Int,.I, De,', BioI. 42: 701-707 (1998) Oligil/a/ Article Expression of PAX2 gene during human development JANOS TERZIC', CHRISTIANE MULLER', SRECKO GAJOVIC3 and MIRNA SARAGA-BABIC:'* IDepartment of Physiology, 20epartment of Histology and Embryology, Medical School. University of Split, Split, Croatia and JDepartment of Molecular Cell Biology, Max Planck Institute of Biophysical Chemistry. Gottingen. Germany ABSTRACT The expression of human paired-box-containing PAX2gene was examined in 7 human conceptuses 6 to 9 weeks old by in situ hybridization. The embryos were collected after legal abortions. embedded in paraffin, serially cut in transversal direction and treated with 535 labeled probe for PAX2. In the neural tube of 6-week embryos, PAX2was expressed in the outer part of the ventricular zone on both sides of the sulcus limitans. At later stages, it was expressed in the intermediate zone of the spinal cord, both in alar and basal plates except in the region of motor neuroblasts. In the brain, expression of PAX2 extended from mesencephalic-rhombencephalic border along the entire rhombencephalon in a manner similar to that described for the spinal cord. Expression of PAX2 gene in the eye was seen in the optic cup and stalk, and later in the optic disc and nerve. In the ear, expression was restricted to the part of the otic vesicle flanking the neural tube and later to the utricle and cochlea. Expression of PAX2was observed in developing kidneys as well. During human development PAX2 has a spatially restricted expression along the compartmental boundaries of the neural tube, and within developing eye, ear and kidneys. Differentiation of those organs seems to be mediated by PAX2 gene at the defined stages of human development. KEY WORDS: hmnrm embry.o, PAX2 geT/e, "puTOgfnfS;J, .~fTlSt' 0'Kfms Introduction Development, regional specification and morphogenesis of the human brain seem to be controlled by multigene families whose products act as transcriptional regulators that bind to specific DNA sequences. Recent evidence from mouse (Nornes et al., 1990; Stoykova and Gruss, 1994; St-Onge et a/., 1995) and human embryos (Gerard et al., 1995) indicate that Pax genes play impor- tant roJes in early embryogenesis. Pax genes are characterized by the presence of a highly conserved DNA region referred to as paired box, encoding a DNA-binding protein domain of 128 amino acids, the paired domain (Dressler et al., 1988; Deutsch and Gruss, 1991). Some of the Pax genes (Pax3, Pax4, Pax6, Pax7) addition- ally have a second conselVed DNA region, a homeobox, encoding domain of 61 amino acids (homeodomain) located towards the carboxyterminus of the corresponding protein (Strachan and Read, 1994). Furthermore, a highly conserved sequence that specifies an octapeptide is found in most Pax genes (except for Pax4 and Pax6). Certain isoforms of Pax proteins seem to be tissue specific and could regulate expression of different genes in different tissues (St-Onge at al.. 1995). Pax genes have a restricted expression pattern along the craniocaudal and dorsoventral axes of the neural tube (McGinnis and Krumlauff, 1992; Chalepakis et a/., 1993). The dorsoventral patterning of the neural tube occurs later than the craniocaudal patterning, and requires the notochord (Tessier-Lavigne et al., 1988; van Straaten et al., 1988; Placzek et al., 1990, Monsoro-Burq et al.. 1995). Experimentally, the expression otthe Pax3gene in the neural tube changes by extirpation or grafting of an extra notochord (Goulding et al., 1993). In human embryos notochord abnormali- ties may be associated with dysraphic axial disorders (Sa raga- Babic and Saraga, 1993; Saraga-Babic et al., 1993a) and duplica- tion olthe spinal cord (Saraga-Babic et al., 1993b). Disruplionof Pax genes in animals (Balling etal.. 1988; Epstein etal.. 1991; Hill etal., 1991, Torres et al., 1995,1996) as well as in humans can lead to developmental abnormalities such as Waardenburg syndrome, spina bifida, aniridia, Peter's anomalyorcongenital cataract (Tassabehji st a/.. 1993; Glaser et al.. 1994; Strachan and Read, 1994). Development of the human neural tube involves several tempo- rally restricted processes: cell proliferation, migration, differentiation and cell death. The most caudal part of the human neural tube develops during the process of secondary neurulation (Saraga- Babic at al., 1994,1995, 1996a,b). By the end of the 6th week, three zones differentiate In the lateral walls of the human neural lube: the ventricular, the intermediate and the marginal zone. During the following four weeks mitotic activity gradually ceases and the specific neurons differentiate according to their dorsoventral position, thus forming the definitive spinal cord (Fitzgeraid and Fitzgeraid, 1994). .Address for reprints: Department of Histology and Embryology. Medical School, University of Split, PAK, KB Split. Spinciceva 1, 21000 Split, Croatia. FAX: (385 21) 365 738. 0214-6282/98/5 I 0.00 o t.:8C Prcu Prinlcdin Sp.a,n