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 HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Hughes, C. L.
Right arrow Articles by Kaufman, T. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Hughes, C. L.
Right arrow Articles by Kaufman, T. C.

Exploring the myriapod body plan: expression patterns of the ten Hox genes in a centipede

Cynthia L. Hughes and Thomas C. Kaufman*

Howard Hughes Medical Institute, Department of Biology, Indiana University, Bloomington, IN 47405, USA



View larger version (19K):

[in a new window]
  		Fig. 1. Arthropod body plans and phylogeny. The four major groups of extant arthropods are illustrated here, with a tree based on several recent molecular phylogenies that group the insects with the crustacea (Giribet et al., 2001Go; Hwang et al,. 2001Go; Cook et al., 2001Go; Boore et al., 1998Go; Regier and Shultz, 1997Go; Friedrich and Tautz, 1995Go). In the tree shown, myriapods are retained within the Mandibulata with insects and crustaceans (Giribet et al., 2001Go). Tagmatic boundaries are indicated by broken lines; names for tagmata of different groups are also indicated. Note that some groups of arthropods, for example, the crustaceans, include species with a variety of tagmatic plans not illustrated here.

 


View larger version (116K):

[in a new window]
  		Fig. 2. The centipede extended-germband embryo is illustrated by a schematic diagram (A), a scanning electron micrograph (B) and a DAPI-stained embryo (C). Head segments are labeled in blue lettering: ocular, Oc; antennal, Ant; intercalary, Int; mandibular, Mn; maxillary I, Mx1; and maxillary II, Mx2. The labrum (Lm) probably represents the highly-modified, fused appendages of the intercalary segment (see Haas et al., 2001aGo; Haas et al., 2001bGo). The segment that will give rise to the poison fangs, or maxillipeds, is labeled in purple, as it is a trunk segment that has been co-opted into the head (Mxpd). The leg-bearing trunk segments are labeled in red (L1-L7). (The final L8 segment develops later in embryogenesis than is illustrated here.) The telson is labeled in green (Te). The stomadeum lies just behind the labrum (asterisk); the proctodeum lies to the posterior of the germband (dagger).

 


View larger version (84K):

[in a new window]
  		Fig. 3. Lithobius Hox gene sequences. The partial sequences of cloned portions of the Lithobius Hox genes are aligned with orthologs from a few other arthropod species. Small arrows highlight the centipede sequences (Lithobius). Regions of the homeobox within the clones are marked above the sequences. The primers used for Lithobius are marked with boxes, indicating that that region of the sequence is somewhat uncertain. The sequence corresponding to the 5' end of each in situ probe is marked by a bar. The arrow indicates that the probe sequence extends further to the 3' end of the transcript. All sequences except those of Lithobius atkinsoni were acquired from GenBank; for Accession Numbers, see Materials and Methods.

 


View larger version (118K):

[in a new window]
  		Fig. 4. The head Hox genes. (A) Two embryos stained for labial are shown, one full-length (left) and one magnified to show details of the expression pattern (right). Expression of labial is strong in the labrum (Lm) and the intercalary (Int), with weaker expression in the mandibular segment (Mn). (B) Expression of proboscipedia is shown in a younger (left) and older stage embryo (right). Staining of pb is strong in the labrum and intercalary segment, weaker in the mandibular segment and mandibular limb-buds, and strong in the maxillary I and II distal limb-buds (Mx1, Mx2). The maxillary II appendage is much longer than that of maxillary I. The arrowhead points out the expression of pb in distal maxillary II. (C) Expression of Deformed in two embryos shows expression to be across the mandibular segment, except for spots in the limb-buds (white arrow), in the segment and limb-buds of maxillary I and in a ring around the limb-bud of maxillary II (arrowhead). There is also some expression in the very posterior of the intercalary segment (black arrow). (D) Expression of Sex combs reduced is shown in a younger (left) and an older (right) embryo. In both stages, strongest expression is seen in the maxillary II segment and limb-buds, and the limb-buds only of the maxilliped segment (Mxpd). Expression near the ventral midline extends from the maxillary I to the first leg segment (arrowheads). Additional, presumptive neural expression is seen laterally in all the trunk segments (arrow).

