title: Smad8 is expressed in the anterior necrotic zone: evidence for a role of bone morphogenetic proteins/SMAD signaling in the activation of a molecular cascade that culminates in cell death.
abstract: Bone morphogenetic proteins (BMPs) play a crucial role in programmed cell death (PCD), a biological process required for the sculpturing of the embryonic limbs. However, it is unknown if BMP signaling directly promotes cell death, or if it induces a molecular cascade that culminates in cell death. Given that Smad8, which encodes one component of BMP signaling, is expressed during the regression of interdigital tissue and responds to BMPs, we presumed that it may be expressed in other cell death areas during chick limb development such as the anterior and posterior necrotic zones (ANZ and PNZ). The present study found that the Smad8 expression pattern in the anterior mesoderm of the hindlimb is very similar to that observed in limbs stained to detect cell death. Also, BMPs and retinoic acid, which act as apoptosis-promoting factors, induced expression of Smad8 before the onset of cell death, while sonic hedgehog protein, acting as a survival factor, inhibited Smad8 expression in the ANZ. However, although there was correlation between Smad8 expression patterns and PCD in the ANZ, phosphorylated forms of SMAD1/5/8 and TUNEL staining did not co-localize in dying cells. Interestingly, a short pulse of BMP was sufficient to trigger cell death. On the other hand, most dying cells were located in the avascular region, while many cells expressing Smad8 were located in the vascular region of the ANZ. These results suggest that BMPs mediated by SMAD signaling activate a molecular cascade that culminates in PCD.
authors.affiliation: Departamento de Medicina Genómica y Toxicología Ambiental, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City.
authors.forename: René F
authors.initials: RF
authors.lastname: Abarca-Buis
authors.forename: Marcia
authors.initials: M
authors.lastname: Bustamante
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Cuervo
authors.forename: Dante
authors.initials: D
authors.lastname: Aguilar-Fernández-de-Lara
authors.forename: Jesús
authors.initials: J
authors.lastname: Chimal-Monroy
mesh_terms: D000818:Animals; D055419:Bone Morphogenetic Protein 7 / Q000494:pharmacology*; D016923:Cell Death; D002642:Chick Embryo / Q000166:cytology / Q000187:drug effects* / Q000196:embryology; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D047108:Embryonic Development; D005455:Fluorescent Antibody Technique; D005822:Genetic Vectors / Q000235:genetics / Q000378:metabolism; D053823:Hedgehog Proteins / Q000494:pharmacology; D006614:Hindlimb / Q000166:cytology / Q000187:drug effects / Q000196:embryology*; D006801:Humans; D008648:Mesoderm / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018613:Microscopy, Confocal; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction; D051904:Smad8 Protein / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014212:Tretinoin / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: C525819:BMP7 protein, human; D055419:Bone Morphogenetic Protein 7; D018076:DNA, Complementary; D053823:Hedgehog Proteins; D011994:Recombinant Proteins; D051904:Smad8 Protein; D014212:Tretinoin