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1: Differentiation. 2005 Sep;73(7):364-76.

Ci-Rga, a gene encoding an MtN3/saliva family transmembrane protein, is essential
for tissue differentiation during embryogenesis of the ascidian Ciona
intestinalis.

Hamada M, Wada S, Kobayashi K, Satoh N.

CREST, Japan Science Technology Agency, Kawaguchi, Saitama 333-0012, Japan.
[e-mail]

A novel gene (Ci-Rga) essential for tissue differentiation during embryogenesis
of the ascidian Ciona intestinalis is reported here. This gene was identified
through functional screening of Ciona genes required for development by
translational inhibition experiments with morpholino antisense oligonucleotides. 
The deduced protein of Ci-Rga contains two copies of a domain with unknown
function called the MtN3/saliva domain. Phylogenetic analysis showed that Ci-Rga 
belongs to the MtN3/saliva family of genes conserved among metazoans and plants, 
and is an ortholog of mouse Rga (Recombination-activating gene 1 gene
activation). During Ciona embryogenesis, both maternal and zygotic transcripts of
Ci-Rga were expressed. Translational inhibition of Ci-Rga with specific
morpholino resulted in abnormal embryos in which the cleavage pattern became
atypical and expression of marker genes for each of the six major tissues, namely
the endoderm, muscle, mesenchyme, notochord, neural tissue, and epidermis, was
lost or suppressed at the tailbud stage. Although differentiation of all the six 
major tissues was affected by Ci-Rga knock-down, the degree of abnormalities and 
the timing of appearance of abnormalities were different among tissues.
Expression analysis of developmentally important genes involved in the fate
specification, such as Ci-Bra, Ci-Twist-like1a, Ci-Otx, Ci-Fgf9/16/20, Ci-Lhx3,
Ci-FoxD, and Ci-Tbx6b, showed that an initial step of the fate specification of
notochord, mesenchyme, and neural tissue, but not of endoderm or muscle, is
impaired in the knock-down embryo. These results showed that Ci-Rga is a
multifunctional gene essential for tissue differentiation during embryogenesis,
and is primarily required for the fate specification of notochord, mesenchyme,
and neural tissue, and provide some insights into the function of this
little-known group of genes.

PMID: 16219040 [PubMed - indexed for MEDLINE]

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