 


View larger version (113K):

[in a new window]
  		Fig. 5. The trunk Hox genes. (A) Three embryos illustrate expression of Antennapedia. Strongest expression in is the maxilliped limb-buds and segment (arrows). Weaker expression extends to the posterior in the youngest embryo (left), but extends only from L1 to L4 in the oldest embryo on the right (bracket). The anterior boundary of expression is in the posterior of the maxillary II segment (arrowhead). (B) Expression of Ultrabithorax is shown in three embryos. From the youngest stage shown here (left) to the oldest, expression begins in the limb-buds and the posterior region (arrowhead) of the first leg segment (L1), and extends through most of the trunk. In the later stage (right), expression is absent from the last few segments of the posterior. From late extended germband stage (middle) on, expression in the trunk segments takes the form of a rosette of patches of presumptive neural tissue (arrow). (C) An early- (left) and late-stage embryo (right) show expression of abdominal-A, which is similar to that of Ubx. Expression extends from the limb-buds of L1, with a ventral boundary in the posterior of the segment (arrowheads), and extends all the way along the trunk. Expression of abd-A does not fade from the posterior in older embryos. (D) Embryos of four stages show expression of Abdominal-B. In early embryos, expression comes on in the posterior, even in cells still in the growth zone (top left), with especially strong expression circumferential to the proctodeum (bottom left; arrowhead). In extended-germband embryos, expression is strongest in the last few segments (middle), fading from L8 in the oldest embryos and then limited to the telson (right; Te). Another, weaker domain of expression is seen in segments from extended-germband stage through older embryos (middle and right). This domain extends from the posterior of the L1 segment (arrow) on backwards through segments L2-L7 of the trunk (bracket).

 


View larger version (144K):

[in a new window]
  		Fig. 6. Ubx and abd-A in early embryos. The same embryos are shown with Ubx or abd-A in situ hybridization staining (left) and with DAPI-staining (right) to facilitate identification of segments (labeled). (A) Ubx expression in a very young embryo, which has just formed the L3 segment. Expression is visible in the extreme posterior of the L1 segment (arrow), in the L2 and L3 segments, and further back in unsegmented tissue of the proliferation zone. Punctate expression is due to staining of nascent transcripts. (B) Ubx expression in an embryo that has formed five pairs of walking legs. The lateral expression is beginning to extend more anteriorly (arrowhead). (C) Expression of abd-A in an embryo that has just formed the L6 segment. The anterior boundary is at the posterior of L1 (arrow), even at the limb-bud (arrowhead). (D) Expression of abd-A in an extended-germband embryo. Now the expression domain extends into the L1 limb-buds (arrow). Abbreviations: Int, intercalary; Mn, mandibular; Mx1, maxillary I; Mx2, maxillary II; Mxpd, maxilliped; L1, first leg (etc.); PZ, proliferation zone.

 


View larger version (85K):

[in a new window]
  		Fig. 7. Expression of Hox3. Three embryos illustrate sequential stages of Hox3 expression. In young embryos (A,B), expression is strong throughout the mandibular limb-buds (arrowheads), with small patches of expression in part of the intercalary segment (arrows). (Staining of the antennae in A is background accumulation.) In an older embryo (C), the intercalary expression is gone, and mandibular expression is seen only in the limb-bud mesoderm (black arrowhead), and is absent from the ectodermal layer (white arrowhead).

 


View larger version (148K):

[in a new window]
  		Fig. 8. Expression of fushi tarazu. Embryos of eight successive stages are shown to illustrate the dynamic changes in fushi tarazu expression during development. In the younger embryos (A-D), one can see strong expression in the proliferation zone (brackets), with stripes forming in the newest segments (arrowheads). The older segments have broad expression across them, from the posterior of the maxillary I segment (arrows), across maxillary II (Mx2), on back to the posterior. In older embryos (E-H), expression has faded from the proliferation zone and from across the trunk segments, leaving the strong expression in the maxillary I and II segments (arrows; Mx2), and a presumptive neural pattern in each trunk segment (white arrows). In the oldest embryos (G,H), expression has intensified in the limb-buds of the maxilliped (arrowhead), while strong expression is maintained in the maxillary II segment (Mx2).

 


View larger version (47K):

[in a new window]
  		Fig. 9. Summary of centipede Hox expression. (A) The expression patterns of the ten centipede Hox genes are illustrated in cartoon form for an extended-germband embryo. Note that only the expression domains presumably corresponding to a segment identity function are illustrated here (e.g. for ftz). (B) The same expression data is shown diagramatically, for comparison of domain boundaries with each other and with tagmata and appendages of the centipede (shown for a newly-hatched larva, with seven full-size legs and an eighth not yet full length). Striped patterns indicate weaker expression.

