Mad1 influences interphase nucleoplasm organization and chromatin regulation in Drosophila

• Published in: Open biology Vol. 8; no. 10
• Main Authors: Raich, Natacha, Mahmoudi, Souhir, Emre, Doruk, Karess, Roger E.
• Format: Journal Article
• Language: English
• Published: England Royal Society 17.10.2018; The Royal Society
• Subjects: Animals; Cell Behavior; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Cell Nucleus - metabolism; Cellular Biology; chromatin; Chromatin - metabolism; Cysteine Endopeptidases - genetics; Cysteine Endopeptidases - metabolism; Drosophila melanogaster - genetics; Drosophila melanogaster - metabolism; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; Interphase - physiology; Life Sciences; Male; mitosis; Nuclear Pore - metabolism; nuclear pore complex; Nuclear Pore Complex Proteins - genetics; Nuclear Pore Complex Proteins - metabolism; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; polycomb; Primary Cell Culture; Spermatocytes - cytology; Spermatocytes - metabolism; spindle assembly checkpoint; tpr; nuclear pore complex; Polycomb; chromatin; mitosis; spindle assembly checkpoint; Tpr; Subject Area: cellular biology/genetics Keywords: chromatin
• DOI: 10.1098/rsob.180166
• ISSN: 2046-2441

The Drosophila Mad1 spindle checkpoint protein helps organize several nucleoplasmic components, and flies lacking Mad1 present changes in gene expression reflecting altered chromatin conformation. In interphase, checkpoint protein Mad1 is usually described as localizing to the inner nuclear envelope by binding the nucleoporin Tpr, an interaction believed to contribute to proper mitotic regulation. Whether Mad1 has other nuclear interphase functions is unknown. We found in Drosophila that Mad1 is present in nuclei of both mitotic and postmitotic tissues. Three proteins implicated in various aspects of chromatin organization co-immunoprecipitated with Mad1 from fly embryos: Mtor/Tpr, the SUMO peptidase Ulp1 and Raf2, a subunit of a Polycomb-like complex. In primary spermatocytes, all four proteins colocalized in a previously undescribed chromatin-associated structure called here a MINT (Mad1-containing IntraNuclear Territory). MINT integrity required all four proteins. In mad1 mutant spermatocytes, the other proteins were no longer confined to chromatin domains but instead dispersed throughout the nucleoplasm. mad1 flies also presented phenotypes indicative of excessive chromatin of heterochromatic character during development of somatic tissues. Together these results suggest that Drosophila Mad1, by helping organize its interphase protein partners in the nucleoplasm, contributes to proper chromatin regulation.