ライフサイエンスコーパス: activin receptor

1 possibly through competition for binding to activin receptors.

2 tion and thereby block Nodal from binding to activin receptors.

3 These effects appear to be mediated through activin receptors.

4 ansforming growth factor-beta (TGF-beta) and activin receptors.

5 ansforming growth factor-beta (TGF-beta) and activin receptors.

6 ceptors, and Smad2 and Smad3 by TGF-beta and activin receptors.

7 -11, are dimeric cytokines signaling through activin receptors.

8 ACVR2B/Fc, an inhibitor of the Activin Receptor 2B signaling, has been shown to preserv

9 The activin receptor, a transmembrane serine-threonine kinas

10 ion, while expression of a dominant negative activin receptor abolishes ntl and gata5 expression.

11 forms, we have investigated the mechanism of activin receptor activation.

12 RIE cells expressed activin A, the activin receptors ActRI and ActRII, and the follistatin-

13 Type II activin receptors (ActRII and ActRIIB) are single-transm

14 Here, mutations of activin receptors ActRIIA and ActRIIB are shown to disru

15 the activin betaA and betaB subunits and the activin receptors ActRIIA and ActRIIB was demonstrated b

16 high affinity receptor for activin, type II activin receptor (ActRIIA), by administration of the sol

17 The type II activin receptors, ActRIIA and ActRIIB, have been shown

18 s muscle mass involves activation of type II activin receptors, ActRIIA/B, which yield profound muscl

19 tudy we show that disruption of the type IIB activin receptor (ActRIIB) by gene targeting results in

20 low molecular weight complex that stimulated Activin receptor (Acvr) signaling far more potently than

21 generated mice with conditional deletion of activin receptor (ACVR) type 2A, ACVR2B, or both, in ost

22 by binding to a complex comprising Type I/II Activin receptors (Acvr) and the co-receptor Tdgf1.

23 res functional similarities with the type II activin receptors ACVR2A and ACVR2B, as it interacts wit

24 volvement of the TGFbeta superfamily type II activin receptors, Acvr2a and Acvr2b, in regulating prol

25 s the differential effects of the two type I activin receptors ALK-2 and ALK-4.

26 Here we show that the activin receptor ALK4 is a key regulator of the specific

27 supports activin cross-linking to the type I activin receptor ALK4.

28 of CRFR2beta replaces the ECD of the type 1B activin receptor (ALK4).

29 Here we report that specific deletion of the activin receptor ALK7 in BAT resulted in fasting-induced

30 nce suggests that ActR-IIB acts as a primary activin receptor and ActR-IB acts as a downstream transd

31 Inhibin also binds type II activin receptors and antagonizes many activin effects.

32 Because Cripto mediates signaling via activin receptors and binds directly to ALK4, we tested

33 compete with activin for binding to type II activin receptors and, thus, prevent activin signaling.

34 g diseases, with a decrease of myostatin and activin receptor, and an increase of the myostatin antag

35 m birth to adulthood, activin betaA subunit, activin receptors, and functional activin antagonists we

36 Inhibin competes with BMPs for type II activin receptors, and this competition is facilitated b

37 which would be, therefore, candidate type II activin receptor antagonists.

38 Thus, the type I and type II activin receptors are involved in overlapping but distin

39 esults provide genetic evidence that type II activin receptors are required for egg cylinder growth,

40 ermore, the effects of constitutively active activin receptors are strictly cell-autonomous.

41 Indeed, we found that both activins and activin receptors are upregulated in duct epithelial cel

42 same two ligands act redundantly through the Activin receptor Babo and its transcriptional mediator S

43 an R7-dependent behavior, we identified the Activin receptor Baboon and the nuclear import adaptor I

44 Neuroblasts missing the activin receptor Baboon have a delayed intrinsic program

45 We find that the Activin receptor Baboon is required in R8 to receive non

46 we have pinpointed the residues required for activin receptor binding and activity, as well as for in

47 diated through a competition for the type II activin receptor but also require the presence of an inh

48 ve shown that Nodal signaling is mediated by activin receptors but also requires EGF-CFC coreceptors,

49 Inhibins also bind type II activin receptors but do not recruit ALK4, providing a c

50 family and drive SMAD2/3 phosphorylation via activin receptors, but activins have not been studied in

51 Nodal and Activin both activate Activin receptors, but only Nodal requires EGF-CFC corec

52 ession of a normally right-sided marker, the activin receptor cAct-RIIa.

