C. elegansCLASP/CLS-2 negatively regulates membrane ingression throughout the oocyte cortex and is required for polar body extrusion

Abstract

1 2 3 C. elegans CLASP/CLS-2 negatively regulates membrane ingression 4 throughout the oocyte cortex and is required for polar body extrusion 5 6 Aleesa 11 12 13 Short Title: Spindle structure and polar body extrusion 14 15 2 16 Abstract 17The requirements for oocyte meiotic cytokinesis during polar body extrusion are 18 not well understood. In particular, the relationship between the oocyte meiotic spindle 19 and polar body contractile ring dynamics remains largely unknown. We have used live 20 cell imaging and spindle assembly defective mutants lacking the function of 21 CLASP/CLS-2, kinesin-12/KLP-18, or katanin/MEI-1 to investigate the relationship 22 between meiotic spindle structure and polar body extrusion in C. elegans oocytes. We 23 show that spindle bipolarity and chromosome segregation are not required for polar 24 body contractile ring formation and chromosome extrusion in klp-18 mutants, but 25 oocytes with severe spindle assembly defects due to loss of CLS-2 or MEI-1 have 26 penetrant and distinct polar body extrusion defects: CLS-2 is required early for 27 contractile ring assembly or stability, while MEI-1 is required later for contractile ring 28 constriction. We also show that CLS-2 negatively regulates membrane ingression 29 throughout the oocyte cortex during meiosis I, and we explore the relationship between 30 global cortical dynamics and oocyte meiotic cytokinesis. 313 32 Author Summary 33The precursor cells that produce gametes-sperm and eggs in animals-have 34 two copies of each chromosome, one from each parent. These precursors undergo 35 specialized cell divisions that leave each gamete with only one copy of each 36 chromosome; defects that produce incorrect chromosome number cause severe 37 developmental abnormalities. In oocytes, these cell divisions are highly asymmetric, 38 with extra chromosomes discarded into small membrane bound polar bodies, leaving 39 one chromosome set within the much larger oocyte. How oocytes assemble the 40 contractile apparatus that pinches off polar bodies remains poorly understood. To better 41 understand this process, we have used the nematode Caenorhabditis elegans to 42 investigate the relationship between the bipolar structure that separates oocyte 43 chromosomes, called the spindle, and assembly of the contractile apparatus that 44 pinches off polar bodies. We used a comparative approach, examining this relationship 45 in three spindle assembly defective mutants. Bipolar spindle assembly and 46 chromosome separation were not required for polar body extrusion, as it occurred 47 normally in mutants lacking a protein called KLP-18. However, mutants lacking the 48 protein CLS-2 failed to assemble the contractile apparatus, while mutants lacking the 49 protein MEI-1 assembled a contractile apparatus that failed to fully constrict. We also 50 found that CLS-2 down-regulates membrane ingression throughout the oocyte surface, 51 and we explored the relationship between oocyte membrane dynamics and polar body 52 extrusion. 53 Introduction 54Oocyte meiosis co...

BUB-1 targets PP2A:B56 to regulate chromosome congression during meiosis I in C. elegans oocytes

“…Cytoplasmic Securin IFY-1 degradation proceeded at similar rates in wild type and LET-92depleted oocytes (Figure 1H,I; Video 3), indicating that APC/C activity is largely unperturbed in the absence of PP2A. Given the similarity of this phenotype to the depletion of CLASP orthologue CLS-2 (Dumont et al, 2010;Laband et al, 2017;Schlientz and Bowerman, 2020), we analysed the localisation of CLS-2 and detected no changes in CLS-2 levels throughout meiosis (Figure 1-figure supplement 2; Video 4).…”

“…During anaphase, chromosomes collapse into a small area where, in some cases, two chromosome masses were visible ( Figure 1C, yellow arrow). Interestingly, severe chromosome segregation defects do not necessarily lead to polar body extrusion (PBE) defects (Schlientz and Bowerman, 2020). In the absence of PP2Ac only 15% of oocytes achieved polar body extrusion ( Figure 1E, P<0.0001, Fisher's exact test).…”

BUB-1 targets PP2A:B56 to regulate chromosome congression during meiosis I inC. elegansoocytes

“…Movie 3), indicating that APC/C activity is largely unperturbed in the absence of PP2A. Given the similarity of this phenotype to the depletion of CLASP orthologue CLS-2 I (Dumont et al, 2010;Laband et al, 2017;Schlientz and Bowerman, 2020), we analysed the localisation of CLS-2 and detected no changes in CLS-2 levels throughout meiosis ( Figure S2; Supp Movie 4).…”

“…Interestingly, severe chromosome segregation defects do not necessarily lead to polar body extrusion (PBE) defects (Schlientz and Bowerman, 2020). In the absence of PP2Ac only 15% of oocytes achieved polar body extrusion ( Figure 1E, P<0.0001, Fisher's exact test).…”