Significance of the chromatin structure in expression of the rat prolactin gene

The transactivation-competent carboxyl-terminal domain of AF-9 is expressed within a sexually dimorphic transcript in rat pituitary

We have investigated the biological role of the cellular counterpart of the leukemogenic AF-9 gene by cloning the rat AF-9 (rAF-9) cDNA and defining the regulation of an anterior pituitary-specific rAF-9 transcript that is expressed in a sexually dimorphic manner. Expression of this transcript is down-regulated after puberty in females and can be subsequently up-regulated in adults by ovariectomy. Hormone replacement studies have provided direct evidence that rAF-9 mRNA expression is suppressed by estrogen. Mapping the 1.9 kb anterior pituitary transcript has shown that it corresponds in size to the rAF-9 cDNA clone, which contains an open reading frame (ORF) that is truncated compared with the human AF-9 ORF, but encodes a previously defined transcriptional activation domain. Thus, the cellular AF-9 gene is alternatively expressed in a manner that reflects the presence of translocated, functionally active (oncogenic) AF-9 sequences in leukemias. Using a novel antisera raised against a rAF-9 peptide, we have also demonstrated tissue- and sex-specific expression of a nuclear 41 kDa anterior pituitary protein and have localized this protein to a major population of growth hormone synthesizing cells. By localizing the expression and defining the physiological regulation of rAF-9, our studies have provided novel insights into the AF-9 gene that will facilitate an understanding of both oncogenic and endocrine roles.

Gene structure of rat testicular cell adhesion molecule 1 (TCAM-1), and its physical linkage to genes coding for the growth hormone and BAF60b, a component of SWI/SNF complexes

In the +9.7 to +21.7kb downstream region from the transcriptional start site of the rat growth hormone (GH) gene, a gene specifically expressed in the testis was found to have reverse transcriptional orientation to the GH gene. Its exon comprised 2693 bases encoded a protein having 548 amino acids (60479Da). The amino acid sequence of the testis-specific protein resembled that of the intercellular adhesion molecules (ICAM) 1 and 3. The gene was thus given the name testicular adhesion molecule (TCAM) 1 gene. The TCAM-1 gene was found to be 12041 bases with eight exons. Although exon 1 was noncoding, the remaining seven exons corresponded to the domains coding for the signal sequence, five immunoglobulin (Ig) domains, and the transmembrane plus cytoplasmic domain. The organization of TCAM-1 gene was shown to be the same as that of the ICAM-1 gene. The polyadenylation site of TCAM-1 gene was located 7.6kb downstream of that of the GH gene, whereas the 5' end of TCAM-1 gene was separated 5.9kb from that of the gene coding for BAF60b, a component of SWI/SNF complexes known as the chromatin remodeling factor. Six genes were thus mapped in the following order in the 88kb region of the rat GH locus: Na-channel (5' to 3')-B29/Ig-beta (5' to 3')-GH (5' to 3')-TCAM-1 (3' to 5')-BAF60b (5' to 3')-SUG/p45 (3' to 5').

Physical linkage of the B29/Ig-beta (CD79B) gene to the skeletal muscle, sodium-channel, and growth hormone genes in rat and human

In the region between the polyadenylation site of the rat skeletal muscle (SkM) Na-channel gene and the 5' end of the growth hormone (GH) gene, a gene coding for B-cell-specific membrane protein B29/Ig-beta was found and noted to have the same orientation as the Na-channel and GH genes. Rat B29/Ig-beta gene was 3.1 kb in length with six exons and was separated by 3.3 and 9.3 kb from Na-channel and GH genes, respectively. Rat B29/Ig-beta protein comprised 228 amino acids, and its amino acid sequence was 85 and 69% identical with the mouse and human counterparts, respectively. With the long-area PCR method, genomic DNA connecting human SkM Na-channel (SCN4A) and B29/Ig-beta (CD79B) genes and CD79B and GH (GH1) genes was amplified, and the physical linkage of SCN4A/CD79B/ GH1 genes in the human genome was established. The human CD79B gene was separated by 6.3 and 10.5 kb from the SCN4A and GH1 genes, respectively.

