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Expression of Gcm-2 in
the parathyroid gland and the pharyngeal pouches in the chick. (A#D)
Whole-mount in situ hybridization of chick E11 thyroid (T) and parathyroid
(P) glands for the following probes: Gcm-2 (A), PTH (B), CasR (C), and TTF-1
(D). Gcm-2 can be seen to be expressed in two round masses, the parathyroid
glands, which are adjacent to the thyroid, which expresses TTF-1. The
parathyroid glands additionally express PTH and CasR. (E-I) Expression of
Gcm-2 in chicken embryos, staged as described in ref. 16. In these
micrographs, anterior is to the left and ventral is to the bottom. OV, otic
vesicle; pp, pharyngeal pouch; II-IV, pharyngeal arches. Expression of Gcm-2
starts in the third pharyngeal pouch at stage 18 (E), and then, as
development proceeds, expression is also evident in the fourth pharyngeal
pouch and additionally weakly in the second pouch (F). At stage 24,
expression in the third and fourth pouches is concentrated in a region
dorsal of the pharyngeal pouches and is lost from the second pouch (G). In
Vibratome sections of stage-22 embryos (H), it is clear that Gcm-2
expression is localized to the pharyngeal endoderm and that, by stage 24,
the region of the pharyngeal endoderm expressing Gcm-2 has thickened and
given rise to round masses that are the parathyroid gland rudiments of the
third and fourth pouches (I).
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