Skeletal disorders associated with fibroblast growth factor receptor mutatios

378

Skeletal disorders associated with fibroblast receptor mutations Laurence De Moerlooze* Mutations

in three fibroblast

underlie

several

include

dwarfism

affecting analysis

autosomal

growth

and various

limb and craniofacial of several

a constitutive

of these

activation

factor

dominant

and Clive Dickson? receptor

skeletal

craniosynostosis bone patterning.

mutations

of the receptor

loci

disorders;

these

syndromes A functional

has demonstrated kinase

that

is a common

theme.

Addresses Imperial Cancer Research Fund, 44 Lincoln’s Inn Fields, London WCPA 3PX, UK *e-mail: [email protected] +e-mail: [email protected] Current Opinion in Genetics

& Development

growth factor

1997, 7:378-385

(Table known isoform

1). As the extreme examples, FGFl binds all receptor isoforms, whereas FGF7 binds a single FGFRZ(IIIb). hlost FGFs, however, bind and

activate a subset of two or three receptors usually of the 111~ or IIIb isotype (see [13]). In cell culture, the FGFs may induce cell proliferation, promote cell motility or cell survival, as well as modulate cellular differentiation (reviewed in [8,14]). Gene expression studies in the mouse embryo have shown the FGFs and their receptors to be expressed in complex non-exclusive spatial/temporal patterns (reviewed in [1,3]). Recently, the generation of mice with deficiencies in a number of FGF ligands or their receptors has provided their involvement in embryonic (reviewed in [ 1,3]).

further patterning

evidence for and growth

http://biomednet.com/elecref/O959437XOO700378 Q Current Biology Ltd ISSN 0959-437X

Mutations

Abbreviations FGF fibroblast growth factor FGFR FGF receptor immunoglobulin 19 TD thanatophonc dysplasia TM transmembrane

Achondroplasia is the most common genetic form of dwarfism, which is a fully penetrant autosomal dominant trait. The condition is characterized by a pronounced shortening of the proximal long bones of the limbs, macrocephaly and other skeletal abnormalities. The achondroplasia locus was mapped to chromosome 4~16.3 and the mutated gene identified as FGFK.J [l&16]. In >99% of achondroplasia cases analyzed, a glycine-+arginine (Gly380-+Arg) substitution has occurred within the transmembrane domain of the receptor (see Table 2 for references). Taking into account the mainly sporadic nature of the condition, this substitution mutation is a remarkably specific sequence alteration, which in >95% of cases results from a single glycinejarginine transition. In a few individuals, other missense mutations have been identified that also reside within or close to the transmembrane (Thl) domain of the receptor (Table 2).

Introduction Genetic linkage three members

analysis of the

has implicated the mutation of fibroblast growth factor (FGF)

receptor gene family as the underlying causes of several human dysmorphic diseases, including skeletal dysplasias and autosomal dominant craniosynostosis syndromes (reviewed in [l-l]). The genomes of mouse and man have been shown to encode four FGF receptor genes, FGFRl-4, each comprising an extracellular region containing two or three Ig-like loops, depending on the choice of splice sites, a single transmembrane segment and a cytoplasmic portion encompassing a tyrosine kinase domain (Fig. 1; reviewed in [S-7]). Receptor diversity is further increased by alternative splicing of the membrane-proximal half of the third Ig-loop, which results in receptor isoforms with different ligand-binding specificities (Fig. la: Table 1). The alternative exons are designated IIIb and 111~ and the same terminology is used to denote

specific

receptor

isoforms.

There are at least 10 FGFs which constitute a family of protein ligands with -3O-50% primary sequence identity (reviewed in [2,3,8,9]). FGF signal transduction results from ligand binding to the receptor in conjunction with a cell surface heparan sulphate containing proteoglycan, facilitating oligomerization and autophosphorylation of the receptor [6,10-121. The FGF ligands demonstrate overlapping specificities for the different receptor isoforms

of FGFR3 and skeletal

dysplasias

Whereas the heterozygous mutation rarely causes lethality individuals that are homozygous for the achondroplasia mutation have a very severe disease which is usually fatal soon after birth. This condition resembles a form of lethal neonatal dwarfism known as thanatophoric dysplasia (TD). This disorder was also shown to result from mutations in FGFR.? [17]. TD cases show a characteristic narrowing of the thorax and can be subdivided into two forms on the basis of the radiological appearance of limb and skull anomalies: TD type I is characterized by curved short femurs often in addition to a cloverleaf shaped skull, and type II by straight femurs and a marked cloverleaf skull [17]. The majority of type I TD have either missense mutations at sites in the extracellular region of the receptor or a base change in the stop codon resulting in a 141 amino acid extension of the carboxyl terminus of the protein [17-201. Of the five different missense mutations reported.

