Gene Networks Database

Strongylocentrotus purpuratus Genes in Development: Receptors

SpFGFR

Function

SpFGFR is a new member of the fibroblast growth factor receptor family.
Experiments with E. coli, which lack endogenous tyrosine kinase activity demonstrated the ability of SpFGFR to autophosphorylate tyrosine residues. Therefore, SpFGFR is a functional tyrosine kinase (McCoon et al., 1996).

Protein

SpFGFR is a tyrosine kinase. The structure of SpFGFR contains all of the characteristic structural features of the FGFR receptors.
Following the putative translation initiation codon, the extracellular domain contains a cluster of hydrophobic and charged amino acids characteristic of a signal sequence, then three Ig-like repeats with the motif, C-(X11-12)-W-(X50-60)-D-XGXYXC. A stretch of acidic residues (``acid box'' motif), which distinguishes FGFRs from other receptor tyrosine kinases, is found between the first and second Ig-like repeats, although it is shorter than the acid boxes of vertebrate FGFRs and contains glutamate. The extracellular domain contains 11 potential sites for N-linked glycosylation, and tunicamycin-sensitive modification of this protein has been observed in vivo.
Following the transmembrane domain are two other features characteristic of this class of receptor tyrosine kinases: 1) an unusually long (82-amino acid) juxtamembrane domain; and 2) a kinase domain split by a 15-amino acid insert (KI). The ATP binding motif, GXGXXG, as well as the catalytic motifs DLXXXN, DFG, P(VI)(KR)W(MT)APE, and DVW(SA)(FY)G, found in other protein kinases, are present in the C-terminal half of the TK domain. The sequence motifs DLAARN and PVKWMAPE are diagnostic for protein kinases with tyrosine specificity.
Although the most divergent portions of the cytoplasmic domain are the kinase insert and the C terminus, their lengths are conserved, as are two Tyr residues, which, in vertebrate receptors, have been shown to be important for receptor function
Alternative splicing of SpFGFR generates two variants: longer (Ig3L) and shorter (Ig3S), which differ by insertion in the center of the Ig3 domain of 34 extra amino acids, encoded by an additional exon (McCoon et al., 1996).

Subcellular location

Expression Pattern

Both transcripts (Ig3L and Ig3S) increase in abundance in parallel between late cleavage (12 h) and early gastrula stage (36 h) and persist through pluteus stage (72 h), with the longer variant RNA being severalfold more abundant. But only Ig3L transcripts are detectable in eggs and during early cleavage stages (through 12 h, ~150-cell stage), suggesting that splicing of maternal transcripts is regulated during oogenesis.
There are, on average, ~10-20 SpFGFR transcripts/cell at peak abundance at gastrula (48 h) and pluteus (72 h) stages. Thus, SpFGFR transcript concentrations are relatively low, being only about 10-fold more abundant than typical rare messenger RNAs in the sea urchin embryo.
In situ hybridization assays showed that SpFGFR transcripts (represents the sum of contributions of Ig3S and Ig3L variants) accumulate in all major regions of the embryo. In blastulae, higher transcript concentrations are observed near the animal and vegetal poles. Transcripts are detectable throughout embryos at later stages, with several fold higher levels in archenteron of gastrulae and in ciliary bands, guts, and vertices of pluteus larvae.
RNase protection assay was used to determine whether Ig3S and Ig3L transcripts are represented at the same relative concentrations in endomesoderm and ectoderm tissue fractions of 47-h gastrulae. Results showed that the transcripts encoding the Ig3S variant, whose structure resembles more closely that of vertebrate receptors, are enriched in endomesoderm, suggesting that the SpFGFR variants could play distinct roles in the sea urchin embryo (McCoon et al., 1996).

Ig3S variant mRNA level

Temporal accumulation

Method: RNase protection assay
Reference: McCoon et al., 1996

Stage
Egg
9 hr
12 hr
24 hr
36 hr
72 hr
Level
-
-
-
+
+ +
+

Ig3L variant mRNA level

Temporal accumulation

Method: RNase protection assay
Reference: McCoon et al., 1996

Stage
Egg
9 hr
12 hr
24 hr
36 hr
72 hr
Level
+
+
+
+ +
+ +
+

Spatial localization *

Method: in situ hybridization
Reference: McCoon et al., 1996

Stage
Blastula
Gastrula
Pluteus larvae
Tissue
All tissues, higher signals near the animal and vegetal poles
All tissues, higher levels in archenteron
All tissues, higher levels in ciliary band, gut, vertices

* Sum of contributions of Ig3S and Ig3L variants

Expression of Ig3L and Ig3S transcripts in two fractions of 47-h gastrulae

Method: RNase protection assay
Reference: McCoon et al., 1996

Fraction/transcript
Ig3L
Ig3S
Ectoderm
+
+ -
Endomesoderm
+
+ +

Sequences

Regulatory Regions

Regulatory Connections

Upstream Genes

SpFGFR

Downstream Genes

Evolutionary Homologues

Links

Bibliography
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Comments are welcome to Sveta Surkova
Copyright © 1997 GeNet Team