Localization of Janus Kinase 2 to the Nuclei of Mature Oocytes and Early Cleavage Stage Mouse Embryos

Abstract

Jak2, which is a member of the Janus tyrosine kinase family, plays essential roles in cytokine signal transduction and in the regulation of cell growth and gene expression. To investigate the involvement of Jak2 in the regulation of early preimplantation development, we examined the expression of Jak2 in mouse embryos. Reverse transcription-polymerase chain reaction assays revealed that the relative amount of Jak2 mRNA was highest in unfertilized oocytes, gradually decreased until the four-cell stage, and remained at low levels until the blastocyst stage. Immunocytochemistry showed that Jak2 was localized predominantly to the female pronucleus in one-cell embryos. The immunofluorescence signal was very weak or undetectable in the male pronucleus. In unfertilized oocytes and one-cell embryos at M phase, Jak2 was localized to the chromosomes. After cleavage to the two-cell stage, the intensity of the immunofluorescence signal decreased in the nucleus while the embryos were in late G2. This decrease was independent of DNA synthesis because it was not affected by inhibition of DNA replication. However, inhibition of protein synthesis repressed the disappearance of Jak2 from the nucleus. These results suggest a novel function for Jak2 in the regulation of early preimplantation development.

Zygotically Activated Genes Are Suppressed in Mouse Nuclear Transferred Embryos

“…Since the Dub-1 has deubiquitinating activity and global protein synthesis is largely changed during the preimplantation stages in mouse development (Johnson, 1981), the Dub-1 may play some roles in preimplantation development to control protein stability through ubiquitination. