alphaSU2

Function

alphaSU2 belongs to the family of alpha integrins.
alphaSU2 integrin contributes to epithelial cell-substrate adhesion. It functions in adhesion of epithelia to the basal lamina.
alphaSU2 may serve as a primary receptor binding the blastula- stage cells to the basal lamina (Hertzler et al., 1999).

Protein

alphaSU2 is an alpha integrin.
The first stop codon at nucleotide position 3885-3887 produces an open reading frame of 1041 amino acids, and the mature protein of 1018 amino acids is calculated to have a molecular mass of 110,706 daltons. The protein is approximtely 140 kDa as blotted with the antibody to an expressed fragment of the protein, suggesting thet alphaSU2, like other alpha integrins, is glycosylated.
A large region corresponding to the extracellular domain extends to amino acid residue 982, followed by a stretch of 25 hydrophobic amino acids, which is an acceptable transmembrane domain.
A short cytoplasmic domain of 31 amino acids constitutes the remainder of the sequence. A consensus site for proteolytic cleavage K/RRE/D (Bossy et al., 1991) is present at amino acid residues 876-878.
Alignment of alphaSU2 with other alpha integrins reveals a number of conserved protein domains. Seven repeats characteristic of alpha integrins are present in the extracellular domain. Domains IV-VII each contain potential divalent cation-binding domains corresponding to at least a 11/12 match for the consensus sequence DX(D/N)X(D/N)-GXXDXXV within EF-hand calcium- binding domains (Kretsinger, 1980). Sixteen of eighteen cystein residues are present in conserved positions throughout the extracellular domain. Eleven sites of potential N-glycosylation corresponding to the consensus NX(T/S) are present. The sequence GFFER is located in the cytoplasmic domain adjacent to the transmembrane region, a 4/5 match to the consensus GFFKR in other alpha integrins (Sastry and Horwitz, 1993). A potential tyrosine phosphorylation site is also present in the intracellular domain. Thus, all the major structural elements of alpha integrins are conserved in alphaSU2 (Hertzler et al., 1999).
SWISS_PROT: P46771

Subcellular location

Whole-mount immunofluorescence showed that alphaSU2 protein first appears on the basal cell surface of epithelia at the midblastula stage and remains at high levels on the basal surface of ectoderm cells but is temporary reduced or eliminated from endoderm cells during their convergent-extension movements (Hertzler et al., 1999).

Expression Pattern

Nothern blotting of poly [A]⁺ RNA revealed that a single band approximately 11,3 kb is present in eggs and mesenchyme blastula, midgastrula, late gastrula, prism, and pluteus larval stages. The levels of alphaSU2 integrin RNA remain rather constant or decrease slightly during development.
Western blot data also show the protein to be present throughout development.
Whole-mount immunofluorescence revealed no staining in eggs or embryos up to about 5 h. Beginning in the midblastula stage (6 h), punctate staining is first observed on the basal side of some blastomeres. By 9-10 h, in late blastula stages, there is intense staining on the basal surface of most cells in the blastoderm, especially on the thickened vegetal plate from which the PMCs and secondary mesenchyme cells (SMCs) will later ingress. There are no discontinuities in the staining pattern of the vegetal plate at this stage, so most cells, including most, if not all, PMC and SMC precursors express the integrin at this stage.
Later at PMC ingression (12 h), the basal staining pattern becomes discontinuous in the region of ingression and PMCs fail to stain for the integrin during and following the ingression process.
In early gastrulae (15 h), the basal side of ectodermal cells remains immunopositive but during archenteron invagination endoderm cells stain much less intensively for the integrin. In the early prism stage the archenteron still has reduced integrin staining relative to the basal side of the ectoderm but the ectoderm/endoderm levels appear the same in plutei (Hertzler et al., 1999).

mRNA level

Temporal accumulation
Method: Nothern blot analysis
Reference: Hertzler et al., 1999

Stage	Egg	Midblastula	Midgastrula	Late gastrula	Prism	Pluteus
Level	+	+	+	+	+	+

Protein spatial localization
Method: Whole mount immunofluorescence
Reference: Hertzler et al., 1999

Stage	6-h midblastula	9 h late blastula	12 h mesenchyme blastula	15 h early gastrula	18 h late gastrula	21 h prism	32 h pluteus larva
Tissue	Punctate staining on the basal side of some blastomeres	Intense staining on the basal surface of most cells in the blastoderm, especially on the thickened vegetal plate (including most, if not all, PMC and SMC precursors)	The basal staining pattern becomes discontinuous in the region of ingression and PMCs fail to stain for the integrin during and following the ingression process	The basal side of ectodermal cells remains immunopositive	During archenteron invagination endoderm cells stain much less intensively than ectoderm cells	Archenteron still has reduced integrin staining relative to the basal side of the ectoderm	Ectoderm/endoderm levels appear to be the same

Sequences

partial cds

Regulatory Regions

Regions

Regulatory Connections

Upstream Genes

alphaSU2

Downstream Genes

Evolutionary Homologues

Links

Urchin Web

Bibliography

UrchiNet

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