Gene Networks Database

Strongylocentrotus purpuratus Genes in Development: Primary mesenchyme-specific genes

SM50

Function

The SM50 gene serves as a marker of the earliest known sceletogenic lineage-specific gene expression.
This gene occurs once per haploid genome (Davidson et al.,1989).
SM50 encodes a protein of the matrix within which the mineral elements of the sceletal structures are embedded (Makabe et al., 1995).

Protein

SM50 is the 50-kDa spicule matrix glycoprotein (Davidson et al.,1989).
This protein includes a typical N-terminal signal peptide and an N-linked glycosylation site near the C terminus. About 45% of the length of the protein is included in a domain composed of consecutive approximate repetitions of a 13-amino-acid element, the consensus sequence of which is Trp-Val-Gly-Asp-Asn-Gln-Ala-LeuTrp-Val-IleAsp-Asn-GlnPro+ ++-ValGlu.
The protein also contains an internal domain unusually rich in proline residues and a very basic C-terminal region (Sucov et al.,1987).
SWISS_PROT: P11994

Subcellular location

Expression Pattern

The SM50 gene is expressed in the skeletogenic mesenchyme by the cells located at the original vegetal pole of the egg.
SM50 is silent early in cleavage, it appears to be transcriptionally activated shortly after the 6th or 7th cleavage divisions (Davidson et al.,1989).
The SM50 2,2-kb mRNA attains a maximum level of 8000 to 10,000 transcripts per embryo by the gastrula stage, representing 120 to 200 SM50 mRNAs per primary mesenchyme cell.

mRNA level

Temporal accumulation
Method: solution hybridization (Lee et al., 1986)
Reference: Killian et al., 1989, Davidson, 1986.

Stage	Egg	16-cell	200-cell (12 hr)	Early mesenchyme blastula (18 hr)	Mesenchyme blastula (24 hr)	Gastrula (39 hr)	Prism	3-Day pluteus (72 hr)	4-Day pluteus (96 hr)
Average No. transcripts/per embryo	N.D.	N.D.	70	1.1*10^3	4.3*10^3	7.2*10^3	8.6*10^3	8.1*10^3	1.2*10^4
No. of expressing cells	-	-	8-32	32	32-60	60	60	60	60
Average No. transcripts/per cell	-	-	2-9	30	70-140	120	140	135	200