Notochord signals control the transcriptional cascade of myogenic bHLH genes in somites of quail embryos

Development ◽  
1996 ◽  
Vol 122 (5) ◽  
pp. 1475-1488 ◽  
Author(s):  
M.E. Pownall ◽  
K.E. Strunk ◽  
C.P. Emerson
Keyword(s):  
Gene Expression ◽  
Neural Tube ◽  
Bhlh Gene ◽  
Lateral Plate ◽  
Ventral Neural Tube ◽  
Bhlh Genes ◽  
Somite Formation ◽  
Necessary And Sufficient ◽  
Alpha Actin

Microsurgical, tissue grafting and in situ hybridization techniques have been used to investigate the role of the neural tube and notochord in the control of the myogenic bHLH genes, QmyoD, Qmyf5, Qmyogenin and the cardiac alpha-actin gene, during somite formation in stage 12 quail embryos. Our results reveal that signals from the axial neural tube/notochord complex control both the activation and the maintenance of expression of QmyoD and Qmyf5 in myotomal progenitor cells during the period immediately following somite formation and prior to myotome differentiation. QmyoD and Qmyf5 expression becomes independent of axial signals during myotome differentiation when somites activate expression of Qmyogenin and alpha-actin. Ablation studies reveal that the notochord controls QmyoD activation and the initiation of the transcriptional cascade of myogenic bHLH genes as epithelial somites condense from segmental plate mesoderm. The dorsal medial neural tube then contributes to the maintenance of myogenic bHLH gene expression in newly formed somites. Notochord grafts can activate ectopic QmyoD expression during somite formation, establishing that the notochord is a necessary and sufficient source of diffusible signals to initiate QmyoD expression. Myogenic bHLH gene expression is localized to dorsal medial cells of the somite by inhibitory signals produced by the lateral plate and ventral neural tube. Signaling models for the activation and maintenance of myogenic gene expression and the determination of myotomal muscle in somites are discussed.

Combinatorial signals from the neural tube, floor plate and notochord induce myogenic bHLH gene expression in the somite

Development ◽  
1995 ◽  
Vol 121 (3) ◽  
pp. 651-660 ◽  
Author(s):  
A.E. Munsterberg ◽  
A.B. Lassar
Keyword(s):  
Gene Expression ◽  
Neural Tube ◽  
Developmental Stages ◽  
Floor Plate ◽  
Bhlh Gene ◽  
Neural Tubes ◽  
Bhlh Genes ◽  
Early Developmental ◽  
Somitic Mesoderm

The neural tube, floor plate and notochord are axial tissues in the vertebrate embryo which have been demonstrated to play a role in somite morphogenesis. Using in vitro coculture of tissue explants, we have monitored inductive interactions of these axial tissues with the adjacent somitic mesoderm in chick embryos. We have found that signals from the neural tube and floor plate/notochord are necessary for expression of the myogenic bHLH regulators MyoD, Myf5 and myogenin in the somite. Eventually somitic expression of the myogenic bHLH genes is maintained in the absence of the axial tissues. In organ culture, at early developmental stages (HH 11-), induction of myogenesis in the three most recently formed somites can be mediated by the neural tube together with the floor plate/notochord, while in more rostral somites (stages IV-IX) the neural tube without the floor plate/notochord is sufficient. By recombining somites and neural tubes from different axial levels of the embryo, we have found that a second signal is necessary to promote competence of the somite to respond to inducing signals from the neural tube. Thus, we propose that at least two signals from axial tissues work in combination to induce myogenic bHLH gene expression; one signal derives from the floor plate/notochord and the other signal derives from regions of the neural tube other than the floor plate.

scholarly journals Basic Helix-Loop-Helix Transcription Factors Cooperate To Specify a Cortical Projection Neuron Identity

2007 ◽  
Vol 28 (5) ◽  
pp. 1456-1469 ◽  
Author(s):  
Pierre Mattar ◽  
Lisa Marie Langevin ◽  
Kathryn Markham ◽  
Natalia Klenin ◽  
Salma Shivji ◽  
...  
Keyword(s):  
Gene Expression ◽  
Transcription Factors ◽  
Projection Neuron ◽  
Luciferase Assay ◽  
Bhlh Gene ◽  
Cortical Projection ◽  
Basic Helix Loop Helix ◽  
Helix Loop Helix ◽  
Bhlh Genes ◽  
Cortical Projection Neuron

