Roles
- Maintain the limb mesenchyme in a mitotically active state and focused on its task – the distal outgrowth of the limb. This is achieved by secretion of FGF8, which signals the limb mesodermal cells to continue proliferation, and secreting FGF10, which winds up maintaining the AER.
- Sustain expression of the molecules that establish the anterior-posterior axis. The FGFs secreted by the AER act upon the mesenchyme cells – including the zone of polarizing activity (ZPA). Thus, the AER causes the ZPA to continue secreting Sonic hedgehog (Shh), which is involved with Hox gene expression in establishing the anterior-posterior polarity in the developing limb. Shh also activates Gremlin, which inhibits bone morphogenetic proteins (BMPs) that would normally block FGF expression in the AER. In this manner, the ZPA and AER sustain each other through a positive feedback loop involving FGFs, Shh, and Gremlin.
- Communicate with the proteins that determine the anterior-posterior and dorsal-ventral axes to supply instructions concerning differentiation and cell fates. The FGFs secreted by the AER interact with the limb mesenchyme – including the ZPA – to induce further FGF and Shh expression. These signals then regulate Hox gene expression, which influence differentiation activity and determines what phenotypes the cells will adopt. The secreted Shh also activates Gremlin, which inhibits members of the BMP family. BMPs inhibit FGF expression in the AER, so the FGF secreted by the AER ends up providing feedback (via Shh and Gremlin) that will dictate cellular differentiation involved in sculpting the limb.
Read more about this topic: Apical Ectodermal Ridge
Famous quotes containing the word roles:
“It was always the work that was the gyroscope in my life. I don’t know who could have lived with me. As an architect you’re absolutely devoured. A woman’s cast in a lot of roles and a man isn’t. I couldn’t be an architect and be a wife and mother.”
—Eleanore Kendall Pettersen (b. 1916)
“There is a striking dichotomy between the behavior of many women in their lives at work and in their lives as mothers. Many of the same women who are battling stereotypes on the job, who are up against unspoken assumptions about the roles of men and women, seem to accept—and in their acceptance seem to reinforce—these roles at home with both their sons and their daughters.”
—Ellen Lewis (20th century)
“Productive collaborations between family and school, therefore, will demand that parents and teachers recognize the critical importance of each other’s participation in the life of the child. This mutuality of knowledge, understanding, and empathy comes not only with a recognition of the child as the central purpose for the collaboration but also with a recognition of the need to maintain roles and relationships with children that are comprehensive, dynamic, and differentiated.”
—Sara Lawrence Lightfoot (20th century)