ALBERT

Description: Transcription factors Pax3 and Zic1 are among the earliest genes activated at the neural plate border. In Xenopus , they are necessary and sufficient to promote the formation of multiple neural plate border cell types, including the neural crest, cranial placodes and hatching gland. Pax3 is especially critical for the formation of the hatching gland, a group of cells that produce proteolytic enzymes essential to digest the egg vitelline envelope and jelly coat in order to release the tadpole into the environment. In a screen designed to identify downstream targets of Pax3 we isolated a member of the astacin family of metalloproteases, related to Xenopus hatching enzyme (Xhe), that we named Xhe2 . Xhe2 is exclusively expressed in hatching gland cells as they first emerge at the lateral edge of the anterior neural plate, and persists in this tissue up to the tadpole stage. Knockdown experiments show that Xhe2 expression depends entirely on Pax3 function. Gain-of-function studies demonstrate that Pax3 can induce premature hatching through the upregulation of several proteolytic enzymes including Xhe2. Interestingly, Xhe2 overexpression is sufficient to induce early hatching, indicating that Xhe2 is one of the key components of the degradation mechanism responsible for breaking down the vitelline membrane. This article is protected by copyright. All rights reserved.

Description: The transcription factors Pax3 and Zic1 are critical to specify the neural plate border and to promote neural crest formation. In a microarray screen designed to identify genes regulated by Pax3 and Zic1 in Xenopus we isolated Znf703/Nlz1 a transcriptional repressor member of the NET protein family. At early neurula stage znf703 is expressed in the dorsal ectoderm, spanning the neural plate and neural plate border, with an anterior boundary of expression corresponding to rhombomeres 3 and 4 (r3/r4) in the prospective hindbrain. As a bonafide target of Pax3 and Zic1, znf703 is activated by neural plate border inducing signals, and its expression depends on Pax3 and Zic1 function in the embryo. Znf703 morpholino-mediated knockdown expanded several posterior hindbrain genes, while Znf703 overexpression completely obliterated the expression of these segmental genes, signifying that the transcriptional repressor activity of Znf703 is critical to pattern the hindbrain. Furthermore, snai2 and sox10 expression was severely impaired upon manipulation of Znf703 expression levels in the embryo suggesting that Znf703 participates in neural crest formation downstream of Pax3 and Zic1 in Xenopus . This article is protected by copyright. All rights reserved.