Fibroblast growth factor receptor mutations De Moerlooze

379

and Dickson

Figure 1

FGFR(Nlb) splicing

FGFR(lllc) epliiing \

\

\

\ \

\

\ \

\ \

\ 1

\

\ \

\

‘\’ \\

\

&d

#UrnlHNs

FlwRl FwR2 FOFR3

’ 11 II

I ’

+

\ Amlna

\

\’

\

I

24;)

‘; I I I I

249

312’

’

246 ;

313

I

I

I I I I

I I

380’ 361’

’

310;

I I

I

I

II

‘\I

I I I I

368; I I

I I

I

II

’

I

\

l I

l

’

I

\

I

l

I

I

\ \

\ 0’4

I

I

\

I

I

I \

\ \

\

I

I

I

I

\

’

\

I

\

’ \

\

TKD 2

TKD 1

I-II

Domains

lg.11

11-111

l9_lll

l&

T

I

M

I

L

0 1997 FGF receptor

structure.

(a) Schematic

depiction

of the alternative

splicing

in the portion

of the FGF receptor

specificity. (b) Representation of the FGF receptor polypeptide across the plasma membrane. rectangle), and the membrane proximal (MP) domain comprise the extracellular portion. TM is fragment contains the domains (TKD 1 and TKD 2) of the tyrosine kinase. Alternative splicing alternative proximal half of the third lg-loop (Illb or Illc). The last amino acid numbers encoded

all

introduce

Ig-loop

(Table

a cyst&e residue in or around the third 2). In contrast, the type II TD show much

less allelic heterogeneity with a single known missense substitution, lysine+glutamic acid (Lys650+Glu), in the tyrosine kinase domain of the receptor [17]. Recently, droplasia,

a third autosomal dominant disorder, has been associated with mutations

hypochonin FGFR3

[Zl-231. Clinically, this chondrodysplasia is less severe with no associated craniofacial abnormalities. To date, hypochondroplasia patients have shown a single missense mutation, asparagine-+lysine (Asn540+Lys), in the tyrosine kinase domain of the receptor. To investigate the effect of missense FGFR? mutations, the activity of mutant receptors has been investigated in vitro. Introduction of the Gly380+Arg substitution was shown to confer a modest &and-independent activation of the receptor kinase, which could be further stimulated

I Tyrosine

Ligand binding

kin&se

Current Opimon I” Genetics &Development

gene that affects

ligand-binding

The lg-loops, the acid box (cross-hatched the transmembrane segment. The cytoplasmic of the FGF receptor genes generates an by the exons are indicated above the diagram

[5].

by the addition of ligand [24**-26”]. Similarly, the Arg248+Lys mutation, present in the more severe type I TD, was shown to cause a more pronounced ligandindependent receptor-kinase activation [ZP], whereas the Lys650+Glu mutation characteristic of type II TD caused a strong constitutive activation of the kinase but the receptor retained ligand-dependent sensitivity leading to a super-activation of the kinase [25”,27]. Overall, these reports a constitutive greater

suggest that the missense activation of the receptor

in the more

severe

mutations cause kinase, which is

phenotypes.

several mechanisms have been Although speculative, suggested to explain receptor activation. By analogy to a mutation found in the Neu/ErbBZ receptor [28], the (Gly380--+Arg) substitution in the TM domain probably facilitates receptor oligomerisation by hydrogen bond formation resulting in kinase activation [24**,29]. The extracellular domain point mutations found in type I

380

Genetics

of disease

Table 1 Receptor specificity

of the different

FGF ligands. FGF ligand

(Location)

