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The spatial and temporal dynamics of Sax1 (CHox3) homeobox gene expression in the chick's spinal cord
P Spann1, M Ginsburg, Z Rangini
1Department of Genetics, Hebrew University of Jerusalem, Israel.
Insights
Chicken homeobox gene Sax1 is expressed in the spinal neural plate during embryonic development. Its expression is autonomously regulated after neural plate induction by mesoderm.
Area of Science:
- Developmental biology
- Molecular genetics
- Chicken embryology
Background:
- Sax1 (CHox3) is a chicken homeobox gene homologous to Drosophila NK1 and honeybee HHO.
- Sax1 transcripts are present from early embryonic stages (Stage 2 H&H) through 5 days.
- Early in situ hybridization revealed Sax1 localization primarily in the posterior neural plate from Stage 8- onwards.
Purpose of the Study:
- To investigate the spatiotemporal expression pattern of the chicken homeobox gene Sax1.
- To determine the regulatory mechanisms controlling Sax1 expression during embryonic development.
- To elucidate the role of neighboring tissues in Sax1 gene regulation.
Main Methods:
- In situ hybridization to detect Sax1 transcript localization.
- Embryonic manipulation experiments, including tissue removal (somites, mesodermal plate, notochord) and transplantation (ectopic notochord, neural plate sections).
Main Results:
- Sax1 transcripts are specifically localized in the spinal neural plate from Stage 8- to 15 H&H.
- Sax1 expression borders correlate with somite segregation dynamics and the posterior neural plate.
- Embryonic manipulations indicated that Sax1 is autonomously regulated within the spinal neural plate post-mesodermal induction.
Conclusions:
- Sax1 expression is confined to the spinal neural plate during specific embryonic stages.
- Mesoderm induces the neural plate early in development (full primitive streak stage).
- Sax1 regulation within the spinal neural plate is autonomous, independent of immediate surrounding tissues after induction.
Abstract:
Sax1 (previously CHox3) is a chicken homeobox gene belonging to the same homeobox gene family as the Drosophila NK1 and the honeybee HHO genes. Sax1 transcripts are present from stage 2 H&H until at least 5 days of embryonic development. However, specific localization of Sax1 transcripts could not be detected by in situ hybridization prior to stage 8-, when Sax1 transcripts are specifically localized in the neural plate, posterior to the hindbrain. From stages 8- to 15 H&H, Sax1 continues to be expressed only in the spinal part of the neural plate. The anterior border of Sax1 expression was found to be always in the transverse plane separating the youngest somite from the yet unsegmented mesodermal plate and to regress with similar dynamics to that of the segregation of the somites from the mesodermal plate. The posterior border of Sax1 expression coincides with the posterior end of the neural plate. In order to study a possible regulation of Sax1 expression by its neighboring tissues, several embryonic manipulation experiments were performed. These manipulations included: removal of somites, mesodermal plate or notochord and transplantation of a young ectopic notochord in the vicinity of the neural plate or transplantation of neural plate sections into the extraembryonic area. The results of these experiments revealed that the induction of the neural plate by the mesoderm has already occurred in full primitive streak embryos, after which Sax1 is autonomously regulated within the spinal part of the neural plate.