S9

Function

S9 is a vegetal plate marker gene (Miller et al., 1996).

Protein

Sequence analysis of the S9 clone has revealed the presence of an open reading frame of 122 amino acids that has no significant homology to sequences in GenBank or EMBL databases (Miller et al., 1996).

Subcellular location

Whole mount in situ hybridization demonstrated that at late blastula S9 transcripts are localized predominantly in the cytoplasm at the basal end of the cells in the vegetal plate (Miller et al., 1996).

Expression Pattern

A local accumulation of S9 transripts in the vegetal plate was first detectable by in situ hybridiation at the late blastula stage, at approximately the time PMC ingression was beginning. A lower level of staining throughout the epithelial wall of the embryo was also apparent at this stage, which may represent a transient pattern of early zygotic expression of this gene.
At the mesenchyme blastula stage, after PMC ingression was complete, S9 mRNA was expressed at high levels throughout much of the vegetal plate in a symmetrical pattern. PMCs that had ingressed into blastocoel did not express detectable levels of S9 mRNA, and in specimens that were favorably oriented, a clear zone in the center of the vegetal plate was apparent, suggesting that the descendants of the small micromeres (and possibly other cells) did not express the transcript.
At the early gastrula S9-expressing SMCs are ingressing from the vegetal plate into the blastocoel. At the early-mid gastrula S9-expressing SMCs continue to ingress into the blastocoel and several migrate above the equator of the embryo.
At late gastrula S9 transcripts are apparent in the ectodermal layer. In addition, SMCs at the tip of archenteron express detectable levels of the transcript.
At the prism and pluteus stages S9 mRNA is expressed at high levels by the subset of SMCs that are closely associated with the dorsal (aboral) ectoderm. Cell counts indicated that at the early pluteus stage, there are approximately 33 S9-expressing cells per embryo (Miller et al., 1996).

Spatial localization
Method: Whole mount in situ hybridization
Reference: Miller et al., 1996

Stage	Blastula at beginning of PMCs ingression	Mesenchyme blastula	Early-mid gastrula	Late gastrula	Prism	Pluteus
Tissue	vegetal plate	vegetal plate	SMCs ingressing into the blastocoel	SMCs at the tip of archenteron, ectodermal layer	SMCs associated with AE	SMCs associated with AE