Targeted disruption of the homeobox gene T/ebp (Nkx2.1, Ttf1, Titf1) in mice results in ablation of the pituitary. Paradoxically, while T/ebp is expressed in the ventral diencephalon during forebrain formation, it is not expressed in Rathke's pouch or in the pituitary gland at any time of embryogenesis. Examination of pituitary development in the T/ebp homozygous null mutant embryos revealed that a pouch rudiment is initially formed but is eliminated by programmed cell death before formation of a definitive pouch. In the diencephalon of the mutant, Bmp4 expression is maintained, whereas Fgf8 expression is not detectable. These data and additional genetic and molecular observations suggest that Rathke's pouch develops in a two-step process that requires at least two sequential inductive signals from the diencephalon. First, BMP4 is required for induction and formation of the pouch rudiment, a role confirmed by analysis of Bmp4 homozygous null mutant embryos. Second, FGF8 is necessary for activation of the key regulatory gene Lhx3 and subsequent development of the pouch rudiment into a definitive pouch. This study provides firm molecular genetic evidence that morphogenesis of the pituitary primordium is induced in vivo by signals from the adjacent diencephalon.

REFERENCES

Bach
I.
,
Rhodes
S. J.
,
Pearse
R. V.
II.
,
Gloss
B.
,
Scully
K. M.
,
Sawchenko
P. E.
,
Rosenfeld
M. G.
(
1995
)
P-Lim, a LIM homeodomain factor, is expressed during pituitary organ and cell commitment and synergizes with Pit- 1.
Proc. Natl. Acad. Sci. USA
92
,
2720
2724
Bach
I.
,
Carriere
C.
,
Ostendorff
H. P.
,
Andersen
B.
,
Rosenfeld
M. G.
(
1997
)
A family of LIM domain-associated cofactors confer transcriptional synergism between LIM and Ot x homeodomain proteins.
Genes Dev
11
,
1370
1380
Camper
S. A.
,
Saunders
T. L.
,
Katz
R. W.
,
Reeves
R. H.
(
1990
)
The Pit −1 transcription factor is a candidate for the Snell dwarf mutation.
Genomics
8
,
586
590
Couly
G. F.
,
Le Douarin
N. M.
(
1988
)
The fate map of the cephalic neural primordium at the presomitic to the 3-somite stage in the avian embryo.
Development
103
,
101
113
Crossley
P. H.
,
Martin
G. R.
(
1995
)
The mouse Fgf 8 gene encodes a family of polypeptides and is expressed in regions that direct outgrowth and patterning in the developing embryo.
Development
121
,
439
451
Daikoku
S.
,
Chikamori
M.
,
Adachi
T.
,
Maki
Y.
(
1982
)
Effect of basal diencephalon on the development of Rathke's pouch in rats: A study in combined organ culture.
Dev. Biol
90
,
198
202
Ericson
J.
,
Norlin
S.
,
Jessell
T. M.
,
Edlund
T.
(
1998
)
Integrated FGF and BMP signaling controls the progression of progenitor cell differentiation and the emergence of pattern in the embryonic anterior pituitary.
Development
125
,
1005
1015
Ferrand
R.
(
1972
)
Experimental study of the factors in cytological differentiation of the adenohypophysis in the chick embryo.
Arch. Biol
83
,
293
371
Gage
P. J.
,
Camper
S. A.
(
1997
)
Pituitary homeobox 2, a novel member of the bicoid -related family of homeobox genes, is a potential regulator of anterior structure formation.
Hum. Mol. Genet
6
,
457
464
Hermesz
E.
,
Mackem
S.
,
Mahon
K. A.
(
1996
)
Rpx: a novel anterior-restricted homeobox gene progressively activated in the prechordal plate, anterior neural plate and Rathke's pouch of the mouse embryo.
Development
122
,
41
52
Jones
C. M.
,
Lyons
K. M.
,
Hogan
B. L. M.
(
1991
)
Involvement of bone morphogenetic protein −4 (BMP −4) and Vgr −1 in morphogenesis and neurogenesis in the mouse.
