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Tail development in splotch and truncate mice

Splotch and truncate are the spontaneous mutant mouse strains with the inherited developmental disorders. Splotch phenotype is caused by mutation of Pax3 gene, but for truncate the involved gene is still unknown (1). Homozygous Splotch embryos die at the embryonic day 13, showing malformations of nervous system and heart (2). Truncate homozygotes are viable, but lack a part of the tail (3). In order to investigate the tail development in splotch and truncate mutants we performed the morphological analysis of homozygous 11.5-day embryos by scanning electron microscopy and serial semithin sections. Splotch embryos presented a curved tail and an open neural tube in the lumbosacral region (figure 1). Tail bud and the related structures: medullary and the tail cord were present in the tip of the tail. The three axial structures of the tail (neural tube, notochord and tail gut) were continuous with the tail bud mesenhyme. In the region of the open neural tube, there was an overgrowth of the neuropithelium and the somites were malformed. Truncate embryos were characterized by partial loss of notochord. In the corresponding region development of the somites and the neural tube was affected (figure 2). The observed malformations indicate that the normal sequence of tail development requires the coordinated interactions among the tail axial structures, which can be related to pathogenesis of spina bifida in humans. 1. Epstein DJ, Vogan KJ, Trasler DG, Gros P (1993) Proc Natl Acad Sci U S A 90, 532-536 2. Auerbach R (1954) J Exp Zool 127,305-329 3. Theiler K (1959) Am J Anat 104, 319-343 Figure 1. Scanning electron micrograph of the tail of the splotch homozygous embryo 11.5-days old. Neural tube (NT) is opened in the lumbosacral region. The rest of the tail (T) is highly curved. Bar 500 ľm. Figure 2. Transverse semi-thin section stained with toluidine blue through the tail of 11.5-day truncate homozygous embryo. Notochord is missing. Neural tube (NT) is an irregular accumulation of few cells without lumen, and the somites (S) are medially fused. Bar 50 ľm.

tail; splotch; truncate; Pax3

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