Expression of constitutively active Notch arrests follicle cells at a precursor stage during Drosophila oogenesis and disrupts the anterior-posterior axis of the oocyte

Abstract

During early development, there are numerous instances where a bipotent progenitor divides to give rise to two progeny cells with different fates. The Notch gene of Drosophila and its homologues in other metazoans have been implicated in many of these cell fate decisions. It has been argued that the role of Notch in such instances may be to maintain cells in a precursor state susceptible to specific differentiating signals. This has been difficult to prove, however, due to a lack of definitive markers for precursor identity. We here perform molecular and morphological analyses of the roles of Notch in ovarian follicle cells during Drosophila oogenesis. These studies show directly that constitutively active Notch arrests cells at a precursor stage, while the loss of Notch function eliminates this stage. Expression of moderate levels of activated Notch leads to partial transformation of cell fates, as found in other systems, and we show that this milder phenotype correlates with a prolonged, but still transient, precursor stage. We also find that expression of constitutively active Notch in follicle cells at later stages leads to a defect in the anterior-posterior axis of the oocyte.

Notch receptors and hematopoiesis

“…Activation of Notch inhibits differentiation of precursor cells into hair cells [16][17][18], whereas absence of Notch signal promotes hair-cell differentiation. In addition, the differentiation of ovarian follicle cells is also blocked by Notch at the precursor stage in oogenesis [19]. Notch is not needed to form an appendage but is needed for segmentation into a leg [20][21][22].…”

New mutant alleles for Spargel/dPGC-1 highlights the function of Spargel RRM domain in oogenesis and expands the role of Spargel in embryogenesis and intracellular transport

“…Notch signaling plays a prominent role in Drosophila oogenesis as well as in the mammalian ovary ( Xu et al . 1992 ; Larkin et al . 1996 ; Grammont and Irvine 2001 ; Vanorny and Mayo 2017 ).…”

New Mutations in the 5′ Region of the Notch Gene Affect Drosophila melanogaster Oogenesis

“…Notch signaling is repeatedly required during follicular-cell development. Notch is important for the genesis of the two follicular cell lineages: the stalk/polar cell lineage and the epithelial follicular cell lineage [ 7 , 8 , 26 ]. Subsequently, during stage 6, Notch is necessary throughout the follicular cell epithelium for the switch from mitotic cell divisions to endoreplication [ 10 , 11 ].…”

“…In Drosophila melanogaster , Notch participates in the morphogenesis of both central and peripheral nervous systems and in the development of the eyes, wings, and segmented appendages, such as legs, antennae, and muscles [ 4 , 5 ]. In the adult female, Notch is required for multiple steps in oogenesis, including the formation of the germline stem cell niche, establishment of developmental axes of the oocyte, dorsal appendage patterning [ 6 , 7 , 8 , 9 ], specification and differentiation of follicle cells, their switching from the mitotic cycle to the endocycle [ 10 , 11 ], and migration of border cells [ 12 , 13 ]. Many of these functions have been genetically explored by means of mutations in the Notch gene—as well as genes Delta and Serrate encoding Notch protein ligands—and by ectopic expression of Delta or constitutively activated mutants of receptor Notch [ 14 ].…”