Classification of Developing Structures: Structural Definition and Fate

1. Classification of developing structures • Developing structures are typically classified by developmental biologists according to their fate. • If such terms are to find a home in CARO, they also need a structural definition

2. Developing structures that are structurally types of tissue(?)

3. FMA Definition of tissue • Anatomical structure which consist of similarly specialized cells and intracellular matrix, aggregated according to genetically determined spatial relationships.

4. anlage (synonym: field (?)) Contiguous tissue contributing all or the majority of its cells to one or a few mature structures but not (yet) having distinct morphological boundaries. % determinate anlage Contiguous tissue contributing all of its cells to one or a few mature structures but not (yet) having distinct morphological boundaries. % non-determinate anlage Contiguous tissue defined by lineage labelling as contributing the majority of its cells to some specified mature structure but not (yet) having distinct morphological boundaries. (Also inclusive and specific, as for promordium - see next slide… but this is tangled !!!!)

5. Primordium (synonym: rudiment (?)) Contiguous tissue contributing all of its cells to one or a few mature structures and having morphologically distinct boundaries. % inclusive primordium Contiguous tissue contributing all of its cells to a few mature structures and having morphologically distinct boundaries. % specific primordium Contiguous tissue contributing all of its cells to a single mature structure and having morphologically boundaries. Note – anlage, primordium distinction is largely down to presence of boundaries, should this be reflected in different structural categories?

6. germ layer Primary division of embryo established just prior to &/or during gastrulation. Initially constituting a contiguous tissue contributing all of its cells a large but limited set of mature anatomical structure. is_a ectoderm is_a endoderm is_a mesoderm … compartment Contiguous tissue consisting of cells unable to cross a *compartment boundary* to mix with cells in a neighbouring tissue with which it is contiguous during development.

7. Developing structures that can be structurally defined as anatomical sets (?)

8. Germ layer derivative An anatomical structure which is derived from the a single germ-layer. % mesodermal derivative an anatomical structure derived from the mesoderm. Notes: • individual anlage and primordia can be is_a children of these terms. • At what stage, if any, do we stop classifying developing structures in this way?

9. Developing X terms These terms have multiple primordia and anlage as parts. Different parts are instantiated at different stages. Developing system (e.g.- developing nervous system) Developing (cardinal) body part – e.g.- developing head Developing organ (e.g.- developing brain)

10. Miscellaneous structural types of developing structure

11. Mesenchyme Not defined by developmental fate or potential. Perhaps better defined purely structurally? [Note – mesenchyme is a mass noun (as opposed to a count noun – like neuron. Should be referred to as ‘portion of mesenchyme’ according to Barry.] compartment boundary (Genus is_a 'anatomical line' (?)) A boundary that cuts across a contiguous tissue separating it into two groups of cells that do not mix during development. Compartment boundaries have few, if any, morphological correlates, at least while they function as barriers.

12. Differentia Note that there are two types of fate based differentia working to define these terms: • Is the fate mapping probablistic (some defined percentage of cells in the structure have a specific fate) or deterministic (all the cells in the structure have a specific fate) • Will the structure contribute to 1 (more) mature structures, or multiple (more) mature structures. Can we cope with these while keeping is_a siblings disjoint?