53 ressed alone, the type II but not the type I activin receptor can bind activin.

54 or other TGFbeta family members that bind to activin receptors cannot explain development of maxillar

55 ongly with inactive heteromeric TGF-beta and activin receptor complexes and is released upon activati

56 The activin receptor CPE is bound by a Mr 36 x 10(3) protein

57 nsive because they had reduced expression of activin receptors (eg, ALK-4).

58 h that multiple TGF-beta signals converge on Activin receptor/EGF-CFC complexes and suggest a more wi

59 soluble extracellular domain of the type II activin receptor from mouse (ActRII-ECD).

60 HRadjBMI for variants in ACVR1C, encoding an activin receptor, further highlighting the involvement o

61 onist to the calcium-sensing receptor and an activin receptor fusion protein, which functions as an a

62 recurrent activating mutation affecting the activin receptor gene ACVR1 in 20% of DIPGs.

63 In large part, this function of the activin receptor has been inferred from observations of

64 Activin, Vg-1 and, type II activin receptors have been implicated in regulation of

65 ctivated Smad2 correlated with expression of Activin-Receptor-IB/ALK4, suggesting that although Smad-

66 Analysis of tooth development in activin receptor II and Smad2 mutants shows that a simil

67 We report that RAP-011, an activin receptor IIA (ActRIIA) ligand trap, improved ine

68 type II receptors, such as BMP receptor II, activin receptor IIA, and activin receptor IIB, competed

69 eals the expression of early asymmetry genes activin receptor IIa, sonic hedgehog, Caronte, Lefty-1,

70 (ii) post-natal administration of a soluble activin receptor IIB (ActRIIB-Fc).

71 Our data led us to propose activin receptor IIB as a novel DYNLT1 ligand and sugges

72 In addition, treatment with a soluble activin receptor IIB fusion (sActRIIB-Fc) protein, which

73 LEFTB (formerly LEFTY2) and ACVR2B (encoding activin receptor IIB).

74 s BMP receptor II, activin receptor IIA, and activin receptor IIB, competed with the pd for binding t

75 express myostatin and its putative receptor activin receptor IIB.

76 ignalling are at odds with it behaving as an activin receptor in the early Xenopus embryo.

77 se are the first observations of activin and activin receptor in the normal human breast and in human

78 phenotype obtained using a dominant-negative activin receptor in Xenopus [6], coupled with evidence f

79 s well as constitutively active TGF-beta and activin receptors, indicating that Smad7 transcription w

80 nsitized capsaicin responses and depended on activin receptor kinase activity.

81 tion of RNA encoding a constitutively active activin receptor leads to ectopic expression of gata5 an

82 h a truncated activin/nodal-specific type IB activin receptor leads to efficient neural induction.

83 escribe the basis for biological activity of activin receptor ligand traps, novel fusion proteins suc

84 on with the co-receptor betaglycan, to block activin receptor-ligand binding, complex assembly, and d

85 r binding affinities for the type I receptor activin receptor like kinase 1 (ALK1), ALK2 and ALK3.

86 It includes the activin receptor like kinase 1 gene (ACVRLK1 or ALK1), a

87 Activin receptor type 1 (ACVR1; ALK2) and activin receptor like type 1 (ACVRL1; ALK1) are transfor

88 d crossveinless 2 (CV2), both induced by the activin receptor like-kinase 1 (ALK1) when stimulated by

89 When activated by BMP9, activin receptor-like kinase (ALK) 1 induces HOXD3 expre

90 etween pro- and anti-angiogenic signaling by activin receptor-like kinase (ALK) 1, 5, and TGF-beta ty

91 Several type I receptors exist although activin receptor-like kinase (ALK) 5 mediates the majori

92 I receptor serine/threonine kinase known as activin receptor-like kinase (ALK) 5.

93 , which was impeded by ALK5 knockdown and by activin receptor-like kinase (ALK) receptor inhibitor SB

94 those induced by the receptor serine kinase, activin receptor-like kinase (ALK)-2.

95 factor 6 (ARF6) leads to crosstalk with the activin receptor-like kinase (ALK)-SMAD1/5 pathway.

