Optical coherence tomography as a noninvasive 3D real time imaging tool for the rapid evaluation of phenotypic variations in insect embryonic development

Abstract

Noninvasive visualization of embryos at different development stages is crucial for the understanding of the basic developmental biology. It is therefore desirable to have an imaging tool capable of rapidly evaluating the effects of gene manipulation or genome editing in developing embryos for the studies of gene functions and genetic engineering. Here, we propose and demonstrate a novel use of optical coherence tomography (OCT) to noninvasively exam the embryonic development of the migratory locusts in real time with 3-dimensional (3D) view capability. In particular, we obtain the sufficiently high spatial resolution tomographic 2D and 3D images of live locust embryos throughout their development processes. We show that not only we are able to noninvasively observe all previously known forms of blastokinesis as an embryo develops, such as anatrepsis, katatrepsis, revolution, rotation and diapauses, and determine their precise occurring time or duration, but also discover an unreported rotation form we named "twist." In addition, with the OCT images we determined the exact occurring time of diapauses of the locusts from Tibetan plateau for the first time. Finally, we demonstrate that OCT systems can be used to rapidly capture the development defects of genetically modified embryos in which certain genes essential for embryonic development were suppressed by RNA interference. Our work shows that OCT is an enabling imaging tool with sufficient spatial resolution for the rapid evaluation of embryonic variations of small animals. K E Y W O R D S3D image, embryology, locust, optical coherence tomography Ya Su and Liya Wei contributed equally to this study.

Interactive effect of photoperiod and temperature on the induction and termination of embryonic diapause in the migratory locust

“…Approximately 7 days after the emergence of the migratory locust, damp sand with a 10%–20% moisture content was prepared at the bottom of the cages, and the eggs were collected every 24 h. Subsequently, the eggs were placed in distilled water and washed gently to remove debris and were then soaked in alcohol for a few seconds for sterilization. Finally, the eggs were placed in a culture dish containing gel and arranged in a consistent direction 21 . Half of these eggs were treated at 25 °C and the other half at 28 °C.…”

“…OCT (TEL210C1, Thorlabs, Germany) with a 1325 nm laser source was used to track the embryonic development of the migratory locust. The parameter settings referred to our previous study 21 . The system provided an A‐scan rate of 76 kHz, with a depth measurement range of approximately 7 mm in air and an axial spatial resolution of 12 μm in air.…”

“…Finally, the eggs were placed in a culture dish containing gel and arranged in a consistent direction. 21 Half of these eggs were treated at 25°C and the other half at 28°C. OCT was used to observe the development of the eggs.…”

“…The classical method is to treat eggs with sodium hypochlorite to check the embryonic development of locusts, leading to irreversible injury. We recently developed optical coherence tomography (OCT) technology as a noninvasive 3D real‐time imaging tool to track the total embryonic developmental progress of the migratory locust 21 . With this technology, the incidence of embryonic diapause and diapause termination can be accurately observed and recorded.…”

“…We recently developed optical coherence tomography (OCT) technology as a noninvasive 3D real-time imaging tool to track the total embryonic developmental progress of the migratory locust. 21 With this technology, the incidence of embryonic diapause and diapause termination can be accurately observed and recorded. In this study, we designed crossover experiments involving different photoperiods, temperatures, and treatment times to investigate the incidence of embryonic diapause and diapause termination in locusts using OCT technology.…”