ABSTRACT Several transcription factors are essential determinants of a cortical projection neuron identity, but their mode of action (instructive versus permissive) and downstream genetic cascades remain poorly defined. Here, we demonstrate that the proneural basic helix-loop-helix (bHLH) gene Ngn2 instructs a partial cortical identity when misexpressed in ventral telencephalic progenitors, inducing ectopic marker expression in a defined temporal sequence, including early (24 h; Nscl2), intermediate (48 h; BhlhB5), and late (72 h; NeuroD, NeuroD2, Math2, and Tbr1) target genes. Strikingly, cortical gene expression was much more rapidly induced by Ngn2 in the dorsal telencephalon (within 12 to 24 h). We identify the bHLH gene Math3 as a dorsally restricted Ngn2 transcriptional target and cofactor, which synergizes with Ngn2 to accelerate target gene transcription in the cortex. Using a novel in vivo luciferase assay, we show that Ngn2 generates only ∼60% of the transcriptional drive in ventral versus dorsal telencephalic domains, an activity that is augmented by Math3, providing a mechanistic basis for regional differences in Ngn2 function. Cortical bHLH genes thus cooperate to control transcriptional strength, thereby temporally coordinating downstream gene expression.

Specification and determination of limb identity: evidence for inhibitory regulation of Tbx gene expression

Development ◽  
2002 ◽  
Vol 129 (1) ◽  
pp. 211-220 ◽  
Author(s):  
Daisuke Saito ◽  
Sayuri Yonei-Tamura ◽  
Kohko Kano ◽  
Hiroyuki Ide ◽  
Koji Tamura
Keyword(s):  
Gene Expression ◽  
Culture Medium ◽  
Inhibitory Effects ◽  
Rt Pcr ◽  
Lateral Plate ◽  
Specific Expression ◽  
Type Identity ◽  
Transplantation Experiments ◽  
Inhibitory Regulation

Limb-type-specific expression of Tbx5/Tbx4 plays a key role in drawing distinction between a forelimb and a hindlimb. Here, we show insights into specification and determination during commitment of limb-type identity, in particular that median tissues regulate Tbx expressions. By using the RT-PCR technique on chick embryos, the onset of specific Tbx5/Tbx4 expression in the wing/leg region was estimated to be stage 13. Specification of the limb-type identity is thought to occur before stage 9, since all explants from stage 9 through 14 expressed the intrinsic Tbx gene autonomously in a simple culture medium. The results of transplantation experiments revealed that axial structures medial to the lateral plate mesoderm at the level of the wing region are capable of transforming leg identity to wing identity, suggesting that a factor(s) from the median tissues is involved in the limb-type determination. Nevertheless, the transplanted wing region was not converted to leg identity. The results of the transplantation experiments also suggested that wing-type identity is determined much earlier than is leg-type identity. Finally, we also found that inhibitory effects of median tissues mediate the specific expression of Tbx5/Tbx4 in the presumptive wing/leg region. We propose a model for limb-type identification in which inhibitory regulation is involved in restricting one Tbx gene expression by masking the other Tbx expression there.

achaete-scute feminizing activities and Drosophila sex determination

Development ◽  
1993 ◽  
Vol 117 (2) ◽  
pp. 737-749 ◽  
Author(s):  
S.M. Parkhurst ◽  
H.D. Lipshitz ◽  
D. Ish-Horowicz
Keyword(s):  
Gene Expression ◽  
Protein Expression ◽  
Sex Determination ◽  
Detailed Examination ◽  
Bhlh Gene ◽  
Basic Helix Loop Helix ◽  
Helix Loop Helix ◽  
Bhlh Genes ◽  
Sex Lethal

Sex determination in Drosophila depends on X-linked ‘numerator’ genes activating early Sex-lethal (Sxl) transcription in females. One numerator gene, sisterless-b (sis-b), corresponds to the achaete-scute (AS-C) T4 basic-helix-loop-helix (bHLH) gene. Two other closely related AS-C bHLH genes, T3 and T5, appear not to function as numerator elements. We analyzed endogenous AS-C expression and show that T4 is the major AS-C numerator gene because it is expressed earlier and more strongly than are T3 and T5. Only T4 expression is detectable during the early syncytial stages when Sxl state is being determined. Nevertheless, the effects of ectopic AS-C gene expression show that T3 and T5 proteins display weak but significant feminizing activities, enhancing male-lethality, and rescuing the female-lethality of sis mutations. Detailed examination of Sxl expression in rescued embryos suggests that female cells may be viable in the absence of detectable Sxl protein expression.

scholarly journals A cell lineage analysis of segmentation in the chick embryo

Development ◽  
1988 ◽  
Vol 104 (Supplement) ◽  
pp. 231-244 ◽  
Author(s):  
Claudio D. Stern ◽  
Scott E. Fraser ◽  
Roger J. Keynes ◽  
Dennis R. N. Primmett
Keyword(s):  
Cell Division ◽  
Chick Embryo ◽  
Neural Tube ◽  
Single Cells ◽  
Cell Lineage ◽  
Subsequent Development ◽  
Ventral Horn ◽  
Cell Division Cycle ◽  
Lateral Plate ◽  
Somite Formation