96 inhibition was dependent on type I receptor activin receptor-like kinase (ALK)3-dependent phosphoryl

97 BMP-binding TGF-beta superfamily receptors, activin receptor-like kinase (ALK)3/6, and the Smad2/3 p

98 1542) that was identified as an inhibitor of activin receptor-like kinase (ALK)5 (the TGF-beta type I

99 nase domain of the TGF-beta type I receptor [activin receptor-like kinase (ALK)5] and the substrate,

100 Activin receptor-like kinase (ALK)7 is a type I serine/t

101 Inhibition of activin receptor-like kinase (ALK-1) abolished the induc

102 2 is caused by loss of function mutations in activin receptor-like kinase 1 (ACVRL1 or ALK1).

103 re linked to HHT: endoglin (ENG) in HHT1 and activin receptor-like kinase 1 (ACVRL1; ALK1) in HHT2.

104 Activin receptor-like kinase 1 (Acvrl1; Alk1) is a type

105 We show that vbg encodes activin receptor-like kinase 1 (Acvrl1; also known as Al

106 Activin receptor-like kinase 1 (ALK-1) has homology to t

107 Activin receptor-like kinase 1 (ALK-1), an orphan recept

108 ns were used to determine the involvement of activin receptor-like kinase 1 (ALK1) and ALK5 downstrea

109 Loss-of-function mutations in the activin receptor-like kinase 1 (Alk1) are linked to hemo

110 t of BMPRII receptor is mediated through the activin receptor-like kinase 1 (ALK1) but not the ALK3 r

111 Loss-of-function variations in activin receptor-like kinase 1 (ALK1) cause type 2 hered

112 dent on the endoglin signaling pathway using activin receptor-like kinase 1 (ALK1) Fc blocking peptid

113 Signaling through high-affinity activin receptor-like kinase 1 (ALK1) in endothelial cel

114 The activin receptor-like kinase 1 (ALK1) is a transforming

115 The activin receptor-like kinase 1 (ALK1) is a type I recept

116 Activin receptor-like kinase 1 (ALK1) is an endothelial

117 Activin receptor-like kinase 1 (ALK1) is an endothelial

118 Activin receptor-like kinase 1 (ALK1) is an endothelial-

119 e insight into this question by studying the activin receptor-like kinase 1 (ALK1) pathway.

120 Genetic and molecular studies suggest that activin receptor-like kinase 1 (ALK1) plays an important

121 s crucial for endothelial cell signaling via activin receptor-like kinase 1 (ALK1), a pathway central

122 Genetic and molecular studies suggest that activin receptor-like kinase 1 (ALK1), a transforming gr

123 FK506 released FKBP12 from type I receptors activin receptor-like kinase 1 (ALK1), ALK2, and ALK3 an

124 lk between the insulin receptor and endoglin/activin receptor-like kinase 1 (ALK1), an endothelial ce

125 Activin receptor-like kinase 1 (ALK1), an endothelial ce

126 -of-function mutations in the genes encoding activin receptor-like kinase 1 (ALK1), endoglin, Smad4,

127 pro-domain-complexed BMP9 to type I receptor activin receptor-like kinase 1 (ALK1), type II receptors

128 In zebrafish embryos, arterial expression of activin receptor-like kinase 1 (alk1), which encodes a T

129 UBAC conjugates linear ubiquitin chains onto Activin receptor-like kinase 1 (ALK1), which is responsi

130 Activin receptor-like kinase 1 (ALK1)-mediated endotheli

131 g was reduced in TbetaRII(+/-) ECs; however, activin receptor-like kinase 1 (ALK1)-mediated Smad1/5 p

132 quiescence through its endothelial receptor activin receptor-like kinase 1 (ALK1).

133 mutations in one of several genes, including activin receptor-like kinase 1 (ALK1).

134 emorrhagic telangiectasia type 2 (HHT2) with activin receptor-like kinase 1 (ALK1; ACVRL1) mutations

135 e arterial-specific TGFbeta type I receptor, activin receptor-like kinase 1 (ALK1; ACVRL1), causes he

136 Subsequent activation of activin receptor-like kinase 1 enhances expression of No

137 The activin receptor-like kinase 1 gene (ALK-1) is the secon

138 Small interfering RNA knockdown of activin receptor-like kinase 1 inhibited the BMP9-induce

139 e the physiologic role of BMP9, BMP10, ALK1 (activin receptor-like kinase 1), and SMAD7 in vivo.

