Patterning by heritage in mouse molar row development.
It is known from paleontology studies that two premolars have been lost during mouse evolution. During mouse mandible development, two bud-like structures transiently form that may represent rudimentary precursors of the lost premolars. However, the interpretation of these structures and their significance for mouse molar development are highly controversial because of a lack of molecular data. Here, we searched for typical tooth signaling centers in these two bud-like structures, and followed their fate using molecular markers, 3D reconstructions, and lineage tracing in vitro. Transient signaling centers were indeed found to be located at the tips of both the anterior and posterior rudimentary buds. These centers expressed a similar set of molecular markers as the "primary enamel knot" (pEK), the signaling center of the first molar (M1). These two transient signaling centers were sequentially patterned before and anterior to the M1 pEK. We also determined the dynamics of the M1 pEK, which, slightly later during development, spread up to the field formerly occupied by the posterior transient signaling center. It can be concluded that two rudimentary tooth buds initiate the sequential development of the mouse molars and these have previously been mistaken for early stages of M1 development. Although neither rudiment progresses to form an adult tooth, the posterior one merges with the adjacent M1, which may explain the anterior enlargement of the M1 during mouse family evolution. This study highlights how rudiments of lost structures can stay integrated and participate in morphogenesis of functional organs and help in understanding their evolution, as Darwin suspected long ago.
Prochazka
Jan
J
Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, 142 20 Prague, Czech Republic.
Pantalacci
Sophie
S
Churava
Svatava
S
Rothova
Michaela
M
Lambert
Anne
A
Lesot
Hervé
H
Klein
Ophir
O
Peterka
Miroslav
M
Laudet
Vincent
V
Peterkova
Renata
R
D000818:Animals; D005260:Female; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism; D021621:Imaging, Three-Dimensional / Q000379:methods*; D017403:In Situ Hybridization; D008297:Male; D008334:Mandible / Q000196:embryology / Q000254:growth & development / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D008963:Molar / Q000196:embryology* / Q000254:growth & development*; D009805:Odontogenesis; D013997:Time Factors; D046509:Tissue Culture Techniques
D053823:Hedgehog Proteins; C465570:Shh protein, mouse; D049452:Green Fluorescent Proteins