Fused

Fused

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Symbol: {Links}	Flybase ID: {Flybase_ID}
Synonyms: {Name}	{GadFly}
Function: {Short_Function}	{LocusLink}
Keywords: {Keywords}	{Interactive_Fly}

{Summary}

Function/Pathway

Is a serine/threonine kinase
At A/P boundary Fu kinase activity is involved in maintenance of high ptc and late en (Alves, 1998), b/c it is needed for Ci to go into the nucleus (Wang, 2000)
In more anterior cells Fu plays a role independent of its kinase fxn in regulating Ci stabilization (Alves, 1998) and nuclear import (us)
Fu fxn is necessary for the nuclear import of Ci and counteracts the negative Su(fu) effect on the pathway.
Phosphorylates Cos2 on S572 and to a lesser extent S931 in a Hh dependent fashion (baculovirus system) (Nybakken, 2002)
Fu is able to autophosphorylate itself in baculovirus system (Nybakken, 2002)
Fu is acting downstream of ptc and hh, and upstream of cos2 and ci and possibly pka in imaginal discs (Sanchez-Herrero, 1996)

Genetic interactions

Hedgehog
- transcription of hh persists for longer in embryos lacking wild-type fu activity (Fig 2a), suggesting that fu may act 'downstream' of hh to regulate wg transcription (Ingham, 1993)
Wingless
- in a fu mutant there is no expression of wg in the ventral ectodermal cells of each parasegment in the embryo, though transcript is still found in other cells where wg expression is independent of hh function. The phenotype stays the same even if Hh is overexpressed with HS-hh. (Ingham, 1993)
Ptc and Fu in the germarium undergo changes in expression that are coincident with Sxl (Vied, 2001)
Shown to act upstream of Ci (Slusarski, 1998)
Fu mediates hh-induced en activation in the anterior compartment in wing discs (Sanchez-Herrero, 1996) b/c Fu is need for release (us)
Class 0, I, and II fused phenotype is suppressed by Su(fu)LP (class II has a cos2 phenotype in addition) (Preat, 1993)
cos23 mutation partially suppresses fu vein phenotype just like Su(fu)LP (Preat, 1993)
fu[I]; cos2⁷ flies look like cos27 flies (Preat, 1993)
fu[II]; cos2³ die as late pupae and have extreme adult cos2 phenotype (Preat, 1993)
class II is recessive to fu⁺; class II is recessive to class I; class 0 is recessive to class II
In the embryo Fu product can correct the deficiency in the Hh pathway observed in fu mutants when expressed only in the anterior neighbouring cells of Hh, which are the wg-expressing cells (Thérond, 1999)
Forced expression of Fu in S2 cells stimulates Hh-triggered and Ci-dependent transcriptional activation (Fukumoto, 2001)
N-term kinase domain is required for this activity but the C-term is not (Fukumoto, 2001)
Threonine 158 is essential for Fu activity; may be involved in the activation of the kinase catalytic activity (Fukumoto, 2001)
fu phenotype is exacerbated by reducing col dosage (Vervoort, 1999)
In fu1 mutant discs, col expression at the A/P boundary was interrupted at the dorso-ventral margin (Figure 5c), correlating with local fusion of veins L3–L4 at the margin (Figure 5a). (Vervoort, 1999) kn medial expression in the wing pouch is reduced in fu mutants (Mohler, 2000)

Physical interactions

Immunoprecipitations from ovarian extracts show that Sxl is in a complex with Fu and Cos2, along with b- and g-tubulin (Vied, 2001)
The C-term domain (aa 421-805) of Fu is necessary and sufficient to bind Cos2 (Ascano, 2002)
The C-term domain can compete with endogenous Fu for binding to Cos2 (Ascano, 2002)
There appears to be a separate Cos2-Fu species in gel filtration experiments (Ascano, 2002)
aa 306-436 was sufficient for binding to Su(fu) (Monnier, 1998)
Ci and Fu co-IP (Robbins, 1997)
Ci interacts w/ Fu-reg through Su(fu) (Monnier, 1998)
Cos-2-Fu-Ci complex associates w/ microtubules in absence of Hh signaling (Robbins, 1997, Sisson, 1997)
complex is made irrespective of Fu and Cos-2phosphorylation (Robbins, 1997)
Complex probably contains Su(fu) (Monnier, 1998)
Fu-P might preferentially associate w/ Cos-2 (Robbins, 1997)
Functional Fu kinase is probably not necessary for Fu and Cos-2association (Robbins, 1997)

