Comparative Biochemistry and Physiology Part A 136 (2003) 343–352 1095-6433/03/$ - see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/S1095-6433(03)00169-7 Cross-fertilization and structural comparison of egg extracellular matrix glycoproteins from Xenopus laevis and Xenopus tropicalis L.L. Lindsay*, T.R. Peavy, R.S. Lejano, J.L. Hedrick Section of Molecular and Cellular Biology, University of California, One Shields Avenue, Davis, CA 95616, USA Received 28 March 2003; received in revised form 3 June 2003; accepted 5 June 2003 Abstract While the anuran amphibian Xenopus laevis is a widely used vertebrate model system, it is not optimal for genetic manipulations due to its tetraploid genome and long generation time. A current alternative amphibian model system, Xenopus tropicalis, has the advantages of a diploid genome and a much shorter generation time. We undertook a comparative investigation of X. tropicalis egg extracellular matrix glycoproteins in relation to those already characterized in X. laevis. Fertilization methods and isolation of egg extracellular molecules were directly transferable from X. laevis to X. tropicalis. Cross-fertilizations were successful in both directions, indicating similar molecules involved in sperm– egg interactions. Egg envelopes analyzed by SDS-PAGE were found to have almost identical gel patterns, whereas jelly component profiles were similar only for the larger macromolecules ()90 kDa). The cDNA sequences for egg envelope glycoproteins ZPA, ZPB, ZPC, ZPD and ZPAX, and also egg cortical granule lectin involved in the block to polyspermy, were cloned for X. tropicalis and showed a consistent ;85% amino acid identity to the X. laevis sequences. Thus, homologous egg extracellular matrix molecules perform the same functions, and the molecular and cellular mechanisms of fertilization in these two species are probably equivalent.  2003 Elsevier Inc. All rights reserved. Keywords: Xenopus tropicalis; Xenopus laevis; Fertilization; Egg extracellular matrix 1. Introduction The anuran amphibian Xenopus laevis is one of the most widely used vertebrate model systems in studies of fertilization and developmental mecha- nisms. It is particularly suited for experimental use due to the ease in raising and maintaining animals in the laboratory, the ability to obtain large num- bers of gametes upon demand through hormone injections, external fertilization and development and the large size of the eggs (Amaya et al., 1998; Gurdon, 1996; Kay and Peng, 1991; Seidman and *Corresponding author. Tel.: q1-530-752-9024; fax: q1-530-752-3085. E-mail address: lllindsay@ucdavis.edu (L.L. Lindsay). Soreq, 1997). These characteristics have allowed for research leading to major advances in the understanding of fertilization and development (Conlon and Kessler, 2000; Lohr and Yost, 2000; Munoz-Sanjuan and Brivanlou, 2001; Vogel, 1999). Recently, transgenics has advanced as the method of choice to examine gene function through gene knockout or mutation, and X. laevis has proven valuable in such types of experiments (Seidman and Soreq, 1997). However, there are some drawbacks to the use of X. laevis in trans- genics, including the long generational time (1–2 years) compared to mice (6 weeks), and also because X. laevis is a tetraploid that complicates gene manipulation experiments. Recently, a close