Early and dynamic expression of cSfrp1 during chick embryo development

Abstract

Secreted frizzled related proteins (SFRPs) are a new class of signalling molecules that appear to antagonise the activity of the Wnt proteins. Here we report the dynamic expression pattern of cSfrp1, a new member of this family, at early stages of chick embryo development. cSfrp1 transcripts are first detected at pre-streak stages throughout the chick blastula but, during early primitive streak formation, expression is restricted to the anterior primitive streak and later to the blastoderm anterior to the Hensen' s node. This pattern of expression overlaps with that of Otx2 and is complementary to that of cWnt8c. During neural plate formation cSfrp1 mRNAs are abundantly localized only to the anterior domain of the embryo but, as neural tube closes, the expression extends caudally. Later, the main sites of expression in the neural tissue are the telencephalic vesicles, the epiphysis, the developing eyes and the ventral hindbrain and neural tube. Additionally, cSfrp1 transcripts were found in the axial and lateral mesoderm, the otic placode, the trigeminal ganglia, the mesoderm of the branchial arches, the developing limb buds, as well as in the mesodermal component of the developing kidney.

Expression analysis of chick Wnt and frizzled genes and selected inhibitors in early chick patterning

“…sFRP1 expression is detected in embryos from prestreak stages onward (Esteve et al, 2000). In the stage 4 midline sagittal section shown here, low levels of transcripts are detected in the rostral ectoderm, whereas the endoderm has a larger number of transcripts, with the definitive endoderm just rostral to the streak having the highest levels ( Fig.…”

“…A posterior to anterior gradient of Wnt signaling, with Wnts being more highly expressed posteriorly and Wnt inhibitors being more highly expressed anteriorly, results in posterior to anterior allocation of cell fate in the neural plate. Known Wnt inhibitors of the extracellular pathway include molecules such as the sFRPs (secreted Frizzled Related Proteins; Leyns et al, 1997;Pfeffer et al, 1997), Cerberus (Bouwmeester et al, 1996;Rattner et al, 1997;Wang et al, 1997;Zhu et al, 1999;Esteve et al, 2000;Ladher et al, 2000) and Dkk1 (Dickkopf1; Glinka et al, 1998;Piccolo et al, 1999;Mukhopadhyay et al, 2001). These molecules act by means of at least two mechanisms to reduce Wnt levels in rostral neuroectoderm: sFRPs and Cerberus directly bind Wnts, preventing interaction with the Frizzled receptors (Fzs), whereas Dkk1 interacts with LRP5/6 (LDL-receptor-related proteins 5/6), which in turn acts as a high affinity antagonist to the Fzs (Bafico et al, 2001;Mao et al, 2001;Semenov et al, 2001).…”

Frizzled/RYK mediated signalling in axon guidance

“…The example of the Eph2A receptor, which is locally translated in the commissural growth cones as they cross the midline (Brittis et al, 2002), offers an attractive example of how sensitivity to Wnt4 could be regulated. Alternatively, as in RGC, Sfrp1, strongly expressed in the ventral midline (Esteve et al, 2000), may provide guidance information to commissural axons at the ipsilateral side by binding to Fz, thus temporarily excluding it from Wnt binding.…”

Canonical Wnt activity regulates trunk neural crest delamination linking BMP/noggin signaling with G1/S transition

“…Whether Wnt protein activity in the dorsal neural tube is also modulated by its known antagonists, such as BMP, is regulated by noggin, remains to be clarified. In the trunk of avian embryos, Sfrp-1 and Sfrp-2 are expressed in the neural tube but are excluded from the dorsal midline, where the premigratory NC resides (Terry et al, 2000) (see also Esteve et al, 2000). The expression of another inhibitor, frzb-1 (Sfrp-3), is graded along the tube resembling that of noggin mRNA, with high levels being transcribed in the neural folds opposite the segmental plate and turning to low up to undetectable when advancing rostralward along the tube Duprez et al, 1999;Jin et al, 2001;Ladher et al, 2000).…”