140 letion of ETS1 decreased the levels of Alk1 (activin receptor-like kinase 1), Cldn5 (claudin 5), Sox1

141 to the lack of MGP induces expression of the activin receptor-like kinase 1, a BMP type I receptor, i

142 bone morphogenetic protein receptor type 2, activin receptor-like kinase 1, endoglin, and mothers ag

143 ovenous fate, acting via EphrinB2 and ACVRL1/activin receptor-like kinase 1.

144 IL-1beta reduced the number of activin receptor-like kinase 2 (ALK-2) and ALK-3 recepto

145 dependent upon the type I TGFbeta receptor, activin receptor-like kinase 2 (ALK2), and the downstrea

146 sease driven by gain-of-function variants in activin receptor-like kinase 2 (ALK2), the most common v

147 xpression of type I TGFbeta receptors, chick activin receptor-like kinase 2 and 5 increased with a 2.

148 Constitutively active activin receptor-like kinase 2 inhibited Galpha(i2) prom

149 increased with a 2.3-fold higher increase in activin receptor-like kinase 2.

150 f the pVent reporter, which is downstream of activin receptor-like kinase 2.

151 hogenetic protein signaling, most likely via activin receptor-like kinase 3.

152 Activin receptor-like kinase 4 (ALK4), a type I TGF-beta

153 ely with the ECDs of native type I receptors activin receptor-like kinase 4 (ALK4), ALK7, or ALK3.

154 mouse model with conditional inactivation of activin receptor-like kinase 5 (ALK5) in the mouse uteru

155 Activin receptor-like kinase 5 (Alk5) inhibitor (Alk5i),

156 Activin receptor-like kinase 5 (ALK5) is the major type

157 to the TGF-beta type I receptor (also termed activin receptor-like kinase 5 (ALK5)), in a similar fas

158 growth factor beta receptor I (TGF-betaRI) (activin receptor-like kinase 5 [ALK-5]) and TGF-beta rec

159 he p3TP-lux reporter, which is downstream of activin receptor-like kinase 5 and had no effect on the

160 hese data are consistent with a role for the activin receptor-like kinase 5 in the progression of idi

161 potential of a well-characterized and potent activin receptor-like kinase 5 inhibitor, SB525334 [6-(2

162 at, conversely, the type I TGF-beta receptor activin receptor-like kinase 5 is dispensable for trypsi

163 Aberrant signaling via TGF-beta receptor I/activin receptor-like kinase 5 may be important for both

164 min preferentially induces activation of the activin receptor-like kinase 5 pathway of TGF-beta recep

165 pid acting, and mediated by TGF-beta-induced activin receptor-like kinase 5 signaling in endothelial

166 hic PAH and imply that strategies to inhibit activin receptor-like kinase 5 signaling may have therap

167 oter activity, whereas constitutively active activin receptor-like kinase 5 stimulated Galpha(i2) pro

168 n a small increase in TGF-beta signaling via activin receptor-like kinase 5 to maintain early integri

169 TGFbetaRI kinase/activin receptor-like kinase 5 was inhibited with pharma

170 ylated via JAK1 and acts as a critical ALK5 (activin receptor-like kinase 5) downstream signaling mol

171 ed the TGF-beta type 1 receptor (also termed activin receptor-like kinase 5) in renal epithelial cell

172 ve inhibitor of the type 1 TGF-beta receptor activin receptor-like kinase 5, orally active) to inhibi

173 ced expression of BMP2 through activation of activin receptor-like kinase 5.

174 However, activin receptor-like kinase 7 (ALK7), one of the TGFbet

175 dependent signaling via the type I receptor, activin receptor-like kinase 7 (ALK7).

176 ur variants in the gene ACVR1C (encoding the activin receptor-like kinase 7 receptor expressed on adi

177 nt lost-a-fin (laf) is defective in the gene activin receptor-like kinase 8 (alk8), which encodes a n

178 K), transforming growth factor beta receptor/activin receptor-like kinase beta, estrogen receptor, an

179 in zebrafish embryos harboring a mutation in activin receptor-like kinase I (alk1), which encodes a T

180 treatment with Fstl3 or by a pharmacological activin receptor-like kinase inhibitor.