FGF receptor

FGFl

FGF2

FGF3

++

FGF4

FGF5

FGF6

+-I-+

++

++

+

FGF7

FGF8b

FGF8c

FGF9

-

+

(8pl2-p21) FGFRl lllb

+++

++

Ilk

-I-++

i-i-+

(1 Oq25-q26) FGFRP lllb

+++

lllc

cc+

++

++ +++

+++

+++ +++

+++

++

+++

+++

+++

if

i-I-+

+

(4~1’3 FGFR3 lllb lllc (5q35) FGFR4 Relative

(Illc) mitogenic

The chromosome

activity locations

normalized

to that of FGFl

for the receptor

(100%):

+++ +++,

>70°/o;

++, 46-70%;

+, 20-45%;

+++

++

+ +-I-+

++

+

+++

-, ~20%

(data taken from [21 and 1131).

genes are given in brackets.

TD individuals all introduce a cyst&e (Table Z), that could promote homodimerization through disulphide bond formation; evidence for ligand-independent dimerization has been demonstrated for the Arg248+Lys mutation [25**,26**]. In contrast, the Lys650+Glu substitution, which is within the kinase activation loop, appears to result in direct activation of the kinase [25”,27]. This idea is supported by the finding that the two tyrosines associated with ligand-dependent activation of the kinase are not necessary for activity in the presence of the Lys650+Glu substitution [27]. A diminished rate of endochondral ossification is the apparent cause of the reduced bone elongation. In the mouse, the Fgfr3 receptor is expressed in bone cartilage during endochondral ossification [30] and mice deficient for Fgf3 show skeletal abnormalities affecting the vertebrae, ribs and long bones [31*,32*]. Contrary to the human chondrodysplasias, however, their proximal

limb bones are disproportionately lengthened. both phenotypes suggest that FGFR3 signalling negatively regulate endochondral bone growth.

Hence, acts to

FGF receptor mutations associated with craniosynostosis syndromes Premature fusion of the cranial sutures, or craniosynostosis, results in an abnormal skull shape usually manifest as a tall forehead, widely spaced and prominent eyes (proptosis) and mid-face hypoplasia. Several disorders with these characteristics are inherited as autosomal dominant traits but can be distinguished as different syndromes by the severity of the craniofacial anomalies and associated limb and skin conditions. Over the last three years, mutations in FGFRI, FGFRZ and FGFR3 have been linked to several of these syndromes which include Crouzon, Jackson-Weiss, Pfeiffer, Apert and Beare-Stevenson cutis gyrata (see Table 3 for references). The most common and mildest of these disorders is

Table 2 Mutations

associated

with chondrodysplasias.

Chondrodysplasia

FGF receptor FGFR3

Achondroplasia

Missense

mutation G380R

(99%)

Exon

Domaln

TM

TM

115,161 [65,661

TKl

[21-231

G375C Hypochondroplasia Thanatophonc

FGFR3

Missense

FGFR3

Missense

N540K

dysplasia

Type t

R248C

(50%)

s249c s371c G370C Y373C stop

FGFR3

Type 2 MP, membrane

References

proximal

domain;

TK, tyrosine

Missense kinase domain;

11-111

TM

MP

1171 [201

Cytoplasmic

X807G X807R X807C K650E TM, transmembrane

llla

TK2 segment.

1171 [191 [181

[t 71

Fibroblast growth factor receptor mutations De Moerlooze and Dickson

Crouzon

syndrome

which

primarily

affects

craniofacial

features. The majority of Crouzon syndrome cases show missense mutations of FGFRP located in exons IIIa and IIIc, although insertions, deletions and aberrant splicing have also been reported, testifying to the allelic heterogeneity associated with this disorder (see Table 3 for references). is also linked

Beare-Stevenson cutis with missense mutations

gyrata syndrome adjacent to the

transmembrane domain of FGFRZ ([33]; Table 3). In addition to craniosynostosis, the syndrome is characterized by a furrowed and corrugated skin and an extensive acanthosis nigricans and hyperpigmentation