We have studied the lineage history of the progenitors of the somite mesoderm and of the neural tube in the chick embryo by injecting single cells with the fluorescent tracer, rhodamine-lysine-dextran. We find that, although single cells within the segmental plate give rise to discrete clones in the somites to which they contribute, neither the somites nor their component parts (sclerotome, dermatome, myotome or their rostral and caudal halves) are `compartments' in the sense defined in insects. Cells in the rostral two thirds or so of the segmental plate contribute only to somite tissue and divide about every 10 h, while those in the caudal portions of this structure contribute both to the somites and to intermediate and lateral plate mesoderm derivatives. In the neural tube, the descendants of individual prospective ventral horn cells remain together within the horn, with a cycle time of 10 h. We have also investigated the role of the cell division cycle in the formation and subsequent development of somites. A single treatment of 2-day chick embryos with heat shock or a variety of drugs that affect the cell cycle all produce repeated anomalies in the pattern of somites and vertebrae that develop subsequent to the treatment. The interval between anomalies is 6-7 somites (or a multiple of this distance), which corresponds to 10 h. This interval is identical to that measured for the cell division cycle. Given that cell division synchrony is seen in the presomitic mesoderm, we suggest that the cell division cycle plays a role in somite formation. Finally, we consider the mechanisms responsible for regionalization of derivatives of the somite, and conclude that it is likely that both cell interactions and cell lineage history are important in the determination of cell fates.

scholarly journals Evolution of Antennapedia-Class Homeobox Genes

Genetics ◽  
1996 ◽  
Vol 142 (1) ◽  
pp. 295-303 ◽  
Author(s):  
Jianzhi Zhang ◽  
Masatoshi Nei
Keyword(s):  
Gene Expression ◽  
Homeobox Genes ◽  
Amino Acid Sequences ◽  
Gene Arrangement ◽  
Gene Duplications ◽  
Group I ◽  
Group 3 ◽  
Group Ii ◽  
Anterior Posterior

Antennapedia (Antp)-class homeobox genes are involved in the determination of pattern formation along the anterior-posterior axis of the animal embryo. A phylogenetic analysis of Antp-class homeodomains of the nematode, Drosophila, amphioxus, mouse, and human indicates that the 13 cognate group genes of this gene family can be divided into two major groups, i.e., groups I and II. Group I genes can further be divided into subgroups A (cognate groups 1–2), B (cognate group 3), and C (cognate groups 4–8), and group II genes can be divided into subgroups D (cognate groups 9–10) and E (cognate groups 11–13), though this classification is somewhat ambiguous. Evolutionary distances among different amino acid sequences suggest that the divergence between group I and group II genes occurred ∼1000 million years (MY) ago, and the five different subgroups were formed by ∼600 MY ago, probably before the divergence of Pseudocoelomates (e.g., nematodes) and Coelomates (e.g., insects and chordates). Our results show that the genes that are phylogenetically close are also closely located in the chromosome, suggesting that the colinearity between the gene expression and gene arrangement was generated by successive tandem gene duplications and that the gene arrangement has been maintained by some sort of selection.

Study of Dosage Compensation in Drosophila

Genetics ◽  
2003 ◽  
Vol 165 (3) ◽  
pp. 1167-1181
Author(s):  
Pei-Wen Chiang ◽  
David M Kurnit
Keyword(s):  
Gene Expression ◽  
X Chromosome ◽  
Dosage Compensation ◽  
Qpcr Assay ◽  
Male And Female ◽  
Multiple Genes ◽  
Chromosomal Changes ◽  
Regulatory Effects

Abstract Using a sensitive RT-QPCR assay, we analyzed the regulatory effects of sex and different dosage compensation mutations in Drosophila. To validate the assay, we showed that regulation for several genes indeed varied with the number of functional copies of that gene. We then confirmed that dosage compensation occurred for most genes we examined in male and female flies. Finally, we examined the effects on regulation of several genes in the MSL pathway, presumed to be involved in sex-dependent determination of regulation. Rather than seeing global alterations of either X chromosomal or autosomal genes, regulation of genes on either the X chromosome or the autosomes could be elevated, depressed, or unaltered between sexes in unpredictable ways for the various MSL mutations. Relative dosage for a given gene between the sexes could vary at different developmental times. Autosomal genes often showed deranged regulatory levels, indicating they were in pathways perturbed by X chromosomal changes. As exemplified by the BR-C locus and its dependent Sgs genes, multiple genes in a given pathway could exhibit coordinate regulatory modulation. The variegated pattern shown for expression of both X chromosomal and autosomal loci underscores the complexity of gene expression so that the phenotype of MSL mutations does not reflect only simple perturbations of genes on the X chromosome.

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