181 treatment of SB-431542, an inhibitor of the activin receptor-like kinase receptors, to enhance myoge

182 anti-activin A-blocking Ab or inhibitors of activin receptor-like kinase receptors.

183 sociate with either nodal or the type I ALK (activin receptor-like kinase) 4 receptor in coimmunoprec

184 TGFbeta1 levels, endothelial TGFbetaRI/ALK1 (activin receptor-like kinase), and TGFbetaRI/ALK5 expres

185 s-of-function mutations in the gene encoding activin receptor-like kinase-1 (ACVRL1).

186 Activin receptor-like kinase-1 (ALK1) is an endothelial

187 LK1-Fc, a BMP9 ligand trap consisting of the activin receptor-like kinase-1 extracellular domain, exa

188 endogenous BMP-2 ligand and ALK-1 receptor (activin receptor-like kinase-1; known to activate Smads

189 landscape surrounding DIPG has revealed that activin receptor-like kinase-2 (ALK2) constitutes a pote

190 Activin receptor-like kinase-2 (ALK2) is the only type I

191 c ossification in transgenic mice expressing activin receptor-like kinase-2 (ALK2) Q207D, a constitut

192 pe II receptor and the type I receptor Alk2 (activin receptor-like kinase-2) decreased.

193 n granulosa cells via type I receptors (i.e. activin receptor-like kinase-4/5 (ALK4/5)) and SMAD2/3 t

194 or-beta superfamily receptors and found that activin receptor-like kinase-6 extracellular domain most

195 , saxophone (sax), the ortholog of the human Activin Receptor-Like Kinase1 and -2 (ALK1/ACVRL1 and AL

196 ized the chicken homologues of two mammalian activin receptor-like kinases (ALK), ALK2 and ALK5, and

197 As type I activin receptor-like kinases (ALKs) are necessary for S

198 Activin receptor-like kinases 1-7 (ALK1-7) regulate a co

199 ta-receptor proteins, including endoglin and activin-receptor-like kinase 1 (ALK1), and BMPR2.

200 pulmonary vascular endothelial expression of activin-receptor-like kinase 1 in normal and diseased pu

201 We identified amino acid changes in activin-receptor-like kinase 1 that were inherited in su

202 liferation at a high level by stimulation of activin-receptor-like kinases.

203 Thus, activin receptor-mediated signaling regulates axial patt

204 ment, we predicted in a previous report that activin receptor mRNA expression in embryos might be reg

205 Naturally occurring activin receptor mRNA is maternally inherited and contai

206 r this factor between mRNAs in vivo inhibits activin receptor mRNA polyadenylation.

207 how that not only do endogenous and injected activin receptor mRNAs undergo cytoplasmic polyadenylati

208 C12 and activin receptor mRNAs, both of which contain eCPEs, are

209 ts range is influenced by numbers of type II activin receptors on responding cells.

210 opus Vg1 and GDF1 bind to and signal through Activin receptors only in the presence of EGF-CFC protei

211 Finally, pharmacological inhibition of TGF-B/activin receptors or genetic silencing of SMAD4, a trans

212 describe the role of Baboon (Babo), a type I Activin receptor previously called Atr-I, in Drosophila

213 We find that a constitutively active Activin receptor promotes differentiation throughout the

214 demonstrate that the interaction between the activin receptor R1 and the immunophilin protein FKBP12

215 Transient overexpression of the two types of activin receptor results in ligand-independent receptor

216 et cell and beta-cell proliferation, and the activin receptors RIIA and RIIB are required for the ful

217 ns in the ACVR1 gene, which encodes a type I activin receptor serine/threonine kinase, in 21% of DIPG

218 ation of Dp/E2f1 or Fs in CySCs or promoting Activin receptor signaling in hub cells causes transdiff

219 steoblasts, to determine the contribution of activin receptor signaling in regulating bone mass.

220 Therefore, inhibitors of the activin receptor signaling pathways (IASPs) are potentia

221 Activin receptor signaling, including the transcription

222 Taken together, these results indicate that activin receptor signaling, predominantly through ACVR2A

223 ings suggest that AP-1 mediates FGF, but not activin, receptor signaling during mesoderm induction an

224 ad2 pathways, including a truncated type IIB activin receptor, Smad7 and Ski, induce early neural mar

225 The restricted expression of activin receptor subunits and Smad2 in cells of the adre

226 and-mediated cooperative assembly of BMP and activin receptors that does not rely on receptor-recepto

227 rom the source of activin require functional activin receptors to activate Xbrachyury, a result sugge

228 form heteromeric complexes with the type II activin receptors to mediate activin signal.

