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doi: 10.1242/10.1242/dev.00532

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Segment polarity and DV patterning gene expression reveals segmental organization of the Drosophila brain

Institut für Genetik, Universität Mainz, D-55099 Mainz, Germany

View larger version (100K): [in a new window]   Fig. 1. Expression of segment polarity genes at embryonic stages 9 (st9) and 10 (st10). Colour code indicates the expression pattern of engrailed-lacZ/Invected protein (en/inv; red), hedgehog-lacZ (hh; purple), mirror-lacZ (mirr; blue), wingless-lacZ/Wingless protein (wg; green), and Gooseberry-distal protein (gsb-d; pink) at the level of identified brain NBs (A,D) and procephalic neuroectoderm (B,C,E,F). All panels show semi-schematic representations of a ventral view of the left half of head flat preparations; anterior (a) is towards the top and dorsal (d) is towards the left. Nomenclature of brain NBs is according to their position in the trito- (T), deuto- (D) and protocerebrum (P) [for details of the nomenclature see Urbach et al. (Urbach et al., 2003)]. In (B,C,E,F), thick hatching marks strong expression and thin hatching marks weak expression of the respective gene; for comparison, NBs underlying the peripheral ectoderm are encircled by broken lines. The expression of en, gsb-d and wg is confined to intermediate and dorsal brain NBs (A,D) and corresponding sites of the peripheral procephalic ectoderm (B,C,E,F). By stage 10, Gsb-d is detected in the ectoderm of all four pregnathal head segments (E). In the gsb-d ocular domain (gsb-d oc) and two corresponding NBs (Ppd3, Ppd10) gsb-d expression is transient (compare with Fig. 2). It is also transiently expressed (between stages 10 and 11) in the clypeolabral ectoderm [in the gsb-d labral spot, which is partly colocalized with the wg labral spot (E)] from which no NBs emerge (see also Fig. 2). mirr-lacZ is not segmentally expressed in the procephalic neuroectoderm; it is observed in the invaginating foregut and flanking neuroectoderm, and is additionally detected in a more intermediate ectodermal antennal spot (from which Dd6 arises). A large wg domain extends from the antennal into the ocular head region (B), but later separates into an antennal stripe (wg as) and ocular head blob (wg hb) (E). hh-lacZ expression accumulates in posterior regions of the antennal and ocular ectoderm (F; see also Fig. 2J). (A,D) Note that a large number of identified brain NBs (especially protocerebral) do not express any segment polarity gene. For a detailed description, see text. Stars indicate mandibular NBs. as, en antennal stripe; CL, clypeolabrum; FG, foregut; gsb-d as, gsb-d antennal stripe; gsb-d is, gsb-d intercalary stripe; gsb-d lr, gsb-d labral spot; gsb-d oc, gsb-d ocular domain; hs, en head spot; is, en intercalary stripe; ML, ventral midline; wg as, wg antennal stripe; wg lr, wg labral spot; wg fg, wg expression in the foregut; wg is, wg intercalary spot.; wg hb, wg ocular head blob [for nomenclature of en and wg expression domains in the procephalic ectoderm, see Schmidt-Ott and Technau (Schmidt-Ott and Technau, 1992)].

View larger version (142K): [in a new window]   Fig. 2. Expression of segment polarity genes at embryonic stage 11 (st11). (A,C,E,G) Left half of head flat preparations double labelled for segment polarity gene expression and en-lacZ, invected (inv) or ladybird (lbe); focus is on the peripheral head ectoderm; broken line marks the ventral midline; insets depict lateral views of stage 11 whole-mount preparations. (B,D,F,H) Close-ups of regions indicated in A,C,E,G by black frames; focus is on the level of NBs; immunopositive NBs are indicated by white inscription, immunonegative NBs are indicated by black inscription. (A,B) Only part of the antennal/ocular hh-lacZ domain co-expresses inv. Note the strong hh-lacZ signal in the dorsal Ppd5, Ppd8, Ppd10, Ppd11, Ppd15 and Ppd16. (C) gsb-d is downregulated in the ocular neuroectoderm, and is detectable in four tritocerebral NBs deriving from the gsb-d intercalary stripe, and in three deutocerebral NBs deriving from the gsb-d antennal stripe (D,I,J). (E,F) mirr-lacZ expression shows no segmental pattern and is mainly limited to the ventral part of the PNR and corresponding NBs. (G) lbe is segmentally expressed in the procephalic neuroectoderm [arrows; for details, see Urbach and Technau (Urbach and Technau, 2003)], where it is co-expressed with wg, except in the wg hb and wg fg. (H) lbe is co-expressed with wg in Dd7 but not in the ocular Ppv3 and Pcv8. (I) Segment polarity gene expression in identified brain NBs at stage 11; nomenclature of brain NB has been described previously (Urbach et al., 2003). Colour intensity reflects weak () and strong (+) expression levels of inv, hh-lacZ and wg. Stars indicate mandibular NBs. (J,K) Segment polarity gene expression in the peripheral procephalic ectoderm. (L-N) inv expression in the dorsal hemispheres (dh). (L) Lateral view of late stage 11 head, showing a faint inv expression in the dh. Note that en expression in the dh is not detected using en-lacZ and was only observed with anti-Inv antibodies from late stage 11 onwards. (M) Left half of a head flat preparation. The dh comprises about 10 Inv-positive NBs (as depicted in I). (N) inv expression in the brain and sub-oesophageal ganglion (SOG) of a stage 16 embryo (horizontal view). Note, that Inv staining in the dh corresponds to the pars intercerebralis of postembryonic stages. The secondary head spot (shs) marks a small group of cells which secondarily separates from the hs (see Schmidt-Ott and Technau, 1992). AN, IC, MD, MX, antennal, intercalary, mandibular and maxillary segment, respectively; CL, clypeolabrum; FG, foregut; ML, ventral midline; OA, Bolwig organ/optic lobe anlagen; as, en antennal stripe; cl, en expression in the clypeolabrum; dh, en expression in the dorsal hemispheres; hs, en head spot; is, en intercalary stripe; shs, en secondary head spot; gsb-d as, gsb-d antennal stripe; gsb-d is, gsb-d intercalary stripe; gsb-d lr, gsb-d labral spot; wg as, wg antennal stripe; wg fg, wg expression in the foregut; wg hb, wg ocular head blob; wg is, wg intercalary spot; wg lr, wg labral spot.

