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Fig. 2. Intermediate mesoderm gives rise to the collecting system and nephron
epithelia. (A) Model of the developing avian urinary tract showing
the position of the gonads (g), mesonephros (ms), nephric duct (nd),
metanephros (mt), ureter (u) and cloaca (c). (B,C) The ureter
and intra-renal collecting system derive from rostral intermediate mesoderm.
Images of representative chick embryos with replication-defective retrovirus
encoding lacZ injected into the intermediate mesoderm between the
axial levels of somites 6-10. Injection performed at HH st10. After 6 days
(B), blue lacZ-expressing lineage-tagged cells are present in short
tubules (*) extending into the mesonephros (ms), the nephric duct
(nd) and the ureteric bud (ub), which has yet to undergo branching
morphogenesis. Lineage-tagged cells are not present in the cloaca (c), the
tissue that gives rise to the terminal portions of the conduit system. After
14 days (C) ß-gal-positive, lineage-tagged cells are present in the
nephric duct (nd), the ureter (u) and the branched, metanephric (mt)
intra-renal collecting system (ct). (D) Metanephric nephron epithelia
derive from caudal intermediate mesoderm as determined by lacZ
transfer into this tissue at HH st14. Examination of representative urinary
tract 14 days after lacZ transfer caudal to somite 27 demonstrates
that large populations of lineage-tagged cells are present in the metanephros
(mt). Few, if any, tagged cells were present around the ureter (u) and cloaca
(c). Paraffin sections of the metanephros (D, inset) demonstrate that
lineage-tagged cells exhibit the morphological properties of podocytes (gp),
the specialized nephron epithelia surrounding the glomerular capillary tuft,
and epithelia of the tubular nephron segments (t).
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