229 ad3 may serve as a mediator linking TGF-beta/activin receptors to transcriptional regulation.

230 Activin receptor type 1 (ACVR1; ALK2) and activin recept

231 trol endometrial receptivity via a conserved activin receptor type 2 A (ACVR2A) and SMAD1/5 signaling

232 tead engages the TGF-beta superfamily member Activin receptor type 2B (ACVR2B).

233 Conditional deletion of Activin receptor type I (Acvr1) or Smad4 (a downstream t

234 sequence similarity among p50, p53, Tat, and activin receptor type I on these particular lysines was

235 Conversely, activin receptor type II (ActR-II) contributed more to B

236 rentiation factor 11 (GDF11) through soluble activin receptor type II (ActRII) ligand traps or neutra

237 resonance (BIAcore) we show that BMP-3 binds Activin Receptor type II (ActRII) with Kd approximately

238 Ia (BMPR-Ia)-ECD] and its type II receptor [activin receptor type II (ActRII)-ECD] shows two fundame

239 hree genes likely to be functional (encoding activin receptor type II, a zinc finger, and a putative

240 uired BMP receptor type II (BMPRII), but not activin receptor type IIA (ActRIIA) or ActRIIB, based on

241 and its murine ortholog RAP-011) acts as an activin receptor type IIA ligand trap, increasing hemogl

242 ic approaches for PAH include suppression of activin receptor type IIA signalling with sotatercept, w

243 Sotatercept is an activin receptor type IIA-Fc (ActRIIA-Fc) fusion protein

244 the extracellular domain (ECD) of the native activin receptor type IIB (ActRIIB) alternately with the

245 transmembrane domain serine/threonine kinase activin receptor type IIB (ActRIIB) has been proposed to

246 The activin receptor type IIB (ActRIIB) is a transmembrane r

247 ) mice) to investigate effects of a modified activin receptor type IIB (ActRIIB) ligand trap (RAP-536

248 containing the extracellular domain of human activin receptor type IIB (ActRIIB) modified to reduce a

249 domains of activin-like kinase 4 (ALK4) and activin receptor type IIB (ActRIIB), a naturally occurri

250 inhibited MSTN in adult mice with a soluble activin receptor type IIB and analysed the incorporation

251 We recently reported that an activin receptor type IIB inhibitor produced hypertrophy

252 The ability of the muscles to respond to activin receptor type IIB inhibitor treatment correlated

253 Activin receptor type IIB inhibitor treatment of Mtm1 p.

254 ological blockade of activin A using soluble activin receptor type IIB ligand trap as well as muscle-

255 xpressing a dominant-negative MSTN receptor (activin receptor type IIB) in muscle.

256 ing proteins (i.e., nodal, lefty-1, lefty-2, activin receptor type IIB, and Smad2) in L-R axis determ

257 ow and high affinity ligands using a soluble activin receptor type IIB-Fc chimera (ActRIIB.Fc).

258 n in some cell line(s), such as CD87 and the activin receptor type IIB.

259 se of progressive HO caused by ACVR1(R206H) (Activin receptor type-1 receptor) mutation, to elucidate

260 , follistatin, FSTL3, Bambi, Cripto, and the activin receptors type I (ALK), type II (ACTRII), and be

261 es have elucidated an important role for the activin-receptor type IIB (ActRIIB) in regulation of mus

262 ptor (ActRII.sTbetaRIII complex) but not for activin receptors (type II + type I) and demonstrate tha

263 e cell line, overexpressing the two types of activin receptor upon induction, in the human erythroleu

264 genetic proteins (BMPs) also utilize type II activin receptors, we hypothesized that BMP signaling mi

265 ressed by oogonia, and the betaB subunit and activin receptors were expressed by both oogonia and som

266 Activin receptors were found widely distributed among ad

267 in the dorsal neural tube interact with the Activin receptors, which signal via a different set of S

268 sruption of signaling by a truncated type II activin receptor, XActRIIB (previously called XAR1), blo

269 the cloning and characterization of a type I activin receptor, XALK4.