A Drosophila doublesex-related gene, terra, is involved in somitogenesis in vertebrates.
The Drosophila doublesex (dsx) gene encodes a transcription factor that mediates sex determination. We describe the characterization of a novel zebrafish zinc-finger gene, terra, which contains a DNA binding domain similar to that of the Drosophila dsx gene. However, unlike dsx, terra is transiently expressed in the presomitic mesoderm and newly formed somites. Expression of terra in presomitic mesoderm is restricted to cells that lack expression of MyoD. In vivo, terra expression is reduced by hedgehog but enhanced by BMP signals. Overexpression of terra induces rapid apoptosis both in vitro and in vivo, suggesting that a tight regulation of terra expression is required during embryogenesis. Terra has both human and mouse homologs and is specifically expressed in mouse somites. Taken together, our findings suggest that terra is a highly conserved protein that plays specific roles in early somitogenesis of vertebrates. (+info)
Requirement of a novel gene, Xin, in cardiac morphogenesis.
A novel gene, Xin, from chick (cXin) and mouse (mXin) embryonic hearts, may be required for cardiac morphogenesis and looping. Both cloned cDNAs have a single open reading frame, encoding proteins with 2,562 and 1,677 amino acids for cXin and mXin, respectively. The derived amino acid sequences share 46% similarity. The overall domain structures of the predicted cXin and mXin proteins, including proline-rich regions, 16 amino acid repeats, DNA-binding domains, SH3-binding motifs and nuclear localization signals, are highly conserved. Northern blot analyses detect a single message of 8.9 and 5.8 kilo base (kb) from both cardiac and skeletal muscle of chick and mouse, respectively. In situ hybridization reveals that the cXin gene is specifically expressed in cardiac progenitor cells of chick embryos as early as stage 8, prior to heart tube formation. cXin continues to be expressed in the myocardium of developing hearts. By stage 15, cXin expression is also detected in the myotomes of developing somites. Immunofluorescence microscopy reveals that the mXin protein is colocalized with N-cadherin and connexin-43 in the intercalated discs of adult mouse hearts. Incubation of stage 6 chick embryos with cXin antisense oligonucleotides results in abnormal cardiac morphogenesis and an alteration of cardiac looping. The myocardium of the affected hearts becomes thickened and tends to form multiple invaginations into the heart cavity. This abnormal cellular process may account in part for the abnormal looping. cXin expression can be induced by bone morphogenetic protein (BMP) in explants of anterior medial mesoendoderm from stage 6 chick embryos, a tissue that is normally non-cardiogenic. This induction occurs following the BMP-mediated induction of two cardiac-restricted transcription factors, Nkx2.5 and MEF2C. Furthermore, either MEF2C or Nkx2.5 can transactivate a luciferase reporter driven by the mXin promoter in mouse fibroblasts. These results suggest that Xin may participate in a BMP-Nkx2.5-MEF2C pathway to control cardiac morphogenesis and looping. (+info)
Selective expression of purinoceptor cP2Y1 suggests a role for nucleotide signalling in development of the chick embryo.
Responses to extracellular nucleotides (e.g., ATP, ADP, etc.) have been demonstrated in a number of embryonic cell types suggesting they may be important signalling molecules during embryonic development. Here the authors describe for the first time the expression of a G-protein-coupled receptor for extracellular ATP, chick P2Y1 (cP2Y1), during embryonic development of the chick. During the first 10 days of embryonic development, cP2Y1 is expressed in a developmentally regulated manner in the limb buds, mesonephros, brain, somites, and facial primordia, suggesting that this receptor may have a role in the development of each of these systems. (+info)
Heat shock protein 70 (Hsp70) protects postimplantation murine embryos from the embryolethal effects of hyperthermia.
Previous work has shown that there is a positive correlation between the induction of Hsp70 and its transient nuclear localization and the acquisition and loss of induced thermotolerance in postimplantation rat embryos. To determine whether Hsp70 is sufficient to induce thermotolerance in postimplantation mammalian embryos, we used a transgenic mouse in which the normally strictly inducible Hsp70 is constitutively expressed in the embryo under the control of a beta-actin promoter. Day 8.0 mouse embryos heterozygous for the Hsp70 transgene were not protected from the embryotoxic effects of hyperthermia (43 degrees C); however, homozygous embryos, expressing approximately twice as much Hsp70 as heterozygous embryos, were partially protected (increased embryo viability) from the embryolethal effects of hyperthermia. Although the viability of transgenic embryos was significantly increased compared with that of nontransgenic embryos, this protection did not extend to embryo growth and development. To determine whether the failure to achieve a more robust protection was related to the expression of insufficient Hsp70 in transgenic embryos, we undertook experiments to determine whether the level of Hsp70 correlated with the level of thermotolerance induced by various lengths of a 41 degrees C heat shock. A 41 degrees C, 5-minute heat shock failed to induce Hsp70 or thermotolerance, a 41 degrees C, 15-minute heat shock induced Hsp70 and a significant level of thermotolerance, while a 41 degrees C, 60-minute heat shock induced an even higher level of Hsp70 as well as a higher level of thermotolerance. Quantitation of Hsp70 levels indicated that thermotolerance was associated with levels of Hsp70 of 820 pg/microg embryo protein or greater. Subsequent quantitation of the amount of Hsp70 expressed in homozygous transgenic embryos indicated a level of 577 pg/microg embryo protein, that is, a level below that associated with induced thermotolerance. Overall, results presented indicate that Hsp70 does play a direct role in the induction of thermotolerance in postimplantation mouse embryos; however, the level of thermotolerance is dependent on the level of Hsp70 expressed. (+info)
Dynamic expression of lunatic fringe suggests a link between notch signaling and an autonomous cellular oscillator driving somite segmentation.