(verrucous of the

hyperplasia, hypertrophy skin). Interestingly, a few

cases of Crouzon syndrome have also been reported with an associated acanthosis nigricans skin condition but these are linked to a mutation (Ala391+Glu) in the transmembrane region of FGFRS [34,35]. Surprisingly, dwarfism is not apparent in these Crouzon patients, although the mutation lies within the TM domain only a few amino acids from the achondroplasia mutations Gly375+Cys and Gly380+Arg. The FGFR2 and FGFR3 mutations associated with accompanying skin disorders are located outside the differentially spliced region of the receptor and therefore affect both the IIIb and IIIc isoforms (Fig. 1). The IIIb isoforms of both receptors are expressed in skin and FGFRZ(IIIb) has been implicated in wound repair, suggesting a potential link to explain the skin phenotype [36-381. Jackson-Weiss syndrome is distinguished clinically from Crouzon’s on the basis of additional foot anomalies primarily in the form of enlarged and sideways-pointing great toes, whereas Pfeiffer syndrome patients invariably show both foot and hand deformity. The hands of Pfeiffer patients have characteristically broad thumbs associated with varying degrees of cutaneous syndactyly (fusion of the digits). The most disfiguring of all these autosomal dominant craniosynostoses is Apert syndrome, where the syndactyly of the hands and feet often include bone and soft tissue fusions. Despite the clinical differences between majority

the various craniosynostosis syndromes, the vast of the mutations have been shown to occur in

[37,41].

Like

FGFR3

the

mutations

chondrodysplasia, all the FGFRZ mutations been shown to cause a ligand-independent

associated

381

with

analyzed have activation of

the receptor kinase [26**,42’,43’]. The creation of an unpaired cysteine by gain or loss of one cysteine of a pair in Ig-loop III is the most common mutation and can lead to receptor dimerization by disulphide bonding [43*]. Despite

the common

theme

of receptor

kinase

activation,

there is a confusing plasticity of phenotype associated with the same or similar mutations; for example, the Cys342+Arg mutation in FGFRZ has been associated with Crouzon, Pfeiffer and Jackson-Weiss syndromes in different patients, and there are several other examples indicated (in bold type) in Table 3. This range of phenotypes suggests the strong influence of other non-linked loci. In contrast, different FGF receptors have been implicated in the same disorder (e.g. FGFRZ and FGFRS mutations in Crouzon syndrome and FGFR2 and FGFRI in Pfeiffer syndrome). Furthermore, the mutation found in some Pfeiffer syndrome patients involving FGFRl (ProZSZ+Arg) is analogous to the FGFRZ (Pro253+Arg) substitution in Apert syndrome and an FGFR3 (ProZO+Arg) mutation found in a number of families with non-classical craniosynostosis (Table 3) [44]. This latter mutation together with Ala391+Glu of Crouzon with acanthosis nigricans both lie in FGFRS but they do not cause a dwarfism. Taken together, these observations suggest that substantial functional redundancy could be associated with FGFR signalling involved in the intramembranous ossification of the skull flat bones. There are some inherited craniosynostoses that are not associated with FGFR mutations. These include a Pfeiffer mutation at lOq25 [45] which is also the location of FGF8, a known ligand for FGFRZ(IIIc) [13,46], and Saethere-Chotzen syndrome which involves craniosynostosis and limb abnormalities. In the latter case, a candidate gene has been mapped to 7p21-p22 and shown to encode a helix-loop-helix transcription factor designated TlVZS” [47*,48*]. The Drosophila homologue of TWIST has been

the IIIc isoform of FGFRZ (Fig. 1; Table 3). There are a few exceptions, as indicated above, and also some Pfeiffer syndrome patients have shown a mutation in the FGFRl gene (see Table 3).

implicated in the formation of embryonic mesoderm, a process which also requires FGFR function, although the precise relationship of these genes is unknown [49]. Furthermore, mice null for Twist show defects in cranial neural tube morphogenesis, whereas the heterozygotes

As a general rule, mutations found in Crouzon and Pfeiffer syndrome patients lie within or adjacent to Ig-loop III of the receptor (Fig. 1; Table 3). This region of the receptor together with Ig-loop II constitutes the ligand-binding domain [36,39,40]. hlany of the mutations occur in the membrane proximal half of the third Ig-loop which can include sequences encoded by either the IIIb or IIIc exon. To date, mutations have been found exclusively in the 111~ exon (see Fig. l), which is consistent with the expression of this receptor isoform in the pre-bone cartilage rudiments, the presumptive sites of osteogenesis

show anomalies is the intriguing common

pathway

Conclusions

in digit development [48*,50]. Thus, there possibility that these loci form part of a of bone

development.

