ABSTRACT
All insect ovaries are composed of functional units called ovarioles, which contain sequentially developing egg chambers. The number of ovarioles varies between and within species. Ovariole number is an important determinant of fecundity and thus affects individual fitness. Although Drosophila oogenesis has been intensively studied, the genetic and cellular basis for determination of ovariole number remains unknown. Ovariole formation begins during larval development with the morphogenesis of terminal filament cells (TFCs) into stacks called terminal filaments (TFs). We induced changes in ovariole number in Drosophila melanogaster by genetically altering cell size and cell number in the TFC population, and analyzed TF morphogenesis in these ovaries to understand the cellular basis for the changes in ovariole number. Increasing TFC size contributed to higher ovariole number by increasing TF number. Similarly, increasing total TFC number led to higher ovariole number via an increase in TF number. By analyzing ovarian morphogenesis in another Drosophila species we showed that TFC number regulation is a target of evolutionary change that affects ovariole number. In contrast, temperature-dependent plasticity in ovariole number was due to changes in cell-cell sorting during TF morphogenesis, rather than changes in cell size or cell number. We have thus identified two distinct developmental processes that regulate ovariole number: establishment of total TFC number, and TFC sorting during TF morphogenesis. Our data suggest that the genetic changes underlying species-specific ovariole number may alter the total number of TFCs available to contribute to TF formation. This work provides for the first time specific and quantitative developmental tools to investigate the evolution of a highly conserved reproductive structure.
Subject(s)
Drosophila melanogaster/genetics , Drosophila/genetics , Ovary/cytology , Ovary/metabolism , Animals , Animals, Genetically Modified , Cell Count , Cell Size , Drosophila/growth & development , Drosophila/metabolism , Drosophila Proteins/genetics , Drosophila Proteins/metabolism , Drosophila melanogaster/growth & development , Drosophila melanogaster/metabolism , Eating , Female , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , Immunohistochemistry , Intracellular Signaling Peptides and Proteins/genetics , Intracellular Signaling Peptides and Proteins/metabolism , Larva/genetics , Larva/growth & development , Larva/metabolism , Male , Morphogenesis , Ovary/growth & development , Protein Kinases/genetics , Protein Kinases/metabolism , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , RNA Interference , Ribosomal Protein S6 Kinases/genetics , Ribosomal Protein S6 Kinases/metabolism , Signal Transduction/genetics , Species Specificity , Temperature , Wings, Animal/cytology , Wings, Animal/growth & development , Wings, Animal/metabolismABSTRACT
The Notch signalling pathway regulates proliferation, cell death and cell type specification that is critical for organogenesis. Mouse models carrying mutations in the Notch signalling pathway display defects in development of the placenta, suggesting that this pathway is required for placental development. In particular, Notch1 mutant embryos exhibit abnormal placental morphogenesis and arrest early in development. However, expression of Notch1 gene has not been detected during placental development. Trophoblast stem cells are derived from the precursor of the placenta and express Notch1. We report that Notch1 is also expressed in differentiated trophoblast cells. Under standard differentiation conditions, Notch1 expression ceases by day 6. Furthermore, the activated NOTCH1 intracellular domain is enriched at the nucleolus of trophoblast stem cells and differentiated trophoblast cells. Our results suggest that NOTCH1 is active in both trophoblast stem cells and differentiated trophoblast cells.