Development
111
,
531
542
Kawamura
K.
,
Kikuyama
S.
(
1995
)
Induction from posterior hypothalamus is essential for the development of the pituitary proopiomelacortin (POMC) cells of the toad (Bufo japonicus).
Cell Tiss. Res
279
,
233
239
Kimura
S.
,
Hara
Y.
,
Pineau
T.
,
Fernandez-Salguero
P.
,
Fox
C. H.
,
Ward
J. M.
,
Gonzalez
F. J.
(
1996
)
The T/ebp null mouse: thyroid-specific enhancer-binding protein is essential for the organogenesis of the thyroid, lung, ventral forebrain, and pituitary.
Genes Dev
10
,
60
69
Kusakabe
M.
,
Sakakura
T.
,
Sano
M.
,
Nishizuka
Y.
(
1984
)
Early development of mouse anterior pituitary: role of mesenchyme.
Dev. Growth Differ
26
,
263
271
Lamonerie
T.
,
Tremblay
J. J.
,
Lanctot
C.
,
Therrien
M.
,
Gauthier
Y.
,
Drouin
J.
(
1996
)
Ptx 1, a bicoid -related homeobox transcription factor involved in transcription of the pro-opiomelancortin gene.
Genes Dev
10
,
1284
1295
Lanctot
C.
,
Lamolet
B.
,
Drouin
J.
(
1997
)
The bicoid -related homeoprotein Ptx 1 defines the most anterior domain of the embryo and differentiates posterior from anterior lateral mesoderm.
Development
124
,
2807
2817
Lazzaro
D.
,
Price
M.
,
De Felice
M.
,
Di Lauro
R.
(
1991
)
The transcription factor TTF- 1 is expressed at the onset of thyroid and lung morphogenesis and in restricted regions of the foetal brain.
Development
113
,
1093
1104
Li
S.
,
Crenshaw
E. B.
,
Rawson
E. J.
,
Simmons
D. M.
,
Swanson
L. W.
,
Rosenfeld
M. G.
(
1990
)
Dwarf locus mutants lacking three pituitarycell types result from mutations in the POU-domain gene Pit −1.
Nature
347
,
528
530
Li
H.
,
Witte
D. P.
,
Branford
W. W.
,
Aronow
B. J.
,
Weinstein
M.
,
Kaur
S.
,
Wert
S.
,
Singh
G.
,
Schreiner
C. M.
,
Whitsett
J. A.
, et al. 
(
1994
)
Gsh-4 encodes a LIM-type homeodomain, is expressed in the developing central nervous system and is required for early postnatal survival.
EMBO J
13
,
2876
2885
Meyers
E. N.
,
Lewandoski
M.
,
Martin
G. R.
(
1998
)
An Fgf 8 mutant allelic series generated by Cre-and Flp-mediated recombination.
Nat. Genet
18
,
136
141
Mucchielli
M. L.
,
Martinez
S.
,
Pattyn
A.
,
Gordis
C.
,
Brunet
J. F.
(
1996
)
Otlx 2, and Otx -related homeobox gene expressed in the pituitary gland and in a restricted pattern in the forebrain.
Mol. Cell. Neurosci
8
,
258
271
Oliver
G.
,
Mailhos
A.
,
Wehr
R.
,
Copeland
N. G.
,
Jenkins
N.
,
Gruss
P.
(
1995
)
Six 3, a murine homologue of the sine ocularis gene, demarcates the most anterior border of the developing neural plate and is expressed during eye development.
Development
121
,
4045
4055
Pfaff
S. L.
,
Mendelsohn
M.
,
Stewart
C. L.
,
Edlund
T.
,
Jessell
E. M.
(
1996
)
Requirement for LIM homeobox gene Isl 1 in motor neuron generation reveals a motor neuron-dependent step in interneuron differentiation.
Cell
84
,
309
320
Robinson
G. W.
,
Wray
S.
,
Mahon
K. A.
(
1991
)
Spatially restricted expression of a member of a new family of murine Distal-less homeobox genes in the developing forebrain.
