pubmed.ncbi.nlm.nih.gov

Ancestral role of caudal genes in axis elongation and segmentation - PubMed

  • ️Thu Jan 01 2004

Ancestral role of caudal genes in axis elongation and segmentation

Tijana Copf et al. Proc Natl Acad Sci U S A. 2004.

Abstract

caudal (cad/Cdx) genes are essential for the formation of posterior structures in Drosophila, Caenorhabditis elegans, and vertebrates. In contrast to Drosophila, the majority of arthropods generate their segments sequentially from a posteriorly located growth zone, a process known as short-germ development. caudal homologues are expressed in the growth zone of diverse short-germ arthropods, but until now their functional role in these animals had not been studied. Here, we use RNA interference to examine the function of caudal genes in two short-germ arthropods, the crustacean Artemia franciscana and the beetle Tribolium castaneum. We show that, in both species, caudal is required for the formation of most body segments. In animals with reduced levels of caudal expression, axis elongation stops, resulting in severe truncations that remove most trunk segments. We also show that caudal function is required for the early phases of segmentation and Hox gene expression. The observed phenotypes suggest that in arthropods caudal had an ancestral role in axis elongation and segmentation, and was required for the formation of most body segments. Similarities to the function of vertebrate Cdx genes in the presomitic mesoderm, from which somites are generated, indicate that this role may also predate the origin of the Bilateria.

PubMed Disclaimer

Figures

Fig. 1.
Fig. 1.

Caudal expression in Tribolium and Artemia.(A) Blastoderm fate map in Tribolium, indicating the position of the serosa (s), anterior head (head), gnathal (g), thoracic (th), and growth zone (gz) anlage. (B) Immunochemical staining showing the distribution of Caudal in the blastoderm of Tribolium. (C–E) Immunochemical staining showing Caudal expression in the growth zone (gz) of Tribolium, during successive stages of segmentation. The growth zone lies at the posterior-most end of the elongating germ band. (F–H) Illustrations of Artemia larvae, showing three successive stages of segmentation. The growth zone (indicated in gray) is located subterminally, lying anterior to the differentiated telson/anus. (I–K) Immunochemical stainings showing the expression of Caudal in the growth zone (gz) of Artemia, at similar stages to those shown in F–H. Anterior is up in all panels.

Fig. 3.
Fig. 3.

caudal RNAi phenotype in Artemia.(A) Morphology of a normal fully segmented Artemia, with 11 thoracic segments (numbered), 2 genital segments (G), and 6 postgenital segments (PG). (B and C) Morphology of caudal RNAi-treated Artemia, showing severe truncations that remove many thoracic, genital, and postgenital segments. The telson/anus at the posterior end of the body is still present (arrowhead); the affected individuals are viable. (D) Frequency of phenotypes obtained in a typical RNAi experiment. Injection of a control dsRNA gives rise to 100% normal, fully segmented larvae. Injection of caudal dsRNAs gives rise to ≈30% larvae with severe truncations, in addition to larvae with minor phenotypes (few posterior segments missing, misshaped segments) and normal-looking larvae. Absolute numbers of surviving larvae are indicated in parentheses. (E) Western blots with extracts from wild-type and caudal RNAi-affected individuals, probed with an anti-Caudal and an anti-β-tubulin (control) antibody. Quantification of these bands shows that caudal RNAi has caused a 3- to 4-fold reduction in the levels of Caudal protein. (F) Graph depicting the association between the timing of caudal dsRNA injections and the extent of truncations. Individuals injected at the first larval stage (L1) usually develop five to six normal segments (filled circles). Individuals injected about a day later (stage L2–L3) develop a longer series of normal segments (open circles).

Fig. 2.
Fig. 2.

caudal RNAi phenotype in Tribolium. (A) Late embryo showing the caudal RNAi phenotype. Only the antenna (Ant) and pigmented eyes (Oc) can be identified. All of the gnathal, thoracic, and abdominal segments are missing. The yolk (y) lies posterior to the truncated embryo. (B) caudal RNAi embryo stained with DAPI. The labrum (Lr) and antennae (Ant) are visible anterior to the yolk (y). (C) Detail of DAPI-stained caudal RNAi embryo, focusing on the head. (D) caudal RNAi embryo immunochemically stained for the expression of Engrailed. The antennae (Ant) and the position of the mouth (mo) are outlined. The ocular segments (Oc) and the labrum (Lr) are also visible.

Fig. 4.
Fig. 4.

Effects of caudal RNAi on segmentation and Hox gene expression. (A) Wild-type Tribolium embryo immunochemically stained for the expression of Even-skipped (Eve). Expression is detected in the growth zone (gz) and in a series of stripes in the segments that arise from this zone. (B) Eve staining in a caudal RNAi-treated Tribolium embryo. Eve staining is irregular in the region of the growth zone, and the segmental expression is absent. This is a weakly affected embryo that has achieved some degree of axial elongation. (C and D) Eve expression in the growth zone (gz) of normal Artemia larvae. Eve is expressed in a solid band of cells in the growth zone; the band is broad in early stages (C) and becomes narrower with time (D). (E and F) Eve expression in the region of the growth zone of caudal RNAi-treated Artemia larvae. Expression is irregular; in some individuals the band has become discontinuous, with patches of cells not expressing Eve (E), and in others expression is only seen in isolated patches of cells (F). (G) Segmental pattern of Engrailed (En) expression in normal Artemia larva. The growth zone lies posterior to (below) the last stripes of En expression. (H) En expression in caudal RNAi-treated larva. Normal stripes of En expression are seen in mature segments, but the stripes in newly formed segments are replaced by isolated patches of cells expressing En. (I) Ubx/AbdA expression in normal Artemia larva, focusing on the segmentally repeated pattern in new segments arising from the growth zone (gz). As segments mature (toward to top of the panel) the expression becomes stronger and more uniform. (J) Ubx/AbdA expression in caudal RNAi-treated larva, showing strong uniform expression in mature segments but no early segmental expression in the region of the growth zone. Anterior is up in all panels.

Similar articles

Cited by

References

    1. Macdonald, P. M. & Struhl, G. (1986) Nature 324, 537–545. - PubMed
    1. Moreno, E. & Morata, G. (1999) Nature 400, 873–877. - PubMed
    1. Hunter, C. P. & Kenyon, C. (1996) Cell 87, 217–226. - PubMed
    1. Edgar, L. G., Carr, S., Wang, H. & Wood, W. B. (2001) Dev. Biol. 229, 71–88. - PubMed
    1. Meyer, B. I. & Gruss, P. (1993) Development (Cambridge, U.K.) 117, 191–203. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources