Analysis of several mutations in the mouse is providing useful insights into the nature of the genes required for the establishment of the left-right axis during early development. Here we describe a new targeted allele of the mouse Tg737 gene, Tg737(Delta)2-3(beta)Gal), which causes defects in left-right asymmetry and other abnormalities during embryogenesis. The Tg737 gene was originally identified based on its association with the mouse Oak Ridge Polycystic Kidney (orpk) insertional mutation, which causes polycystic kidney disease and other defects. Complementation tests between the original orpk mutation and the new targeted knock-out mutation demonstrate that Tg737(Delta)2-3(beta)Gal) behaves as an allele of Tg737. The differences in the phenotype between the two mutations suggest that the orpk mutation is a hypomorphic allele of the Tg737 gene. Unlike the orpk allele, where all homozygotes survive to birth, embryos homozygous for the Tg737(Delta)2-3(beta)Gal) mutation arrest in development at mid-gestation and exhibit neural tube defects, enlargement of the pericardial sac and, most notably, left-right asymmetry defects. At mid-gestation the direction of heart looping is randomized, and at earlier stages in development lefty-2 and nodal, which are normally expressed asymmetrically, exhibit symmetrical expression in the mutant embryos. Additionally, we determined that the ventral node cells in mutant embryos fail to express the central cilium, which is a characteristic and potentially functional feature of these cells. The expression of both Shh and Hnf3(beta) is downregulated in the midline at E8.0, indicating that there are significant alterations in midline development in the Tg737(Delta)2-3(beta)Gal) homozygous embryos. We propose that the failure of ventral node cells to fully mature alters their ability to undergo differentiation as they migrate out of the node to contribute to the developing midline structures. Analysis of this new knockout allele allows us to define a critical role for the Tg737 gene during early embryogenesis. We have named the product of the Tg737 gene Polaris, which is based on the various polarity related defects associated with the different alleles of the Tg737 gene.

REFERENCES

Beddington
R. S.
(
1994
)
Induction of a second neural axis by the mouse node.
Development
120
,
613
620
Bellomo
D.
,
Lander
A.
,
Harragan
I.
,
Brown
N. A.
(
1996
)
Cell proliferation in mammalian gastrulation: the ventral node and notochord are relatively quiescent.
Dev. Dyn
205
,
471
485
Casey
B.
(
1998
)
Two rights make a wrong: human left-right malformations.
Hum. Mol. Genet
7
,
1565
1571
Collignon
J.
,
Varlet
I.
,
Robertson
E. J.
(
1996
)
Relationship between asymmetric nodal expression and the direction of embryonic turning.
Nature
381
,
155
158
Davidson
B. P.
,
Kinder
S. J.
,
Steiner
K.
,
Schoenwolf
G. C.
,
Tam
P. P. L.
(
1999
)
Impact of node ablation on the morphogenesis of the body axis and the lateral asymmetry of the mouse embryo during early organogenesis.
Dev. Biol
211
,
11
26
Fujinaga
M.
,
Baden
J. M.
(
1991
)
Critical period of rat development when sideness of asymmetric body structure is determined.
Teratology
44
,
453
462
Goebl
M.
,
Yanagida
M.
(
1991
)
The TPR snap helix: a novel protein repeat motif from mitosis to transcription.
Trends Biochem. Sci
16
,
173
177
Groves
M. R.
,
Barford
D.
(
1999
)
Topological characteristics of helical repeat proteins.
Curr. Opin. Struct. Biol
9
,
383
389
Henrique
D.
,
Adam
J.
,
Myat
A.
,
Chitnis
A.
,
Lewis
J.
,
Ish-Horowicz
D.
(
1995
)
Expression of a Delta homologue in prospective neurons in the chick.
Nature
375
,
787
790
Lamb
J. R.
,
Michaud
W. A.
,
Sikorski
R. A.
,
Hieter
P. A.
(
1994
)
Cdc16p, Cdc23p and Cdc27p form a complex essential for mitosis.
EMBO J
13
,
4321
4328
Lowe
L. A.
,
Supp
D. M.
,
Sampath
K.
,
Yokoyama
T.
,
Wright
C. V. E.
,
Potter
S. S.
,
Overbeek
P.
,
Kuehn
M. R.
(
1996
)
Conserved left-right asymmetry of nodal expression and alterations in murine situs inversus.
Nature
381
,
158
161
McCarthy
A.
,
Brown
N. A.
(
1998
)
Specification of left-right asymmetry in mammals: embryo culture studies of stage of determination and relationships with morphogenesis and growth.
Reprod. Toxicol
12
,
177
184
Meno
C.
,
Shimono
A.
,
Saijoh
Y.
,
Oishi
S.