 


View larger version (43K):

[in a new window]
  		Fig. 10. Shifting Hox domains across the arthropods. The expression domains of Hox genes from studies of various arthropods are illustrated here in simplified fashion for ease of comparison. Solid bars indicate strong expression, while striped bars indicate weak or transient expression. As this diagram represents the temporal and spatial complexity of each gene as a single bar, in some cases using information from multiple species, it is necessarily highly simplified. Therefore, we have included the source references, listed on the right (1-43), in addition to special notes on the expression patterns (a-p). For this information see below. Different arthropod species often have differing numbers of segments; the segment-boxes illustrated here are based on the spiders Cupiennius and Achaearanea (Chelicerate); the centipede Lithobius, at hatching (Myriapod); the pillbug Porcellio (Crustacean); and the firebrat Thermobia (Insect). Question marks for Hox3 and ftz indicate that these genes have not yet been analyzed in a crustacean. In the insects, Hox3 homologs and ftz have highly diverged functions, so these are treated separately in Figs 11 and 12.

References

(1) Damen et al., 1998Go; (2) Telford and Thomas, 1998aGo; (3) Abzhanov et al., 1999Go; (4) Telford and Thomas, 1998bGo; (5) Damen and Tautz, 1998Go; (6) Telford, 2000Go; (7) Damen and Tautz, 1999Go; (8) this work; (9) Grenier et al., 1997Go; (10) Abzhanov and Kaufman, 1999aGo; (11) Abzhanov and Kaufman, 1999bGo; (12) Abzhanov and Kaufman, 2000bGo; (13) Abzhanov and Kaufman, 2000aGo; (14) Averof and Akam, 1995Go; (15) Averof and Patel, 1997Go; (16) Peterson et al., 1999Go; (17) Rogers and Kaufman, 1997Go; (18) Nie et al., 2001Go; (19) Diederich et al., 1989Go; (20) Rogers et al., 2002Go; (21) Shippy et al., 2000Go; (22) Pultz et al., 1988Go; (23) Fleig et al., 1992Go; (24) Brown et al., 1999Go; (25) Chadwick and McGinnis, 1987Go; (26) Kokubo et al., 1997Go; (27) Rogers et al., 1997Go; (28) Walldorf et al., 2000Go; (29) Curtis et al., 2001Go; (30) Martinez-Arias et al., 1987Go; (31) Wirz et al., 1986Go; (32) Hayward et al., 1995Go; (33) Zheng, 1999Go; (34) Nagata, 1996Go; (35) Kelsh et al., 1994Go; (36) Bennett et al., 1999Go; (37) White and Wilcox, 1985Go; (38) Tear et al., 1990Go; (39) Shippy et al., 1998Go; (40) Nagy et al., 1991Go; (41) Macias et al., 1990Go; (42) Kelsh et al., 1993Go; (43) Delorenzi and Bienz, 1990Go.

Notes

aRef. 3 also reports weak staining throughout the opisthosoma.

bRef. 2 also reports staining in the opisthosoma; Ref. 3 reports two paralogs of Dfd.

cIn early embryos, there is also some opisthosomal staining.

d Ref. 1 reports two paralogs of Ubx, and Ubx-2 mRNA is expressed slightly more anteriorly than that of Ubx-1 or protein.

eAdditional small spots of expression in the Op2 segment correspond to the future genital pores.

fOnly the ‘Hox’ domain of ftz is illustrated here.

gIn early embryos, expression of Antp extends along the entire trunk, but later fades from posterior segments.

hStriped bars indicate that translation of Scr transcript in the Mx2 and T1(Mxpd) segments is delayed until late embryogenesis, where the appearance of Scr protein correlates with transformation of the maxillipeds (in Porcellio); expression is absent from Mx1 in Procambarus (Ref. 12).

iExpression of Porcellio Antp is shown here; expression in Procambarus becomes restricted more to the anterior; expression in Artemia extends from posterior Mx1 to the end of the thorax (T11).

jThe anterior border of Ubx varies in correspondence with the number of maxilliped segments (Ref. 15); in Artemia expression extends to the end of the thorax (T11) (Ref. 14).