The metameric organization of the vertebrate trunk is a characteristic feature of all members of this phylum. The origin of this metamerism can be traced to the division of paraxial mesoderm into individual units, termed somites, during embryonic development. Despite the identification of somites as the first overt sign of segmentation in vertebrates well over 100 years ago, the mechanism(s) underlying somite formation remain poorly understood. Recently, however, several genes have been identified which play prominent roles in orchestrating segmentation, including the novel secreted factor lunatic fringe. To gain further insight into the mechanism by which lunatic fringe controls somite development, we have conducted a thorough analysis of lunatic fringe expression in the unsegmented paraxial mesoderm of chick embryos. Here we report that lunatic fringe is expressed predominantly in somite -II, where somite I corresponds to the most recently formed somite and somite -I corresponds to the group of cells which will form the next somite. In addition, we show that lunatic fringe is expressed in a highly dynamic manner in the chick segmental plate prior to somite formation and that lunatic fringe expression cycles autonomously with a periodicity of somite formation. Moreover, the murine ortholog of lunatic fringe undergoes a similar cycling expression pattern in the presomitic mesoderm of somite stage mouse embryos. The demonstration of a dynamic periodic expression pattern suggests that lunatic fringe may function to integrate notch signaling to a cellular oscillator controlling somite segmentation. (+info)
Chick Barx2b, a marker for myogenic cells also expressed in branchial arches and neural structures.
We have isolated a new chicken gene, cBarx2b, which is related to mBarx2 in sequence, although the expression patterns of the two genes are quite different from one another. The cBarx2b gene is expressed in craniofacial structures, regions of the neural tube, and muscle groups in the limb, neck and cloaca. Perturbation of anterior muscle pattern by application of Sonic Hedgehog protein results in a posteriorization of cBarx2b expression. (+info)
Expression of Zkrml2, a homologue of the Krml1/val segmentation gene, during embryonic patterning of the zebrafish (Danio rerio).
We have identified Zkrml2, a novel homologue of the segmentation gene Krml/val in zebrafish (Danio rerio). Zkrml2 shows 72% and 92% identity in its basic leucine zipper domain with mouse Krml1 and zebrafish val, respectively. Zkrml2 is expressed coincident with MyoD throughout the somites starting at the three somite stage, becomes restricted to the dermomyotome, and subsequently disappears. Transient expression is also detected in the reticulospinal and oculomotor neurons. Zkrml2 maps to the Oregon linkage group 11 (Boston Linkage group 14) with no mapped zebrafish mutations nearby. (+info)
Pax3 functions in cell survival and in pax7 regulation.
In developing vertebrate embryos, Pax3 is expressed in the neural tube and in the paraxial mesoderm that gives rise to skeletal muscles. Pax3 mutants develop muscular and neural tube defects; furthermore, Pax3 is essential for the proper activation of the myogenic determination factor gene, MyoD, during early muscle development and PAX3 chromosomal translocations result in muscle tumors, providing evidence that Pax3 has diverse functions in myogenesis. To investigate the specific functions of Pax3 in development, we have examined cell survival and gene expression in presomitic mesoderm, somites and neural tube of developing wild-type and Pax3 mutant (Splotch) mouse embryos. Disruption of Pax3 expression by antisense oligonucleotides significantly impairs MyoD activation by signals from neural tube/notochord and surface ectoderm in cultured presomitic mesoderm (PSM), and is accompanied by a marked increase in programmed cell death. In Pax3 mutant (Splotch) embryos, MyoD is activated normally in the hypaxial somite, but MyoD-expressing cells are disorganized and apoptosis is prevalent in newly formed somites, but not in the neural tube or mature somites. In neural tube and somite regions where cell survival is maintained, the closely related Pax7 gene is upregulated, and its expression becomes expanded into the dorsal neural tube and somites, where Pax3 would normally be expressed. These results establish that Pax3 has complementary functions in MyoD activation and inhibition of apoptosis in the somitic mesoderm and in repression of Pax7 during neural tube and somite development. (+info)