XB-ART-25313Development January 1, 1991; Suppl 2 59-62.
Conserved segmental expression of Krox-20 in the vertebrate hindbrain and its relationship to lineage restriction.
The zinc-finger gene Krox-20 is expressed in two alternating segments, rhombomeres (r) 3 and 5, in the developing mouse hindbrain. This expression pattern is established prior to rhombomere formation in the mouse, but it is not known how the timing of expression relates to cellular events of segmentation, such as lineage restriction. We have cloned Krox-20 sequences from Xenopus and the chick and shown that its alternating expression pattern is conserved in these systems, suggesting that its role in hindbrain development is conserved. Analysis of the early stages of Krox-20 expression in the chick show that both domains of expression precede the restriction of cell lineage to specific rhombomeres, consistent with a role of this gene in early events of hindbrain segmentation. The finding that expression is not coincident with lineage restriction indicates that early expression may not reflect an irreversible commitment of cells to r3 and r5 and/or may be mosaic.
PubMed ID: 1688180
Genes referenced: egr1 egr2 hoxb3 tbx2
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|Fig. 1. Conserved structure of the zinc-fingers of Krox-20. The deduced amino acid sequences of the zinc-fingers of mouse (M), Xenopus (X) and chick (C) Krox-20 and mouse Krox-24 are compared. Dashes indicate amino acid identity with mouse Krox-20, and asterisks the regions that correspond to the oligonucleotides used to amplify Krox-20 from chick genomic DNA. Xenopus Krox-20 sequences (Bradley et al. unpublished data), mouse Krox-20 sequences from Chavrier et al. (1988) and mouse Krox-24 sequences from Lemaire et al. (1988).|
|Fig. 2. Conserved patterns of Krox-20 expression in mouse, Xenopus and chick. In situ hybridisation was carried out using appropriate homologous Krox-20 probes as described (Wilkinson and Green, 1990). (a) 9.5 day mouse embryo; (b) stage 28 Xenopus embryo; (c) stage 15 chick embryo, r, rhombomere. The apparent signal in the endoderm (e) of the Xenopus embryo is due to the refraction of light by yolky cells, not the hybridisation of probe. Anterior is to the right in all photographs. Bar=100/«m.|
|Fig. 3. Onset of Krox-20 expression in the mouse and chick embryo. In situ hybridisation analysis was carried out to examine the early stages of Krox-20 expression, (a) 8 day mouse embryo; (b) 8.5 day mouse embryo; (c,e) 3 somite chick embryo; (d,f) 7 somite chick embryo, e and f are higher magnification views of the embryos shown in c and d. The arrows indicate sites of Krox-20 expression, ne, neural epithelium. Anterior is to the right in all photographs, a and b are from Wilkinson et al. (1989b). Bar=100/«n.|
|Fig. 4. Krox-20 expression and rhombomere boundary formation. The diagram indicates the expression of Krox-20 (shaded) and the time course of rhombomere boundary formation in the developing chick hindbrain (data from Vaage, 1969). s, somite stage; r, rhombomere.|