kThe top bar indicates expression of abdA in Porcellio and Procambarus (although Porcellio lack the extension of expression into T7 and T8); the bottom bar indicates the expression of abd-A in Artemia.

lExpression of Abd-B in Artemia is in genital segments I and II, which lie between the thorax and abdomen; the genital segments are followed by six abdominal segments that are not shown here.

mThe typical insect expression in the Mx and Lb segments is indicated here by a solid bar; the striped bar indicates that some insects have additional weak expression in the Mn and/or Int segments. Note that Oncopeltus lacks expression of pb in the Mx appendage, a change in expression that may be correlated to the unique sucking mouthparts of Hemipterans (Ref. 17).

nThe striped bar indicates that although in Drosophila expression of Scr is strong throughout the T1 segment, in other insects expression is limited to a few specific patches in the T1 segment (Ref. 27). Note that there is also expression of Scr in the mesoderm of the legs.

oExpression is shown as for Thermobia; in later embryos of Drosophila expression of Antp becomes restricted to the thorax.

pExpression shown is based on Thermobia and Schistocerca; in Drosophila, two Abd-B transcripts, m and r, have unique functions, and the m domain extends more anteriorly (Ref. 43).

 


View larger version (15K):

[in a new window]
  		Fig. 11. Evolution of Hox3 expression and function. The expression domains of Hox3 homologs from work in other species are illustrated here in cartoon-form for comparison to that of Lithobius. In the mite, expression of Hox3 is in a typical Hox-like segmental domain, extending from the pedipalps into the opisthosoma (Telford and Thomas, 1998bGo). A similar Hox-like pattern is seen in spiders as well (Damen and Tautz, 1998Go; Abzhanov et al., 1999Go). Lithobius expression is also Hox-like, but is limited to the mandibular segment, plus a small anterolateral region of the intercalary segment. As indicated by the question marks, the expression of Hox3 has not yet been analyzed in a crustacean or a basal insect. Within the insects, the Hox3 ortholog zen is expressed in the extra-embryonic tissues of the grasshopper Schistocerca, the beetle Tribolium and the fruit fly Drosophila (Falciani et al., 1996Go; Rushlow and Levine, 1990Go). The extra-embryonic tissue is located primarily at the posterior pole of the Schistocerca egg, at the anterior and dorsal edge of the Tribolium egg, and along the dorsal surface of the Drosophila egg. There is also a duplicate copy of the zen gene in Drosophila called z2, which has a very similar expression pattern (Rushlow and Levine, 1990Go). In Drosophila, the Hox3 ortholog bicoid is maternally loaded into the anterior of the egg (Frohnhöfer and Nüsslein-Volhard, 1986Go). Thus, three separate functions are illustrated for homologs of Hox3 in the arthropods: a Hox-like segmental identity function (Hox3 in the mite and centipede), a function in extra-embryonic tissues (zen in the insects) and a function in early anteroposterior polarity (bicoid in Drosophila).

 


View larger version (33K):

[in a new window]
  		Fig. 12. Temporal dynamics of ftz in the centipede, and evolution of ftz expression. (A) The changing expression patterns of ftz during Lithobius embryonic development are shown in cartoon form. Three major expression domains are seen: expression in the posterior, probably related to segmentation; expression in the developing nervous system; and a Hox-like expression domain in the maxillary II segment and maxillipeds. (B) The expression of ftz homologs from work in arthropod species are illustrated for comparison to Lithobius. In the mite, expression of ftz extends from the second to the fourth leg, in a typical Hox-like segmental domain (expression in the fourth limb-bud, and earlier expression in the opisthosoma are not illustrated here) (Telford, 2000Go). In Lithobius, both a Hox-like and a segmentation-related expression domain are seen (representations of the two expression patterns are combined onto an extended germband embryo for simplicity). In the grasshopper Schistocerca, expression is mostly in the posterior region of the growth zone, but without stripes. There are also patches of expression in the three thoracic segments, in addition to strong nervous system expression that is not illustrated here (Dawes et al., 1994Go). In the beetle Tribolium, expression of ftz has a pair-rule pattern, with stripes appearing out of the growth zone in alternate segments, and fading out in the anterior (Brown et al., 1994Go). In the fruit fly Drosophila, seven pair-rule stripes of ftz expression appear in alternating segments synchronously along the germband (Carroll and Scott, 1985Go).

 




© The Company of Biologists Ltd 2002