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Biol Open 2019 Mar 04;83:. doi: 10.1242/bio.038422.
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De novo transcription of multiple Hox cluster genes takes place simultaneously in early Xenopus tropicalis embryos.

Kondo M , Matsuo M , Igarashi K , Haramoto Y , Yamamoto T , Yasuoka Y , Taira M .

hox genes are found as clusters in the genome in most bilaterians. The order of genes in the cluster is supposed to be correlated with the site of expression along the anterior-posterior body axis and the timing of expression during development, and these correlations are called spatial and temporal collinearity, respectively. Here we studied the expression dynamics of all hox genes of the diploid species Xenopus tropicalis in four Hox clusters (A-D) by analyzing high-temporal-resolution RNA-seq databases and the results showed that temporal collinearity is not supported, which is consistent with our previous data from allotetraploid Xenopuslaevis Because the temporal collinearity hypothesis implicitly assumes the collinear order of gene activation, not mRNA accumulation, we determined for the first time the timing of when new transcripts of hox genes are produced, by detecting pre-spliced RNA in whole embryos with reverse transcription and quantitative PCR (RT-qPCR) for all hoxa genes as well as several selected hoxb, hoxc and hoxd genes. Our analyses showed that, coinciding with the RNA-seq results, hoxa genes started to be transcribed in a non-sequential order, and found that multiple genes start expression almost simultaneously or more posterior genes could be expressed earlier than anterior ones. This tendency was also found in hoxb and hoxc genes. These results suggest that temporal collinearity of hox genes is not held during early development of Xenopus.

PubMed ID: 30651235
PMC ID: PMC6451350
Article link: Biol Open

Species referenced: Xenopus tropicalis
Genes referenced: dicer1 hoxa1 hoxa10 hoxa11 hoxa13 hoxa2 hoxa3 hoxa4 hoxa5 hoxa6 hoxa7 hoxa9 hoxb1 hoxb2 hoxb3 hoxb9 hoxc13 hoxc3 hoxc6 hoxd1 hoxd13 hoxd3 hoxd9 prps1
GO keywords: axis specification

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References [+] :
Bel-Vialar, Initiating Hox gene expression: in the early chick neural tube differential sensitivity to FGF and RA signaling subdivides the HoxB genes in two distinct groups. 2002, Pubmed, Xenbase