Overexpression of hNRG1 type III in all neurons leads to the ectopic migration of Schwann cells into the spinal cord. (A-K2) Images from in vivo time-lapse movies. Schwann cells are marked by the Foxd3:GFP transgene (green) and oligodendrocytes and motoneurons are marked by Olig2:dsRed (red). Numbers at top right denote time (minutes) elapsed since the start of the movie. (A-C) Schwann cells (carets) along motor nerves undergo little movement in the control embryo; asterisks mark motor nerves on the contralateral side. (D-I) Embryos overexpressing hNRG1 type III in all neurons. The open arrowhead follows a Schwann cell that migrates up a motor nerve and into the spinal cord; the white arrowhead follows a Schwann cell that divides and produces one daughter that moves into the spinal cord; and blue and purple asterisks follow Schwann cells already present in the spinal cord as they migrate along spinal axons. (J,K) Lateral views of single scans from in vivo time-lapse movies of control (J) and transgenic (K) embryos at 125 minutes. (J2,K2) Orthogonal view of the yz plane indicated by the vertical red lines in J and K. The open arrowhead marks the Schwann cell that is tracked by the open arrowhead in D-I. (L,M) Excess Schwann cells (arrows) are present along motor nerves of embryos overexpressing hNRG1 type III (M) as compared with control embryo (L) at 2 dpf. Anterior is to the left, dorsal is up. Comparable regions over the yolk extension were imaged. Embryos were genotyped after imaging. Scale bars: 50 μm in A-I,L-M; 20 μm in J,K.
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