Distinct regulation of Snail in two muscle lineages of the ascidian embryo achieves temporal coordination of muscle development

Abstract

The transcriptional repressor Snail is required for proper differentiation of the tail muscle of ascidian tadpole larvae. Two muscle lineages (B5.1 and B6.4) contribute to the anterior tail muscle cells, and are consecutively separated from a transcriptionally quiescent germ cell lineage at the 16- and 32-cell stages. Concomitantly, cells of these lineages begin to express () at the 16- and 32-cell stages, respectively. Meanwhile, expression begins in these two lineages simultaneously at the 32-cell stage. Here, we show that expression is regulated differently between these two lineages. In the B5.1 lineage, was activated through, which is activated by maternal factors, including Zic-r.a. In the B6.4 lineage, the MAPK pathway was cell-autonomously activated by a constitutively active form of Raf, enabling Zic-r.a to activate independently of As a result, begins to be expressed at the 32-cell stage simultaneously in these two lineages. Such shortcuts might be required for coordinating developmental programs in embryos in which cells become separated progressively from stem cells, including germline cells.

Regulation and evolution of muscle development in tunicates

“…In the comprehensive studies of the genetic interactions of the transcription factors expressed during the early development of Ciona , Tbx6-r.b and Tbx6-r.c were found to directly activate Snail and Mrf [154, 178]. Recently, it was demonstrated that Snail is regulated in primary muscles by two distinct mechanisms, only one of which is Tbx6-r-dependent [328]. In the B5.1 lineage, Snail is directly activated by Tbx6 - r.b, while in the B6.4 lineage Snail is activated by Macho-1 and ERK signaling.…”

The gene regulatory system for specifying germ layers in early embryos of the simple chordate

“…The distribution of the upstream factors shown in Fig. 1B is based on observations in previous studies ( 5 – 7 , 9 , 12 , 13 , 15 – 21 ) (Supplementary Text), and expression patterns of the downstream genes shown in Fig. 1C are based on in situ hybridization in a previous study ( 3 ).…”

“…Snail is also activated by different mechanisms between the B6.4 lineage and other lineages ( 15 ). The DNFs ( F Wnt3 and F Wnt5 ) for Wnt3 and Wnt5 , which are expressed in the same pattern as Snail , were identical to F Snail ( Table 1 and Supplementary Text).…”

“…Sequences of the MOs (Gene Tools LLC) are as follows: Sox1/2/3 , 5′-CAGTTTAATGACGTGTGAGACTTTA-3′ ( 35 ); Foxa.a , 5′-ATCCGATTTCAAAAGCTTTCTCAGA-3′ ( 11 , 36 ); Foxd , 5′-GCACACAACACTGCACTGTCATCAT-3′ ( 3 , 11 , 36 ); Tbx6-r.b , 5′-TTGAGCCTCTCACGTCGCCAT-3′ and 5′-TTACAATTTCCTCTCTCTTTCGATT-3′ (a mixture of these two oligonucleotides was used for simultaneous knockdown of paralogs) ( 11 , 37 ); Tfap2-r.b , 5′-CGGACAGAATTCGAATATCACTCAT-3′ ( 35 ); Hes.a , 5′-TTCTTCGTTCAACAGGCATGATTGT-3′ ( 13 , 38 , 39 ); Fgf9/16/20 , 5′-CATAGACATTTTCAGTATGGAAGGC-3′ ( 3 , 11 , 15 , 18 , 19 , 40 ); Efna.d , 5′-TTGAGTTGCCATTCTTCGTTTTAAT-3′ ( 11 , 18 , 19 ); Gdf1/3-r , 5′-CATCTTTAACCCAACACTTTCAACG-3′ ( 18 , 19 ); Admp , 5′-TATCGTGTAGTTTGCTTTCTATATA-3′ ( 11 , 18 , 19 , 41 ); β-catenin, 5′-CTGTTCATCATCATTTCAGCCATGC-3′ ( 3 , 7 ); Macho-1 , 5′-ATCCCATCGTACCAGTAAAGGCCAT-3′ ( 7 , 20 ); and Prdm1-r , 5′-CGTAACTTTCGCGGTGATTCCTCAT-3′ and 5′-GTCTGAACACACATGATTCCGACAT-3′ (a mixture of these two oligonucleotides was used for simultaneous knockdown of paralogs) ( 38 ). The above MOs that block translation were used previously, and therefore, additional specificity tests were not performed in the present study.…”

“…In addition, Pem1 always represses transcription by suppressing the function of RNA polymerase II ( 16 , 17 ), and it is therefore unnecessary to consider this upstream factor explicitly. Ets1/2 acts as an effector of the MAPK pathway, which is regulated positively by Fgf9/16/20 signaling and CA-Raf and negatively by Efna.d signaling ( 4 , 15 , 22 ). Therefore, we do not consider Ets1/2 explicitly either.…”