Isaac, Alison Joan; (1997) A functional analysis of a Drosophila snail-related gene in chick development. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Drosophila snail, a gene encoding a zinc-finger protein, is essential for the correct specification of ventral cell types, the future mesodermal cells, of the Drosophila embryo. This gene is also implicated in the maintenance of wing development later in Drosophila embryogenesis. This work characterises the expression pattern and attempts to elucidate the functions of a chick gene related to Drosophila snail (cSnR). The gene is first expressed briefly throughout the presumptive neurectoderm just before it forms the neural plate at the full length streak stage. At head fold stages this ectodermal expression is replaced by expression in the heart forming mesoderm. On the formation of two or three somites, cSnR expression becomes markedly asymmetrical in the lateral plate mesoderm; on the right hand side of the embryo only, it is expressed in regions containing material that will migrate into the heart. This asymmetry continues until approximately twelve somites have formed. Expression is also found in the lateral edges of the somites on their formation, followed shortly by expression throughout the whole ventral region of the somite. After regionalisation of the somite, transcripts are found in the myotome and sclerotome, but are absent from the dermatome. Expression of cSnR is also found in the gut endoderm, a subset of neural crest derivatives, and the limb mesenchyme from the time of limb bud initiation. I have used phosphorothioated antisense oligodeoxynucleotide treatment to disrupt cSnR function. Consistent with the asymmetrical nature of the expression pattern of this gene, treatment during the hours immediately preceding heart formation leads to randomisation of heart handedness and the associated embryo torsion. Laterally implanted ectopic sources of Hedgehog and activin proteins, known to cause heart situs randomisation, also result in altered expression of cSnR in the lateral plate mesoderm. The results provide evidence that cSnR also has a role in left-right asymmetry, reading and acting on left-right information rather than initiating the information itself. The antisense oligonucleotide interference also leads to abnormal segmentation. Somites are another region of cSnR expression, suggesting that cSnR also plays an important role in segmentation. Implanting ectopic sources of bFGF into the flank regions of chick embryos in vivo, a procedure known to lead to ectopic limb formation, leads to very early induction of cSnR, implicating cSnR at an early point in limb specification.

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