Howe C C, Overton G C
Mol Cell Biol. 1986 Jan;6(1):150-7. doi: 10.1128/mcb.6.1.150-157.1986.
Three cDNA clones coding for the 3' region of the intracisternal A-particle (IAP), a mouse endogenous retrovirus, were isolated during screening of a library for genes whose expression was modulated during the retinoic acid-induced differentiation of the embryonal carcinoma cell line F9 into parietal endoderm-like (PE-like) cells. In contrast to previously reported results, no IAP transcripts were detected in either F9 cells or two pluripotent cell lines tested. Instead, IAP transcripts as well as IAPs were abundant in the PE-like cells PYS-2 and F9AcCl 9 and in retinoic acid-induced F9 cells but not in the other differentiated cell types of teratocarcinoma origin which were examined. A comparison of the nucleotide sequences of the three IAP cDNA clones with a genomically integrated proviral sequence (MIA14) demonstrated heterogeneity in both length and sequence among the clones. The position of the poly(A) addition site was determined to be 15 nucleotides from the proposed poly(A) addition signal and to occur after the sequence CAGA, not CA, as previously proposed. Length heterogeneity was greatest in a region of TC repeats 80 base pairs 5' to the poly(A) addition site. Additionally, the putative TATAA box found in MIA14 was deleted in the cDNA clones and in the long terminal repeat regions from two other genomic clones examined. The heterogeneity evident among the cDNA clones further demonstrated that at least two distinct IAP genes are activated during differentiation. An analysis of the rate of transcription in isolated nuclei indicated that the activation of expression of IAP genes in PE-like cells is the result of transcriptional regulation. Together, these observations suggest that the modulation of IAP transcription is regulated autonomously rather than by the fortuitous integration of an IAP sequence adjacent to a developmentally regulated cellular gene.
在筛选一个文库以寻找那些在维甲酸诱导胚胎癌细胞系F9分化为壁内胚层样（PE样）细胞过程中表达受到调控的基因时，分离出了三个编码小鼠内源性逆转录病毒——脑内A颗粒（IAP）3'区域的cDNA克隆。与先前报道的结果相反，在F9细胞或所检测的两种多能细胞系中均未检测到IAP转录本。相反，IAP转录本以及IAP在PE样细胞PYS - 2和F9AcCl 9以及维甲酸诱导的F9细胞中大量存在，但在所检测的其他源于畸胎癌的分化细胞类型中则没有。将这三个IAP cDNA克隆的核苷酸序列与基因组整合的前病毒序列（MIA14）进行比较，结果表明这些克隆在长度和序列上均存在异质性。多聚腺苷酸添加位点的位置被确定为距离推测的多聚腺苷酸添加信号15个核苷酸，且发生在序列CAGA之后，而非如先前所提出的在CA之后。长度异质性在多聚腺苷酸添加位点5'端80个碱基对的TC重复区域最为显著。此外，在MIA14中发现的推测的TATA框在cDNA克隆以及另外两个所检测的基因组克隆的长末端重复区域中均被缺失。cDNA克隆之间明显的异质性进一步表明，在分化过程中至少有两个不同的IAP基因被激活。对分离细胞核中转录速率的分析表明，PE样细胞中IAP基因表达的激活是转录调控的结果。综合这些观察结果表明，IAP转录的调节是自主调控的，而非由与发育调控的细胞基因相邻的IAP序列的偶然整合所导致。
