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

ABSTRACT: In eukaryotic cells, the Wee1 protein kinase phosphorylates and inhibits Cdc2, thereby creating an interphase of the cell cycle. In Xenopus, the conventional Wee1 homolog (termed Xe-Wee1A, or Wee1A for short) is maternally expressed and functions in pregastrula embryos with rapid cell cycles. Here, we have isolated a second, zygotic isoform of Xenopus Wee1, termed Xe-Wee1B (or Wee1B for short), that is expressed in postgastrula embryos and various adult tissues. When ectopically expressed in immature oocytes, Wee1B inhibits Cdc2 activity and oocyte maturation (or entry into M phase) much more strongly than Wee1A, due to its short C-terminal regulatory domain. Moreover, ectopic Wee1B, unlike Wee1A, is very labile during meiosis II and cannot accumulate in mature oocytes due to the presence of PEST-like sequences in its N-terminal regulatory domain. Finally, when expressed in fertilized eggs, ectopic Wee1B but not Wee1A does affect cell division and impair cell viability in early embryos, due primarily to its very strong kinase activity. These results suggest strongly that the differential expression of Wee1A and Wee1B is crucial for the developmental regulation of the cell cycle in Xenopus.

SUBMITTER: Okamoto K

PROVIDER: S-EPMC126008 | biostudies-literature | 2002 May

REPOSITORIES: biostudies-literature

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

Okamoto Kengo K Nakajo Nobushige N Sagata Noriyuki N

The EMBO journal 20020501 10

In eukaryotic cells, the Wee1 protein kinase phosphorylates and inhibits Cdc2, thereby creating an interphase of the cell cycle. In Xenopus, the conventional Wee1 homolog (termed Xe-Wee1A, or Wee1A for short) is maternally expressed and functions in pregastrula embryos with rapid cell cycles. Here, we have isolated a second, zygotic isoform of Xenopus Wee1, termed Xe-Wee1B (or Wee1B for short), that is expressed in postgastrula embryos and various adult tissues. When ectopically expressed in imm ...[more]

PMID: 12006499

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Project description:UnlabelledEndogenous retroviruses (ERVs) are the remnants of ancient retroviral infections of germ cells. Previous work identified one of the youngest feline ERV groups, ERV-DC, and reported that two ERV-DC loci, ERV-DC10 and ERV-DC18 (ERV-DC10/DC18), can replicate in cultured cells. Here, we identified another replication-competent provirus, ERV-DC14, on chromosome C1q32. ERV-DC14 differs from ERV-DC10/DC18 in its phylogeny, receptor usage, and, most notably, transcriptional activities; although ERV-DC14 can replicate in cultured cells, it cannot establish a persistent infection owing to its low transcriptional activity. Furthermore, we examined ERV-DC transcription and its regulation in feline tissues. Quantitative reverse transcription-PCR (RT-PCR) detected extremely low ERV-DC10 expression levels in feline tissues, and bisulfite sequencing showed that 5' long terminal repeats (LTRs) of ERV-DC10/DC18 are significantly hypermethylated in feline blood cells. Reporter assays found that the 5'-LTR promoter activities of ERV-DC10/DC18 are high, whereas that of ERV-DC14 is low. This difference in promoter activity is due to a single substitution from A to T in the LTR, and reverse mutation at this nucleotide in ERV-DC14 enhanced its replication and enabled it to persistently infect cultured cells. Therefore, ERV-DC LTRs can be divided into two types based on this nucleotide, the A type or T type, which have strong or attenuated promoter activity, respectively. Notably, ERV-DCs with T-type LTRs, such as ERV-DC14, have expanded in the cat genome significantly more than A-type ERV-DCs, despite their low promoter activities. Our results provide insights into how the host controls potentially infectious ERVs and, conversely, how ERVs adapt to and invade the host genome.ImportanceThe domestic cat genome contains many endogenous retroviruses, including ERV-DCs. These ERV-DCs have been acquired through germ cell infections with exogenous retroviruses. Some of these ERV-DCs are still capable of producing infectious virions. Hosts must tightly control these ERVs because replication-competent viruses in the genome pose a risk to the host. Here, we investigated how ERV-DCs are adapted by their hosts. Replication-competent viruses with strong promoter activity, such as ERV-DC10 and ERV-DC18, were suppressed by promoter methylation in LTRs. On the other hand, replication-competent viruses with weak promoter activity, such as ERV-DC14, seemed to escape strict control via promoter methylation by the host. Interestingly, ERV-DCs with weak promoter activity, such as ERV-DC14, have expanded in the cat genome significantly more than ERV-DCs with strong promoter activity. Our results improve the understanding of the host-virus conflict and how ERVs adapt in their hosts over time.

Dataset Information

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

Publications

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

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