Biomedical subjects

D A Siever

Publications and source records attributed to D A Siever.

4 recordsLinked to original sources

PubMed1997

Shared and distinct functions of RAGS and ELF-1 in guiding retinal axons.

Two ligands for Eph-related receptor tyrosine kinases, RAGS and ELF-1, have been implicated in the control of development of the retinotectal projection. Both molecules are expressed in overlapping gradients in the tectum, the target area of retinal ganglion cell axons. In two in vitro assays ELF-1 is shown to have a repellent axon guidance function for temporal, but apparently not for nasal axons. RAGS on the other hand is repellent for both types of axons, though to different degrees. Thus, RAGS and ELF-1 share some and differ in other properties. The biological activities of these molecules correlate with the strength of interaction with their receptors expressed on RGC axons. The meaning of these findings for guidance of retinal axons in the tectum is discussed.

Animals↗

PubMed1997

Extracellular annexin II.

Annexin II belongs to a family of calcium-dependent, phospholipid binding proteins. Annexin II was first identified as an intracellular protein and attributed intracellular functions. Although it lacks a signal peptide and its mechanism of secretion is unknown, extracellular annexin II has recently been found in several tissues as both soluble and membrane-bound protein. Cell-surface annexin II has been identified as a receptor for a number of polypeptide ligands. Extracellular annexin II may be important in several biological processes, such as fibrinolysis, cell adhesion, ligand-mediated cell signaling and virus infection. These processes provide several possibilities for therapeutic approaches targeting extracellular annexin II, and future research should further illuminate the biology of this molecule.

Annexin A2↗

PubMed1995

cDNA cloning and characterization of a Cek7 receptor protein-tyrosine kinase ligand that is identical to the ligand (ELF-1) for the Mek-4 and Sek receptor protein-tyrosine kinases.

We have isolated a murine cDNA encoding a ligand for the Cek7 receptor protein-tyrosine kinase (RPTK), a member of the Eph/Eck RPTK subfamily. Sequence analysis predicts an open reading frame of 209 amino acids with a predicted molecular mass of 24 kDa. The Cek7 ligand shows a 48% sequence identity at the protein level to B61, a ligand for the related Eck RPTK, 30% to the Cek5 ligand, 59% to the recently cloned Ehk1-L, and identity to ELF-1, a recently described ligand for the Mek4 and Sek RPTKs. The expressed Cek7 ligand is functionally active as it induces autophosphorylation of the Cek7 RPTK.

Amino Acid Sequence↗

PubMed1994

Identification of a complete Cek7 receptor protein tyrosine kinase coding sequence and cDNAs of alternatively spliced transcripts.

Receptor protein tyrosine kinases (RPTK) are critical components of signal transduction pathways in multicellular organisms. Identification of new RPTK constitutes an initial step in understanding the variety of signalling pathways in which these proteins participate. In this study, a cDNA containing a complete coding sequence for Cek7 (chicken RPTK) has been cloned from a chicken embryo expression library using anti-phosphotyrosine antibodies (Ab). Cek7 is a member of the EPH (human RPTK) subfamily of RPTK; this subfamily is characterized by extracellular domains containing an immunoglobulin-like motif, a Cys-rich region and two fibronectin type-III repeats. Analysis of additional cDNAs revealed that two positions of alternative splicing in primary transcripts may produce several isoforms of this RPTK; cDNAs corresponding to three isoforms of this receptor are reported. These isoforms are predicted to have altered extracellular ligand-binding domains and/or altered cytoplasmic juxtamembrane regions. The nucleotide sequence of cek7 cDNAs identified in this study diverges at the 3' end from the sequence found in a recently described partial cek7 cDNA [Sajjadi and Pasquale, Oncogene 8 (1993) 1807-1813]. Therefore, a third position of alternative splicing may produce Cek7 RPTK with divergent C-terminal tails. RNA blot analysis revealed expression of this receptor at highest levels in the central nervous system and eyes of 10-day-old chicken embryos.

Alternative Splicing↗