,
Mochida
S.
,
Noji
S.
,
Kondoh
H.
,
Hamada
H.
(
1998
)
lefty-1 is required for left-right determination as a regulator of lefty-2 and nodal.
Cell
94
,
287
298
Mochizuki
T.
, et al. 
(
1998
)
Cloning of inv, a gene that controls left/right asymmetry and kidney development.
Nature
395
,
177
181
Morgan
D.
, et al. 
(
1998
)
Inversin, a novel gene in the vertebrate left-right axis pathway, is partially deleted in the inv mouse.
Nature Genetics
20
,
149
156
Moyer
J. H.
,
Lee-Tischler
M. J.
,
Kwon
H.
,
Schrick
J. J.
,
Avner
E. D.
,
Sweeney
W. E.
,
Godfrey
V. L.
,
Cacheiro
N. L. A.
,
Wilkinson
J. E.
,
Woychik
R. P.
(
1994
)
Candidate gene associated with a mutation causing recessive polycystic kidney disease in mice.
Science
264
,
1329
1333
Murcia
N. S.
,
Woychik
R. P.
,
Avner
E. D.
(
1998
)
The molecular biology of polycystic kidney disease.
Ped. Nephrol
12
,
721
726
Murcia
N. S.
,
Sweeney
W. E.
,
Avner
E. D.
(
1999
)
New insights into the molecular pathophysiology of polycystic kidney disease.
Kidney Int
55
,
1187
1197
Nonaka
S.
,
Tanaka
Y.
,
Okada
Y.
,
Takeda
S.
,
Harada
A.
,
Kanai
Y.
,
Kido
M.
,
Hirokawa
N.
(
1998
)
Randomization of left-right asymmetry due to loss of nodal cilia generating leftward flow of extraembryonic fluid in mice lacking KIF3B motor protein.
Cell
95
,
829
837
Richards
W. G.
,
Sweeney
W. E.
,
Yoder
B. K.
,
Wilkinson
J. E.
,
Woychik
R. P.
,
Avner
E. D.
(
1998
)
Epidermal growth factor receptor activity mediates renal cyst formation in polycystic kidney disease.
J. Clin. Invest
101
,
935
939
Ryan
A. K.
, et al. 
(
1998
)
Pitx2 determines left-right asymmetry of internal organs in vertebrates.
Nature
394
,
545
551
Shih
J.
,
Fraser
S. E.
(
1996
)
Characterizing the zebrafish organizer: Microsurgical analysis at the early-shield stage.
Development
122
,
1313
1322
Sulik
K.
,
Dehart
D. B.
,
Inagaki
T.
,
Carson
J. L.
,
Vrablic
T.
,
Gesteland
K.
,
Schoenwolf
G. C.
(
1994
)
Morphogenesis of the murine node and notochordal plate.
Dev. Dyn
201
,
260
278
Supp
D. M.
,
Witte
D. P.
,
Potter
S. S.
,
Brueckner
M.
(
1997
)
Mutation of an axonemal dynein affects left-right asymmetry in inversus viscerum mice.
Nature
389
,
963
966
Sweeney
W. E.
,
Avner
E. D.
(
1998
)
Functional activity of epidermal growth factor receptors in autosomal recessive polycystic kidney disease.
Am. J. Physiol
275
,
387
394
Wilkinson
D. G.
,
Bhatt
S.
,
Herrmann
B. G.
(
1990
)
Expression pattern of the mouse T gene and its role in mesoderm formation.
Nature
343
,
657
659
Yoder
B. K.
,
Richards
W. G.
,
Sweeney
W. E.
,
Wilkinson
J. E.
,
Avner
E. D.
,
Woychik
R. P.
(
1995
)
Insertional mutagenesis and molecular analysis of a new gene associated with polycystic kidney disease.
Proc. Assoc. Am. Phys
103
,
314
323
Yoder
B. K.
,
Richards
W. G.
,
Sommardahl
C.
,
Sweeney
W. E.
,
Michaud
E. J.
,
Wilkinson
J. E.
,
Avner
E. D.
,
Woychik
R. P.
(
1996
)
Functional correction of renal defects in a mouse model for ARPKD through expression of the cloned wild-type Tg737 cDNA.
Kidney Int
50
,
1240
1248
Yoder
B. K.
,
Richards
W. G.
,
Sommardahl
C.
,
Sweeney
W. E.
,
Michaud
E. J.
,
Wilkinson
J. E.
,
Avner
E. D.
,
Woychik
R. P.
(
1997
)
Differential rescue of the renal and hepatic disease in an autosomal recessive polycystic disease mouse mutant. A new model to study the liver lesion.
Am. J. Pathol
150
,
2231
2241
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