and future perspectives

hlissense mutations causing the constitutive activation of three different FGFRs appear to underlie several inherited autosomal dominant skeletal disorders. The chondrodysplasias specifically demonstrate mutations of FGFR3, whereas the craniosynostosis syndromes show a marked allelic heterogeneity and phenotypic plasticity

382

Genetics

of disease

Table 3 Mutations

associated

Craniosynostotic

with craniosynostosis

syndromes.

syndrome

-

FGF receptor

Crouzon

FGFR2

mutation

Missense

Exon

Domaln

Ma

ll-lll

[621

lg-Ill

1561

S252L S267P

References

C278F

b6,601 KX',561

CU89P W290GIR Y328C N3311

lllc

1511 (631 (41 [51,541 [541 152,561 [SOI 1511 1541 141 [5 1,54,68]

G338R Y340H C342SIRN C342WlF A344G

MP

s347c s354c Splice site deletion Deletion Insertion Crouzon

with acanthosis

nigricans

Jackson-Weiss

FGFR3 FGFR2

Missense Missense

Pfeiffer

FGFRP

Missense

Apert Non-syndromic

craniosynostosis

Splice

site

Splice

site deletion

FGFRl FGFRP

Missense Missense

FGFRB FGFRP

Missense Sphce site deletion

V359F A344A-6345-381

lilt

A287-289 A356-358

llla lllc

T268TG DA336-337DADA A391 E

llla lllc TM

Q289P C342R A344G S252F+P253S C278F D321A T341P C342 R/Y/S A344P V359F A-iG T-iG A31 4s A345-381 P252R S252WlF P253R P250R

llla lllc

Beare-Stevenson

Mutations

cutls gyrata

in bold type are present

FGFR2

Missense

in more than one syndrome.

MP, membrane

involving mutations in three different FGF receptor genes. A common theme is emerging, however, where the functional consequences of the various missense mutations is a ligand-independent activation of the receptor tyrosine kinase. This presumably causes inappropriate receptor signalling which negatively affects the growth and/or patterning of bone. The ability to introduce specific mutations into the FGFR genes in the mouse germline should facilitate the further dissection of the role FGFs have in cellLcell signalling during mammalian development. Combinations of FGFR and ligand mutations could provide much-needed insight into the degree of functional redundancy of this signalling

proximal

system

domain;

that

[561 I631

lg-Ill

I591 1631 [341 [591 [521 [511 [621 [591 1581 [611 [5%611 [591

TM lg-Ill MP ll-lll

llla

lg-Ill lllc

MP lllc (5’)

lg-Ill

[581 [451

lllc llla

MP ll-lll

llla

ll-lll

(591 [551 [57,621 [571 1441 b41 [661

Y105C G338E s351c G348R S372C Y375C

Missense

MP lg-Ill MP

llla

ll-lll

lllc

MP lg.1

lllc

lg-Ill

TM

MP TM

TM

MP

TM, transmembrane

affects

bone

1331

segment.

patterning

and

growth.

The

determination of the three-dimensional structure for these receptors should be particularly informative for understanding the complexities which lead to the observed phenotypic plasticity. Finally, and most importantly, it is possible that specific inhibitors of FGFR signalling can be developed that might be used to inhibit receptor signalling in these patients during postnatal development and help to ameliorate the phenotypic consequences associated with inappropriate FGFR signalling.

Fibroblast

References

and recommended

reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

. ..

Wilkie AOM, Morrisskay GM, Jones EY, Heath JK: Functions of fibroblast growth-factors and their receptors. Curr Biol 1995, 5:500-507.

2.

Muenke M, Schell U: Fibroblast-growth-factor receptor mutations in human skeletal disorders. Trends Genet 1995, 11:308-313. Yamaguchi TP, Rossant J: Fibroblast growth-factors in mammalian development Curr Opm Genef Dev 1995, 5:485-491.

factor

receptor

mutations

of FGFR3 in thanatophoric 1995,4:2175-2177.

