WEE1-like CDK tyrosine kinase mRNA level is regulated temporally and spatially in sea urchin embryos

Abstract

A cDNA from the sea urchin Strongylocentrotus purpuratus encodes a 624 amino acid polypeptide (WEE1S.purp) with a high degree of similarity to the Mik1 and Wee1 protein tyrosine kinases. These kinases act as negative regulators of mitosis by inactivating cyclin-dependent kinases (CDK). Wee1 activity varies during the cell-cycle, and is generated only when required. The pattern of WEE1S.purp mRNA expression was examined temporally and spatially in sea urchin embryos. Only a trace amount of WEE1S.purp mRNA is present in the egg and through the fifth cell cycle post-fertilization. During the next three cycles to the mid-blastula stage, its concentration rises transiently to 2.5 x 10(4) transcripts per embryo. Its developmental profile during this early period is the inverse of that reported for cyclin mRNAs, which are at a high level in the egg and through the fifth cell cycle, then decline upon further development. WEE1S.purp mRNA in the gastrula and pluteus stages becomes restricted to cells engaged in DNA replication, including the endoderm (gut), oral ectoderm, and arm rudiments. It is absent from the aboral ectoderm, which lacks cycling cells. In the pluteus larva of the species Lytechinus pictus, WEE1 mRNA was detected in the arm rudiments during cellular proliferation and arm elongation, but not after the completion of the arms. Putative regulatory motifs in the sea urchin Wee1-like cDNA suggest a capacity for rapid turnover of both its mRNA and protein: The WEE1S.purp mRNA 3' UTR contains 13 AUUUA pentamers, which have been characterized as determinants of mRNA lability; and the N-terminal domain of the predicted WEE1S.purp polypeptide is enriched in S/TP-containing, potential kinase-target sites, as well as high-value "PEST' sequences, associated with protein lability. The developmental appearance of WEE1S.purp mRNA may coincide with the introduction of a gap phase in the cell cycle. Its spatial pattern during embryogenesis appears to reflect distinct programs of regulated cell cycling in differentiating tissues.

PLAUF is a novel P. lividus sea urchin RNA-binding protein

“…In fact the presence of high multiplicity of AUUUA pentamers was already demonstrated in the 3VUTR of other sea urchin messenger RNAs, like WEE 1 S. purpuratus, and it was indirectly correlated with high turnover rate (Nemer and Stubing, 1996). Moreover the cDNA clone encodes a novel protein highly homologous to the AUF1 family members that are heterogeneous nuclear ribonucleoproteins implicated in mRNA stability regulation.…”

The genomic repertoire for cell cycle control and DNA metabolism in S. purpuratus

“…similarity with the corresponding starfish Asterina pectinifera genes (Table S1, Nemer and Stuebing, 1996;Okano-Uchida et al, 1998;Okumura et al, 2002). Vertebrates have three CDC25 homologues (CDC25A, B and C), whereas only one was found in S. purpuratus, similar to its homologue in A. pectinifera (Deshimaru et al, 2002).…”

The existence of two distinct Wee1 isoforms in Xenopus: implications for the developmental regulation of the cell cycle

“…The figures in the dendrogram represent bootstrap values. Sequence data were taken from Drosophila Wee1 (Dm; Campbell et al ., 1995), sea urchin Wee1 (Su; Nemer and Stuebing, 1996), starfish Wee1 (Sf; DDBJ/EMBL/GenBank accession No. ), maternally expressed Xenopus Wee1 (Xe‐A; Mueller et al ., 1995a), zygotically expressed Xenopus Wee1 (Xe‐B; this work or accession No.…”

“…Wee1 homologs have been isolated from a variety of organisms, ranging from yeast through Drosophila and Xenopus to humans (Russell and Nurse, 1987; Igarashi et al ., 1991; Booher et al ., 1993; Campbell et al ., 1995; Mueller et al ., 1995a; Watanabe et al ., 1995). Structurally, they commonly consist of a long N‐terminal regulatory domain, a central kinase domain and a short C‐terminal regulatory domain (Watanabe et al ., 1995; Nemer and Stuebing, 1996). During the mitotic cell cycle in many cell types, Wee1 protein is active and relatively stable during G 1 , S and early G 2 phases, but is inactive and unstable during late G 2 and M phases (McGowan and Russell, 1995; Mueller et al ., 1995a; Watanabe et al ., 1995; Aligue et al ., 1997; Michael and Newport, 1998; Sia et al ., 1998).…”