Zhu K , Spaink HP , Durston AJ .

             BMP signaling pathway
             head development

	Figure 1. Timed Noggin-injection in wild-type embryos resulted in progressive arrest of head patterning: 200 nL of 1 ng/µL Noggin was injected into the blastocoel of the embryo at different stages. Anterior is to the left and dorsal is up. Black arrows point to the position of the cement gland. These experiments were repeated at least three times and more than 80 embryos were used for each time point.
	Figure 2. Timed anti-BMP treatments in ventralized embryos led to sequential fixation of anterior genes. The expression of xcg-1, six3, otx2, gbx2, and hoxd1 in bmp4-injected embryos that were subjected to Smad6 treatment at different stages. These experiments were repeated at least three times and >40 embryos were used for each condition. Black arrows indicate the anterior borders of the expression domains.
	Figure 3. The expression of six3, otx2, gbx2 and hoxd1 at different stages in wild-type and smad6-injected embryos. Embryos are vegetal views with dorsal to the top. These experiments were repeated at least three times and >40 embryos were used for each condition.
	Figure 4. Hypothesis for head patterning by BMP signaling. A currently unknown, BMP-dependent timer is running during head patterning. The timer can be fixed by anti-BMP signals and regulates the expression of anterior genes: xcg-1, six3, otx2, gbx2, and hoxd1, resulting in the head being progressively patterned.

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