Figure 6

Proposed model of group IV DUB genes in the BMP pathway. Group IV DUB genes (otud4, usp5, usp15 and usp25) are involved in the BMP pathway. Panel A shows the normal wild type embryo with usual BMP activity. Panel B shows that single group IV MO knockdown results in dorsalized phenotypes. Panel C shows that overexpression of smad1 leads to ventralized phenotypes (V1-V3). Panel D shows that bmp4 overexpression results in severe ventralized phenotypes (V3, V4). Panel E shows that co-injection of combination of group IV MOs and smad1 mRNA results in mild ventralized phenotypes. Panel F shows that co-injection of combination group IV MOs and bmp4 mRNA causes severe dorsalized phenotypes as in panel B. Double knockdown of group IV MOs with bmp4 or smad1 overexpression causes different results. Overexpression of bmp4 could not rescue the dorsalized phenotypes that caused by double MOs knockdown, while smad1 could. This implies that group IV DUBs function between Bmp4 and Smad1 in the BMP pathway. Since co-injection experiments could not result in absolute dorsalized or ventralized phenotypes, which suggests that the DUB genes might interact with other dorsoventral signaling pathways. The proposed working model is shown in G. Taken together with the real-time results (Additional file 9), the group IV MO will increase the mRNA expression of different signaling genes (bolded), which results in stimulating Chd and inhibiting Smad. Collectively, all the effects will inhibit the BMP pathway and cause dorsalized effect. We propose that group IV DUBs will act on the substance X that is directly involved in the BMP pathway. Besides, they may interact with another common substrate X' that stimulates different signaling genes and generates secondary dorsal-ventral effects in the zebrafish early development.