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An androgen receptor mRNA isoform associated with hormone-induced cell proliferation.
Fischer L
,
Catz D
,
Kelley D
.
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The larynx of male Xenopus laevis undergoes an androgen-driven developmental transformation that enables the adult to produce his complex mate attraction song. During the early postmetamorphic period, androgen directs proliferation and differentiation of laryngeal muscle and cartilage. To explore the cellular and molecular basis of androgen control, we have cloned an androgen receptor cDNA from juvenile larynx. Here we identify two androgen receptor mRNA isoforms, alpha and beta, differing within the A/B, or hypervariable, domain. Northern blot analyses reveal that the beta isoform is transiently expressed during early juvenile stages, whereas the alpha transcript is expressed throughout postmetamorphic life. Using in situ hybridization and [3H]thymidine autoradiography, we examined the expression of androgen receptor mRNA isoforms during androgen-evoked cell proliferation and differentiation. The alpha and beta transcripts are coexpressed in proliferating tissues of the juvenile larynx; in postmitotic differentiated tissues, only the alpha transcript is expressed. Because androgen receptor beta mRNA is specifically expressed during hormone-evoked cell proliferation, we propose that this developmentally regulated mRNA isoform is required for the masculine program of cell addition within the developing vocal organ.
FIG. 1. Two AR mRNAs are present in developing larynx. (Upper) Schematic representation of the AR molecule. Positions ofcDNA probes
used in Northern analyses (Lower) are indicated. Probe I is a 1.1-kb cDNA fragment confined entirely to the 5' hypervariable or A/B domain
of the AR. Probes II and III are cDNA fragments from the DNA binding or ligand binding domains, respectively. Probe I hybridizes only to
the AR a mRNA, while probes II and III hybridize to both the alpha and beta transcripts.
FIG. 2. Southern analysis reveals at least two genes for the X.
laevis AR. Genomic DNA was digested with BamHI (lane B) or
HindIII (lane H) and hybridized to a 500-bp EcoRI/EcoRI fragment
from the 3' UTR. Band sizes are indicated in kb.
FIG.3. AR mRNAs are developmentally regulated. AR expression
in male laryngeal muscle and cartilage at PM2, -3, and -6 was
examined by Northern blot analysis.
FIG. 4. Androgen-evoked cell proliferation and expression ofAR
mRNA isoforms in developing larynx. (A) Cell proliferation in
developing larynx evoked by dihydrotestosterone and visualized by
[3H]thymidine autoradiography. Proliferation is prominent in the
elastic cartilage precursor zone (open arrow; this zone surrounds an
unlabeled blood vessel), the developing muscle (arrowhead), and
adjacent to the hyaline cartilageperichondrium (solid arrow). Hyaline
and thyrohyal cartilages are, for the most part, postmitotic in
PM2 males but proliferation can be induced with exogenous androgen.
(B) In situ hybridization, using a probe that recognizes both AR
a and 8 mRNAs, to a similar section through the larynx of a PM2
male. (C) In situ hybridization using a probe that recognizes only the
AR a mRNA; section adjacent to that shown in B. ep, Elastic
cartilage precursor zone; pc, perichondrium; m, muscle; hc, hyaline
cartilage; th, thyrohyal cartilage. Sections adjacent to those shown
in B and C hybridized with AR sense transcripts as a control for
nonspecific hybridization revealed only a low level of nonspecific
hybridization (data not shown). (Bar = 100 Iam.)
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