovery after stroke.

Cyclins regulate progression through the cell cycle. Control of cyclin levels is essential in Drosophila oogenesis for the four synchronous divisions that generate the 16 cell germ line cyst and for ensuring that one cell in each cyst, the oocyte, is arrested in meiosis, while the remaining fifteen cells become polyploid nurse cells. Changes in cyclin levels could be achieved by regulating transcription, translation or protein stability. The proteasome limits cyclin protein levels in the Drosophila ovary, but the mechanisms regulating RNA turnover or translation remain largely unclear. Here, we report the identification of twin, a homolog of the yeast CCR4 deadenylase. We show that twin is important for the number and synchrony of cyst divisions and oocyte fate. Consistent with the deadenylase activity of CCR4 in yeast, our data suggest that Twin controls germ line cyst development by regulating poly(A) tail lengths of several targets including Cyclin A (CycA) RNA. twin mutants exhibit very low expression of Bag-of-marbles (Bam), a regulator of cyst division, indicating that Twin/Ccr4 activity is necessary for wild-type Bam expression. Lowering the levels of CycA or increasing the levels of Bam suppresses the defects we observe in twin ovaries, implicating CycA and Bam as downstream effectors of Twin. We propose that Twin/Ccr4 functions during early oogenesis to coordinate cyst division, oocyte fate specification and egg chamber maturation

In most organisms, primordial germ cells (PGCs) arise far from the region where somatic gonadal precursors (SGPs) are specified. Although PGCs in general originate as a single cluster of cells, the somatic parts of the gonad form on each site of the embryo. Thus, to reach the gonad, PGCs not only migrate from their site of origin but also split into two groups. Taking advantage of high-resolution real-time imaging, we show that in Drosophila melanogaster PGCs are polarized and migrate directionally toward the SGPs, avoiding the midline. Unexpectedly, neither PGC attractants synthesized in the SGPs nor known midline repellents for axon guidance were required to sort PGCs bilaterally. Repellent activity provided by wunen (wun) and wunen-2 (wun-2) expressed in the central nervous system, however, is essential in this migration process and controls PGC survival. Our results suggest that expression of wun/wun-2 repellents along the migratory paths provides faithful control over the sorting of PGCs into two gonads and eliminates PGCs left in the middle of the embryo

Lipid phosphates can act as signaling molecules to influence cell division, apoptosis, and migration. wunen and wunen2 encode Drosophila lipid phosphate phosphohydrolases, integral membrane enzymes that dephosphorylate extracellular lipid phosphates. wun and wun2 act redundantly in somatic tissues to repel migrating germ cells, although the mechanism by which germ cells respond is unclear. Here, we report that wun2 also functions in germ cells, enabling them to perceive the wun/wun2-related signal from the soma. Upon Wun2 expression, cultured insect cells dephosphorylate and internalize exogenously supplied lipid phosphate. We propose that Drosophila germ cell migration and survival are controlled by competition for hydrolysis of a lipid phosphate between germ cells and soma

RNApolII-dependent transcription is repressed in primordial germ cells of many animals during early development and is thought to be important for maintenance of germline fate by preventing somatic differentiation. Germ cell transcriptional repression occurs concurrently with inhibition of phosphorylation in the carboxy-terminal domain (CTD) of RNApolII, as well as with chromatin remodeling. The precise mechanisms involved are unknown. Here, we present evidence that a noncoding RNA transcribed by the gene polar granule component (pgc) regulates transcriptional repression in Drosophila germ cells. Germ cells lacking pgc RNA express genes important for differentiation of nearby somatic cells and show premature phosphorylation of RNApolII. We further show that germ cells lacking pgc show increased levels of K4, but not K9 histone H3 methylation, and that the chromatin remodeling Swi/Snf complex is required for a second stage in germ cell transcriptional repression. We propose that a noncoding RNA controls transcription in early germ cells by blocking the transition from preinitiation to transcriptional elongation. We further show that repression of somatic differentiation signals mediated by the Torso receptor-tyrosine kinase is important for germline development

3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCoAr) provides attractive cues to Drosophila germ cells, guiding them toward the embryonic gonad. However, it remains unclear how HMGCoAr mediates this attraction. In a genomic analysis of the HMGCoAr pathway, we found that the fly genome lacks several enzymes required for cholesterol biosynthesis, ruling out cholesterol and cholesterol-derived proteins as mediators of PGC migration. Genetic analysis of the pathway revealed that two enzymes, farnesyl-diphosphate synthase and geranylgeranyl-diphosphate synthase, required for the production of isoprenoids, act downstream of HMGCoAr in germ cell migration. Consistent with a role in geranylgeranylation, embryos deficient in geranylgeranyl transferase type I show germ cell migration defects. Our data, together with similar findings in zebrafish, implicate an isoprenylated protein in germ cell attraction. The specificity and evolutionary conservation of the HMGCoAr pathway for germ cells suggest that an attractant common to invertebrates and vertebrates guides germ cells in early embryos

In Drosophila, primordial germ cells (PGCs) are set aside from somatic cells and subsequently migrate through the embryo and associate with somatic gonadal cells to form the embryonic gonad. During larval stages, PGCs proliferate in the female gonad, and a subset of PGCs are selected at late larval stages to become germ line stem cells (GSCs), the source of continuous egg production throughout adulthood. However, the degree of similarity between PGCs and the self-renewing GSCs is unclear. Here we show that many of the genes that are required for GSC maintenance in adults are also required to prevent precocious differentiation of PGCs within the larval ovary. We show that following overexpression of the GSC-differentiation gene bag of marbles (bam), PGCs differentiate to form cysts without becoming GSCs. Furthermore, PGCs that are mutant for nanos (nos), pumilio (pum) or for signaling components of the decapentaplegic (dpp) pathway also differentiate. The similarity in the genes necessary for GSC maintenance and the repression of PGC differentiation suggest that PGCs and GSCs may be functionally equivalent and that the larval gonad functions as a 'PGC niche'

The passage of an individual's genome to future generations is essential for the maintenance of species and is mediated by highly specialized cells, the germ cells. Genetic studies in a number of model organisms have provided insight into the molecular mechanisms that control specification, migration and survival of early germ cells. Focusing on Drosophila, we will discuss the mechanisms by which germ cells initially form and remain transcriptionally silent while somatic cells are transcriptionally active. We will further discuss three separate attractive and repellent guidance pathways, mediated by a G-protein coupled receptor, two lipid phosphate phosphohydrolases, and isoprenylation. We will compare and contrast these findings with those obtained in other organisms, in particular zebrafish and mice. While aspects of germ cell specification are strikingly different between these species, germ cell specific gene functions have been conserved. In particular, mechanisms that sense directional cues during germ cell migration seem to be shared between invertebrates and vertebrates