Learning Activity

Our experiments have shown that the somitic cells have a certain intrinsic knowledge about their fate. Furthermore, they maintain this knowledge, (and thus their blue color in the animation) as the primaxial population expands to form the ribs and intercostal muscles. The nature of this information is autonomous, and it is maintained regardless of surgical perturbations.

These same experiments also show that the muscle precursor cells that leave their parental somite, and migrate across the frontier to inhabit the abaxial domain are not restrained by the fate of their parental somites. As they cross the frontier they come under the influence of patterning information in the lateral plate. This is reflected by the colors in the animation. Cells crossing the frontier leave the primaxial (blue) environment and enter the abaxial domain (green). As part of this Learning Object, we offer the following hypothetical experiments and ask you to predict the morphological results.

The illustration below is a fate map of the chick somitic mesoderm (anterior to the top). Structures in the primaxial domain are listed on the left. The structures listed on the right are abaxial structures that form from lateral plate mesoderm at the levels indicated, and include muscle cells originating from the indicated somites. The picture would be easy to colorize- but, either avoid blue and green or make the somites all shades of blue, and the text of the abaxial structures in green.

Diagram

1. Surgical perturbations

  • What would be the anatomical result if somites 20 through 24 were transplanted to the position of somites 10-14?
  • What would result from the transplant of somites 21-24 to the position of somites 26-29?
  • What would be the result from the transplant of somites 10-14 to the position of 20-24?
  • If our hypothesis is correct, what would be the anatomical result of transplanting lateral plate mesoderm from the cervical level (e.g. adjacent to  so. 5-15) to the thoracic region (e.g. adjacent to so. 20-26).
  • If our hypothesis is correct, what would be the anatomical result of transplanting lateral plate mesoderm from the cervical level (e.g. adjacent to so. 5-10) to the lumbar region (e.g. adjacent to so. 26-29).

2. Molecular perturbations

  • If transcription factors X,Y and Z are normally expressed only in somites at the thoracic level, and are closely correlated with the development of the thoracic morphology (i.e. ribs, intercostal muscles), what do you predict the out come would be if you misexpressed these factors in cervical somites?
  • If transcription factors P, Q & R are normally expressed in the lateral plate mesoderm at the level of the lumbar region (e.g. adjacent to so. ~26-29) , and are closely correlated with the development of normal abdominal muscles, what do you predict the out come would be if you misexpressed these factors in lateral plate at cervical levels? What would you expect to see in the ‘abaxial’ domain of the neck?

For questions or clarifications regarding your predictions on morphological results, please email acburke@wesleyan.edu.