New Biol
3
,
1183
1194
Schwind
J. L.
(
1928
)
The development of the hypophysis cerebri of the albino rat.
Am. J. Anat
41
,
295
315
Semina
E. V.
,
Reiter
R.
,
Leysens
N. J.
,
Alward
W. L.
,
Small
K. W.
,
Datson
N. A.
,
Siegel-Bartelt
J.
,
Bierke-Nelson
D.
,
Bitoun
P.
,
Zabel
B. U.
, et al. 
(
1996
)
Cloning and characterization of a novel bicoid -related homeobox transcription factor gene, RIEG, involved in Rieger syndrome.
Nat. Genet
14
,
392
399
Sheng
H. Z.
,
Zhadanov
A. B.
,
Mosinger
A. B.
,
Fujii
T.
,
Bertuzzi
S.
,
Grinberg
A.
,
Lee
E. J.
,
Huang
S. P.
,
Mahon
K. A.
,
Westphal
H.
(
1996
)
Specification of pituitary cell lineages by the LIM homeobox gene Lhx 3.
Science
272
,
1004
1007
Sheng
H. Z.
,
Moriyama
K.
,
Yamashita
T.
,
Li
H.
,
Potter
S. S.
,
Mahon
K. A.
,
Westphal
H.
(
1997
)
Multistep control of pituitary organogenesis.
Science
278
,
1809
1812
Shimamura
K.
,
Hartiganm D
J.
,
Martinez
S.
,
Puelles
L.
,
Rubenstein
J. L.
(
1995
)
Longitudinal organization of the anterior neural plate and neural tube.
Development
121
,
3923
3933
Sornson
M. W.
,
Wu
W.
,
Dasen
J. S.
,
Flynn
S. E.
,
Norman
D. J.
,
O'Connell
S. M.
,
Gukovsky
I.
,
Carriere
C.
,
Ryan
A. K.
,
Miller
A. P.
, et al. 
(
1996
)
Pituitary lineage determination by the prophet of Pit- 1 homeodomain factor defective in Ames dwarfism.
Nature
384
,
327
333
Szeto
D. P.
,
Ryan
A. K.
,
O'Connel
S. M.
,
Rosenfeld
M. G.
(
1996
)
P - OTX: a Pit −1-interacting homeodomain factor expressed during anterior pituitary gland development.
Proc. Natl. Acad. Sci. USA
93
,
7706
7710
Treier
M.
,
Rosenfeld
M. G.
(
1996
)
The hypothalamic-pituitary axis: co-development of two organs.
Current Opinion in Cell Biology
8
,
833
843
Treier
M.
,
Gleiberman
A. S.
,
O'Connell
S. M.
,
Szeto
D. P.
,
McMahon
J. A.
,
McMahon
A. P.
,
Rosenfeld
M. G.
(
1998
)
Multistep signaling requirements for pituitary organogenesis in vivo.
Genes Dev
12
,
1691
1704
Watanabe
Y. G.
(
1982
)
Effects of brain and mesenchyme upon the cytogenesis of rat adenohypophysis in vitro. Differentiation of adrenocorticotropes.
Cell Tiss. Res
227
,
257
266
Watanabe
Y. G.
(
1982
)
An organ culture study of the site of determination of ACTH and LH cells in the rat adenohypophysis.
Cell Tiss. Res
227
,
267
275
Watkins-Chow
D. E.
,
Camper
S. A.
(
1998
)
How many homeobox genes does it take to make a pituitary gland?.
Trends in Genet
14
,
284
290
Winnier
G.
,
Blessing
M.
,
Labosky
P. A.
,
Hogan
B. L. M.
(
1995
)
Bone morphogenetic protein −4 is required for mesoderm formation and patterning in the mouse.
Genes Dev
9
,
2105
2116
Zimmerman
L. B.
,
De Jesus-Escobar
J. M.
,
Harland
R. M.
(
1996
)
The Spemann organizer signal noggin binds and inactivates bone morphogenetic protein 4.
Cell
86
,
599
606
This content is only available via PDF.