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A complete cDNA encoding the Xenopus laevis homologue of the aggrecan/versican family member, brevican (Xbcan) was cloned from an embryonic stage 42 cDNA library. In the deduced amino acid sequence, 1152 in length, similarity to the hyaluronan-binding (link) domains of brevicans from other species were present in the N-terminal region as well as EGF-, lectin- and complement regulatory protein-like domains in the C-terminal part, the latter three being characteristic for brevican found within the extracellular matrix (J. Biol. Chem. 269 (1994) 10119). Indeed, Xbcan was secreted into the extracellular space as a soluble protein when expressed in oocytes. No cDNAs encoding a GPI-anchored bcan variant could be isolated from that cDNA library. During embryonic development, the expression of this gene was first observed in the notochord of neurula stage embryos. In addition to this, in tailbuds, Xbcan was also found to be expressed within the fifth and sixth rhombomere of the hindbrain. In tadpole stage embryos, expression was furthermore observed in periventricular regions of the developing brain and the rostral part of the spinal cord.
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11287204
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Fig. 2. Xbcan in situ hybridization. The first sign of Xbcan expression was detected during mid-neurula stages (according to Nieuwkoop and Faber (NF), 1967: stage 17) as shown in (A): after in situ hybridization, the specimen was dehydrated and soaked in tetrahydronaphtalin to achieve optical transparency. Expression is restricted to the developing notochord (n). (B) Cleared late neurula stage (NF 25) embryo: beside the notochord, Xbcan transcription takes place in a confined stripe-like pattern in the fifth and sixth rhombomere (marked by an arrow head). (C) Xkrox20 is used as a positional marker for being expressed in the third and fifth hindbrain segment. Xbcan transcription, see arrow head. (D) Slant-frontal histological cross-section through the mid- and hindbrain region of an tailbud stage embryo (NF 32) hybridized both with Xbcan and Xkrox20: expression of both Xbcan and Xkrox20 is detectable within the fifth rhombomere (arrow head); 3., 5.: third and fifth rhombomere, respectively. (E) Slant histological section through the brain region of a late tailbud stage embryo (NF 32): Xbcan expression was observable in a broad area in the hindbrain as well as in the inner epithelial layer of the posterior part of the rhombencephalon extending into the medulla oblongata (m). (F–H) Horizontal histological sections across the head region of a late tailbud stage embryo (NF 35), sectional planes were as indicated as in the inlet on the mid-left side of the panel, anterior to the top; d, diencephalon; e, eye; mc, mesencephalon; p, prosencephalon; o, otic anlage; r, rhombencephalon. (F) Note Xbcan expression is detectable in the inner epithelial layer of the prosencephalon and right below the cephalic flexure in the diencephalon (G) as well as in the notochord. (H) Furthermore, Xbcan expression is also visible in the anterior part of the rhombencephalon. (I) Tadpole stage embryo (NF 40): Xbcan expression is detectable in various brain regions other than the hindbrain. (J) Close-up view at the head region of specimen shown in I in clearing solution (as described in A), upper part: dorsal view, lower part: lateral view; III, third ventricle; IV, fourth ventricle.
bcan (brevican) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 40, lateral view, anteriorleft, dorsal up.
bcan (brevican) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 26, lateral view, anteriorleft, dorsal up.
