spacer gif spacer gif spacer gif spacer gif spacer gif
QUICK SEARCH:   [advanced]


spacer gif
     Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents    

This Article
Right arrow Summary Freely available
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Deshpande, N.
Right arrow Articles by Urban, J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Deshpande, N.
Right arrow Articles by Urban, J.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?

Successive specification of Drosophila neuroblasts NB 6-4 and NB 7-3 depends on interaction of the segment polarity genes wingless, gooseberry and naked cuticle

Nirupama Deshpande, Rainer Dittrich, Gerhard M. Technau and Joachim Urban*

Institut für Genetik, Universität Mainz, Saarstraße 21, D-55122 Mainz, Germany



View larger version (112K):

[in a new window]
  		Fig. 1. Loss of NB 7-3 in hh mutant embryos can be rescued by ectopic wg expression. Flat preparation of embryos at stage 12, anterior is upwards. Eg expression is seen in blue and En expression in brown with the first three segments from the top being thoracic. The black bar represents the midline. In B-F, arrows denote the presence of an NB and arrowheads denote the absence of the NB in a given hemisegment. (A) Wild type Eg/En expression pattern: two thoracic hemisegments on either side of the midline are shown. Eg antibody stains four NBs and its progeny belonging to NBs 6-4 (shown in shades of blue) and 7-3 (yellow cells) in the En domain, and NBs 2-4 (black cells) and 3-3 (green cells) outside the En domain. NB 6-4 in the thoracic segments characteristically produces three glial cells (two MM-CBG glia that migrate towards the midline and one M-CBG glia) and a cluster of laterally located neurons. (B) Wild-type embryos show Eg expression in two cell clusters in the En domain: NB 6-4 and its progeny are anteriorly located (black arrows); NB 7-3 and its progeny are posteriorly located (white arrows). (C) enE embryos, which are double mutant for en and inv, show no Eg expression at the position of NB 6-4 (black arrowheads) and NB 7-3 (white arrowheads). In all (n=52) of the hemisegments counted, En expression is completely abolished. (D) wgCX4 mutant embryos look similar to enE mutant embryos: Eg expression is absent at the position of NB 6-4 in 100% (n=54) (black arrowheads) and, for NB 7-3, in 75% (n=88) (white arrowheads) of hemisegments counted. (E) hhAC mutant embryos show Eg expression to be missing in 40% (n=60) at NB 6-4 position (black arrowheads) and in 40% (n=202) for NB 7-3 position (white arrowheads) of the hemisegments counted. Occasionally, residual En expression can be seen around the Eg-positive cells clusters. (F) Expression of UAS-wg by en-Gal4 in hhAC mutant embryos rescues the formation of NB 6-4 to 98% (n=109) (black arrows) and NB 7-3 to 95% (n=66) (white arrows) of the hemisegments counted. En expression is rescued.

 


View larger version (113K):

[in a new window]
  		Fig. 2. NB 7-3 is transformed to NB 6-4 fate in embryos mutant for nkd and in embryos with ectopic Gsb expression in the whole En domain. Flat preparation of embryos with anterior upwards. (A-C) Ey expression in blue and En expression in brown at late stage 12; the first three segments from the top are thoracic. The black bar represent the midline. (D-F) Combined sections of confocal images of fluorescence antibody staining against Eg in red and Repo in green at stage 13. Double-labelled cells are seen in yellow with the first two segments from the top being thoracic. The white bar represents the midline. (A) In the En domain of wild-type embryos, Ey expression is seen only in the position of NB 7-3 (black arrows). Ey is expressed additionally in five NBs and their progeny outside the En domain. (B) In nkd mutant embryos, Ey expression is absent at the position of NB 7-3 in 81% (n=80) of the hemisegments counted (white arrowheads). (C) In embryos with ectopic Gsb expression in the En stripe, Ey expression is absent at the position of NB 7-3 in 84% (n=86) of the hemisegments counted (white arrowheads). (D) Wild-type embryos showing cells double labelled for Eg and Repo, which are unique to the glial cells produced by NB 6-4 (white arrows). In each thoracic hemisegment, two of these cells are seen along the midline (MM-CBG) and one more laterally (M-CBG). (E) In embryos with ectopic Gsb expression in the En domain, cells co-expressing Repo and Eg are seen in addition to the three genuine NB 6-4 progeny (white arrows), which are present in the ventral focal planes. At the position of NB 7-3, such cells are seen in the dorsal focal plane in 52% (n=40) (white arrowheads) of the hemisegments counted, suggesting a transformation of NB 7-3 to NB 6-4 fate. (F) In nkd mutant embryos phenotype similar to that in E is seen. At the position of NB 7-3, cells co-expressing Repo and Eg are seen in 54% (n=40) at stage 12 (white arrowheads) of the hemisegments counted, suggesting a transformation of NB 7-3 to NB 6-4 fate. For the purpose of clarity, not all sections of the confocal images are combined here.

 


View larger version (119K):

[in a new window]
  		Fig. 3. Gsb expression is expanded posteriorly in embryos mutant for nkd. Flat preparation of embryos (early stage 12), Gsb expression as revealed by anti-Gsbd serum (brown); anterior is upwards. The first three segments from the top are thoracic. The black bar represents the midline. (A) Wild-type embryos show Gsb expression in all NBs belonging to rows 5 and 6. Only one NB, NB 7-1, belonging to row 7 is Gsb positive. The region of NB 7-3 is Gsb negative (black asterisks). (B) In nkd mutant embryos, Gsb expression is derepressed and now expressed in additional NBs belonging to row 7, which must include NB 7-3 (black arrows).

