ABSTRACT
Understanding limb development not only gives insights into the outgrowth and differentiation of the limb, but also has clinical relevance. Limb development begins with two paired limb buds (forelimb and hindlimb buds), which are initially undifferentiated mesenchymal cells tipped with a thickening of the ectoderm, termed the apical ectodermal ridge (AER). As a transitional embryonic structure, the AER undergoes four stages and contributes to multiple axes of limb development through the coordination of signalling centres, feedback loops, and other cell activities by secretory signalling and the activation of gene expression. Within the scope of proximodistal patterning, it is understood that while fibroblast growth factors (FGFs) function sequentially over time as primary components of the AER signalling process, there is still no consensus on models that would explain proximodistal patterning itself. In anteroposterior patterning, the AER has a dual-direction regulation by which it promotes the sonic hedgehog (Shh) gene expression in the zone of polarizing activity (ZPA) for proliferation, and inhibits Shh expression in the anterior mesenchyme. In dorsoventral patterning, the AER activates Engrailed-1 (En1) expression, and thus represses Wnt family member 7a (Wnt7a) expression in the ventral ectoderm by the expression of Fgfs, Sp6/8, and bone morphogenetic protein (Bmp) genes. The AER also plays a vital role in shaping the individual digits, since levels of Fgf4/8 and Bmps expressed in the AER affect digit patterning by controlling apoptosis. In summary, the knowledge of crosstalk within AER among the three main axes is essential to understand limb growth and pattern formation, as the development of its areas proceeds simultaneously.
Subject(s)
Animals , Mice , Apoptosis , Body Patterning , Bone Morphogenetic Proteins/biosynthesis , Developmental Biology , Ectoderm/metabolism , Extremities/embryology , Fibroblast Growth Factor 10/metabolism , Fibroblast Growth Factors/biosynthesis , Gene Expression Regulation , Hedgehog Proteins/biosynthesis , Homeodomain Proteins/biosynthesis , Mesoderm/metabolism , Signal Transduction , Wnt Proteins/biosynthesisABSTRACT
Amniotic band syndrome [ABS] or amniotic band disruption is a common cause of sporadic miscellaneous fetal malformation involving limbs, trunk and the craniofacial region. Diagnosis is mainly suspected by ultrasound imaging, where the fetus is seen attached to the amniotic bands. Clinical manifestation is variable from minor constriction rings to fetal or neonatal demise secondary to severance of the umbilical cord or the associated malformation. Therefore, management options vary depending on the associated anomalies. The aim of this report is to highlight this condition, emphasize that subsets of amniotic bands exist which do not pose a threat to the fetus. Prospective study. Ultrasound unit in the Department of Obstetrics and Gynaecology, Salmaniya Medical Complex, Kingdom of Bahrain. Patients with suspected diagnosis of amniotic bands by ultrasound scanning during the study period [January 2005 to December 2007] were followed up till delivery to confirm the diagnosis. Patients Characteristic, clinical presentation, gestational age at the time of presentation, ultrasound images and outcome were reviewed. Three patients were encountered during the study period. The first patient was twenty years old primigravida, while the other two were middle age multiparous ladies. The clinical presentations were variable, however, they all presented with hydramnios. Two cases had typical severe malformations with fetal demise in the neonatal period. The third presented with only amniotic bands demonstrated in the scan but no fetal attachment, which had good outcome. Amniotic band syndrome is a common cause of sporadic and bizarre form of fetal malformation. An isolated finding exists where the amniotic band floats freely in the amniotic fluid and do not attach to the fetal parts. These pose no threat for the fetus. We are reporting three cases of Amniotic bands. The first two cases were the typical presentation of Amniotic band syndrome; whereas the third case highlights the possibility that a subset of amniotic sheets exist that do not disturb the fetus
Subject(s)
Humans , Female , Extremities/embryology , Fetus , Gravidity , Congenital Abnormalities/etiology , Prospective StudiesABSTRACT
El esbozo de miembro cuenta con un núcleo mesenquimático cubierto por un epitelio ectodérmico, los que experimentan interacciones, durante el desarrollo, conducentes a la formación de una extremidad normal. En los últimos años, utilizando la técnica de lectinas-HRP, se han estudiado la distribución y el significado de residuos glicosídicos en las interacciones epitelio-mesenquimáticas que ocurren durante la organogénesis. Así, se han identificado y caracterizado los cambios que experimentan diversos glicoconjugados en la diferenciación, reconocimiento e interacciones celulares en diversos sistemas embrionarios. Para conocer estos aspectos, hemos utilizado embriones de pollo con diferentes edades (72, 92, 120 y 168 horas), que sirvieron como dadores de los esbozos de miembros. Este material fue sometido a técnica histológica corriente y a la técnica lectinas, utilizando las siguientes lectinas-HRP:UEA (ulex europaeus agglutinin), DBA (dolichos biflorus agglutinin), ECL (erithyna cristagalli lectin), RCA (ricinus communis agglutinin), LTA (lotus tetragonolobus agglutinin), BSL (Bandeiraea simplicifolia lectin), SBA (glycine max agglutinin), además, sus respectivos inhibidores, para verificar la específidad de cada lectina. Los resultados mostraron existencia de varios residuos glicosídicos, siguiendo un patrón cambiante a lo largo, tantro a nivel del epitelio, como del mesénquima. Se analiza el siginificado de los resultados y se concluye que los patrones glicosídicos detectados peden tener algún significado en el proceso de diferenciación del esbozo en estudio.