Dev Biol 1996 Aug 25;178(1):113-123
Department of Biological Sciences, Columbia University, New York,
New York 10027, USA.
Exposure to exogenous androgen regulates cell number in the
developing larynx of Xenopus laevis and hormone-regulated laryngeal
development requires secretion of thyroid hormone (TH). We sought to
determine whether exposure to TH is both sufficient and necessary for
androgen-evoked cell proliferation (androgen competency) in
developing larynx. Androgen competency was not observed in the
premetamorphic larynx (tadpole stage 53, before TH secretion) but was
present just prior to metamorphic climax (stage 58, during TH
secretion). However, when TH is administered precociously (between
stages 48 and 50), androgen competency can be observed at stage 53.
The stage 52 larynx expresses high levels of the mRNA for TH receptor
alpha. The duration of TH exposure required at tadpole stage 48 is
greater than 2 days; studies in juveniles indicate that TH exposure
need not be maintained in order for androgen competency to persist.
The effects of exposure to TH on androgen competency are long lasting
and perhaps permanent. While organotypic cultures obtained from
tadpoles during premetamorphosis (stage 52) can proliferate in vitro
and proliferation is augmented by TH exposure as it is in vivo,
precocious exposure to TH does not induce androgen competency. In
contrast, androgen does evoke cell proliferation in cultures obtained
from metamorphosing (stage 58) tadpoles; proliferation is confined to
the cartilage component. Thus, unlike larynges in vivo, muscle will
not proliferate in response to androgen, indicating the necessity for
an additional factor not present in vitro. Androgen receptor mRNA
expression, believed required for androgen competency, was assessed
in vivo and in vitro. The tadpole larynx strongly expresses AR mRNA,
expression does not require exposure to TH nor is expression
diminished in culture.
PMID: 8812113, MUID: 97223510