Gene Networks Database

Strongylocentrotus purpuratus Genes in Development: Epidermal growth factor-related proteins

SpEGF2

Function

The sea urchin SpEGF2 gene belongs to a family of developmentally important genes which encode proteins that contain repeated epidermal growth factor-like motifs.
The structure of the SpEGF2 protein and the pattern of accumulation of its messenger RNA suggest that it may have important functions as a secreted factor during development of sea urchin embryos (Yang et al., 1989).

Protein

SpEGF2 gene codes for a protein related to epidermal growth factor (EGF). It has an unusually simple structure, including four tandem EGF-like repeats and a hydrophobic leader, but lacking a potential transmembrane domain.
This protein contains 325 amino acids and has a predicted molecular mass of 36.9 kD. Most (at least 263 of 325 amino acids) of the predicted protein consists of four tandem EGF-like repeats that can be aligned by the six cysteine residues found in each repeat spaced as CX₆CX₅CX_8-13CXCX_11-12C. These are within the range of spacings (CX_4-14CX_3-8CX_8-14CXCX_8-14C) for 63 EGF-like repeats from functionally diverse proteins.
Other than the four EGF-like repeats and hydrophobic leader, the protein contains two stretches of 30 or fewer amino acids surrounding the EGF-like repeats, which do not correspond to any sequence in the National Biomedical Recearch foundation protein database. Some features of the sequence suggest that the SpEGF2 protein may be cleaved and modified: repeats 1 to 4 are preceded by Arg-Asp at a conserved position, and the four related peptides from A. crassispina all have NH₂-terminal Asp residues ( Suyemitsu et al., 1989). Three pairs of basic amino acids, two of which flank the fourth repeat, could also serve as proteolytic processing sites. The predicted peptide lacks N-X-S/T signals for N-linked glycosylation but contains several clusters of serine or threonine (or both) that could serve as sites of O-linked glycosylation (Yang et al., 1989).
SWISS_PROT: P15216

Subcellular location

At late blastula stage SpEGF2 mRNA is concentrated at the basal sides of the cells (Yang et al., 1989).

Expression Pattern

Northern blot hybridization detected a single 1.8-kb transcript, which is undetectable in unfertilized eggs, begins to accumulate around mesenchyme blastula stage to an appericable fraction of its maximum abundance, which occurs during gastrulation, and persists at slightly reduced levels in pluteus larvae.
Hybridization in situ showed that SpEGF2 mRNA accumulates only in ectoderm in a spatial pattern that is unusual because it does not correspond to known histological borders. In pluteus larvae a major site of SpEGFR2 mRNA accumulation is in the histologically uniform cells of aboral ectoderm. In contrast to other messages expressed in aboral ectoderm, SpEGFR2 transcripts are not uniformly distributed in this tissue but instead accumulate to higher levels at the pointed vertex opposite the mouth and at the border with the ciliary band. This nonuniform distribution, and the manner in which it is progressively established from uniform distribution in presumptive aboral ectoderm of the blastula, are reminiscent of similar phenomena observed for another mRNA, SpHbox1. However, the tissue specifity of the SpEGF2 message is broader than that of SpHbox1, it is expressed in oral ectoderm cells. In these cells, also, it is unhomogenously distributed among epithelial cells that surround the mouth, being most abundant in cells immediately adjacent to the mouth on its anal side, and absent from the histologically distinct cells that constitute the ciliary band (Yang et al., 1989).

mRNA level

Temporal accumulation
Method 1: Nothern blot analysis
Reference: Yang et al., 1989

Stage	Egg	9 hr late cleavage	15 hr early blastula	24 hr mesenchyme blastula	48 hr late gastrula	72 hr pluteus
Level	-	-	-	+	+ +	+

Spatial localization
Method: in situ hybridization
Reference: Yang et al., 1989

Stage	Pluteus larvae
Tissue	Aboral ectoderm (higher levels at the pointed vertex opposite the mouth and at the border with the ciliary band), oral ectoderm (unhomogenously distributed among epithelial cells that surround the mouth, being most abundant in cells immediately adjacent to the mouth on its anal side, absent from the histologically distinct cells that constitute the ciliary band)