Guidance of Primordial Germ Cell Migration by the Chemokine SDF-1

Abstract

The signals directing primordial germ cell (PGC) migration in vertebrates are largely unknown. We demonstrate that sdf-1 mRNA is expressed in locations where PGCs are found and toward which they migrate in wild-type as well as in mutant embryos in which PGC migration is abnormal. Knocking down SDF-1 or its receptor CXCR4 results in severe defects in PGC migration. Specifically, PGCs that do not receive the SDF-1 signal exhibit lack of directional movement toward their target and arrive at ectopic positions within the embryo. Finally, we show that the PGCs can be attracted toward an ectopic source of the chemokine, strongly suggesting that this molecule provides a key directional cue for the PGCs.

Probing events with single molecule sensitivity in zebrafish and Drosophila embryos by fluorescence correlation spectroscopy

“…These receptors play an important role in defining directionality of cell migration of germ cells, lateral line, and somites during embryogenesis (Doitsidou et al, 2002;Gilmour et al, 2004;Hollway et al, 2007). We further injected Cxcr4b-EGFP plasmid into a single blastomere at 16-cell stage and observed distribution of EGFP-tagged Cxcr4b in labeled cells.…”

“…5C). In following experiments, Cxcr4b-EGFP plasmid was injected in lower concentration (40 ng/ll) as it has been shown that overexpression of Cxcr4b leads to developmental abnormalities (Doitsidou et al, 2002). The EGFP-tagged Cxcr4b was found to be uniformly distributed along the muscle fiber plasma membrane.…”

Transition from non-motile behaviour to directed migration during early PGC development in zebrafish

“…Attraction assay Wild-type 1-cell-stage donor embryos were injected with 240 pg sdf1a-globin-3ЈUTR RNA [morpholino-resistant sdf-1a; (Doitsidou et al, 2002)], sdf-1a and sdf-1b morpholino (0.4 pmol each) and dextran Alexa Fluor 568 (10,000 kDa; Molecular Probes, 0.15 ng). Progeny of kop-EGFP-F-nos1-3ЈUTR transgenic females injected at the 1-cell stage with sdf-1a and sdf-1b morpholino (0.4 pmol each) served as hosts.…”

“…Acquistion of PGC responsiveness to SDF-1a represents a cellular differentiation step that is temporally distinct from their specification The ability to observe PGC behaviour in vivo at the earliest stages of their development allows us to investigate the progression of the cellular response to external cues namely, to SDF-1a, the chemokine that directs PGC migration (Doitsidou et al, 2002). The lack of PGC migration at early stages could result from high levels of SDF-1a expression where they reside similar to the situation found at their intermediate or final targets (Reichman-Fried et al, 2004).…”

“…These properties provide a unique opportunity to study cell migration and development at a high resolution within the intact organism. PGC migration in zebrafish is guided by binding of the chemokine stromal-cellderived-factor (SDF)-1a, a small-secreted molecule that is dynamically expressed in the regions toward which the PGCs migrate (Doitsidou et al, 2002), to its receptor, CXCR4b (Doitsidou et al, 2002;Knaut et al, 2003). Whereas the development and migration of zebrafish PGCs have been studied in great detail starting at mid-gastrulation stages when the cells exhibit active guided migration [7-8 hours post fertilization (hpf)] (Braat et al, 1999;Knaut et al, 2002;Reichman-Fried et al, 2004;Weidinger et al, 2003;Weidinger et al, 1999;Weidinger et al, 2002;Yoon et al, 1997), earlier stages have not yet been examined.…”