Dorothea Godt

Cadherins in embryonic and neural morphogenesis

Cadherins not only maintain the structural integrity of cells and tissues but also control a wide array of cellular behaviours. They are instrumental for cell and tissue polarization, and they regulate cell movements such as cell sorting, cell migration and cell rearrangements. Cadherins may also contribute to neurite outgrowth and pathfinding, and to synaptic specificity and modulation in the central nervous system.

Drosophila oocyte localization is mediated by differential cadherin-based adhesion

In a Drosophila follicle the oocyte always occupies a posterior position among a group of sixteen germline cells. Although the importance of this cell arrangement for the subsequent formation of the anterior–posterior axis of the embryo is well documented, the molecular mechanism responsible for the posterior localization of the oocyte was unknown. Here we show that the homophilic adhesion molecule DE-cadherin mediates oocyte positioning. During follicle biogenesis, DE-cadherin is expressed in germline (including oocyte) and surrounding follicle cells, with the highest concentration of DE-cadherin being found at the interface between oocyte and posterior follicle cells. Mosaic analysis shows that DE-cadherin is required in both germline and follicle cells for correct oocyte localization, indicating that germline–soma interactions may be involved in this process. By analysing the behaviour of the oocyte in follicles with a chimaeric follicular epithelium, we find that the position of the oocyte is determined by the position of DE-cadherin-expressing follicle cells, to which the oocyte attaches itself selectively. Among the DE-cadherin positive follicle cells, the oocyte preferentially contacts those cells that express higher levels of DE-cadherin. On the basis of these data, we propose that in wild-type follicles the oocyte competes successfully with its sister germline cells for contact to the posterior follicle cells, a sorting process driven by different concentrations of DE-cadherin. This is, to our knowledge, the first in vivo example of a cell-sorting process that depends on differential adhesion mediated by a cadherin.

The large Maf factor Traffic Jam controls gonad morphogenesis in Drosophila

Interactions between somatic and germline cells are critical for the normal development of egg and sperm. Here we show that the gene traffic jam (tj) produces a soma-specific factor that controls gonad morphogenesis and is required for female and male fertility. tj encodes the only large Maf factor in Drosophila melanogaster, an orthologue of the atypical basic Leu zipper transcription factors c-Maf and MafB/Kreisler in vertebrates. Expression of tj occurs in somatic gonadal cells that are in direct contact with germline cells throughout development. In tj mutant gonads, somatic cells fail to inter-mingle and properly envelop germline cells, causing an early block in germ cell differentiation. In addition, tj mutant somatic cells show an increase in the level of expression for several adhesion molecules. We propose that tj is a critical modulator of the adhesive properties of somatic cells, facilitating germline–soma interactions that are essential for germ cell differentiation.

Cell sorting in animal development: signalling and adhesive mechanisms in the formation of tissue boundaries

The organisation of the animal body into distinct tissues requires adhesive mechanisms that promote and maintain the physical segregation, the sorting, of different cell populations. Signals that control differential cell affinities across tissue boundaries have been identified, including Hedgehog, Notch, and EGF receptor signalling. Further, several examples demonstrate that cell sorting in vivo can be driven by Eph/ephrin signalling and by the differential expression of cadherins that modulate cell adhesion and motility.

Drosophila melanogaster Cad99C, the orthologue of human Usher cadherin PCDH15, regulates the length of microvilli

Actin-based protrusions can form prominent structures on the apical surface of epithelial cells, such as microvilli. Several cytoplasmic factors have been identified that control the dynamics of actin filaments in microvilli. However, it remains unclear whether the plasma membrane participates actively in microvillus formation. In this paper, we analyze the function of Drosophila melanogaster cadherin Cad99C in the microvilli of ovarian follicle cells. Cad99C contributes to eggshell formation and female fertility and is expressed in follicle cells, which produce the eggshells. Cad99C specifically localizes to apical microvilli. Loss of Cad99C function results in shortened and disorganized microvilli, whereas overexpression of Cad99C leads to a dramatic increase of microvillus length. Cad99C that lacks most of the cytoplasmic domain, including potential PDZ domain–binding sites, still promotes excessive microvillus outgrowth, suggesting that the amount of the extracellular domain determines microvillus length. This study reveals Cad99C as a critical regulator of microvillus length, the first example of a transmembrane protein that is involved in this process.

Mutational analysis supports a core role for Drosophila α-Catenin in adherens junction function

α-catenin associates the cadherin–catenin complex with the actin cytoskeleton. α-catenin binds to β-catenin, which links it to the cadherin cytoplasmic tail, and F-actin, but also to a multitude of actin-associated proteins. These interactions suggest a highly complex cadherin–actin interface. Moreover, mammalian αE-catenin has been implicated in a cadherin-independent cytoplasmic function in Arp2/3-dependent actin regulation, and in cell signaling. The function and regulation of individual molecular interactions of α-catenin, in particular during development, are not well understood. We have generated mutations in Drosophila α-Catenin (α-Cat) to investigate α-Catenin function in this model, and to establish a setup for testing α-Catenin-related constructs in α-Cat-null mutant cells in vivo. Our analysis of α-Cat mutants in embryogenesis, imaginal discs and oogenesis reveals defects consistent with a loss of cadherin function. Compromising components of the Arp2/3 complex or its regulator SCAR ameliorate the α-Cat loss-of-function phenotype in embryos but not in ovaries, suggesting negative regulatory interactions between α-Catenin and the Arp2/3 complex in some tissues. We also show that the α-Cat mutant phenotype can be rescued by the expression of a DE-cadherin::α-Catenin fusion protein, which argues against an essential cytosolic, cadherin-independent role of Drosophila α-Catenin.

