Biology subjects

Nsamba, E. T.

Publications and source records attributed to Nsamba, E. T..

4 recordsLinked to original sources

bioRxiv2025

Differential contributions of β tubulin isotypes to acentrosomal oocyte meiosis in C. elegans

Oocyte meiotic spindles must achieve bipolarity and segregate chromosomes in the absence of centrosomes. Here we use high-resolution immunofluorescence microscopy and live imaging to investigate the differential contributions of {beta}-tubulin isotypes (TBB-1 and TBB-2) to assembly and function of acentrosomal spindles in Caenorhabditis elegans oocytes. By combining strains with altered {beta}-tubulin isotype composition with mutations affecting microtubule-crosslinking motor KLP-18 and/or mutations affecting katanin-mediated microtubule severing, we show that TBB-1 and TBB-2 make distinct contributions to promoting spindle bipolarity. Further, by measuring multiple spindle features in wild-type and {beta}-tubulin isotype substitution strains, we reveal contributions of isotype composition to spindle morphology, kinetics of anaphase chromosome separation and maintenance of spindle structural integrity under stress. Together, our data support a model in which {beta}-tubulin isotype composition helps to maintain a balance between microtubule crosslinking and severing activities during oocyte meiosis. We further propose that this balance is crucial for establishing spindle bipolarity, maintaining spindle structures, and modulating the dynamics of chromosome separation.

cell biology↗

bioRxiv2025

Active maintenance of meiosis-specific chromosome structures in C. elegans by the deubiquitinase DUO-1

Meiotic prophase is characterized by a dynamic program in which germ cells undergo a complex series of associations and dissociations of protein complexes that drive assembly, remodeling, and disassembly of meiosis-specific chromosome structures and dramatic changes in chromosome compaction. Failure to properly coordinate these processes can result in improper chromosome segregation, producing aneuploid gametes and inviable zygotes. Here, we investigate the roles of C. elegans DUO-1, an ortholog of mammalian ubiquitin-specific proteases USP26 and USP29, in mediating these dynamic chromosomal events during meiotic prophase. Cytological analyses of duo-1 null mutants indicate that loss of DUO-1 function leads to impaired assembly of synaptonemal complexes (SCs), loss of integrity of meiotic chromosome axes, ineffective homolog pairing, premature separation of sister chromatids, and late-prophase chromosome decompaction. Further, SC instability in duo-1 mutants correlates with depletion of REC-8 cohesin complexes and is accompanied by massive accumulation of early DSB repair intermediates. By using a dual-AID-tagged allele to deplete DUO-1 during meiotic development, we demonstrate that DUO-1 is continually required throughout meiotic prophase progression, to promote proper axis/SC assembly in early prophase, to maintain axis/SC stability during the late pachytene stage, and to promote/maintain chromosome compaction at the end of meiotic prophase. Together, our data reveal that meiotic chromosome structure and meiosis-specific chromosome architecture require active maintenance throughout meiotic prophase, and that this maintenance is necessary for successful meiosis.

developmental biology↗

bioRxiv2025

Tubulin isotypes contribute opposing properties to balance anaphase spindle morphogenesis

Faithful chromosome segregation requires proper function of the mitotic spindle, which is built from, and depends on, the coordinated regulation of many microtubules and the activities of molecular motors and MAPs. In addition, microtubules themselves are assembled from multiple variants, or isotypes of - and {beta}-tubulin, yet whether they mediate the activities of motors and MAPs required for proper spindle function remains poorly understood. Here, we use budding yeast to reveal that -tubulin isotypes regulate opposing outward- and inward-directed forces in the spindle midzone that facilitate optimal spindle elongation and length control. Moreover, we show that the isotypes mediate balanced spindle forces by differentially localizing the antagonistic force generators Cin8 (kinesin-5) and Kar3 (kinesin-14) to interpolar microtubules. Our results reveal new roles for tubulin isotypes in orchestrating motor and MAP activities and provide insights into how forces in the spindle are properly calibrated to ensure proper mitotic spindle morphogenesis.

cell biology↗

bioRxiv2023

Uncovering the multi-step process of stable microtubule bundle formation upon entry into quiescence

Cells fine-tune microtubule assembly in both space and time, to give rise to distinct edifices with specific cellular functions. In proliferating cells, microtubules are highly dynamics, and proliferation cessation often leads to their stabilization. One of the most stable microtubule structures identified to date is the nuclear bundle assembled in quiescent yeast. In this report, we characterize the original multistep process driving the assembly of this structure. This Aurora B-dependent mechanism follows a precise temporality that relies on the sequential actions of kinesin-14, kinesins-5 and involves both microtubule-kinetochore and kinetochore-kinetochore interactions. Upon quiescence exit, the microtubule bundle is disassembled via a cooperative process involving kinesin-8 and its full disassembly is required prior to cells re-entry into proliferation. Overall, our study provides the first description, at the molecular scale, of the entire life cycle of a stable microtubule structure in vivo, and sheds light on its physiological function.

cell biology↗