Transcriptional Regulation

Fu protein is throughout wing disc, but higher in A

Structure

N-term (1 - ~268aa) domain has ~30% identity with catalytic domain of serine-threonine kinases (Therond, 1993)
C-term domain has no significant similarity with any known protein and may represent the regulatory domain of the kinase (Therond, 1993)

Location (protein and transcript)

Fu transcripts are uniformly distributed in embryo (Thérond, 1993)
Fu protein is present throughout the entire wing disc, but its level is much higher in the anterior compartment (Fig. 1D Alves, 1998)
Fu and Cos2 can enter the nucleus, but the rate of entry does not change with Hh signaling (Methot, 2000)

Protein Modifications and Regulation

Becomes phosphorylated in both embryos and S2 cells in response to Hh activity (Therond, 1996)
becomes hyperphosphorylated (on serines) in response to Hh activity
- appears as long as 30 minutes after induction, suggesting that it represents a feedback device rather than an event in initial signal transduction. This leads in turn to the possibliity that Fused is not autophosphorylating, even though the phosphoryation can be abolished by mutations in the catalytic domain of Fused. Similarly, Fused is apparently not directly responsible for the phosphorylation of Cos2, which occurs even when inactivating mutations are present in the kinase domain of Fused (Robbins, 1997).

Related to

human fused (Murone, 2000)

Mutations

Class 0: large deletions encompassing the whole fu gene and some neighboring genes (Preat, 1993)
- completely suppressed for all their mutant phenotypes by Su(fu)^LP (Preat, 1993)
Class I: mutation in kinase domain that doesn’t affect open reading (Preat, 1993)
- completely suppressed for all their mutant phenotypes by Su(fu)^LP (Preat, 1993)
Class II: mutates regulatory domain (Preat, 1993)
- although suppressed for their fused phenotype, display a new maternal and zygotic phenotype with Su(fu)^LP, which looks like cos-2 mutations (Preat, 1993)
Class dominace I > II > 0 : class mutants are dominant over class II in fuII; Su(fu)^LP flies whereas class 0 mutants are recessive over class II in fu0 / fuII; Su(fu)^LP
Fu phenotype:
- embryos:
  - fuII; Su(fu)^LP embryos lack the median anterior part of each segment with mirror-image duplication of the remaining most anterior structures (Preat, 1993)
- adult wings:
  - reduction of the 3-4 intervein region; anterior double row bristles reach the fourth vein
  - Only fu- clones located between veins 3 and 4 generate a mutant phenotype; fu clones never effected vein 4 (Alves, 1998)
  - fu- clones never crossed the A/P boundary (Alves, 1998)
  - fuII; Su(fu)^LP adults display duplication of the wing and leg anterior compartments (Preat, 1993)
A lot of fu mutations are in (Therond, 1996) see also: FlyBase Report
Mutations in the extracatalytic domain abolish both the biological fxn of Fu and its association w/ Cos-2 (Robbins, 1997)
Eliminating Fu kinase activity reduces Hh-target gene expression while inc. [Ci-155]
The absence of late en expression in fu mutants could account for the expansion of the dpp stripe up to the A/P boundary and for the concomitant extension of the double row bristles (Alves, 1998)
In fu mutants Ci accumulates at a high level in a 10 cell wide stripe which displays a sharp posterior limit along the A/P border (Alves, 1998) fuA and fu94 have high levels throughout the A (Alves, 1998, Wang, 2000)
Fu mutations suppress the effects of ectopic hh expression (Alves, 1998)
In fu mutants late en expression is lost which might result in the wider dpp stripe due to absence of en (Sanchez-Herrero, 1996)
In fused mutant wing discs Col and Ptc expression (protein and transcript) is absence approximately six rows of cells on either side of the DV boundary (Fig 1) (Glise, 2002) and the stripe is broadened due to increased range of Hh in fused mutants (Fig 1) (Glise, 2002)
In fused mutant wing discs dpp expression is down-regulated at the DV boundary, but this is not detectable by dpp-lacZ staining (Fig 1) (Glise, 2002)

Overexpression / Ectopic expression

Overexpression using several strains that strongly express Gal4 throughout the wing disc, did not lead to any abnormalities in an otherwise wild-type background (Alves, 1998)

Reagents

Ab made against 419-493aa (Robbins, 1997)