QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online 13 May 2004
doi: 10.1242/dev.01159

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Robertson, L. K. Articles by Mahaffey, J. W. Search for Related Content PubMed PubMed Citation Articles by Robertson, L. K. Articles by Mahaffey, J. W. Social Bookmarking                         What's this?

An interactive network of zinc-finger proteins contributes to regionalization of the Drosophila embryo and establishes the domains of HOM-C protein function

Department of Genetics, Campus Box 7614, North Carolina State University, Raleigh NC, 27695-7614, USA

View larger version (80K): [in a new window]   Fig. 1. DISCO and DFD are required for maxillary identity. (A) In otherwise normal embryos, ectopic DFD, which is driven by prd-Gal4 in this example, induced maxillary structures in the trunk segments. Cirri (ci) and, occasionally, sclerotized rod-like structures (see Fig. 2B) appear in the trunk cuticle. (B) Without disco and disco-r, no ectopic gnathal structures appeared in Df(1)XR14/Y embryos ectopically expressing Dfd. (C-F) Together, ectopic DFD and DISCO activate 1.28 transcription. Segment abbreviations in white letters indicate those with ectopic 1.28 RNA. (C) In wild-type embryos 1.28 transcripts accumulate along the posterior edge of the maxillary epidermis, as well as in the gut and anterior spiracles (out of the plane of focus) and in the posterior spiracles (not shown). (D) 1.28 transcript distribution was normal in prddisco. (E) In prdDfd embryos, in addition to normal transcript accumulation, 1.28 transcripts were detected in the labial segment, which has been transformed toward a maxillary identity, and weakly in the posterior-lateral edge of the expressing segments (not visible in figure). (F) In embryos co-expressing disco and Dfd, 1.28 transcripts significantly accumulate in the posterior portion of each affected trunk segment, in addition to the maxillary and labial segments. (G) disco expression in an early stage 12 wild-type Drosophila embryo. The regions of disco mRNA accumulation relevant to this study are the gnathal segments (mn, mandibular; mx, maxillary; lb, labial) which make up the visibly segmented region of the head, and the bilaterally symmetric spots along the ventrolateral region of each trunk segment (t2, second thoracic; a, abdominal segments). (H) disco mRNA distribution in an early stage 12 prddisco embryo. prd-Gal4 activates disco expression in cells forming the posterior portion of alternating segments, beginning at about stage 10 and continuing through early stage 13. In addition to the regions described in G, disco mRNA accumulates in stripes encompassing the posterior half of the mn, lb, t2, a1, a3, a5, a7 and a9/10 segments. (I) prddisco expression in segments a1-a3. Red circles represent nuclei expressing the EN protein. prddisco expression includes the five posterior-most cells (green cells) of every other segment. [Staging is according to Campos-Ortega and Hartenstein (Campos-Ortega and Hartenstein, 1997).]

View larger version (115K): [in a new window]   Fig. 3. The role of TSH in disco mRNA distribution. (A) disco mRNA accumulation in a wild-type embryo as the germband begins to retract. Segment abbreviations are as in Fig. 1. Note the spots of expression in the thorax and abdomen, indicated by white arrows. In the thorax, these demark the Keilin's Organ precursors. (B) In homozygous tsh8 embryos, gnathal expression of disco is normal, but the trunk distribution is altered. There is a wider distribution in the ventral and ventral-lateral region of trunk segments, particularly notable in the thoracic segments. Note that the spots marking the Keilin's Organs are missing. (C) Ectopic activation of disco caused by Gal4-driven DFD. Interestingly, the distribution of disco mRNA is quite similar to that in B, above, except that the spots marking the Keilin's Organ precursors are still present in C. (D-F) Ectopic expression of tsh represses the normal accumulation of disco mRNA in the gnathal segments. (D) Wild-type late stage 12 embryo. disco mRNA distribution is fairly uniform in the gnathal segments except where the maxillary and labial sense organs will form and in the salivary primordia (ventral labial). (E) In armtsh embryos (stage 12), as the germband retracts, disco mRNA diminishes in the epidermis of the gnathal lobes. However, staining increases in the central region of the mandibular, maxillary and labial lobes. Later (stage 13) (F), the labial lobe has taken on the appearance of a first thoracic segment, and disco is strongly expressed in the sensory precursor, which has been transformed toward a Keilin's Organ. No difference was noted in the trunk disco expression.

View larger version (103K): [in a new window]   Fig. 2. Trunk to gnathal transformation is more complete in tsh mutant embryos. Each panel shows a whole embryo image and higher magnifications from abdominal segments of two independent individuals. Ectopic structures are indicated in the whole embryo images by arrowheads. (A) Wild-type larval cuticle and normal maxillary structures. (B) Ventral cuticle of a terminal homozygous tsh8 larva. Small spots of sclerotized material (arrows in high-magnification panels) are occasionally present. (C) In the trunk segments of prdDfd embryos, cirri and, occasionally, rod-shaped sclerotic structures are present. (D) tsh8, UAS-Dfd/tsh8; prd-Gal4/+ embryos demonstrate a more complete transformation. Mouthpart-like material and cirri are present in each affected segment, with well-shaped mouth hooks frequently observed, though the ectopic sclerotized material also can lack a specific shape. (E) tsh8, UAS-Dfd, UAS-disco/tsh8; prd-Gal4/+ embryos exhibit a more consistent transformation. Mouth hooks form in all expressing segments, and we did not observe amorphous sclerotized material as seen in tsh8, UAS-Dfd/tsh8; prd-Gal4/+ embryos shown in D. (F) In tsh8, UAS-Dfd, UAS-disco/tsh8; arm-Gal4/+ embryos, the trunk-to-maxillary transformation is striking, with ectopic maxillary structures appearing in virtually all segments.

