Genetics of shoulder girdle formation: roles of Tbx15 and aristaless-like genes
2005
The diverse cellular contributions to the skeletal elements of the
vertebrate shoulder and pelvic girdles during embryonic development complicate
the study of their patterning. Research in avian embryos has recently
clarified part of the embryological basis of shoulder formation. Although
dermomyotomal cells provide the progenitors of the scapular blade, local
signals appear to have an essential guiding role in this process. These
signals differ from those that are known to pattern the more distal
appendicular skeleton. We have studied the impact of Tbx15 ,
Gli3 , Alx4 and related genes on formation of the skeletal
elements of the mouse shoulder and pelvic girdles. We observed severe
reduction of the scapula in double and triple mutants of these genes. Analyses
of a range of complex genotypes revealed aspects of their genetic
relationship, as well as functions that had been previously masked due to
functional redundancy. Tbx15 and Gli3 appear to have
synergistic functions in formation of the scapular blade. Scapular truncation
in triple mutants of Tbx15 , Alx4 and Cart1
indicates essential functions for Alx4 and Cart1 in the
anterior part of the scapula, as opposed to Gli3 function being
linked to the posterior part. Especially in Alx4/Cart1 mutants, the
expression of markers such as Pax1 , Pax3 and
Scleraxis is altered prior to stages when anatomical aberrations are
visible in the shoulder region. This suggests a disorganization of the
proximal limb bud and adjacent flank mesoderm, and is likely to reflect the
disruption of a mechanism providing positional cues to guide progenitor cells
to their destination in the pectoral girdle.
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