De Moerlooze

dysplasia type-l.

and Dickson

383

Hum MO/ Genet

21.

Bellus GA, McIntosh I, Smith EA, Aylsworth AS, Kaitila I, Horton WA, Greenhaw GA, Hecht JT, Francomano CA: A recurrent mutation in the tyrosine kinase domain of fibroblast growth factor receptor 3 causes hypochondroplasia. Nat Gener 1995, 10:357-359.

22.

Rousseau F, Bonaventure J, Legeai-Mallet L, Schmidt H, Weissenbach J, Maroteaux P, Munnich A, Le Merrer M: Clinical and genetic heterogeneity of hypochodroplasia. J Med Genet 1996, 33:749-752.

23.

Prinos P, Costa T, Sommer A, Kilpatnck M, Tsipouras P: A common FGFR3 gene mutation in hypochondroplasia. Hum MO/ Genet 1995, 4:2097-2101.

of special interest of outstanding interest

1.

3.

growth

Webster MK, Donoghue DJ: Constitutive activation of fibroblast growth-factor receptor-3 by the transmembrane domain point mutation found in achondroplasia. EM60 J 1996, 15:520-527. The achondroplasia mutation, as well as several other possible substitutions at the same or an adjacent site, shows constitutive activation of the receptor kinase. There is a correlation between the capacity to participate in hydrogen bond formation and kinase activation. 24. ..

4.

Park W-J, Bellus G, Jabs E: Mutations in fibroblast growth factor receptors: phenotypic consequences during eukaryotic development Am J Hum Genet 1995. 571740-754.

5.

Johnson D, Williams L: Structural and functional diversity in the FGF receptor multigene family. Adv Cancer Res 1993, 60:1-41.

6.

Mason IJ: The ins and outs of fibroblast growth-factors. 1994, 78:547-552.

7.

Green PJ. Walsh FS, Doherty P: Promiscuity of fibroblast growth-factor receptors. Bfoessays 1996, 18:639-646.

6.

Basilic0 C, Moscatelli D: The FGF family of growth-factors oncogenes. Adv Cancer Res 1992, 59:115-l 65.

9.

Yamasaki M, Miyake A, Tagashira S, ltoh N: Structure and expression of the rat mRNA encoding a novel member of the fibroblast growth factor family. J Biol Chem 1996, 271 :15916-l 5921.

Cell

and

10.

Spivak-Krouman T, Lemmon MA, Dikic I, Ladbury JE, Pinchasi D, Huang J, Jaye M. Crumley G, Schlesslnger J, Lax I: Heparininduced oligomerization of FGF molecules is responsible for FGF receptor dimerization, activation, and cell-proliferation. Cell 1994, 79:1015-l 024.

11.

Omitz DM, Leder P: Ligand specificity and heparin dependence of fibroblast growth-factor receptor-l and receptor-3. J Biol Chem 1992, 267:16305-l 6311.

12.

Ornitz DM, Herr AB, NIlsson M, Westman J, Svahn CM, Waksman G: FGF binding and FGF receptor activation by synthetic heparan-derived disaccharides and trisaccharides. Soence 1995, 268:432-436.

13.

Ornitz DM, Xu JS, Calvin JS. McEwen DG, MacArthur CA, Coulier F, Gao GX, Goldfarb M: Receptor specificity of the fibroblast growth-factor family. J Biol Chem 1996, 271 :15292-l 5297.

14.

Burgess W, Maciag T: The heparin binding (fibroblast) growth factor family proteins. Annu Rev Biochem 1989, 58:575-606.

15.

Shiang R, Thompson LM, Zhu YZ, Church DM, Fielder TJ, Boclan M, Winokur ST, Wasmuth JJ: Mutations in the transmembrane domain of FGFR3 cause the most common genetic form of dwarfism, achondroplasia. Cell 1994, 78:335-342.

16.

Rousseau F, Bonaventure J, Legeai ML, Pelet A, Rozet JM, Maroteaux P, Le MM, Munnlch A: Mutations in the gene encoding fibroblast growth factor receptor-3 in achondroplasia. Nature 1994, 371:252-254.

