Inscuteable‐independent apicobasally oriented asymmetric divisions in the Drosophila embryonic CNS

Abstract

Inscuteable is the founding member of a protein complex localised to the apical cortex of Drosophila neural progenitors that controls their asymmetric division. Aspects of asymmetric divisions of all identified apicobasally oriented neural progenitors characterised to date, in both the central and peripheral nervous systems, require inscuteable. Here we examine the generality of this requirement. We show that many identified neuroblast lineages, in fact, do not require inscuteable for normal morphological development. To elucidate the requirements for apicobasal asymmetric divisions in a context where inscuteable is not essential, we focused on the MP2 > dMP2 + vMP2 division. We show that for MP2 divisions, asymmetric localisation and segregation of Numb and the specification of distinct dMP2 and vMP2 identities require bazooka but not inscuteable. We conclude that inscuteable is not required for all apicobasally oriented asymmetric divisions and that, in some cellular contexts, bazooka can mediate apicobasal asymmetric divisions without inscuteable.

Notch signaling acts before cell division to promote asymmetric cleavage and cell fate of neural precursor cells

“…Like GMC-1s, other neural precursor cells, including GMC1-1a and NB7-1 cells, require Insc for asymmetric division (27). However, MP2 cells do not have Insc and thus do not require Insc for asymmetric division (22). Yet, Notch loss of function disrupted basal localization of Numb in MP2 cells.…”

“…In embryos homozygous for insc 22 , RP2 duplication occurred in most hemisegments (85% of hemisegments), and most of duplicated RP2s were of the same size (80% of hemisegments) (Fig. 4B).…”

“…Images are representative of n ≥ 20 hemisegments from at least four embryos per condition. (E and F) Immunohistochemical labeling for Eve shows GMC-1s and their progeny in wild-type embryos, homozygous numb df embryos, or embryos homozygous for insc 22 and numb df (E) or Hsp70-Notch intra (N intra ) (F). Hsp70-Notch intra was either uninduced or induced in 6-hour-old embryos that were shifted to 29°C for 30 min.…”

“…Oregon-R wild-type flies and flies with genotypes Notch ts1 (encoding Notch with a G1272D amino acid substitution), Hsp70-N intra , insc 22 …”

“…Numb and Insc are required for asymmetry in the GMC-1 lineage, as well as several other cell lineages (6,21). However, there are some cell lineages, for example, the MP2 lineage, where Numb is required, but Insc is not (22). MP2 cells are similar to NBs in terms of the expression of genes that determine neural differentiation of the ectoderm but behave like GMCs by undergoing terminal cell division to generate two different neurons (16).…”