Figure 8: Integrin mutants exhibit defects in niche morphogenesis.

A-B) In intergrin mutants niche cells begin assembly, with most cells relocating to the anterior periphery of the gonad, but then dropping internally. A, B) Selected stills from two different in vivo time series of myospheroid mutants, imaged to follow all SGPs (six4nlsGFP), and PS11 SGPs (prd>tdTomato). A, B, merge; A’, B’ single six4nlsGFP channel. Each frame is taken at a different depth into the gonadal sphere, with the distance in from the periphery marked for each panel in microns (um; minutes, m).Scale bar is 10 microns. A) t=0, an assembly phase gonad, with the pro-hub consisting of a mix of PS10 cells (green only, 5 cells visible) and PS11 cells (red+green, 2 visible). Within 45 minutes, the assembled niche began to internalize before completing compaction. Over the next 2 hours, two PS11 SGPs (white arrowheads) dropped inwards; note the section depth changing from 1 to 13 um. Simultaneously, another PS11 SGP (blue arrowhead), which had not assembled at the anterior, migrated in and joined the internalizing niche. Lastly, between 45min and 90 min three orignially assembled PS10 SGPs separated (asterisk), with two internalizing and one remaining peripheral. B) Shows a partial, face-on view of the niche, just after initial assembly. A PS11 SGP was initally on the periphery of the gonad, but was internalized as the niche dropped inwards (arrowhead). Similar to the case shown in ‘A’, internalization began before compaction was completed. Note also that an adjacent PS10 SGP that remained on the gonad periphery (asterisk) and did not internalize with the rest of the pro-niche cells. C) A schematic of a mys mutant gonad depicting various defects observed in live imaging of panels A and B. In this lateral, 2D view, only relevant proniche cells are shown. Of seven pro-niche cells (green), 6 have asembled at the anterior. These cells are all on the gonad periphery (left panel), which is difficult to convey in 2D. Five of these cells leave the periphery and move internally over time (curved blue arrow), similar to the case shown in panels A-B. The cluster adopts a more compact form only after it internalizes (i.e., by the fourth frame). Note also that one proniche cell, Cell #1, never migrated to the anterior. Instead, it migrates into the milieu of the gonad (curved black arrow) from its initially more posterior position, and joins the five internalizing niche cells (frames 2 -4). This behavior is similar to the the cell marked by the blue arrowhead in ‘A’. Finally, of the six cells that assembled at the anteior only five leave the gonad periphery. Cell #2 is left behind at the gonad periphery during internalization of the niche. This behavior is similar to the cell marked by an asterisk in ‘B’.