View larger version (84K): [in a new window]   Fig. 4. Neuromeric model of the early embryonic brain. Based on the expression of the segment polarity genes en/inv and hh as well as the DV patterning genes msh and vnd we propose the pregnathal brain to consist of four neuromeres. Red lines indicate the borders between the tritocerebrum (Tc; comprising about 13 NBs), the deutocerebrum (Dc; comprising about 21 NBs), the ocular part of the protocerebrum (Oc-Pc; comprising about 60 NBs) and the labral part of the protocerebrum (Lr-Pc; comprising about 10 Inv-positive NBs). Note, the ventral part of the posterior border of the deutocerebrum is given by Dv2 and Dv4, which at stage 10 (st10) transiently express vnd. The neuromeric identity of Ppd2 is unclear; colour intensities indicate low () and high (+) expression levels of en/inv and hh. AN, IC, MD, MX, antennal, intercalary, mandibular and maxillary segment, respectively; CL, clypeolabrum; Dc, deutocerebrum; Lr-Pc, labral part of the protocerebrum; Oc-Pc, ocular part of the protocerebrum; Tc, tritocerebrum; FG, foregut; ML, ventral midline; OA, Bolwig organ/optic lobe anlagen.

View larger version (114K): [in a new window]   Fig. 3. Expression of DV patterning genes at embryonic stages 9 (st9),10 (st10) and 11 (st11). Colour code indicates the expression of msh (msh-lacZ and Msh protein), ind transcripts and vnd (vnd-lacZ and Vnd protein) in identified NBs (A,B,E) and the procephalic neuroectoderm (C,D,F). en expression domains are shown for comparison. Orientation of the semi-schematic representations is as in previous figures. (A,C) Stage 9; note the spot-like ind expression in the intercalary (ind is; ind intercalary spot), antennal (ind as; ind antennal spot) and ocular (ind oc; ind ocular spot) head region; the ind antennal spot, in contrast to the intercalary, overlaps completely with the ventral vnd domain; the emerging Dd1 does not express vnd. (B,D) Stage 10; vnd is already downregulated in part of the ventral antennal ectoderm and corresponding Dv3 and Dv6, and is also not expressed in the newly developed Dv5. msh and vnd expression overlaps in a small area of the antennal ectoderm and emerging Dd5. (E,F) Stage 11; note that most of the identified brain NBs (especially protocerebral NBs) do not express any DV patterning gene. (G,I,K) Left half of head flat preparations double labelled for en expression (en-lacZ; Inv protein) and msh (msh-lacZ, Msh protein), ind (transcripts) or vnd (vnd-lacZ and Vnd protein), respectively; broken line marks the ventral midline; insets depict lateral views of stage 11 whole-mount heads. (H,J,L) Close-ups of regions indicated in G,I,K by frames (focus on the level of NBs). Immunopositive NBs are indicated by white, immunonegative NBs by black inscription. (G,H) msh-lacZ/Inv-antibody double labelling. The anterior border of the msh expression domain is positioned immediately posterior to the en hs (G), and runs between the deutocerebral and ocular protocerebral NBs (H). (I,J) DIG ind mRNA/Inv antibody double labelling. (K,L) en-lacZ/Vnd antibody double labelling. Vnd protein has disappeared in most parts of the antennal ectoderm (K) and NBs (L); note the dorsally directed extension of vnd domains in the antennal and ocular procephalic regions. The antennal vnd expression overlaps dorsally with the En-positive Dv8 and Dd5. The posterior border of the ocular vnd domain runs between deuto- and protocerebral NBs (L). AN, IC, MD, MX, antennal, intercalary, mandibular and maxillary segment, respectively; CL, clypeolabrum; FG, foregut; ML, ventral midline; OA, Bolwig organ/optic lobe anlagen; as, en antennal stripe; cl, en expression in the clypeolabrum; hs, en head spot; is, en intercalary stripe; ind is, ind intercalary spot; ind as, ind antennal spot; ind oc, ind ocular spot.

View larger version (41K): [in a new window]   Fig. 5. Comparison of expression domains of DV patterning genes in the embryonic Drosophila and mouse CNS. (A,B) DV gene expression (as indicated by colour code) in the embryonic CNS of Drosophila at developmental stage 11 (A; compare Fig. 3) and mouse at 10 days after gestation (B). Note, that anteriorly, the extent of expression is specific for each gene. Regional variabilities in the DV expansion of the respective expression domains is neglected. Mouse expression data are from Shimamura et al. (Shimamura et al., 1995) (Nkx-2.2), Valerius et al. (Valerius et al., 1995) (Gsh-1) and Shimeld et al. (Shimeld et al., 1996) (Msx-3). MD, MX, LA indicate mandibular, maxillary and labial neuromer; rh1-8, rhombomeres 1-8, respectively.