Pleiotropic Functions of the Chromodomain-Containing Protein Hat-trick During Oogenesis in Drosophila melanogaster

Special Nuclear Structures in the Germinal Vesicle of the Common Frog with Emphasis on the So-Called Karyosphere Capsule

The karyosphere (karyosome) is a structure that forms in the oocyte nucleus-germinal vesicle (GV)-at the diplotene stage of meiotic prophase due to the assembly of all chromosomes in a limited portion of the GV. In some organisms, the karyosphere has an extrachromosomal external capsule, the marker protein of which is nuclear F-actin. Despite many years of theories about the formation of the karyosphere capsule (KC) in the GV of the common frog Rana temporaria, we present data that cast doubt on its existence, at least in this species. Specific extrachromosomal strands, which had been considered the main elements of the frog's KC, do not form a continuous layer around the karyosphere and, according to immunogold labeling, do not contain structural proteins, such as actin and lamin B. At the same time, F-actin is indeed noticeably concentrated around the karyosphere, creating the illusion of a capsule at the light microscopy/fluorescence level. The barrier-to-autointegration factor (BAF) and one of its functional partners-LEMD2, an inner nuclear membrane protein-are not localized in the strands, suggesting that the strands are not functional counterparts of the nuclear envelope. The presence of characteristic strands in the GV of R. temporaria late oocytes may reflect an excess of SMC1 involved in the structural maintenance of diplotene oocyte chromosomes at the karyosphere stage, since SMC1 has been shown to be the most abundant protein in the strands. Other characteristic microstructures-the so-called annuli, very similar in ultrastructure to the nuclear pore complexes-do not contain nucleoporins Nup35 and Nup93, and, therefore, they cannot be considered autonomous pore complexes, as previously thought. Taken together, our data indicate that traditional ideas about the existence of the R. temporaria KC as a special structural compartment of the GV are to be revisited.

Somatic Clonal Analyses Using FLP/FRT and MARCM System to Understand Notch Signaling Mechanism and Its Regulation

Notch signaling regulates an array of developmental decisions and has been implicated in a multitude of diseases, including cancer over the past a few decades. The simplicity and versatility of the Notch pathway in Drosophila make it an ardent system to study Notch biology, its regulation, and functions. In this chapter, we highlight the use of two powerful techniques, namely, FLP/FRT and MARCM in the study of Notch signaling. These mosaic analysis techniques are powerful tools to analyze gene functions in different biological processes. The section briefly explains the principle and the protocols with suitable examples.

Polyploidy in development and tumor models in Drosophila

Polyploidy, a cell status defined as more than two sets of genomic DNA, is a conserved strategy across species that can increase cell size and biosynthetic production, but the functional aspects of polyploidy are nuanced and vary across cell types. Throughout Drosophila developmental stages (embryo, larva, pupa and adult), polyploid cells are present in numerous organs and help orchestrate development while contributing to normal growth, well-being and homeostasis of the organism. Conversely, increasing evidence has shown that polyploid cells are prevalent in Drosophila tumors and play important roles in tumor growth and invasiveness. Here, we summarize the genes and pathways involved in polyploidy during normal and tumorigenic development, the mechanisms underlying polyploidization, and the functional aspects of polyploidy in development, homeostasis and tumorigenesis in the Drosophila model.

Regulation of notch signaling by a chromatin modeling protein Hat-trick

Notch signaling plays pleiotropic role in astounding variety of cellular processes including cell fate determination, differentiation, proliferation and apoptosis. The increasingly complex regulatory mechanisms of Notch signaling account for the multitude of functions exhibited by Notch during development. We identified Hat-trick (Htk), a DNA binding protein, as an interacting partner of Notch-ICD in a yeast two-hybrid screen and their physical interaction was further validated by co-immunoprecipitation experiments. htk genetically interacts with Notch pathway components in trans-heterozygous combinations. Loss of htk function in htk mutant somatic clones showed down-regulation of Notch targets, whereas over-expression of htk caused ectopic expression of Notch target, without affecting the level of Notch protein. Immunocytochemical analysis has demonstrated that Htk co-localizes with over-expressed Notch-ICD in the same nuclear compartment. We have shown here that Htk cooperates with Notch-ICD and Suppressor of Hairless to form activation complex and binds to the regulatory sequences of Notch downstream targets, Enhancer of Split complex genes to direct their expression. Taken together, our results suggest a novel mode of regulation of Notch signaling by a chromatin modeling protein Htk.