HCP-1 plays a primary role in promoting central spindle MT assembly. (A) Schematic of kinetochore (KT)-dependent central spindle MT assembly in the one-cell C. elegans embryo. Top: CLS-2 recruitment to the KTs in metaphase. Bottom: Localization to the spindle midzone in anaphase, where it promotes central spindle MT assembly. (B) Schematic of line scan analysis of central spindle MT fluorescence intensity; white dashed line outlines the embryo. (C) Left: Representative time-lapse images of GFP::TBB-2^β-tubulin-expressing (green) and mCherry::H2B-expressing (magenta) embryos undergoing the first mitotic cell division; see Video 4. hcp-1Δ; hcp-2(RNAi) embryos with (red) and without (maroon) chromosome bi-orientation and metaphase plate formation. White arrows, no central spindle MTs. Right: Quantification of central spindle MT intensity 30 s post-chromosome segregation on sum projections of all Z-planes. Individual (thin lines) and average (bold lines) line scans are shown for each genotype. n is listed to the right of each graph [n = 13 control(RNAi), n = 8 hcp-1Δ; hcp-2(RNAi) no metaphase plate, n = 9 hcp-1Δ; hcp-2(RNAi) with metaphase plate, n = 12 hcp-1Δ, n = 12 hcp-2Δ, n = 11 spd-1(oj5ts), and n = 10 zen-4(or153ts)]. Average levels in controls are shown on each graph for reference (gray). Error bars represent the SEM; scale bars, 10 µm.