Requirement for mast cell growth factor for primordial germ cell survival in culture

Abstract

Mast-cell growth factor (MGF) is encoded by the murine steel (Sl) locus and is a ligand for the tyrosine kinase receptor protein encoded by the proto-oncogene c-kit at the murine dominant white spotting (W) locus. Mutations at both these loci affect mast cells, primordial germ cells (PGCs), haemopoietic stem cells and melanocytes. In many Sl and W mutants, the rapid proliferation of PGC that normally occurs between day 7 and 13.5 of embryonic development fails to occur. As c-kit is expressed in PGCs while MGF is expressed in the surrounding mesenchyme, MGF might promote the proliferation of PGCs. Here we report that MGF is essential for PGC survival in culture, but does not stimulate PGC proliferation. Moreover, whereas both the transmembrane and soluble proteolytic cleavage forms of MGF stimulate mast-cell proliferation, soluble MGF has a relatively limited ability to support survival of PGCs in culture, thus explaining the sterility in mice carrying the steel-dickie (Sld) mutation, which encodes only a soluble form of MGF, and providing a functional role for a transmembrane growth factor.

Essential Role of Sox2 for the Establishment and Maintenance of the Germ Cell Line

“…Notably, the first Kit intron was previously shown to be essential for Kit expression in these cells as well as in hematopoietic precursors [22,47]. Since Kit signaling is essential for survival and proliferation of germ cells [25,27,48], we can hypothesize that one of the mechanisms by which Sox2 ablation affects PGCs is through downregulation of Kit transcription. Although it is generally accepted that Kit is not strictly required for the establishment of the germline [49], more recent work has shown that PGCs are dependent on Kitl expression from the surrounding environment as early as at the time of their specification [50].…”

“…One of these genes is Kit, which encodes the tyrosine-kinase receptor for Kit Ligand (Kitl), essential for PGCs development [27]. Sox2 overexpression in ES cells has been shown to induce high levels of Kit mRNA, as evaluated by microarray analysis [38].…”

“…5-bromo-2 0 -deoxyuridine (BrdU) incorporation was performed as previously described in Dolci et al [27] with minor modifications. Briefly, 8.5 dpc PGCs from Sox2 loxP/loxP -Rosa26 Cre-ERT or from Sox2 loxP/loxP embryos were seeded onto mitomycin-C-treated Sl4-m220 fibroblasts in complete PGC medium and immediately treated with 0.2 lM 4OH-Tamoxifen or with vehicle.…”

The extracellular regulation of growth factor action.

“…However, mice with this mutation are anemic, sterile, and have altered pigmentation. Other experiments performed in vitro demonstrate that membrane-anchored kit-ligand supports primordial germ cell growth, whereas soluble kit-ligand does not (Dolci et al, 1991). Thus, the physiological consequences of the Sld mutation probably reflect the requirement of a membranebound form of kit-ligand in normal development.…”

Transforming growth factor-β regulates Kit ligand expression in rat ovarian surface epithelial cells

“…KL stimulates colony formation of primitive hematopoietic precursors from bone marrow (Metcalf and Nicola, 1991) and induces the proliferation of mast cells (Tsai et al, 1991). Like somatic cells, primordial germ cells, which express Kit receptors, respond to KL in culture with increased survival (Dolci et al, 1991;Godin et al, 1991;Pesce et al, 1993) and proliferation (Matsui et al, 1991). In prepubertal male mice, KL selectively stimulates DNA synthesis in type A spermatogonia (Rossi et al, 1993).…”