Biology subjects

Hair, M.

Publications and source records attributed to Hair, M..

6 recordsLinked to original sources

bioRxiv2026

Ultrastructural dynamics of basal bodies during microgamete formation and fertilisation in Plasmodium

Cilia and flagella are microtubule-based organelles found in a wide range of eukaryotic organisms that form cilia and flagella are assembled from basal bodies. In the malaria parasite, eight flagellated microgametes are assembled from 8 basal bodies that form de novo as a single group (not next to a parent basal body) in the cytoplasm of microgametocytes extremely rapidly, in as little 8 minutes but is not synchronised. The flagellated microgametes exit from a microgametocyte, each consisting of an axoneme and a haploid nucleus. Fertilisation occurs via a HAP2-mediated fusion with the macrogamete. Despite the essential role of microgametes in malaria transmission and being the only flagellated stage, little is known about the process of basal body formation, biogenesis at the ultrastructure level and their role in fertilisation. We used dual axis serial section electron tomography (ssET) to reveal the unusual single microtubule structure of the basal body and discovered an associated electron dense basal body granule. Using whole cell reconstructions of microgametocytes, free microgametes and macrogametes by serial block face scanning electron microscopy (SBF-SEM), we discovered a deuterosome-like structure only present during the initial formation of 8 basal bodies that could be a nucleating platform for de novo basal body formation. Finally, we reveal that entry of the microgamete into the macrogamete occurs via directed event at a single point of entry with the basal body and granule leading entry. These discoveries highlight the essential functions of basal bodies from initial microgamete assembly to male-female gamete fertilisation.

cell biology↗

bioRxiv2026

Plasmodium Protein Kinase 2 is required for ookinete to oocyst transition, and parasite transmission by the mosquito.

Plasmodium spp., the parasites that are the causative agents of malaria, encode a repertoire of divergent protein kinases that coordinate essential processes including cell division and host cell invasion, yet the functions of many kinases are poorly defined. Plasmodium Protein Kinase 2 (PK2) is essential for asexual blood-stage proliferation and has been implicated in P. falciparum merozoite invasion of red blood cells. However, its role in the sexual stages of the Plasmodium life cycle responsible for transmission is unknown. Here, using live cell imaging, functional analyses, ultrastructure microscopy and phosphoproteomics, we demonstrate that PK2 has a significant role in the Plasmodium berghei life cycle in the mosquito. We show that PK2 is expressed in merozoites, ookinetes and sporozoites - the invasive stages of the parasite life cycle. A conditional knockdown approach revealed that PK2 is required for the ookinete to oocyst transition in the mosquito midgut, potentially associated with altered microneme positioning. Using haemocoel injection to bypass the midgut barrier revealed that PK2 is also required for sporozoite development after midgut invasion. Following PK2 knockdown, global proteome abundance was largely unaffected at 24 h post activation, whereas phosphoproteomics identified changes in phosphorylation of proteins linked to midgut traversal, parasite architecture, and gene regulation. These studies provide insight into the importance of PK2 function in Plasmodium sexual stages and parasite transmission through the mosquito, highlighting its essential function during the three invasive stages of the parasites life cycle.

microbiology↗

bioRxiv2025

A divergent Plasmodium NEK4 acts as a key regulator driving the early events of meiosis

Meiosis is a conserved yet evolutionarily varied process underpinning sexual reproduction in eukaryotes. In the malaria parasite Plasmodium, meiosis is unconventional: it occurs immediately after fertilisation (post-zygotic) and must be coordinated with the transformation of the zygote into a motile ookinete. The mechanisms synchronising these meiotic and morphogenetic programmes remain unknown. Here, we identify the Plasmodium berghei NIMA-related kinase NEK4 as a key regulator that couples meiotic initiation with zygote morphogenesis. Using ultrastructure expansion microscopy, we show that NEK4 accumulates at the microtubule-organising centre (MTOC) and the apical polar complex (APC) shortly after fertilisation, preceding the assembly of perinuclear and cortical microtubules. We reveal that Plasmodium zygotes undergo MTOC-associated nuclear migration, analogous to the meiotic nuclear movement in fission yeast. Deletion of the Pbnek4 gene results in complete developmental arrest: MTOC duplication and microtubule formation are blocked, chromatin remains uncondensed, and nuclear migration and cell polarity fail to establish. Transcriptomic and phosphoproteomic analyses reveal that absence of NEK4 causes a collapse in transcriptional and phosphoregulatory networks governing meiosis and cytoskeletal organisation, leading to reduced expression and phosphorylation of important players, including HOP1, REC8, and AP2-O. These findings establish NEK4 as a key regulator driving meiotic entry and zygote maturation.

