hold up is required for establishment of oocyte positioning, follicle cell fate and egg polarity and cooperates with Egfr during Drosophila oogenesis

Expression pattern of immunoglobulin superfamily members in the silkworm, Bombyx mori

Immunoglobulin superfamily (IgSF) proteins are involved in cell adhesion, cell communication and immune functions. In this study, 152 IgSF genes containing at least one immunoglobulin (Ig) domain were predicted in the Bombyx mori silkworm genome. Of these, 145 were distributed on 25 chromosomes with no genes on chromosomes 16, 18 and 26. Multiple sequence alignments and phylogenetic evolution analysis indicated that IgSFs evolved rapidly. Gene ontology (GO) annotation indicated that IgSF members functioned as cellular components and in molecular functions and biological processes. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis suggested that IgSF proteins were involved in signal transduction, signaling molecules and interaction, and cell communication. Microarray-based expression data showed tissue expression for 136 genes in anterior silkgland, middle silkgland, posterior silkgland, testis, ovary, fat body, midgut, integument, hemocyte, malpighian tubule and head. Expression pattern of IgSF genes in the silkworm ovary and midgut was analyzed by RNA-Seq. Expression of 105 genes was detected in the ovary in strain Dazao. Expression in the midgut was detected for 74 genes in strain Lan5 and 75 genes in strain Ou17. Expression of 34 IgSF genes in the midgut relative to the actin A3 gene was significantly different between strains Lan5 and Ou17. Furthermore, 1 IgSF gene was upregulated and 1 IgSF gene was downregulated in strain Lan5, and 4 IgSF genes were upregulated and 2 IgSF genes were downregulated in strain Ou17 after silkworms were challenged with B. mori cypovirus (BmCPV), indicating potential involvement in the response to BmCPV-infection. These results provide an overview of IgSF family members in silkworms, and lay the foundation for further functional studies.

Bazooka regulates microtubule organization and spatial restriction of germ plasm assembly in the Drosophila oocyte

Localization of the germ plasm to the posterior of the Drosophila oocyte is required for anteroposterior patterning and germ cell development during embryogenesis. While mechanisms governing the localization of individual germ plasm components have been elucidated, the process by which germ plasm assembly is restricted to the posterior pole is poorly understood. In this study, we identify a novel allele of bazooka (baz), the Drosophila homolog of Par-3, which has allowed the analysis of baz function throughout oogenesis. We demonstrate that baz is required for spatial restriction of the germ plasm and axis patterning, and we uncover multiple requirements for baz in regulating the organization of the oocyte microtubule cytoskeleton. Our results suggest that distinct cortical domains established by Par proteins polarize the oocyte through differential effects on microtubule organization. We further show that microtubule plus-end enrichment is sufficient to drive germ plasm assembly even at a distance from the oocyte cortex, suggesting that control of microtubule organization is critical not only for the localization of germ plasm components to the posterior of the oocyte but also for the restriction of germ plasm assembly to the posterior pole.

dSTAM expression pattern during wild type and mutant egg chamber development in D. melanogaster

STAM (signal-transducing adaptor molecule) is a protein highly conserved from yeast to mammals. In Drosophila melanogaster the basic molecular architecture of the protein is comprised of a N-terminal VHS domain, an ubiquitin-interacting motif and a central Src homology-3 domain. In this paper we examine the expression pattern of the stam gene and the localisation of the STAM protein during D. melanogaster oogenesis. Its transcript is present throughout egg chamber development in all germ-line cells, including the oocyte. dSTAM is firstly detected in germarial region 2, where the protein is present in the newly formed germ-line cysts and is mainly accumulated into the oocyte. As oogenesis proceeds, dSTAM is enriched in the perinuclear region of the nurse cells and is also found in the somatic polar follicular cells. In the oocyte, the protein is more abundant posteriorly and becomes restricted to the posterior pole just before disappearing at stage 10b. We show that dSTAM localisation is unaffected in the oocyte of grk mutant egg chambers, indicating that it is not dependent on the polarity of the microtubule network. In contrast, dSTAM distribution is remarkably altered in cup mutant oocytes where the protein accumulates in a round central spot and never reaches the posterior pole.

