Strongylocentrotus purpuratus Genes in Development:
VEB genes
SpAN
Function
SpAN is a VEB (very early blastula) gene family member. It encodes
a protein similar to astacin proteases (Kozlowski et al., 1996).
It has been proposed to play a role in assembly of the
early blastula-stage embryo and in the differentiation
of ectodermal lineages and subsequent patterning of the
embryo (Hwang et al., 1994).
Protein
SpAN is a protease. SpAN contains a signal peptide at its
N-termini, followed by an activation region, protease (P) domain,
cysteine-rich region, C1r/C1s domain, and threonine-rich domain.
The P domain exhibits sequence identity with
that of the astacin metalloprotease.
The C1r/C1s domain is similar to domain I of human C1r and C1s serine
proteases in the complement cascade. This domain
also shares sequence homology with the C-terminal
region of the calcium-dependent serine protease precursor.
The threonine-rich domain is inserted inside the C1r/C1s domain
(Hwang et al., 1994).
SWISS_PROT: P98068
Subcellular location
Cytoplasmic
Expression Pattern
The VEB genes are the earliest activated genes identified that
encode strictly zygotic products.
SpAN mRNA is undetectable in the egg.
RNAase protection assay, which can detect as few as 10 transcripts per embryo
indicated that SpAN transcripts begin to accumulate at 8-cell stage.
RNA blot analysis demonstrate that the SpAN transcripts reach peak
abundance from 9 hours (128 cells) to 15 hours (250 cells) post-fertilization
and disappear by mesenchyme blastula stage (25 hours postfertilization).
Solution titration indicates that there are approximately 25,000 SpAN
transcripts per embryo at 12 hours.
In situ hybridization showes that in 12-hour embryos the VEB transcripts
always accumulate in presumptive ectoderm but to a
variable extent in cells of the endoderm and mesenchymal lineages.
SpAN gene is asymmetrically expressed
along the maternally determined animal-vegetal axis. Its
transcripts are undetectable in a region around the
vegetal pole, a pattern that's termed "non-vegetal" (Reynolds et al., 1992).
mRNA level
Temporal accumulation
Method: RNAase protection assay (up to 64 cells)
Reference: Reynolds et al., 1992
Method: RNA blot analysis
Reference: Reynolds et al., 1992
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