Heliocidaris erythrogramma Genes in Development: Apextrin

HeET-1 (apextrin)

Function

HeET-1 encodes a novel secreted protein (apextrin).
Apextrin protein appears to be a part of the innermost layer of the H. erythrogramma apical ECM, beneath the classically defined hyaline layer and apical lamina.
Apextrin is involved in apical cell adhesion and its high level of expression may be necessary for strengthening the large H. erythrogramma embryo (Haag et al., 1999).

Protein

The antibodies produced to peptides encoded by the HeET-1 gene detect a 74 kDa protein in embryonic protein extracts. This size is roughly 20 kDa larger than that predicted for the amino acid sequence of the complete HeET-1 cDNA (Haag and Raff, 1998), which is consistent with the posttranslational modification of apextrin. Given the existence of four potential N-linked glycosylation sites, it is likely that much of all of the additional apparent molecular weight of the mature protein represents carbohydrate moieties (Haag et al., 1999).
GenBank: 3378105

Subcellular location

The HeET-1 maternal protein is packaged into secretory vesicle during oogenesis, and these take up a largely but not exclusively cortical position in the unfertilized egg.
After fertilization, apextrin is secreted uniformly to the periphery of blastomeres, a process that continues during the early cleavage stages.
At gastrula the HeET-1 protein in ectodermal cells forms a cap around the apex of each cell. The protein is called apextrin for its apical extracellular localization (Haag et al., 1999).

Expression Pattern

HeET-1 protein gel blot analysis showed that the abundance of the HeET-1 protein does not vary greatly over the stages assayed. This is in contrast to the HeET-1 mRNA, which is gradually upregulated from undetectable levels in the egg to great abundance by the time rudiment development begins (Haag and Raff, 1998).
A significant maternal load of HeET-1 protein exists in unfertilized eggs. This maternal protein persists with some attrition at least until transcription becomes active in the blastula. After the onset of transcription, levels of HeET-1 protein rise overall, but plateau by 36 h of development.
By day 4 after fertilization, larvae competent to undergo metamorphosis have a reduced amount of protein relative to this plateau.
Immunolocalization experiments revealed the cortically enriched, punctate distribution of HeET-1 protein in unfertilized eggs.
4-cell embryo showed extracellular staining and intracellular vesicles lined up along the cleavage furrow.
In cleavage stages the bulk of immunopositive particles exists at the cortices of the blastomeres, the staining is apparent in the hyalin layer portion of the extracellular matrix.
Beginning in blastula, staining becomes localized to the apical ends of the blastoderm. As gastrulation begins, invaginating cells of the archenteron remain seropositive, as do nascent mesenchyme cells ingressing from the vegetal plate. However, these latter cells lose their columnar shape and contain intracellular HeET-1-staining particles.
High-magnification views of dissociated gastrula ectodermal cells reveal that the HeET-1 protein in ectoderm forms a cap around the apex of each cell.
20-h gastrula showed apical staining of ectoderm and archenteron and additional staining in ingressing mesenchyme.
In 38-h embryos that are developing the echinus rudiment the antibody detects apextrin on the apical faces of the gut and coelom, but this staining is weaker and less uniform than apical staining in ectodermal cells.
In metamorphosing animals, at late stage of larval development, staining is detected only in the extravestibular ectoderm.
This staining is not seen in 11-day postfertilization juveniles, indicating that the apextrin protein is destroyed within a week after metamorphosis (Haag et al., 1999).

Protein level

Temporal accumulation

Method: Western blot analysis
Reference: Haag et al., 1999

Stage
Unfertilized egg
4-cell stage
32-cell stage
Unhatched blastula (10 h)
Gastrula (23 h)
Vestibule stage(36 h)
Advanced rudiment stage (62.5 h)
Competent larva (98.5 h)
Level
+
+
+
+
+ +
+ +
+ +
+ -

Spatial localization

Method: Immunolocalization assay
Reference: Haag et al., 1999

Stage
Unfertilized egg
4-cell stage
20-h gastrula
38-h (vestibular stage)
Late stage of larval development
11-day juveniles
Tissue
Immunopositive particles are either uniform throughout the cytoplasm, or concentrated around the cortex of the cell
Extracellular staining and intracellular vesicles lined up along the cleavage furrow
Apical staining of ectoderm and archenteron and additional staining in ingressing mesenchyme
Apical faces of the gut and coelom, but this staining is weaker and less uniform than apical staining in ectodermal cells
Staining is detected only in the extravestibular ectoderm
No staining

Sequences

GenBank:

Regulatory Regions

Regulatory Connections

Upstream Genes

HeET-1

Downstream Genes

Evolutionary Homologues

Links

Bibliography
[Previous]UrchiNet homepage              [Up] Search UrchiNet
Comments are welcome to Sveta Surkova
Copyright © 1997 GeNet Team