ABSTRACT
The vertebrate homeobox genes Msx-1 and Msx-2 are related to the Drosophila msh gene and are expressed in a variety of tissues during embryogenesis. We have examined their expression by in situ hybridisation during critical stages of cardiac development in the chick from stages 15+ to 37. Msx-1 expression is apparent in a number of non-myocardial cell populations, including cells undergoing an epithelial to mesenchymal transformation in the atrioventricular and the outflow tract regions that play an integral role in heart septation and valve formation. Msx-2 expression is restricted to a distinct subpopulation of myocardial cells that, in later stages, coincides morphologically with the cardiac conduction system. The timing of Msx-2 expression suggests that it plays a role in conduction system tissue formation and that it identifies precursor cells of this specialised myocardium. The pattern of Msx-2 expression is discussed with reference to current models of conduction tissue development.
Subject(s)
Genes, Homeobox/genetics , Heart/embryology , Homeodomain Proteins , Animals , Avian Proteins , Chick Embryo , DNA-Binding Proteins/biosynthesis , DNA-Binding Proteins/genetics , Genes, Homeobox/physiology , In Situ Hybridization , MSX1 Transcription Factor , Myocardium/metabolismABSTRACT
We have analysed the effect of a 1.4 kb segment of DNA containing the upstream alpha globin regulatory element (HS-40) on human alpha globin gene expression in fetal mice and lines of transgenic mice. High levels of tissue-specific, human alpha mRNA expression were seen in all transgenic animals and in this sense expression was position independent. However, the level of human alpha mRNA expression per integrated gene copy decreased during development and was inversely related to copy number. The limitation in expression with increasing gene copy number was shown to be in cis since homozygotes for the transgene produced twice as much human alpha mRNA as hemizygotes. In many respects HS -40 appears similar to single elements within the previously described beta globin locus control region and in cross breeding experiments we have shown that HS -40 behaves in a similar manner to such elements in transgenic mice.
Subject(s)
Globins/genetics , Regulatory Sequences, Nucleic Acid , Animals , DNA/genetics , Female , Homozygote , Humans , Male , Mice , Mice, Inbred C57BL , Mice, Inbred CBA , Mice, Transgenic , Plasmids , RNA, Messenger/genetics , Restriction MappingABSTRACT
The beta-globin gene complex is regulated by an upstream locus control region (LCR) which is responsible for high-level, position-independent, erythroid-cell-specific expression of the genes in the cluster. Its role in the developmental regulation of beta-like globin gene transcription remains to be established. We have examined the effect of a single LCR element, hypersensitive site 2 (HS2), on the developmental regulation of the human fetal gamma and adult beta genes in transgenic mice. In mice bearing HS2A gamma beta and HS2G gamma A gamma-117 delta beta human globin gene constructs, switching from gamma- to beta-gene expression begins at about day 13.5 of gestation and is largely completed shortly after birth. The larger construct also demonstrates a switch in G gamma- to A gamma-gene expression during the gamma-to-beta switch similar to that observed during normal human development. We conclude that HS2 alone is sufficient for developmental regulation of the human beta-globin genes.
Subject(s)
Gene Expression Regulation , Genes, Regulator , Globins/genetics , Multigene Family , Regulatory Sequences, Nucleic Acid , Transcription, Genetic , Aging , Animals , Crosses, Genetic , DNA/genetics , DNA/isolation & purification , Female , Gestational Age , Hemoglobins/genetics , Humans , Male , Mice , Mice, Transgenic , RNA/genetics , RNA/isolation & purification , RNA, Messenger/genetics , RNA, Messenger/metabolism , Restriction MappingABSTRACT
The vertebrate heart forms as two concentric epithelial cylinders of myocardium and endocardium separated by an extended basement membrane matrix commonly referred to as cardiac jelly. Subsequent maturation involves a complex series of events including asymmetric changes in cell shape and division which contribute to bending and the formation of the bulboventricular loop, the formation of specialised tissues including endocardial cushion tissue of the atrioventricular (AV) and outflow tract regions, the development of conductive tissue and myocyte maturation leading to the overall pattern of expression characteristic of mature heart muscle. These processes depend on a precise spatial and temporal control of gene expression both of genes encoding regulatory molecules and those encoding structural components of the heart. In this chapter we address three aspects of cardiac development, namely, the determination of cell fate during formation of endocardial cushion tissue in the embryonic heart, transitions in troponin gene expression during fetal myocyte maturation, and the use of cloning techniques based on the polymerase chain reaction for identifying transcription factors present in the heart.