 


View larger version (111K):

[in a new window]
  		Fig. 4. Loss of Gsb function as well as ectopic Nkd expression in the En-domain results in an additional NB 7-3-like fate. Confocal images of embryos between stage 10-13 with anterior upwards. Ey expression seen in red, En in green and double staining in yellow. The first three segments from the top are thoracic. The white bar represents the midline. (A) Wild-type embryo at stage 10 shows no Ey expression in the En domain. (B) gsb mutant embryos at stage 10 show Ey expression in 65% (n=60) of the hemisegments counted (white arrowheads). (C) Wild-type embryo at late stage 11 shows Ey expression in the En domain at the position of NB 7-3 (white arrows) and its progeny in 100% (n=50) of the hemisegments counted. (D) gsb mutant embryos at late stage 11 show Ey expression at the position of NB 7-3 (white arrows) and its progeny. An additional Ey-positive cell cluster in a different focal plane is seen at the position of NB 6-4 (white arrowheads) in 70% (n=82) of hemisegments counted. (E) gsb;nkd double mutant embryos show a phenotype similar to gsb mutant embryos. Ey expression is found at the position of NB 6-4 (white arrowheads) in 76% (n=86) of the hemisegments counted. (F) UAS-nkd driven by en-Gal4 results in Ey expression at the position of NB 6-4 (white arrowheads) in 40% (n=80) of the hemisegments counted.

 


View larger version (135K):

[in a new window]
  		Fig. 5. Duplicated NB 6-4 in embryos with ectopic Gsb expression is born at the time of NB 7-3. Flat preparation of embryos at stages 10 (A,B) and 11 (C,D) stained against Eg in blue and En in brown, anterior is upwards. The first three segments from the top are thoracic. The black bar represents the midline. (A) Wild-type embryos at stage 10 show Eg expression in the En domain only at the position of NB 6-4 (black arrows) and not in the position of NB 7-3, as it is not yet delaminated. (B) Eg expression in embryos with ectopic Gsb expression in the En domain at stage 10 is indistinguishable from that in wild-type embryos. (C) Wild-type embryos at stage 11 show Eg expression in the En domain at the position of NB 6-4 (black arrows) and NB 7-3 (white arrowheads). (D) Eg expression of embryos with ectopic Gsb expression in En domain at stage 11 is again similar to that of wild-type embryos, although the cells at NB 7-3 position (white arrowheads) now express characteristic markers of NB 6-4 progeny (see Fig. 2E).

 


View larger version (120K):

[in a new window]
  		Fig. 6. Ectopic En expression results in duplication of NB 7-3 fate. Flat preparation of embryos at stage 15 with the midline represented by a black bar (A-F) and an isolated CNS of a first instar larva (G,H) with the midline represented by a white bar; anterior is upwards. (A-C) Eg expression in brown; (D-F) Eve expression in blue; (G-H) serotonin expression in green. (A) Wild-type embryos showing strong Eg expression in the position of NB 7-3 (black arrowheads). (B) Hs-en embryos subjected to a heat pulse between 4 and 5 hours after egg laying: the CNS is malformed but NB 7-3 and its progeny (black arrowheads) can still be identified. (C) Hs-en embryos subjected to heat pulse between 5 and 6 hours after egg laying: ectopic NB 7-3 like cluster (white arrowheads) can be found just below the wild-type NB 7-3 (black arrowheads) in 20% (n=100) of the hemisegments counted. (D) Wild-type embryos showing Eve expression in the position of EL cells (black arrows), which are the progeny of NB 3-3. (E) Hs-en embryos subjected to heat pulse between 5 and 6 hours after egg laying: Eve expression is often missing in the position of EL cells (black stars). (F) ptc mutant embryos shows Eve expression missing in the position of EL cells in many hemineuromeres (black stars). (G) The CNS of a first instar wild-type larva. Two serotonergic neurons are seen per hemisegment. (H) The CNS of a first instar Hs-en larva. Heat shock was applied as in C. Ectopic serotonin expression was found in several hemisegments (white arrows).

 


View larger version (61K):

[in a new window]
  		Fig. 7. A model for the mechanism leading to the formation of NB 6-4 and NB 7-3 identities. (A) The top figure shows the situation in wild type where at time T1 (during S3 NB delamination) in row 6, which is the overlapping domain of GSB (green hatched lines) and EN (yellow) expression, the delaminating NB takes a NB 6-4 identity. The bottom figure shows that at time T2 (during S5 NB delamination) NKD activity (red) inhibits GSB expression in row 7, and the delaminating NB in this region has a NB 7-3 identity. (B) In absence of GSB expression in gsb mutant embryos at time T1 (top figure) in row 6, an NB with an identity of NB 7-3 delaminates at the position of NB 6-4. At time T2 (bottom figure) in row 7, the normal NB 7-3 delaminates. (C) In absence of NKD activity in nkd mutants, the GSB and EN expression is broadened. At time T1 (top figure) in row 6, the normal NB 6-4 delaminates. At time T2 (bottom figure) in row 7, a NB with an identity of NB 6-4 delaminates at the position of NB 7-3.

 

Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?



© The Company of Biologists Ltd 2001