The mouse liver contains a group of 10-12 different tissue-specific mRNAs, each present at an average concentration of 12,000-15,000 copies per cell [Hastie, N. D. & Bishop, J. 0. (1976) Cell 9, 761-774]. We have determined, by translation in vitro, that these mRNAs are developmentally regulated in the liver. We have also used specific cloned probes to quantitate the developmental time course of expression of five different abundant liver mRNAs. We have found that there are at least three periods during liver development when specific abundant mRNAs are first detectable: prior to 14 days postconception, at birth, and during the onset of sexual maturity. These results indicate that all the members of this mRNA group are not under common developmental regulation. One of the abundant liver mRNAs (p54 mRNA) increases more than 1000-fold in the liver 1 day before birth. We discuss factors that may be involved in the developmental regulation of expression of the genes encoding these mRNAs.

No abstract

The control of expression of the Drosophila melanogaster tropomyosin I (TmI) gene has been investigated by P-element transformation and rescue of the flightless and jumpless TmI mutant strain, Ifmn(3)3. To localize cis-acting DNA sequences that control TmI gene expression, Ifm(3)3 ffies were transformed with P-element plasmids containing various deletions and rearrangements of the TmI gene. The effects of these mutations on TmI gene expression were studied by analyzing both the extent of rescue of the Ifm(3)3 mutant phenotypes and determining TmI RNA levels in the transformed ffies by primer extension analysis. The results of our analysis indicate that a region located within intron 1 of the gene is necessary and sufficient for directing muscle-specific TmI expression in the adult fly. This intron region has characteristics of a muscle regulatory enhancer element that can function in conjunction with the heterologous nonmuscle hsp70 promoter to promote rescue of the mutant phenotypes and to direct expression of an hsp7O-Escherichia coil lacZ reporter gene in adult muscle.The enhancer can be subdivided further into two domains of activity based on primer extension analysis of TmI mRNA levels and on the rescue of mutant phenotypes. One of the intron domains is required for expression in the indirect flight muscle and jump muscle of the adult. The function of the second domain is unknown, but it could regulate the level of expression or be required for expression in other muscle.

The control of expression of the Drosophila melanogaster tropomyosin I (TmI) gene has been investigated by P-element transformation and rescue of the flightless and jumpless TmI mutant strain, Ifm(3)3. To localize cis-acting DNA sequences that control TmI gene expression, Ifm(3)3 flies were transformed with P-element plasmids containing various deletions and rearrangements of the TmI gene. The effects of these mutations on TmI gene expression were studied by analyzing both the extent of rescue of the Ifm(3)3 mutant phenotypes and determining TmI RNA levels in the transformed flies by primer extension analysis. The results of our analysis indicate that a region located within intron 1 of the gene is necessary and sufficient for directing muscle-specific TmI expression in the adult fly. This intron region has characteristics of a muscle regulatory enhancer element that can function in conjunction with the heterologous nonmuscle hsp70 promoter to promote rescue of the mutant phenotypes and to direct expression of an hsp70-Escherichia coli lacZ reporter gene in adult muscle. The enhancer can be subdivided further into two domains of activity based on primer extension analysis of TmI mRNA levels and on the rescue of mutant phenotypes. One of the intron domains is required for expression in the indirect flight muscle of the adult. The function of the second domain is unknown, but it could regulate the level of expression or be required for expression in other muscle.