The JIL-1 kinase interacts with lamin Dm0 and regulates nuclear lamina morphology of Drosophila nurse cells

We have used a yeast two-hybrid screen to identify lamin Dm0 as an interaction partner for the nuclear JIL-1 kinase. This molecular interaction was confirmed by GST-fusion protein pull-down assays and by co-immunoprecipitation experiments. Using deletion construct analysis we show that a predicted globular domain of the basic region of the COOH-terminal domain of JIL-1 was sufficient for mediating the molecular interactions with lamin Dm0. A reciprocal analysis with truncated lamin Dm0 constructs showed that the interaction with JIL-1 required sequences in the tail domain of lamin Dm0 that include the Ig-like fold. Further support for a molecular interaction between JIL-1 and lamin Dm0 in vivo was provided by genetic interaction assays. We show that nuclear positioning and lamina morphology were abnormal in JIL-1 mutant egg chambers. The most common phenotypes observed were abnormal nurse cell nuclear lamina protrusions through the ring canals near the oocyte, as well as dispersed and mislocalized lamin throughout the egg chamber. These phenotypes were completely rescued by a full-length JIL-1 transgenic construct. Thus, our results suggest that the JIL-1 kinase is required to maintain nuclear morphology and integrity of nurse cells during oogenesis and that this function may be linked to molecular interactions with lamin Dm0.

Selection of initial conditions for recursive production of multicellular organisms

The development of a multicellular organism is a dynamic process. Starting from one or a few cells, the organism becomes a set of cells with different types that form well-determined patterns. It is rather surprising that differentiation in cell types and formation of controlled patterns are compatible, because the former gives morphogenetic diversification whereas the latter implies recursive production of a cell ensemble, reducing individual differences. We studied this problem by taking a simple cell model with intracellular reaction dynamics of chemical concentrations, cell-cell interactions, and increase in cell numbers. We observed successive differentiation from a cell type with diverse chemicals and chaotic concentration dynamics to cell types with oscillatory or fixed-point dynamics, leading to morphogenetic diversity in a spatial pattern. We further show that, by starting from an initial object consisting of both the former cell type with diverse chemicals and the latter differentiated cell type, the recursive production of a multicellular organism with morphogenetic diversity is possible. By relating the former type to a cell in the vegetal pole and the latter to one in the animal pole, classic experimental results with separation of blastomeres in sea urchin eggs are coherently explained, while some predictions are made for in vitro morphogenesis from embryonic stem cells.

EGF receptor signaling in Drosophila oogenesis

The spatial regulation of Egfr activity in the follicular epithelium of the ovary is achieved by the localization of its ligand, Gurken, within the germline. The final distribution of Gurken within the oocyte appears to be specified both by the localization of the gurken RNA and by regulation of Gurken protein accumulation, possibly at the level of translation. Localized activation of the Egfr distinguishes certain subpopulations of follicle cells, thereby generating asymmetry within the follicular epithelium. In early oogenesis, Egfr activation in posterior follicle cells defines the AP polarity of the egg chamber, and in midoogenesis restriction of Egfr activity to dorsal follicle cells determines DV polarity. A number of factors required downstream of the Egfr have been identified, but the mechanism by which the observed patterning of the follicular epithelium is achieved remains unclear. The dynamic expression patterns of some of these targets suggest that the initial Gurken-Egfr signal at the dorsal side of the follicular epithelium mediates an initial distinction between dorsal and ventral follicle cells and also initiates subsequent refinement processes that determine the final pattern of cell fates. In the dorsal follicle cells, this refinement appears to involve interactions between Egfr targets and may also involve feedback regulation of Egfr activity such that the profile of Egfr activity is modulated over time. In addition, the initial Gurken-Egfr signal negatively regulates the functional domain of another patterning process that governs the establishment of the DV axis of the developing embryo.