ABSTRACT
The nephric duct is the first epithelial tubule to differentiate from intermediate mesoderm that is essential for all further urogenital development. In this study we identify the domain of intermediate mesoderm that gives rise to the nephric duct and demonstrate that the surface ectoderm is required for its differentiation. Removal of the surface ectoderm resulted in decreased levels of Sim-1 and Pax-2 mRNA expression in mesenchymal nephric duct progenitors, and caused inhibition of nephric duct formation and subsequent kidney development. The surface ectoderm expresses BMP-4 and we show that it is required for the maintenance of high-level BMP-4 expression in lateral plate mesoderm. Addition of a BMP-4-coated bead to embryos lacking the surface ectoderm restored normal levels of Sim-1 and Pax-2 mRNA expression in nephric duct progenitors, nephric duct formation and the initiation of nephrogenesis. Thus, BMP-4 signaling can substitute for the surface ectoderm in supporting nephric duct morphogenesis. Collectively, these data suggest that inductive interactions between the surface ectoderm, lateral mesoderm and intermediate mesoderm are essential for nephric duct formation and the initiation of urogenital development.
Subject(s)
Bone Morphogenetic Proteins/metabolism , Ectoderm , Embryonic Induction , Kidney Tubules/embryology , Mesoderm , Animals , Bone Morphogenetic Protein 4 , Cell Lineage , Chick Embryo , DNA-Binding Proteins/biosynthesis , DNA-Binding Proteins/genetics , In Situ Hybridization , PAX2 Transcription Factor , RNA, Messenger/isolation & purification , Repressor Proteins/biosynthesis , Repressor Proteins/genetics , Signal Transduction , Transcription Factors/biosynthesis , Transcription Factors/geneticsABSTRACT
The importance of proportioning kidney size to body volume was established by clinical studies which demonstrated that in-born defecits of nephron number predispose the kidney to disease. As the kidney develops, the expanding ureteric bud or renal collecting system induces surrounding metanephric mesenchyme to proliferate and differentiate into nephrons. Thus, it is likely that nephron number is related to ureteric bud growth. The expression patterns of mRNAs encoding Fibroblast Growth Factor-7 (FGF-7) and its high affinity receptor suggested that FGF-7 signaling may play a role in regulating ureteric bud growth. To test this hypothesis we examined kidneys from FGF-7-null and wild-type mice. Results of these studies demonstrate that the developing ureteric bud and mature collecting system of FGF-7-null kidneys is markedly smaller than wild type. Furthermore, morphometric analyses indicate that mature FGF-7-null kidneys have 30+/-6% fewer nephrons than wild-type kidneys. In vitro experiments demonstrate that elevated levels of FGF-7 augment ureteric bud growth and increase the number of nephrons that form in rodent metanephric kidney organ cultures. Collectively, these results demonstrate that FGF-7 levels modulate the extent of ureteric bud growth during development and the number of nephrons that eventually form in the kidney.
Subject(s)
Fibroblast Growth Factors , Growth Substances/physiology , Kidney/embryology , Ureter/embryology , Animals , Cell Differentiation , Fibroblast Growth Factor 10 , Fibroblast Growth Factor 7 , Growth Substances/genetics , Mice , Mice, Inbred C57BL , Nephrons/embryology , Organ Culture Techniques , Rats , Signal TransductionABSTRACT
In the fission yeast Schizosaccharomyces pombe, the cdc10+/SWI family members constitute the cell cycle 'start' genes. res1+ and res2+ are the newly identified members of this family and encode putative association partners of the Cdc10 protein. The Pat1 kinase plays a pivotal role in switching between vegetative growth and sexual development, and its inactivation in haploid cells induces unconditional growth arrest and subsequent meiosis. We have identified as an extragenic suppressor of a temperature sensitive pat1-114 mutant, a new B-type cyclin that negatively regulates conjugation by interacting with these 'start' genes. This cyclin, named Cyc17, is highly homologous with Cdc13, but has no detectable activity as a mitotic cyclin. Deletion of cyc17+ markedly enhances conjugation, despite the presence of nitrogen source, and accelerates growth arrest in G1 upon nitrogen starvation. Conversely, overexpression of the cyc17+ gene strongly inhibits conjugation. The cyc17+ gene is transcribed into 3.2 kb poly(A)+ and 3.0 kb poly(A)- RNAs. Only the poly(A)+ species is expressed during vegetative growth and periodically with a peak in the G1 and S phases of the cell cycle. On the other hand, the poly(A)- transcript is highly induced during conjugation. This induction is lost in res2- cells, whereas the poly(A)+ transcript is significantly reduced in res1- cells. However, the mating inhibition as well as the ability to rescue the pat1 mutation by overexpression of res1+ and res2+ are totally abolished in cyc17- cells. Thus, in S.pombe, a B-type cyclin, regulated by the newly identified cell cycle 'start' genes, plays a crucial role in the control of sexual development.
