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The serotonin receptor 5-HT2B has been shown to be critically important during embryogenesis as the knockout of this gene in mice causes heart defects and embryonic lethality that impairs further analyses on other embryonic cell and tissue types. In the present review, we highlight how the use of Xenopus laevis, an alternative vertebrate model suitable for gene loss and gain of function analyses, has contributed to our understanding of the role of 5-HT2B signaling during development. In vivo studies showed that 5-HT2B signaling is not only required for heart development, but that it also has a crucial role in ocular and craniofacial morphogenesis, being involved in shaping the first branchial arch and the jaw joint, in retinogenesis and possibly in periocular mesenchyme development. These findings may be relevant for our understanding of congenital defects including human birth malformations. In addition, 5-HT2B appears to be required for the therapeutic actions of selective serotonin reuptake inhibitors commonly prescribed as antidepressant drugs to pregnant and lactating women. We discuss how the understanding of the molecular basis of serotonin signaling in a suitable animal embryogenesis model may open new lines of investigations and therapies in humans.

Xfin is a member of a Zn-finger multigene family that shares homology with the Drosophila segmentation gene, Krüppel. This paper reports on our identification and cellular localization, through the utilization of specific antibodies, of the expression product of Xfin in the Xenopus laevis retina, and its pattern of expression during the retinal developmental stages. By immunostaining sections of the retina, we show that the major staining is localized in the cytoplasm of the cones. The protein appears at an early differentiation stage of the cones, when they can not be univocally identified by morphological criteria, and is maintained up to the adult retina. The same antigenicity pattern is detectable in the retina of the anuran genus Bufo. The immunostaining data are confirmed by Western blot analysis on Xenopus eye protein extracts. Because of its cytoplasmic localization, and because of the ability of Zn-finger proteins to bind nucleic acids, we think that Xfin may be involved in the terminal differentiation of the cones through RNA-protein interactions.