View larger version (63K): [in a new window]   Fig. 4. HOM-C proteins accumulate in the proper register in embryos with ectopic DFD and DISCO but lacking TSH. Stage 12 embryos are shown. In A-C, we show Antennapedia (ANTP) accumulation; the arrowhead marks the beginning of ANTP accumulation in posterior t1. (A) Wild-type embryo. (B) Homozygous tsh8 embryo. (C) tsh8, UAS-disco, UAS-Dfd/tsh8; arm-Gal4/+ embryo. In D-F, Ultrabithorax (UBX) accumulation is shown with the arrowhead marking posterior t3. (D) Wild-type embryo. (E) Homozygous tsh8 embryo. (F) tsh8, UAS-disco, UAS-Dfd/tsh8; arm-Gal4/+ embryo. Note that the register of expression is the same in all cases. The tint to the embryos in B,C,E, F is a consequence of in situ localization of tsh mRNA to unequivocally identify tsh mutant embryos.

View larger version (110K): [in a new window]   Fig. 5. Dorsal closure is blocked by prddisco expression. (A) In wild-type stage 13 embryos, note the dorsoventral stripes of EN marking the posterior compartment of each segment. (B) In prddisco embryos the segments expressing disco do not complete dorsal closure. The EN stripes in these segments extend only about halfway up the embryo. Note that the affected segments are curved and resemble the gnathal lobes. (C-D) pnr mRNA distribution in prddisco embryos. (C) In early stage 12 wild-type embryos, pnr mRNA accumulates along the dorsal edge of the segments, beginning in the posterior maxillary and extending posteriorly through the eighth abdominal segment. (D) In prddisco embryos, this continuous line of pnr mRNA is disrupted. Cells expressing prddisco do not accumulate pnr. (E-G) disco expression limits the gnathal contribution to the dorsal ridge. (E) Morphology of a normal wild-type stage 13 dorsal ridge. Note the separation of the dorsal ridge from the labial lobe, from which many of the dorsal ridge cells arise. (F) In embryos expressing prddisco, the dorsal ridge is quite reduced. The few EN-positive cells remaining are those that arise from the posterior maxillary/anterior labial where prddisco is not expressed. (G) In Df(1)XR14/Y embryos, the dorsal ridge is broadened and contiguous with labial, and sometimes as in this case, maxillary lobes. The embryos were stained to detect EN to facilitate identification of prddisco embryos. dr, dorsal ridge. Anterior is towards the left; dorsal is upwards.

View larger version (136K): [in a new window]   Fig. 6. Ectopic DISCO alters the trunk segments. In an early stage 13 wild-type embryo (A) note the regular appearance of salm mRNA in the dorsal tracheal cells (vertical arrows) and the oenocytes (angled arrowheads). (B) In a similarly staged prddisco embryo dorsal tracheal cells and oenocytes are missing in the segments ectopically expressing disco. (C,D) The trunk sensory neurons are remodeled by ectopic disco expression. Embryo `fillets' are shown where the gut has been removed and the embryos have been flattened so the neurons are in the same approximate focal plane. Anterior is upwards and dorsal is towards the right in both images. (C) Wild-type sensory neurons of the first abdominal segment. A similar pattern is found in all abdominal segments. Several characteristic neurons and sensory structures are labeled. isn, intersegmental neuron; sn, segmental neuron; vg, ventral sensory organ group; vch, ventral chordotonal organ; lch, lateral chordotonal organ; dg, dorsal sensory group; dg-t3, dorsal group from t3. In prddisco embryos (D), both unaffected (a2, bottom) and affected (a1, top) segments are shown. Note the absence of chordotonal organs in a1, and that the neurons do not extend as far dorsally. The position of the sensory cells in affected segments does not match those in the unaffected or normal trunk segments.

View larger version (120K): [in a new window]   Fig. 7. Activation of the SCR target gene PB by ectopically expressed disco and Scr. (A) The ectopic expression of Scr, using the prd-Gal4 driver, sometimes results in weak PB activation in some affected segments. The embryo shown was chosen because it was among the most strongly staining for PB accumulation. (B) By contrast, expressing both disco and Scr in embryos caused significantly increased ectopic PB accumulation, easily visible in each affected segment in all expressing embryos. mx, maxillary; lb, labial; t2, second thoracic; a, abdominal segments.

View larger version (18K): [in a new window]   Fig. 8. An interactive hierarchy of zinc-finger transcription factors establishes trunk and gnathal/head segment types. In the trunk segments, TSH represses disco expression and directs segments along the trunk developmental pathway. SALM defines the boundary between the head and trunk (broken line) by repressing tsh in the gnathal segments. disco is expressed in the gnathal segments activating the gnathal development pathway. In this manner, the distribution of TSH and DISCO regionalizes the embryo. When combined with the HOM-C proteins, specific segment identities arise. Note that the HOM-C protein SCR is expressed in both the gnathal and trunk domains and yields a different identity depending upon which co-factor is present. DFD can establish either a maxillary or mandibular identity depending upon the presence of the Cap-n-collar (CNC) protein (Mohler et al., 1995). mn, mandibular; mx, maxillary; lb, labial; t2, second thoracic.

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

Twitter