The utlity of this database, like all others, depends on a clear definition and understanding of the terms used to classify tissues and to describe gene expression. Definitions are as follows;

Tissue Classification

• Metaneprhos Tables
• unind ub - (uninduced uteric bud) ureteric bud that has not yet reached the metanephric mesenchyme (qv) and has not therefore received signals to make it branch.
• duct tip - the tip region of the developing collecting duct system, at any stage from contact between ureteric bud (the progenitor of the duct) and the metanephric mesenchyme, at any stage from the once-branched ureteric bud to the cessation of branching. The distinction between 'tip' and 'trunk' is at the moment rather subjective.
• duct trunk - all regions of the collecting duct except the duct tip; at any stage from the once-branched ureteric bud to the cessation of branching.
• unind mm - (uninduced metanephric mesenchyme) where the metanephric mesenchyme (mm) has not yet been induced by the ureteric bud (or anything else) even as far as the formation of stem cells which is characterised by rise in DNA synthesis, fall in apoptosis and weak 'condensation'. This tissue is only available for study in very early kidneys when compared with the cortical rind around later ones which is composed of stem cells NOT uninduced metanephric mesenchyme (Bard, McConnell & Davies 1994).
• blastema - cells one step beyond the uninduced mm described above: those cells near the branching ureteric bud in very young kidneys and in the cortex of older ones (see reference above). Note: This model of renal development is still somewhat contentious as it assumes that there are two stages in the 'induction' of mm. The first rescues the mm from apoptosis and promotes multiplication, but does not commit to nephrogenesis - cells that have made this first transition are the ones we call 'blastema'. Transition to neprhogenesis, in this view, is a second step. There is now fairly good evidence that long-range molecules can promote just the first stage without the second (Barasch, Pressler, Connor & Malik 1996). We acknowledge that this model and the term 'blastema' are both contentious issues. In constructing this database, I am not really trying to promote one model of development above another, but it is necessary to organise it in some clear way.
• cond-s - all stages between, and including the pre- epitheliogenic condensate and the S-shaped epithelial tubule. The condensate referred to is a tight aggregate of cells, and should not be confused with the the stem cell population that is a little more closely packed than uninduced mesenchyme which can also be described as being 'condensed' by some authors. Please note we are aware that the condensate-S phases encompass very different states of differentiation, and that they should be separated; our problem in creating a database is that descriptions of gene expression are seldom made with reference to other molecular markers, so it is generally not possible to sort out precisely which stages cells are in when expression begins.
• glom - the epithelial component (Bowman's capsule) of the glomerulus.
• neph - the parts of the nephron that are not the glomerulus
• stroma - developing renal stroma
• Pronephros & Mesonephros Tables
• pro prim - pronephric primordium (before differentiation)
• pro tub - pronephric tubules
• pro glom - pronephric 'glomeruli'
• pro duct - pronephric duct.
• meso m - mesonephrogenic mesenchyme
• meso tub - mesonephric tubules
• meso glom - mesonephric glomerulus
• WD - Wolffian Duct (excluding pronephric duct)

Gene Expression Patterns

[-]	no data available
?	uncertain or disputed
n	not expressed
(y)	expressed at very low level
y	expressed at low level
Y	expressed strongly

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Date of last revision: January 2006
Comments about the database are always welcome.
Email: Jamie.Davies@ed.ac.uk