Quantitative microscopy uncovers ploidy changes during mitosis in live Drosophila embryos and their effect on nuclear size

Evaluation of chromatin mesoscale organization

Chromatin organization in the nucleus represents an important aspect of transcription regulation. Most of the studies so far focused on the chromatin structure in cultured cells or in fixed tissue preparations. Here, we discuss the various approaches for deciphering chromatin 3D organization with an emphasis on the advantages of live imaging approaches.

The Enigma of Centriole Loss in the 1182-4 Cell Line

The Drosophila melanogaster cell line 1182-4, which constitutively lacks centrioles, was established many years ago from haploid embryos laid by females homozygous for the maternal haploid (mh) mutation. This was the first clear example of animal cells regularly dividing in the absence of this organelle. However, the cause of the acentriolar nature of the 1182-4 cell line remained unclear and could not be clearly assigned to a particular genetic event. Here, we detail historically the longstanding mystery of the lack of centrioles in this Drosophila cell line. Recent advances, such as the characterization of the mh gene and the genomic analysis of 1182-4 cells, allow now a better understanding of the physiology of these cells. By combining these new data, we propose three reasonable hypotheses of the genesis of this remarkable phenotype.

ELUCIDATING NUCLEAR SIZE CONTROL IN THE XENOPUS MODEL SYSTEM

Background.

Nuclear size is a tightly regulated cellular feature. Mechanisms that regulate nuclear size and the functional significance of this regulation are largely unknown. Nuclear size and morphology are often altered in many diseases, such as cancer. Therefore, understanding the mechanisms that regulate nuclear size is crucial to provide insight into the role of nuclear size in disease.

Scope and Approach.

The goal of this review is to summarize the most recent studies about the mechanisms and functional significance of nuclear size control using the Xenopus model system. First, this review describes how Xenopus egg extracts, embryos, and embryo extracts are prepared and used in scientific research. Next, the review focuses on the mechanisms and functional effects of proper nuclear size control that have been learned using the Xenopus system.

Key Findings and Conclusions.

Xenopus is an excellent in vivo and in vitro experimental platform to study mechanisms of nuclear size control. Given its close evolutionary relationship with mammals and that most cellular processes and pathways are highly conserved between Xenopus and humans, the Xenopus system has been a valuable tool to advance biomedical research. Some of the mechanisms that regulate nuclear size include components of nuclear import such as importin α and NTF2, nuclear lamins, nucleoporins, proteins that regulate the morphology of the endoplasmic reticulum, and cytoskeletal elements.