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

First published online 26 January 2005
doi: 10.1242/dev.01651

This Article Summary Full Text Full Text (PDF) Supplementary Material 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 Houghton, L. Articles by Morgan, B. A. Search for Related Content PubMed PubMed Citation Articles by Houghton, L. Articles by Morgan, B. A.

The ectodysplasin pathway in feather tract development

Cutaneous Biology Research Center, Massachusetts General Hospital and Harvard Medical School, 149 13th Street, Charlestown, MA 02129, USA

View larger version (84K): [in a new window]   Fig. 1. Amino acid sequences of chicken Edar, Eda and Edaradd. The inferred amino acid sequences of the chicken proteins are compared with their mouse orthologs. The valine and glutamine present in Eda-A1 and absent from Eda-A2, and the TRAF interaction consensus sequence (PXQXT) of Edaradd, are marked by asterisks. Death domains of Edar and Edaradd, and the furin cleavage site of Eda, are underlined.

View larger version (120K): [in a new window]   Fig. 2. Expression of Edar, Edaradd and Eda in the developing feather tract. (A) In situ detection of ß-catenin transcripts shown as an example of the pattern exhibited by a class of `early genes' during development of the femoral tract. Expression begins as a band (yellow bracket) at the distal border (yellow arrowhead) and spreads towards the trunk. It is repressed in interfollicular epidermis and increased in the epidermal placodes. The first bud to form is marked by an asterisk. Younger buds are added sequentially within a row (red arrow) and additional rows arise progressively closer to the trunk (black arrow) as development progresses so that rows closer to the trunk have buds at earlier stages of development than those more distal on the leg. (B,E,H) Edar is expressed in a similar pattern. Initial diffuse expression (B) becomes restricted and upregulated in the nascent placode (B,E). (C,F) Initial diffuse Eda expression (C) becomes restricted to interfollicular skin (F). (D,G) Edaradd expression resembles that of Edar (B,E) at all stages analyzed. In older embryos, Edar expression persists in feather bud epithelium (H), whereas Eda is detected in the posterior and distal regions of the most mature buds (I). Embryos were harvested at day 7.5 (A), day 7.25 (B-D), day 8 (E-G) and day 10 (H,I).

View larger version (81K): [in a new window]   Fig. 3. Eda pathway expression in tissue sections. In situ hybridization to tissue sections from embryos at day 7.5 (A,B), day 8 (C-F) and day 10.25 (G,H) of incubation. (A) Eda expression is detected in the epidermis of the presumptive feather tract at the extreme right of the section, but drops below the level of detection in the more developed epidermis of the medial tract (left). Note the lack of signal in the epidermis where it has separated from dermis (blue arrowheads). Expression is observed throughout the dermis at this stage, with the exception of the extreme left, where a dermal condensation has formed (red arrowhead). (B) Edaradd expression is observed in an adjacent section throughout the tract epidermis, although expression is augmented in the epidermal placodes (arrowheads). (C) Edar expression is largely restricted to epidermal placodes as buds are formed. (D-F) Adjacent sections show placodal expression of Edaradd (D) overlying dermal condensations that express Bmp4 (E) but do not express Eda (F). Eda expression is observed in the interfollicular dermis. (G,H) Adjacent sections show Eda expression persists in the interfollicular dermis at lower levels and is highly expressed in the posterior distal mesenchyme of the feather bud, while Edaradd expression is confined to the epidermis.

View larger version (62K): [in a new window]   Fig. 4. Timing of gene expression changes. Gene expression was compared in the left and right femoral tracts. (A) Four rudiments lacking Eda expression are observed in the left femoral tract, (B) six rudiments with localized Edar expression are observed in the corresponding row of the right tract and additional rudiments are observed in the next row. Corresponding rudiments are noted by black arrows; rudiments with local Edar expression but without a corresponding region of suppressed Eda expression are marked by red arrows. The left femoral tract (C) shows three well-resolved spots of Bmp2 expression, while the right femoral tract (D) shows a single well-resolved spot of Edar expression (black arrow). While local Bmp2 expression in the next rudiments to form is well resolved (C, red arrow), Edar expression in the corresponding rudiments is not (D, red arrow). (E,F) By contrast, three well-defined spots of Bmp4 expression are observed in the second row of follicles on the right leg (E, black arrows) when, in addition to the corresponding spots of Edar expression (F, black arrows), two additional spots are observed in the corresponding row on the right leg (F, red arrows). (G,H) Comparison of Eda expression (G) and Bmp2 expression (H) reveals additional rudiments with local Bmp2 expression within the corresponding row (black arrows), and an additional row of rudiments expressing Bmp2 (red arrows).

View larger version (76K): [in a new window]   Fig. 5. Edar expression correlates with ß-catenin pathway activation. (A,B) Detection of Edar transcripts (A) and ß-catenin protein (B) on adjacent sections of skin from an embryo at day 8 of incubation. Nuclei are stained red and nuclear ß-catenin appears yellow. In lateral regions (left), Edar is not detected and no accumulation of ß-catenin in the nuclei is observed (left inset). In more medial regions, a band of Edar expression correlates with moderate nuclear accumulation of ß-catenin (middle inset). At the dorsal midline, nascent buds (right inset, yellow bar) express high levels of Edar and nuclear accumulation of ß-catenin, whereas adjacent interplacodal epidermis does not (right inset, red bar). (C-E) Adjacent sections from skin harvested at day 10 show that Eda expression in the bud dermis (E) corresponds to regions of nuclear ß-catenin accumulation (D), whereas Edaradd expression in the epidermis of the bud does not (C).

View larger version (100K): [in a new window]   Fig. 6. ß-Catenin pathway activation induces Edar but not Eda. (A) Embryos infected with a virus that activates the ß-catenin pathway show ectopic and precocious expression of Edar in the presumptive feather tract (PT) ahead of the morphogenetic wave, as well as in the pseudoapteria (PA). (B) Subsequent detection of viral transcripts in the same embryo reveals infection in the areas of ectopic expression. (C,D) Higher magnification of the boxed areas in A and B reveals a correspondence between infection (D) and ectopic Edar expression (C) in coherent patches of infection (arrows). (E) Embryos infected with this virus also show ectopic expression of Eda ahead of the morphogenetic wave. (F) Subsequent detection of viral transcripts shows infection in the areas of ectopic expression. (G,H) higher magnification views of the boxed areas in E and F show the induced expression of Eda (black arrows, G) is in dermis surrounding the dermal condensations induced indirectly by foci of infection with the ß-catenin virus in the epidermis (black arrows, H). Foci of infection within the bud (red arrow, H) do not alter Eda expression.

View larger version (61K): [in a new window]   Fig. 7. BMP suppresses Edar but not Eda. (A) An embryo infected with a virus that encodes BMP4 shows suppression of Edar in the feather tract where bud formation is suppressed (black arrows), and no effect ahead of the morphogenetic wave or in the pseudoapteria (red arrows). (B) Detection of viral transcripts reveals infection in the areas where bud formation is suppressed (black arrows), as well as in the lateral regions of the flank (red arrows). (C) An infected embryo shows maintenance of the diffuse expression of Eda in an area of suppressed bud formation that would normally exhibit the honeycomb pattern of expression at this stage (black arrow). No alteration of Eda expression is observed ahead of the morphogenetic wave or in the pseudoapteria (red arrows). (D) Subsequent detection of viral transcripts demonstrates infection in the areas of bud suppression (black arrow), as well as in the lateral regions indicated in C (red arrows).