Liu D, Le Drean Y, Ekker M, Xiong F, Hew C L
Hospital for Sick Children, Department of Clinical Biochemistry, University of Toronto, Ontario, Canada.
Mol Endocrinol. 1997 Jun;11(7):877-90. doi: 10.1210/mend.11.7.9947.
Steroidogenic factor 1, a member of the fushi tarazu factor 1 (FTZ-F1) subfamily of nuclear receptors, is a key regulator in mammalian reproduction. From an embryonic complementary DNA library, the zebrafish homolog of FTZ-F1 (zFF1A) and an alternatively spliced variant (zFF1B) were isolated. zFF1B represented a C-terminally truncated version of zFF1A. Whole mount in situ hybridization and reverse transcriptase-PCR analysis revealed that both zFF1A and B transcripts were present in the developing pituitaries, adult fish brain, gonads, and liver, albeit zFF1B messenger RNA was absent in testis. Comparison of the primary sequences of zFF1 with those of other FTZ-F1 subfamily members showed a close structural relationship between the mouse liver receptor homolog, which activated the alpha1-fetoprotein gene in rodent liver. However, similar to mouse steroidogenic factor 1, zFF1A regulated chinook salmon gonadotropin IIbeta subunit gene expression. On the contrary, zFF1B, which could bind a consensus gonadotrope-specific element with an affinity similar to that of zFF1A, lacked both the trans-activation function and synergistic interaction with the estrogen receptor. Furthermore, cotransfection studies in HeLa cells showed that zFF1B was a strong competitor for the action of zFF1A on the chinook salmon gonadotropin IIbeta subunit gene promoter. Our investigation suggests that 1) zFF1 represents an ancestor protein of the vertebrate FTZ-F1 homologs; 2) the antagonistic relationship between zFF1A and -B may dictate the expression of the FTZ-F1 target genes in a variety of tissues, including the pituitary; and 3) the naturally occurring zFF1B provides evidence that the C-terminal portion of zFF1A (80 amino acid residues) contains a major trans-activation function and a protein-protein interface.
类固醇生成因子1是核受体的腹侧无肢因子1（FTZ-F1）亚家族成员，是哺乳动物生殖中的关键调节因子。从胚胎互补DNA文库中分离出FTZ-F1的斑马鱼同源物（zFF1A）和一个选择性剪接变体（zFF1B）。zFF1B代表zFF1A的C末端截短版本。整体原位杂交和逆转录酶-PCR分析显示，zFF1A和B转录本都存在于发育中的垂体、成年鱼脑、性腺和肝脏中，尽管睾丸中不存在zFF1B信使RNA。将zFF1的一级序列与其他FTZ-F1亚家族成员的序列进行比较，结果表明，小鼠肝脏受体同源物与zFF1在结构上关系密切，该同源物可激活啮齿动物肝脏中的甲胎蛋白基因。然而，与小鼠类固醇生成因子1类似，zFF1A可调节奇努克鲑鱼促性腺激素IIβ亚基基因的表达。相反，zFF1B虽然能以与zFF1A相似的亲和力结合促性腺激素细胞特异性共有元件，但既缺乏反式激活功能，也缺乏与雌激素受体的协同相互作用。此外，在HeLa细胞中的共转染研究表明，zFF1B是zFF1A对奇努克鲑鱼促性腺激素IIβ亚基基因启动子作用的强竞争性抑制剂。我们的研究表明：1）zFF1代表脊椎动物FTZ-F1同源物中的祖先蛋白；2）zFF1A和-B之间的拮抗关系可能决定了FTZ-F1靶基因在包括垂体在内的多种组织中的表达；3）天然存在的zFF1B证明zFF1A的C末端部分（80个氨基酸残基）包含主要的反式激活功能和蛋白质-蛋白质相互作用界面。
