Gene Networks Database

Strongylocentrotus purpuratus Genes in Development: homeobox-containing transcription factors

SpOtx

Function

SpOtx encodes a homeobox-containing protein belonging to the orthodenticle (otd)/Otx family (Gan et al., 1995).
SpOtx is a transcription factor.
SpOtx belongs to bicoid class of homeobox-containing genes, which are distinguished by the presence of a lysine in position 51 of the homeodomain that lies within the recognition (third) helix.
SpOtx is involved in aboral ectoderm differentiation by activating aboral ectoderm-specific genes. Modulation of SpOtx expression can lead to changes in cell fate (Mao et al., 1996).

Protein

SpOtx exists in two forms (alpha and beta) that are generated by alternative RNA splicing from a single SpOtx gene. SpOtx(alpha) and SpOtx(beta) had identical C-termini and homeoboxes but were entirely different in their N-terminal domains (Li et al., 1997).
The homeobox and regions in the N-terminal and C-terminal halves of protein are required for morphological alterations caused by overexpression of wild-type SpOtx protein (Mao et al., 1996). The N-terminal regions of both SpOtx(alpha) and SpOtx(beta) as well as C-terminal regions (between amino acid positions 270-371) are transactivation domains in the yeast transactivation assay, indicating that the biological effects of overexpressing SpOtx are due to its action as transcription factor (Mao at al.,1996).
SWISS_PROT: Q26417

Subcellular location

Cytoplasmic and nuclear.
Indirect fluorescence method (Gan et al, 1995) showed that unfertilized egg gives a weak signal distributed throughout the cytoplasm. By blastula stage SpOtx protein is found equally distributed in the nuclei of all cells. At the pluteus stage the level of SpOtx protein is substantially reduced, but the protein is nethertheless detected in nuclei of aboral ectoderm, endoderm and oral ectoderm cells. SpOtx protein is present in aboral ectoderm cells of late stage embryos several hours after SpOtx mRNA has disappeared from these cells.

Expression Pattern

At least 4 different SpOtx mRNA were generated at the SpOtx locus (Li et al., 1997). SpOtx(alpha) mRNAs are transcribed from a single start site. Three distinct SpOtx(beta) mRNAs are resulted from two separate transcriptional initiation events.
RNase protection anasysis (Li et al., 1997) showed that SpOtx(alpha) transcripts were present in unfertilized egg, accumulated three- to fourfold during the cleavage stage (1 - 12 hr) and then decreased four- to fivefold in later development (20 to 72 hr). SpOtx(beta1), SpOtx(beta2) and SpOtx(beta3) mRNAs were not found in egg but began accumulating at early cleavage (4 hr), reached peak levels at early gastrula stage (36 hr), and reminded at those level throughout the rest of embryogenesis.

mRNA level

SpOtx (alpha) transcripts

Temporal accumulation
Method: RNAase protection analysis
Reference: Li et al., 1997

Stage unfertilized egg Cleavage Blastula Gastrula Pluteus

Level + + + + +

Spatial localization
Method: in situ hybridization
Reference: Li et al., 1997

Stage Cleavage early, 16 cell (5 hr) Blastula, 200 cell (15 hr) Mesenchyme blastula, 400 cell (24 hr) Midgastrula, 700 cell (35 hr)

Tissue All cells All cells Transcripts are biased in the animal and vegetal regions Transcripts are largely restricted to the gut and oral ectoderm

SpOtx (beta1)/SpOtx (beta2) transcripts

Temporal accumulation
Method: mRNA injection
Reference: Li et al., 1997

Stage unfertilized egg Cleavage Blastula Gastrula Pluteus

Level - + + + +

Spatial localization
Method: mRNA injection
Reference: Li et al., 1997

Stage Cleavage early, 16 cell (5 hr) Blastula, 200 cell (15 hr) Mesenchyme blastula, 400 cell (24 hr) Midgastrula, 700 cell (35 hr)

Tissue - All cells More prevalent in ectoderm compared to vegetal plate Mostly in oral ectoderm and endoderm

SpOtx(beta3) is a very rare transcript and attempts to determine its distribution have not been successful (Li et al., 1997).
Overexpression of SpOtx(alpha) and SpOtx(beta) induced in sea urchin embryos by mRNA injection demonstrated that SpOtx(alpha) was able to repress the accumulation of SpOtx(beta) transcripts, whereas SpOtx(beta) has no effects on accumulation of SpOtx(alpha) transcripts (Li et al., 1997)

Sequences

GenBank:

mRNA

Regulatory Regions

Regions

Regulatory Connections

Upstream Genes

SpOtx

Endo16 SpHE Spec2a

Downstream Genes

Evolutionary Homologues

Otx1 and Otx2 mouse
otd Drosophila

Links

Urchin Web

Bibliography

UrchiNet

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Stage	unfertilized egg	Cleavage	Blastula	Gastrula	Pluteus
Level	+	+	+	+	+

Stage	Cleavage early, 16 cell (5 hr)	Blastula, 200 cell (15 hr)	Mesenchyme blastula, 400 cell (24 hr)	Midgastrula, 700 cell (35 hr)
Tissue	All cells	All cells	Transcripts are biased in the animal and vegetal regions	Transcripts are largely restricted to the gut and oral ectoderm