1 7.

Tavormma PL, Shiang R, Thompson LM, Zhu YZ, Wilkin DJ, Lachman RS, Wilcox WR, Rimoln DL, Cohn DH, Wasmuth JJ: Thanatophoric dysplasia (type-l and type-10 caused by distinct mutations in fibroblast growth-factor receptor-3. Nat Genet 1995, 9:321-328.

18.

Rousseau F, Saugier P, Le Merrer M, Munnich A, Delezoide A-L, Martoteaux P, Bonaventure J. Narcy F, Sanak M: Stop codon FGFRJ mutations in thanatophoric dwarfism type 1. Nat Genet 1995, lO:ll-12.

19.

Rousseau F, Elghouzzi V, Delezoide AL, Legeaimallet L, Lemerrer M, Munnich A, Bonaventure J: Missense FGFR3 mutations create cysteine residues in thanatophoric dwarfism type-i (tdl). Hum Mot Genet 1996, 5:509-512.

20.

Tavormina PL. Rimoin DL. Cohn DH, Zhu YZ, Shiang R, Wasmuth JJ: Another mutation that results in the substitution of an unpaired cysteine residue in the extracellular domain

25. ..

Naski MC, Wang Q, Xu JS, Ornltz DM: Graded activation of fibroblast growth-factor receptor 3 by mutations causing achondroplasia and thanatophoric dysplasia. Nat Genet 1996, 13:233-237. This paper shows that the achondroplasia and TD mutations result in constitutive activation of the FGFR3 receptor kinase. They also demonstrate that the receptor kinase activity may or may not retain ligand responsiveness depending on the mutation; there is an approximate correlation between the level of kinase activation and the severity of the phenotype. Neilson KM, Friesel R: Ligand-independent activation of fibroblast growth-factor receptors by point mutations in the extracellular, transmembrane, and kinase domains. J B/o/ Chem 1996, 271:25049-25057. An examination of the biochemical and functional consequences of several FGF receptor mutations identified in inherited chondrodysplasias and cranlosynostosis syndromes. The mutations have been transposed to the highly homologous Xenopus FGFRl and FGFR2 cDNAs and the effects on cellular tyrosine phosphorylation, receptor autophosphorylation and mesoderm induction in animal caps have been assessed. All but one of the mutations scored positive In these assays 26. ..

27.

Webster MK, Davis PY, Robertson SC, Donoghue DJ: Profound ligand-independent kinase activation of fibroblast growthfactor receptor-3 by the activation loop mutation responsible for a lethal skeletal dysplasia, thanatophoric dysplasia type-II. MO/ Cell t3iol 1996, 16:4081-4087.

28.

Bargmann C, Hung M. Weinberg R: Multiple independent activations of the neu oncogene by a point mutation altering the transmembrane domain of ~185. Cell 1986, 45:649-657.

29.

Sternberg M, Gullick W: Neu receptor dimerization. i 989, 339:587.

30.

Peters K, Omitz D, Werner S, Williams L: Unique expression pattern of the fgf receptor-3 gene during mouse organogenesis. Dev Biol 1993, 155:423-430.

Nature

31.

Calvin JS, Bohne BA, Harding GW, McEwen DG, Ornitz DM: Skeletal overgrowth and deafness in mice lacking fibroblast growth factor receptor 3. Nat Genet 1996, 12:390-397. See annotation [32’].

.

32. .

Deng C, Wynshaw BA. Zhou F, Kuo A, Leder P: Fibroblast growth factor receptor 3 is a negative regulator of bone growth. Cell 1996, 84:91 I-921. These two papers [31’,32’] show that mice deficient for FGFR3 exhibtt prolonged endochondral bone growth which causes skeletal abnormalities such as disproportionately extended limbs. These findings together with histological evidence demonstrate a role for FGFR3 as a negative regulator of endochondral ossification. This work provides a conceptual framework for understanding the consequences of inappropriate FGFRB activation found in various chondrodysplasias. 33.

Przylepa KA, Paznekas W, Zhang MH. Golabl M. Bias W, Bamshad MJ, Carey JC, Hall BD, Stevenson R, Orlow SJ ef a/.: Fibroblast

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35.

Cutis

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