Expression profile of the cadherin family in the developing Drosophila brain

The Drosophila genome encodes 17 members of the cadherin family of adhesion molecules, which in vertebrates has been implicated in patterning the nervous system through cell and axon sorting. With only a few exceptions all cadherins show widespread expression in the larval brain. What expression patterns have in common is that 1) they are global, in the sense that all lineages of the central brain or optic lobe, or both, show expression; and 2) expression is stage‐specific: some cadherins are expressed only in primary neurons (located closest to the neuropile), others in early secondary neurons (near the brain surface), or primaries plus late secondaries. The Fat‐like cadherins, Fat and Dachsous, as well as Cad96Ca and Cad74A, are expressed in the epithelial optic lobe anlagen, which matches the widespread epithelial expression of these molecules in the embryo. DE‐cadherin is restricted to immature secondary neurons and glia; by contrast, DN‐cadherin, Flamingo, Cad87A, Cad99C, and Calsyntenin‐1 appear in differentiating primary neurons and, at a later stage, some or all secondary neurons. Cad87A is strongly enriched apically in epithelia and in neuronal dendrites. Fat‐like, Cad86C, Cad88C, Cad89D, and Dret are expressed ubiquitously in embryonic and larval brains at low or moderate levels. We conclude from this analysis that cadherins are likely to play a role in ‘generic’ neural functions, such as neurite fasciculation, branching, and synapse formation. J. Comp. Neurol. 506:469–488, 2008.

The germline stem cells of Drosophila melanogaster partition DNA non-randomly

The Immortal Strand Hypothesis proposes that asymmetrically dividing stem cells cosegregate chromatids to retain ancestral DNA templates. Using both pulse-chase and label retention assays, we show that non-random partitioning of DNA occurs in germline stem cells (GSCs) in the Drosophila ovary as these divide asymmetrically to generate a new GSC and a differentiating cystoblast. This process is disrupted when GSCs are forced to differentiate through the overexpression of Bag of Marbles, a factor that impels the terminal differentiation of cystoblasts. When Decapentaplegic, a ligand which maintains the undifferentiated state of GSCs, is expressed ectopically the non-random partitioning of DNA is similarly disrupted. Our data suggest asymmetric chromatid segregation is coupled to mechanisms specifying cellular differentiation via asymmetric stem cell division.

Loss of SPARC dysregulates basal lamina assembly to disrupt larval fat body homeostasis in Drosophila melanogaster

Background: SPARC is a collagen‐binding glycoprotein whose functions during early development are unknown. We previously reported that SPARC is expressed in Drosophila by hemocytes and the fat body (FB) and enriched in basal laminae (BL) surrounding tissues, including adipocytes. We sought to explore if SPARC is required for proper BL assembly in the FB. Results: SPARC deficiency leads to larval lethality, associated with remodeling of the FB. In the absence of SPARC, FB polygonal adipocytes assume a spherical morphology. Loss‐of‐function clonal analyses revealed a cell‐autonomous accumulation of BL components around mutant cells that include collagen IV (Col lV), Laminin, and Perlecan. Ultrastructural analyses indicate SPARC‐deficient adipocytes are surrounded by an aberrant accumulation of a fibrous extracellular matrix. Conclusions: Our data indicate a critical requirement for SPARC for the proper BL assembly in Drosophila FB. Since Col IV within the BL is a prime determinant of cell shape, the rounded appearance of SPARC‐deficient adipocytes is due to aberrant assembly of Col IV. Developmental Dynamics 244:540–552, 2015.

Cell dynamics and developmental bias in the ontogeny of a complex sexually dimorphic trait in Drosophila melanogaster

SUMMARY The Drosophila sex comb (SC) has been hailed as a powerful tool for integrative studies in development, evolution, and behavior, but its ontogeny is poorly understood, even in the model organism Drosophila melanogaster. Using 4D live imaging and other techniques, we carried out a detailed analysis of the cellular events that take place during the development of the SC. We showed that the comb and other contiguous bristle formations assemble from noncontiguous precursor cells, which join together through intercalation. Most of the rotation of the SC (which has a longitudinal orientation in D. melanogaster but is initially transverse) occurs after this stage, when the structure is a single unit. We have provided evidence that male‐specific convergent extension through cell rearrangement is responsible for both this rotation and another sexually dimorphic bristle trait. Contiguous bristle formations act as barriers to cell movement within the epithelium, and we demonstrated that a particularly rapid rotation of the proximal region of the comb is associated with the presence of a constricted area between a portion of the SC and a transverse row of contiguous bristle precursors. Our results suggest that the cell dynamics in the neighborhood of the SC may have biased its evolution.