Postembryonic Ventral Nerve Cord Development and Gonad Migration in Steinernema carpocapsae

Hung Xuan Bui; Nathan E. Schroeder

doi:10.21307/jofnem-2018-005

Figure 1

Lateral left view (anterior to left) fluorescent micrographs of J2 (top) and J1 (bottom) Steinernema carpocapsae following 4′, 6-diamidino-2-phenylindole (DAPI) staining. The ventral nerve cord (VNC) comprises a series of putative neurons extending from the retrovesicular ganglion (RVG) (arrowhead) to the preanal ganglion (PAG) (arrow) along the ventral edge of the animal. Between J1 and J2, there is a large increase in the number of VNC neuronal-like nuclei. Scale bar, 10 µm.

Figure 2

Cartoons of Caenorhabditis elegans (A) and Steinernema carpocapsae (B) gonads and lateral left view (anterior to left) micrograph of posterior S. carpocapsae gonad arm (C): differential interference contrast (DIC) alone (top); DIC color overlay (bottom). Unlike C. elegans, which undergoes stereotypical development to a ‘U-shaped’ gonad, the most common S. carpocapsae gonad shape does not include extensive migration along the ventral wall. As shown in the stitched DIC micrograph (C) (top) and with transparent color overlay (bottom), the gonad extends from the central region of the animal near the vulva (position indicated with straight arrow) and immediately extends to the dorsal side where it extends away from the mid-body. It eventually makes a u-turn (curved arrow) and then extends along the dorsal wall back to the mid-body where it then migrates back to the ventral wall. The posterior gonad arm typically wraps around the left side of the intestine, whereas the anterior arm typically wraps around the right side of the intestine. The proximal end of the gonad, including the uterus and spermathecal-uterine complex, is colored red. The distal end of the gonad following the turn includes the ovary and is colored blue. Scale bar, 50 µm.

Figure 3

Lateral left view (anterior to left) differential interference contrast (DIC) micrograph (top) and with transparent color overlay (bottom) of a 96 HET female Steinernema carpocapsae gonad posterior arm. The gonad morphology at 96 HET is similar to that seen at 72 HET. However, by 96 HET, numerous fertilized embryos are seen in the uterus (red). The spermathecal-uterine complex (green) is located at the farthest point away from the mid-body and contains a single oocyte (inset) surrounded by numerous sperm (arrowhead). The ovary (blue) is much longer than in 72 HET females, frequently extending beyond the mid-body plane. In this image, the distal tip cell of the anterior gonad arm (arrow) extends into the posterior half of the female. Scale bars, 50 µm (main figure) 10 µm (inset).

Figure 4

Cartoon depicting the variability in the gonad migration pattern among 72 HET Steinernema carpocapsae females that deviate from the most common phenotype seen in figure 2C. Numbers indicate the ratio of the particular gonad phenotype among the 28 females whose gonads were fully traced.

Figure 5

Lateral left views (anterior to left) of female gonad (red overlay) development in Steinernema carpocapsae at various time points. The gonad of newly hatched S. carpocapsae (A) contained four nuclei with two central larger nuclei and two smaller cap nuclei. By 25 HET (B), the number of nuclei in the gonad noticeably increased and began elongating along the ventral body wall. At 33 HET (C), the gonad extended toward the dorsal surface. Between 44 HET (D) and 54 HET (E), we observed an expansion of the gonad along the dorsal surface. Note that the anterior arm typically wraps around the right side of the intestine and is out of frame at this focal plane, whereas the posterior arm wraps around the left side. Scale bar, 50 µm.

Figure 6

Lateral right (A) and left (B) views of gonad (red) morphology in male Steinernema carpocapsae at 72 HET. In most males (A), the gonad migration pattern is similar to C. elegans. However, 30% of males examined have a gonad that never extends away from the ventral wall (B). Scale bar, 50 µm.

Stage	VNC neuron nuclei mean (range)	n
J1	19 (16-21)	50
J2	69 (50-76)	50
J3	76 (69-88)	46

Postembryonic Ventral Nerve Cord Development and Gonad Migration in Steinernema carpocapsae

Figures & Tables

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Figure 6

Ventral cord neurons of J1, J2, and J3 stage of Steinernema carpocapsae_

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