microbiology↗

bioRxiv2024

Non canonical Sun1-Allan complex orchestrates nuclear envelope remodelling and Basal Body/MTOC Segregation during rapid mitosis in Plasmodium

Mitosis in eukaryotes involves reorganization of the nuclear envelope (NE) and microtubule-organizing centres (MTOCs). During male gametogenesis in Plasmodium, the causative agent of malaria, mitosis is exceptionally rapid and highly divergent. Within 8 min, the haploid male gametocyte genome undergoes three replication cycles (1N to 8N), while maintaining an intact NE. Axonemes assemble in the cytoplasm and connect to a bipartite MTOC-containing nuclear pole (NP) and cytoplasmic basal body, producing eight flagellated gametes. The mechanisms coordinating NE remodelling, MTOC dynamics, and flagellum assembly remain poorly understood. We identify the SUN1-ALLAN complex as a novel mediator of NE remodelling and bipartite MTOC coordination during Plasmodium male gametogenesis. SUN1, a conserved NE protein, localizes to dynamic loops and focal points at the nucleoplasmic face of the spindle poles. ALLAN, a divergent allantoicase, has a location like that of SUN1, and these proteins form a unique complex, detected by live-cell imaging, ultrastructural expansion microscopy, and interactomics. Deletion of either SUN1 or ALLAN genes disrupts nuclear MTOC organization, leading to basal body mis-segregation, defective spindle assembly, and impaired spindle microtubule-kinetochore attachment, but axoneme formation remains intact. Ultrastructural analysis revealed nuclear and cytoplasmic MTOC miscoordination, producing aberrant flagellated gametes lacking nuclear material. These defects block development in the mosquito and parasite transmission, highlighting the essential functions of this complex.

cell biology↗

bioRxiv2023

3D electron microscopy of the Leishmania mexicana cell cycle: Patterns of organelle duplication and segregation and their implications for parasite biology

The unicellular parasite Leishmania has a precisely defined cell architecture that is inherited by each subsequent generation, requiring a highly coordinated pattern of duplication and segregation of organelles and cytoskeletal structures. A framework of nuclear division and morphological changes is known from light microscopy, yet this has limited resolution and the intrinsic organisation of organelles within the cell body and their manner of duplication and inheritance is unknown. Using volume electron microscopy approaches, we have produced three-dimensional reconstructions of different promastigote cell cycle stages to give a spatial and quantitative overview of organelle positioning, division and inheritance. The first morphological indications seen in our dataset that a new cell cycle had begun were the assembly of a new flagellum, the duplication of the contractile vacuole and the increase in volume of the nucleus and kinetoplast. We showed that the progression of the cytokinesis furrow created a specific pattern of membrane indentations and sub-pellicular microtubule organisation indicates that is likely a preferred site of new microtubule insertion. The daughter cells retained these indentations in their cell body for a period post-abscission. By comparing cultured and sand fly derived promastigotes, we found an increase in the number and overall volume of lipid droplets in the promastigotes from the sand fly, reflecting a change in their metabolism to ensure transmissibility to the mammalian host. Our insights into the cell cycle mechanics of Leishmania will be invaluable for future molecular cell biology analyses of these important parasites.

cell biology↗

bioRxiv2023

Atypical flagella assembly and haploid genome coiling during male gamete formation in Plasmodium

Plasmodium spp. sexual reproduction occurs within the Anopheles mosquito and is essential for gametogenesis and onwards transmission to mammalian hosts. Upon activation, the male P. berghei gametocyte undergoes three rounds of inter-nuclear mitosis and assembles eight basal bodies and axonemes around the nucleus prior to ex-flagellation, resulting in 8 flagellated male gametes in 12-15 minutes. However there is little understanding of the 3D organisation of this rapid process of male gametogenesis. In this study we used serial block face scanning electron microscopy (SBF-SEM) and cellular electron tomography (ssET) of P. berghei microgametocytes to examine the 3D architecture of key structures during male gamete formation. Our data has revealed an exquisite organisation of axonemes coiling around the nucleus in opposite directions forming a central axoneme band in microgametocytes. Furthermore, we discovered that the nucleus of microgametes is tightly coiled around the axoneme in an exquisitely complex structure whose formation starts before microgamete emergence during ex-flagellation. Our discoveries of the detailed 3D organisation of the flagellated microgamete and the haploid genome highlights some of the atypical mechanisms of axoneme assembly and haploid genome organisation during male gamete formation in the malaria parasite Plasmodium spp.

cell biology↗