Tissue homeostasis, accomplished through the self-renewai and differentiation of resident stem cells, is critical for the maintenance of adult tissues throughout an animal＇s lifetime, Adult Drosophila Malpighian tubules （MTs or fly kidney） are maintained by renal and nephric stem cells （RNSCs） via self-renewing divisions, however, it is unclear how RNSC proliferation and differentiation are regulated. Here we show that EGFR/MAPK signaling is dispensable for RNSC maintenance, but required for RNSC proliferation in vivo. Inacti- vation of the EGFR/MAPK pathway blocks or greatly retards RNSC cell cycle progression; conversely, over-activation of EGFR/MAPK signaling results in RNSC over-proliferation and disrupts the normal differentiation of renablasts （RBs）, the immediate daughters of RNSC divisions. Our data further suggest that EGFR/MAPK signaling functions independently of JAK/STAT signaling and that dMyc and CycE partially mediate EGFR/MAPK signaling in MTs. Together, our data suggest a principal role of EGFR/MAPK signaling in regulating RNSC proliferation, which may provide important clues for understanding mammalian kidney repair and regeneration following injury.
Heparan sulfate proteoglycans （HSPGs） are critically involved in a variety of biological events. The functions of HSPGs are determined by the nature of the core proteins and modifications of heparan sulfate （HS） glycosaminoglycan （GAG） chains. The distinct O-sulfo- transferases are important for nonrandom modifications at specific positions. Two HS 3-0 sulfotransferase （Hs3st） genes, Hs3st-A and Hs3st-B, were identified in Drosophila. Previous experiments using RNA interference （RNAi） suggested that Hs3st-B was required for Notch signaling. Here, we generated a null mutant of Hs3st-B via ends-out gene targeting and examined its role（s） in development. We found that homozygous Hs3st-B mutants have no neurogenic defects or alterations in the expression of Notch signaling target gene. Thus, our results strongly argue against an essential role for Hs3st-B in Notch signaling. Moreover, we have generated two independent Hs3st-A RNAi lines which worked to deplete Hs3st-A. Importantly, Hs3st-A RNAi combined with Hs3st-B mutant flies did not alter the expression of Notch signaling components, arguing that both Hs3st-A and Hs3st-B were not essential for Notch signaling. The establishment of Hs3st-B mutant and effective Hs3st-A RNAi lines provides essential tools for further studies of the physiological roles of Hs3st-A and Hs3st-B in development and homeostasis.
The highly conserved Notch signaling is precisely regulated at different steps in a series of developmental events. However, little is known about the regulation of Notch receptor at transcriptional level. Here, we demonstrate that dBrmsl is involved in regulating Notch signaling in Drosophila wing. We show that knockdown of dBrmsl by RNA interference （RNAi） in wing disc suppresses the expression of Notch signaling target genes wingless （wg）, cut and Enhancer of split m8 [E（spl）m8]. Consistently, the levels of Wg and Cut are reduced in the dBrmsl mutant clones. Importantly, loss of dBrmsl leads to significant reduction of Notch proteins. Furthermore, depletion of dBrmsl results in apparent downregulation of Notch transcription in the wing disc. Moreover, we find that dBrmsl is functionally conserved with human Breast cancer metastasis suppressor 1 like （hBRMSIL） in the modulation of Notch signaling. Taken together, our data provide important insights into the biological function of dBrmsl in regulating Notch signaling.
