Functional associations of gene clusters. Gene clusters varied
remarkably in terms of major functional classifications of component
genes. Key (Lower right) indicates major gene functional
classifications: B, biosynthetic; CA, cell adhesion; C,
catabolism-small molecules; CC, cell cycle; CS, cytoskeletal; DE,
defense; D, DNA structure or replication; E, extracellular matrix; ED,
endocytosis; EN, energy metabolism; H, homeostasis of the organism; M,
morphogenetic; P, protein synthesis or processing; R, RNA synthesis or
processing; HS, heat-shock proteins; DT, detoxification of exogenous
substances; RD, protection against oxidative stress; T, transport; RT,
retrotransposon; U, unknown function. The icons preceding the group
names were derived from Fig. 4 and display the associated temporal
expression profile. Group 1 expressed earlier in nephrogenesis was most
notable for genes involved in DNA replication (D), RNA production (R),
protein synthesis (P), and morphogenesis (M), consistent with an
actively proliferating tissue. Group 2 (which peaked in
midnephrogenesis) was most notable for genes of the extracellular
matrix (E) as well as morphogenetic genes (M). Group 3 (with a peak in
neonatal life) was dominated by retrotransposon transcripts (RT). Group
4 was most notable for transport (T) and energy metabolism (EN) related
genes. Group 5 genes (significantly up-regulated in the adult vs. all
previous times) was more heterogeneous and included genes specifying
catabolic enzymes (C), defense and immune recognition (DE), homeostasis
of the organism as a whole (H), detoxification (DT), oxidative stress
(RD), and transport (T).