Inhibitory neuron migration and IPL formation in the developing zebrafish retina.
Bottom Line: Finally, HCs, iACs and dACs each undergo cell type-specific migration.In contrast to current hypotheses, we find that most dACs send processes into the forming inner plexiform layer (IPL) before migrating through it and inverting their polarity.By imaging and quantifying the dynamics of HCs, iACs and dACs from birth to final position, this study thus provides evidence for distinct and new migration patterns during retinal lamination and insights into the initiation of IPL formation.
Affiliation: Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, UK.Show MeSH
Mentions: As the Ptf1a:DsRed signal only became visible postmitotically, an alternative strategy was needed to observe the earliest stages in RIN migration. The bHLH transcription factor Ath5 (Atoh7 – Zebrafish Information Network) is expressed during the G2 phase of the final cell cycle in most RINs (Poggi et al., 2005). Therefore, we transplanted cells from Ptf1a:DsRed; Ath5:gapGFP or Ptf1a:GFP;Ath5:gapRFP transgenic lines into WT embryos. We followed 25 Ath5+ and Ptf1a+ cells from their time of birth. Of these cells, 23/25 were born at the apical surface of the retina (Fig. 2A-C), and two cells were born near the outer plexiform layer (OPL) (supplementary material Fig. S3). All of these cells became elongated in the apical-basal direction immediately after birth (Fig. 2A-C; supplementary material Fig. S3). More than two processes may extend from the cell body, but one or two dominant processes are always aligned in the apical or basal direction such that the cells appear bipolar or unipolar (Fig. 2D; supplementary material Movie 2, 5.0 h). Sixteen of these cells were tracked long enough to identify their cell type based on their eventual morphology, position and, in the case of HCs, a secondary division. Four were HCs (Fig. 2A; supplementary material Movie 3), eight were iACs (Fig. 2B; supplementary material Movie 4) and four were DACs (Fig. 2C; supplementary material Movie 5). These experiments confirmed that early phase migration in all RINs is associated with bipolar morphology.Fig. 2.
Affiliation: Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, UK.