Pagliaccio (Pag) is a receptor tyrosine kinase of the Eph family that is expressed in Xenopus embryos in a diverse set of localized tissues. Pag is the Xenopus homolog of Hek-8 (human), Sek-1 (mouse), cek8 (chicken), and RTK-1 (zebrafish). We have investigated the function of this protein by injecting RNA encoding an epidermal growth factor receptor-Pag chimera into early Xenopus embryos. Activation of the chimeric receptor results in a kinase-dependent loss of cell-cell adhesion. This dissociation can be reversed by co-injection of RNA encoding C-cadherin, suggesting that one or more cadherins could be the functional targets for Pag activity.

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Keywords 6 7Sex-determining mechanism, genotypic sex determination, temperature-dependent sex 8 determination, gene-dosage, sex microchromosome, reptile, Crotaphytus collaris 9 10 Abstract 11 12The characteristics of a species' evolution can be powerfully influenced by its mode of sex 13 determination and, indeed, sex determination mechanisms vary widely among eukaryotes. In 14 non-avian reptiles, sex was long thought to be determined bimodally, either by temperature or 15 genetics. Here we add to the growing evidence that sex determining mechanisms in reptiles fall 16 along a continuum rather than existing as a mutually exclusive dichotomy. Using qPCR, we 17 demonstrate that the lizard Crotaphytus collaris possesses sex-based gene dosage consistent with 18 the presence of sex michrochromosomes, despite that extreme incubation temperatures can 19 influence hatchling sex ratio. Our results suggest a temperature override that switches genotypic 20 females to phenotypic males at high and low temperatures. 21 22 23 24 25the authors of this study point out that their sample size was low, this indicates a 64 temperature influence on sex determination in C. collaris. However, even at low and high 65 treatments this study did not find ratios of either sex nearing 100%. These findings hint at a more 66 complex mechanism for sex determination than pure TSD or pure GSD in C. collaris, as 67