V. Knezevic et al., 2 NOVEL CHICK T-BOX GENES RELATED TO MOUSE BRACHYURY ARE EXPRESSED INDIFFERENT, NONOVERLAPPING MESODERMAL DOMAINS DURING GASTRULATION, Development, 124(2), 1997, pp. 411-419
The mouse Brachyury (T) gene plays critical roles in the genesis of no
rmal mesoderm during gastrulation and in the maintenance of a function
ing notochord. Abrogation of Brachyury (T) expression within the chord
amesoderm of homozygous null mutants nevertheless spares anterior axis
formation. An intriguing possibility to explain the preservation of a
nterior axis formation in these mutants would be the existence of othe
r genes compensating for the loss of Brachyury. This compensation and
the recent demonstration that Brachyury is the prototype for an evolut
ionarily conserved family, prompted a search for other T-box genes par
ticipating in axis formation. The chick Brachyury orthologue and two r
elated chick T-box genes that are expressed at the onset of gastrulati
on have been isolated. One of these novel genes (Ch-TbxT) becomes rest
ricted to the axial mesoderm lineage and is a potential candidate for
complementing or extending Brachyury function in the anterior axis (fo
rmation of the head process, prechordal plate). The other gene (Ch-Tbx
6L), together with chick T, appears to mark primitive streak progenito
rs before gastrulation. As cells leave the primitive streak, Ch-Tbx6L
becomes restricted to the early paraxial mesoderm lineage and could pl
ay a role in regulating somitogenesis.