Multiple isoforms of the high molecular weight microtubule associated protein XMAP215 are expressed during development in Xenopus

We have cloned and sequenced cDNAs encoding two isoforms of XMAP215, a high molecular weight microtubule-associated protein identified in Xenopus eggs . XMAP215 is similar to 80% identical in amino acid sequence to the product of ch-TOG, a cDNA that is over expressed in certain human tumors [Charrass e et al., 1995: fur J Biochem 234:406-413]. Northern and Western blots demo nstrated that XMAP215 is expressed throughout development, from oogenesis t o tadpole. We identified two XMAP215 transcripts differing only in the pres ence of a 108-bp sequence encoding a 36 amino acid insert. RT-PCR revealed that the transcripts encoding these two isoforms are expressed at distinct times during development: a transcript containing the insert (encoding XMAP 215(M)) is expressed during oogenesis and is present through gastrulation. The second transcript (encoding XMAP215(Z)) lacks the 108-bp insert and is expressed from gastrulation onward. In situ hybridization demonstrated that XMAP215 transcripts are localized to the ectoderm of early embryos and in the developing nervous system during later development. These results sugge st that XMAP215 plays important roles in at least two phases of development : (1) regulating the assembly of MTs during the rapid cell divisions after fertilization, and (2) regulating MT assembly during the development of the nervous system. Cell Motil. Cytoskeleton 47:282-295, 2000. (C) 2000 Wiley- Liss, Inc.