Pole cells move slower in hypoxia.

<p>Selected frames from a time-lapse analysis show α-tubulin green fluorescent protein (α-tub-GFP) <i>Drosophila</i> embryos are exposed to hypoxia <b>(A-F)</b> and normoxia <b>(A’-F’)</b>, respectively. The pole cells migration time is 37 min for a normoxic embryo and 137min for a hypoxic embryo. Stars indicate the center of pole cell clusters. Scale Bar: 100<i>μ</i>m. <b>(G)</b> Pole cells migration time under hypoxia and normoxia.</p

Parameters and values used in the simulation.

<p>Parameters and values used in the simulation.</p

<i>engrailed</i> stripe migration was arrested under hypoxia and quickly resumed upon switching to normoxia.

<p><b>(A)</b> An embryo with a fully developed <i>engrailed</i> pattern was positioned under hypoxia. <b>(B-D)</b> After 245 min of imaging, the stripe migration did not occur. <b>(E)</b> The oxygen condition was changed from hypoxia to normoxia. <b>(F)</b> The stripe migration was captured 12 min after the oxygen condition inside the device was changed. <b>(G, H)</b> The embryo had continuous stripe migration with normal speed. Images were taken every 3 min. Scale bar, 100 μm. Arrows indicate the 9^th stripe location under hypoxia (red) and normoxia (blue).</p

Experimental setup and the quantification methods.

<p><b>(A and A’)</b> An illustration depicting the microfluidic channels and the positioning of the embryos in a microfluidic device, which is designed to establish the oxygen concentration gradients through microchannels with different infused gases. <b>(B)</b> The oxygen concentration profile inside the microfluidic device was measured. The oxygen concentration gradients at 0 μm and 180 μm above the gas emitting surface are plotted using 20 points rolling average, shown as blue and red lines, respectively. <b>(C)</b> The pole cell migration time was measured as the pole cells (white plate) move from 10% to 90% of their total migration distance. <b>(D)</b> An illustration shows two ventral stripes (10^th and 11^th) pass through the posterior (reference point: *) of the embryo body with a counter-clockwise migration as indicated by the pink arrow. The time difference is defined as the <i>engrailed</i> stripe migration time. A: anterior; D: dorsal side; P: posterior; V: ventral side. Scale bar: 100 μm. <b>(E and F)</b> <i>engrailed</i> patterns (14 stripes) are shown before (E) and after (F) the tail retraction. The 9^th-11^th stripes are labeled indicating the stripe migration.</p

Effect of localized hypoxia on <i>Drosophila</i> embryo development

<div><p>Environmental stress, such as oxygen deprivation, affects various cellular activities and developmental processes. In this study, we directly investigated <i>Drosophila</i> embryo development <i>in vivo</i> while cultured on a microfluidic device, which imposed an oxygen gradient on the developing embryos. The designed microfluidic device enabled both temporal and spatial control of the local oxygen gradient applied to the live embryos. Time-lapse live cell imaging was used to monitor the morphology and cellular migration patterns as embryos were placed in various geometries relative to the oxygen gradient. Results show that pole cell movement and tail retraction during <i>Drosophila</i> embryogenesis are highly sensitive to oxygen concentrations. Through modeling, we also estimated the oxygen permeability across the <i>Drosophila</i> embryonic layers for the first time using parameters measured on our oxygen control device.</p></div

<i>engrailed</i> stripe migration time under different oxygen levels.

<p><b>(A)</b> Data (red circles) showed every <i>engrailed</i> stripe migration time that measured at various oxygen conditions. The best-fit (least squares) curve (blue line) showed the delay on <i>engrailed</i> migration time when oxygen concentration dropped. <b>(B)</b> The extended best-fit curve (blue), combined with a horizontal asymptote line (dashed), showed the trend of the delay and the critical condition at 4.9% of oxygen, which could be the cutoff oxygen level that paused the germband shortening process.</p