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Fig. 5. PTHrP signals are necessary to drive Nkx3.2 expression in the growth
plate. (A) Infection of limbs with RCAS-Nkx3.2 results in the loss
of PTHrP and endogenous Nkx3.2 expression. Arrowheads (part a) indicate strong
PTHrP expression in the periarticular region of the control wing; arrowheads
(part c) indicate normal expression of endogenous Nkx3.2 in control wing,
whereas arrows (d) indicate the absence of endogenous Nkx3.2 expression in
RCAS(A)Nkx3.2-infected cartilage. (B) Ectopic PTHrP delays chondrocyte
maturation and maintains uniform Nkx3.2 expression throughout the cartilage.
Wing buds of E3 chick embryos were infected with RCAS(A)-PTHrP virus. Embryos
were harvested at E10, and RCAS(A)-PTHrP-infected wings and contralateral
control wings were analyzed by Alcian Blue/Alizarin Red staining (AB/AR, parts
a,b) or section ISH (c-l). Arrowheads (c,e,g) indicate the central region of
the ulna in which expression of Sox9, Nkx3.2 and col II is downregulated in
the control wing. Arrows (d,f,h) indicate the central region of the ulna in
which expression of these markers is maintained in the RCAS-PTHrP infected
wing. (C) Nkx3.2/Bapx1 expression is lost in PTHrP and PTHrP-receptor
null animals. Bright field (a,d,f) or ISH (b,c,e,g) of E18.5 mouse tibiae with
the indicated probes, taken from mice of indicated genotypes. (D) Loss
of p57 expression rescues the absence of immature chondrocytes but not
Nkx3.2/Bapx1 expression in the absence of PTHrP signals. ISH of E17.5 mouse
ulnae, taken from mice of indicated genotypes, with indicated probes.
(E) PTHrP signals induce the expression of Nkx3.2 in cultured
chondrocytes. Upper sternal chondrocytes (USC) were isolated from the cephalic
portion of 15-day-old chick embryo sternae and cultured for 3 days in either
the absence (lane 1) or presence (lane 2) of 100nM PTHrP. Gene expression was
assayed by RT-PCR.
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