Gene structure of rat BAF60b, a component of mammalian SW1/SNF complexes, and its physical linkage to the growth hormone gene and transcription factor SUG/proteasome p45 gene

In the +27.6 to +36.7 kb downstream region from the transcriptional start site of the rat growth hormone (GH) gene, a gene encoding BAF60b, a component of mammalian SWI/SNF complexes, was found to have the same transcriptional orientation as the GH gene. The 5' end of the BAF60b gene was heterogeneous and the longest gene was 9060 bp long with 13 exons. The largest of all exons was estimated to be 2774 bases. Deduced rat BAF60b protein was made of 531 amino acids and its amino acid sequence was 97% identical with the human counterpart. No TATA box was found up to the -100 bp region but five GC boxes corresponding to the Sp1 binding site were observed up to 640 bp upstream from the transcriptional start site. Sixty-three bases downstream from the BAF60b gene, the polyadenylation site of the gene encoding transcription factor SUG/proteasome p45, whose expression is constant in many tissues, was identified. The BAF60b gene was expressed as 3.0 kb poly(A)-rich RNA in seven tissues and one cell line from rat but its expression varied considerably according to the tissue.

Gene coding for the transcription factor, SUG/proteasome, p45 is located nearly 40 kb downstream from the rat growth hormone gene

About 40 kilobases (kb) downstream of the rat growth hormone gene, a gene was found to be expressed in the liver and placenta as 1.5 kb poly(A)-rich RNA. Using the genomic DNA fragment as a probe, the corresponding cDNA clone containing a 1.3 kb insert was isolated from the rat liver cDNA library. The deduced amino acid sequence having 406 residues was identical with that of the mouse transcription factor, SUG and human proteasome subunit, p45. The gene was thus identified as the rat SUG/p45 (rSUG/p45) gene. The 5' end of the gene was determined by the primer-extension analysis and the exon was noted to comprise 1409 bases. The rSUG/p45 gene, 6.0 kb in length and possessing 12 exons, started at 42.8 and ended at 36.8 kb downstream from the transcription start site of the GH gene. From exon 2 to 11, the size of each rSUG/p45 exon was identical with the corresponding exon of the 4.4 kb pig gene. Rat SUG/p45 mRNA was similarly expressed in seven different tissues and one cell line.

Chromatin structure of the rat somatotropin gene locus and physical linkage of the rat somatotropin gene and skeletal-muscle sodium-channel gene

Cosmid clones from -32 kb to +74 kb region of the rat somatotropin gene locus were isolated for examination of the chromatin structure in the region from -39 kb to +47 kb by DNase I-sensitivity analysis using rat pituitary-derived GC (somatotropin+, prolactin-), and 235 (somatotropin-, prolactin+) cells, and liver-derived BRL (somatotropin-, prolactin-) cells. DNase I-hypersensitive sites (DHS) specific for somatotropin-producing cells were previously shown to be located exclusively in the -2 kb to +9 kb region [Aizawa, A., Yoneyama, T., Kazahari, K. & Ono, M. (1995) Nucleic Acids Res. 23, 2236-2244]. No other DHS having this specificity was found in the region examined in this study. Except for these and two other DHS located in a cluster in this region, no DHS could be found from -23 kb to +22 kb. DHS having no or less cell-type specificity were scattered about in the -39 kb to -23 kb and +22 kb to +47 kb regions. The polyadenylation site of the human skeletal-muscle Na-channel alpha-subunit gene has been shown present 22 kb upstream from the somatotropin gene [Bennani-Baiti, I. M., Jones, B. K., Liebhaber, S. A. & Cooke, N. E. (1995) Genomics 29, 647-652]. Polyadenylation site of the rat skeletal-muscle Na-channel gene was shown in this study to be at -15.7 kb. The skeletal-muscle Na-channel gene was specifically expressed in skeletal-muscle cells but not in somatotropin-producing cells, and thus the boundary region that ensures the cell-type-specific expression of each gene would appear to be situated between two genes. The region prerequisite for cell-type-specific expression of the rat somatotropin gene was estimated based on the present findings.