Based on the phenotypes obtained following thein vivoexpression of Pax6 antibodies in the intercellular space, we propose that, in addition to other regular inducers and growth factors, Pax6 acts as a signaling molecule during eye development. == Results == The presence within the Pax6 sequence of the two small domains allowing homeoprotein internalization and secretion (Figure1a) [33] led us to investigate Pax6 intercellular passage. milieu of Ferrostatin-1 (Fer-1) developing zebrafish embryos. == Results == A first strategy was to inject a one-cell embryo with a mRNA encoding a secreted single-chain anti-Pax6 antibody. A second, complementary, strategy was to inject a Pax6 antibody in the blastula extracellular milieu. In both cases, ‘dissymmetric eyes’, ‘one eye only’ and ‘no eye’ phenotypes were produced. In most cases, lens phenotypes paralleled retina malformations. Although eye phenotypes were analyzed 30 hours post-fertilization, there was a strong correlation between early Ferrostatin-1 (Fer-1) eye field asymmetry, early asymmetry inPax6expression and later-occurring eye malformations. Several controls were introduced, demonstrating that the effect is specific to Pax6 and cannot be explained by intracellular antibody activities. == Conclusion == This study supports the hypothesis that the Pax6 transcription factor is also a signaling molecule with direct non-cell autonomous activity. == Background == Eye formation is one of the most popular models used to study the development and evolution of sensory systems [1]. Similarities exist between vision apparatus across species, leading to the two hypotheses of convergent evolution versus monophyletic origin [2]. This system is also Ferrostatin-1 (Fer-1) widely used for induction studies due to the inductive interactions that take place between neural and non-neural tissues in the course of eye development. Spemann was the first to propose that the interaction between the neural fold and the surface ectoderm is at the origin of the induction of lens formation [3-5]. This induction between the two tissues has been challenged and it has been hinted that all species may not use identical strategies to develop a visual apparatus [6-8]. Although these evolutionary and developmental issues are not fully resolved, it is now largely accepted that certain shared genetic pathways play important functions in the development of vision across species. The main breakthrough in the understanding of how the eye has evolved and develops has come from genetic analysis, in particular the identification of Pax6 as a key transcription factor for eye formation [9]. Indeed,Pax6loss of function, partial or total, leads to abnormal eye development in all species, including human [2,10-12]. Conversely, excessively high expression leads to eye malformation THSD1 [13-16] or to the spectacular formation of ectopic eyes [17,18]. The expression ofPax6in the ‘vision apparatus’ of all species, as well as the possibility to induce eye formation in the fly by expressing vertebratePax6, also strongly supports the idea that, in spite of multiple variations on the theme, there exists a common genetic pathway in whichPax6orPax6-like genes play a major role [19,20]. Interestingly,Pax6is expressed in both neural and surface epithelia that will give birth to retina proper and retina pigmented epithelium (RPE) for the former and to lens and cornea for the latter. This raises two main questions regarding, firstly, the extent of the retina territory within the neural fold and, secondly, the mechanisms of induction between the neural tissue and the surface epithelium (lens induction). In both cases, it has been established that the genetic pathways involve several transcription factors and growth factors of the Fibroblast Growth Factor (FGF) and Bone Morphogenetic Protein (BMP) families [5,21-26]. In Ferrostatin-1 (Fer-1) the present study, we wanted to investigate the possibility that Pax6 could act as both a cell autonomous transcription factor [5] and a non-cell autonomous signaling factor [27,28] capable of inducingPax6expression after intercellular passage [29-32]. The possibility that a transcription factor could have both cell autonomous and non-cell autonomous activity originates from the presence within the homeodomain of a majority of homeoprotein transcription factors, includingPax6, of two short sequences that enable secretion and internalization and, thus, intercellular passage [33-35]. Based on the phenotypes obtained following thein vivoexpression of Pax6 antibodies in the intercellular space, we propose that, in addition to other regular inducers and growth factors, Pax6 acts as a signaling molecule during eye development. == Results == The presence within the Pax6 sequence of the two small domains allowing homeoprotein internalization and secretion (Figure1a) [33] led us to investigate Pax6 intercellular passage. As shown in Figure1bd, intercellular transfer fromPax6-transfected COS cells.