Interdigital webbing retention in bat wings illustrates genetic changes underlying amniote limb diversification - PubMed (original) (raw)

Comparative Study

. 2006 Oct 10;103(41):15103-7.

doi: 10.1073/pnas.0604934103. Epub 2006 Oct 2.

Affiliations

Comparative Study

Interdigital webbing retention in bat wings illustrates genetic changes underlying amniote limb diversification

Scott D Weatherbee et al. Proc Natl Acad Sci U S A. 2006.

Abstract

Developmentally regulated programmed cell death sculpts the limbs and other embryonic organs in vertebrates. One intriguing example of species-specific differences in apoptotic extent is observed in the tissue between the digits. In chicks and mice, bone morphogenetic proteins (Bmps) trigger apoptosis of the interdigital mesenchyme, leading to freed digits, whereas in ducks, Bmp antagonists inhibit the apoptotic program, resulting in webbed feet. Here, we show that the phyllostomid bat Carollia perspicillata utilizes a distinct mechanism for maintaining interdigit tissue. We find that bat forelimb and hindlimb interdigital tissues express Bmp signaling components but that only bat hindlimbs undergo interdigital apoptosis. Strikingly, the retention of interdigital webbing in the bat forelimb is correlated with a unique pattern of Fgf8 expression in addition to the Bmp inhibitor Gremlin. By using a functional assay, we show that maintenance of interdigit tissue in the bat wing depends on the combined effects of high levels of Fgf signaling and inhibition of Bmp signaling. Our data also indicate that although there is not a conserved mechanism for maintaining interdigit tissue across amniotes, the expression in the bat forelimb interdigits of Gremlin and Fgf8 suggests that these key molecular changes contributed to the evolution of the bat wing.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Differential forelimb morphology in mice and bats. (A) An adult mouse, Mus musculus. (B) An adult bat, Carollia perspicillata. Digits are numbered from anterior (I) to posterior (V). Bat digits are elongated compared with mouse digits (Inset) and maintain webbing between the posterior digits.

Fig. 2.

Fig. 2.

Bmp pathway gene expression in developing bat limbs. Analysis of Bmp signaling components in Carollia forelimbs and hindlimbs is shown. (A–D) Bmp2 expression in forelimbs (A and B) and hindlimbs (C and D) at stage 16 (A and C) and stage 17 (B and D). Roman numerals in A and C indicate digit number. (E–H) Bmp4 expression in forelimbs (E and F) and hindlimbs (G and H) at stage 16 (E and G) and stage 17 (F and H). (I–L) Bmp7 expression in forelimbs (I and J) and hindlimbs (K and L) at stage 16 (I and K) and stage 17 (J and L). (M and O) Msx1/2 protein expression on longitudinal sections of stage-15 forelimbs (M) and hindlimbs (O). (N and P) Msx2 RNA expression in forelimbs (N) and hindlimbs (P) at stage 17. Anterior is up in all images. (Scale bars, 1 mm. The scale bar in B also applies to F, J, and N. The scale bar in A also applies to C_–_E, G_–_I, K_–_M, O, and P.)

Fig. 3.

Fig. 3.

Fgf signaling and Gremlin expression in bat limbs. (A–D) Gremlin expression in forelimbs (A and B) and hindlimbs (C and D) at stage 16 (A and C) and stage 17 (B and D). Roman numerals in A and C indicate digit number. (E–H) Fgf8 expression in forelimbs (E and F) and hindlimbs (G and H) at stage 16 (E and G) and stage 17 (F and H). Fgf8 is expressed throughout the hindlimb AER, in the forelimb AER between digits I-III, and in the interdigits of the forelimb. Interdigital expression persists in the forelimb, but AER expression is restricted to the tips of digits II and III, and expression in the hindlimbs is found in remnants of the AER at the tips of all digits. (I–L) Spry2 expression in bat forelimbs (I and J) and hindlimbs (K and L) at stage 16 (I and K) and stage 17 (J and L). Spry2 expression correlates with the domains of Fgf8 expression. Anterior is up in all images. (Scale bars, 1 mm. The scale bar in B also applies to F and J. The scale bar in A also applies to C–E, G–I, K, and L.)

Fig. 4.

Fig. 4.

Functional analysis of Fgf and Bmp signaling in bat limbs. (A–D) Control (A and C) and Bmp- and SU5402-treated (B and D) cultured bat limbs (stage 16 late) after a 23-h incubation. (C and D) Active caspase-3 immunofluorescence on longitudinal bat forelimb sections shows interdigit region IV–V (boxed regions in A and B). Yellow circles are sections through beads, and asterisks mark the position of beads that are not in the plane of section or that fell out after sectioning of the limbs. (E) Schematic of the differences in gene expression in free-toed mouse limbs and webbed duck and bat limbs. Mouse forelimbs show proximally restricted Gremlin expression (red) and high levels of Bmp signaling (yellow) throughout the interdigit, which results in extensive cell death of interdigit tissue and free digits. Duck hindlimbs have strong proximal expression of Gremlin, which blocks Bmp-induced gene expression and apoptosis. Bat forelimbs exhibit Bmp signaling, but cell death is blocked, likely because of the widespread expression of Gremlin and the unique domain of Fgf8 signaling (blue) in forelimb interdigit regions.

Similar articles

Cited by

References

    1. Ganan Y, Macias D, Basco RD, Merino R, Hurle JM. Dev Biol. 1998;196:33–41. - PubMed
    1. Yokouchi Y, Sakiyama J, Kameda T, Iba H, Suzuki A, Ueno N, Kuroiwa A. Development (Cambridge, UK) 1996;122:3725–3734. - PubMed
    1. Zou H, Niswander L. Science. 1996;272:738–741. - PubMed
    1. Macias D, Ganan Y, Sampath TK, Piedra ME, Ros MA, Hurle JM. Development (Cambridge, UK) 1997;124:1109–1117. - PubMed
    1. Guha U, Gomes WA, Kobayashi T, Pestell RG, Kessler JA. Dev Biol. 2002;249:108–120. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources