ZALK-8, A NOVEL TYPE-I SERINE THREONINE KINASE RECEPTOR, - IS EXPRESSED THROUGHOUT EARLY ZEBRAFISH DEVELOPMENT/

Here, we report the isolation and characterization of zebrafish activi n receptorlike kinase-8 (zALK-8), a novel type I serine/threonine (ser /thr) kinase receptor of the transforming growth factor beta (TGF-beta ) family, zALK-8 is novel, in that it contains an extracellular domain that is quite distinct from that of previously identified ALK recepto rs 1 through 7, Analysis of the predicted amino acid sequence of the 5 06 amino acid zALK-8 receptor reveals an ser/thr kinase domain charact eristic of type I TGF-beta family member receptors. zALK-8, therefore, is a traditional type I ser/thr kinase receptor of the TGF-beta famil y, but it may exhibit novel ligand-binding activities, The development al expression of zALK-8 mRNA was examined by wholemount in situ hybrid ization analysis using a probe from the 3'-untranslated sequence of zA LK-8, which does not cross react with other members of the highly cons erved TGF-beta receptor family, zALK-8 mRNA is present as a maternal m essage that is expressed ubiquitously before the start of zygotic tran scription, By 16 hr postfertilization (hpf), zALK-8 mRNA is still expr essed fairly evenly throughout the embryo, In 24-hpf embryos, zALK-8 m RNA is expressed predominantly in the developing eye and neural struct ures, By 48 hpf, zALK-8 mRNA is faintly detectable as a diffuse signal throughout the head, zALK-8 mRNA is not detectable by this method in 72-hpf or 96-hpf embryos, Northern analysis of zALK-8 mRNA in poly(A+) mRNA isolated from 6-9 hpf embryos detects a major transcript of 3.6 kb and a minor transcript of 4.3 kb, zALK-8 mRNA expression correlates well with known functions of TGF-beta family members as early axial p atterning and mesoderm-inducing growth factors and as potent growth an d differentiation factors in craniofacial development. (C) 1998 Wiley- Liss, Inc.