If. Emery et al., DIFFERENTIAL EXPRESSION OF BROAD-COMPLEX TRANSCRIPTION FACTORS MAY FORECAST TISSUE-SPECIFIC DEVELOPMENTAL FATES DURING DROSOPHILA METAMORPHOSIS, Development, 120(11), 1994, pp. 3275-3287
The steroid hormone ecdysone initiates metamorphosis in Drosophila mel
anogaster by activating a cascade of gene activity that includes prima
ry response transcriptional regulators and secondary response structur
al genes. The Broad-Complex (BR-C) primary response gene is composed o
f several distinct genetic functions and encodes a family of related t
ranscription factor isoforms, Our objective was to determine whether B
R-C isoforms were components of the primary ecdysone response in all t
issues and whether tissue-specific isoform expression is associated wi
th tissue-specific metamorphic outcomes, We used specific antibody rea
gents that recognize and distinguish among the Z1, Z2 and Z3 BR-C prot
ein isoforms to study protein expression patterns during the initial s
tages of metamorphosis, Western blot analyses demonstrated that BR-C i
soforms are induced at the onset of metamorphosis, each with unique ki
netics of induction and repression, Whole-mount immunostaining showed
that the BR-C proteins accumulate in the nuclei of all larval and imag
inal tissues indicating that the BR-C is induced as a primary response
in many tissues, Several tissues express different levels and combina
tions of the BR-C isoforms suggesting that the BR-C is important in de
termining the tissue-specific outcome of many parallel ecdysone respon
se cascades, For example, prepupal salivary glands (destined for histo
lysis during metamorphosis) express Z1 isoforms while imaginal discs (
destined for cell differentiation and morphogenesis) shift from the sy
nthesis of Z2 isoforms to the synthesis of Z1 isoforms. The prepupal c
entral nervous system (destined for tissue remodeling) expresses all i
soforms, with Z3 predominating, Salivary gland chromosome immunostaini
ng indicated that BR-C proteins interact directly with numerous loci i
n the polytene genome, Finally, western blot analyses showed that dist
inct BR-C genetic functions can be correlated with single and specific
BR-C protein isoforms.