Congress Abstracts - Society for Developmental Biology

Ibarra Morales, Dafne Andrea; Schnabel Peraza, Denhi; Salas Vidal, Enrique; Lomeli Buyoli, Hilda; Zurita Ortega, Mario (Instituto
de Biotecnologia UNAM, Mexico)
ATRX protein belongs to the SWI/SNF2 family of chromatin remodelers. It consists of an N-terminal ADD domain and a C-terminal
Helicase/ATPase motif. ADD is a histone H3 binding module that recognizes a double mark: H3K9me3 and H3K4me0. The
Helicase/ATPase motif is associated with alteration of DNA-histone interactions through ATP hydrolysis. The role of this protein
during development is evident by the effects of mutations in the gene, known to cause ATR-X syndrome in humans which is
characterized by severe mental retardation, alpha thalassemia, skeletal and urogenital abnormalities, and facial hypotonia. Zebrafish,
our study model, has two copies of the gene (atrx and atrxl). Both transcripts are maternally inherited, have a similar spatiotemporal
expression, and are localized asymmetrically during the early cleavage stage (4-512 cells). Atrx has the greatest identity to the human
protein and at least one isoform that only contains the ADD domain, similar to one previously found in human and mouse.
Interestingly, this isoform is expressed only after the midblastula transition. Embryonic injection with an atrx morpholino
oligonucleotide that inhibits translation produces a weakly ventralized phenotype. Both the pattern of expression and the knockdown
phenotype suggest an implication of Atrx in dorsoventral axis determination. By the study of early dorsal markers in morphant and
wild type embryos our aim is to find whether Atrx is involved in this process.
Program/Abstract # 334
Irx1 and Irx2 are Coordinately Expressed and Regulated by Retinoic Acid, TGFbeta, and FGF Signaling during Chick
Hindlimb Development
Díaz-Hernández, Martha; Bustamante, Marcia; Galván-Hernández, Claudio; Chimal-Monroy, Jesús (Instituto de Investigaciones
Biomédicas UNAM, Mexico)
The Iroquois homeobox (Irx) genes play a crucial role in the regionalization and patterning of tissues and organs during metazoan
development. Since the Irx1 and Irx2 gene expression regulation during hindlimb development has not been investigated yet, the aim
of this study was to evaluate the gene expression pattern of Irx1 and Irx2 as well as their regulation by important development
regulators such as retinoic acid (RA), transforming growth factorβ TGFβ) and fibroblast growth factor (FGF) signaling during chick
hindlimb development. Irx1 and Irx2 were coordinately expressed in the interdigital tissue, digital primordia, joints and in the
boundary between cartilage and non-cartilage tissue. Down-regulation of Irx1 and Irx2 expression at the interdigital tissue coincided
with the onset of cell death. RA was found to down-regulate their expression by a bone morphogenetic protein-independent
mechanism before any evidence of cell death. TGFβ protein regulated Irx1 and Irx2 in a stage-dependent manner at the interdigital
tissue, inhibiting their expression when it was administered to the interdigital tissue at developing stages before their normal downregulation.
TGFβ administration at developing stages after normal down-regulation of Irx1 and Irx2 evidenced that expression of these
genes marked the boundary between cartilage tissue and non-cartilage tissue. It was also found that at early stages of hindlimb
development FGF signaling inhibited the expression of Irx2. In conclusion, the present study demonstrates that Irx1 and Irx2 are
coordinately expressed and regulated during chick embryo hindlimb development. This study was supported by CONACyT grants
53484 and 168642, DGAPA-UNAM grants IN214511 and IN220808.
Program/Abstract # 335
Application of TGFß leads to enhanced chondrogenesis and impairment of posterior element formation in the developing
chick limb.
López-Bayghen, Bruno, Medina-Vázquez, Georgina; García-Cruz, Carla; Chimal-Monroy, Jesús (UNAM, Mexico)
Chondrogenesis is one of the most important events that occur during vertebrate limb morphogenesis. At final stages of limb
development, cells in the autopod (distal-most part) differentiate to give rise to either digits or interdigital areas. However, it is known
that the initiation of a chondrogenic program in cells of the distal interdigit, by ligands of the TGFβ/Activin family, gives rise to an
ectopic digit. To evaluate the effect this could have in stages were the digit/interdigit pattern is being established, beads soaked in
TGFβ were implanted in the posterior distal mesenchyme of chick posterior early limb buds. Limbs were then analyzed by ISH to
determine Sox9 and Tbx3 mRNA distribution and by Alcian blue/Alizarin red staining to show skeletal element formation. Around
the site of implantation, an area of Sox9-positive cells was observed. A similar pattern was observed for Tbx3-negative cells. This
inhibition of Tbx3, a transcription factor highly relevant in posterior element formation, is associated to deficiencies in the formation
of digits III and IV and in some cases tarsal bones. To test the involvement of the Wnt canonical pathway, beads soaked in DKK1, an
inhibitor for this pathway, were implanted in this region. This led to a similar phenotype, characterized by an induction of Sox9, albeit
with less marked effects. These results suggest the importance of Wnt signaling-mediated inhibition of chondrogenesis in the
formation of posterior elements. As such, exogenous application of TGFβ can disrupt this balance leading to impaired development of
the limb. This study was partially supported by CONACyT grants 53484 and 168642, DGAPA-UNAM grants IN214511 and
IN220808.
Program/Abstract # 336
Retinoic acid effectors functions during axolotl limb regeneration
Correa Gallegos, Donovan; Chimal Monroy, Jesús (UNAM, Mexico)
Retinoic acid (RA) participates on several developmental and regenerating systems patterning. During axolotl limb regeneration, an
excess of RA delays regeneration and induces the formation of more proximal structures from the amputation site which do not
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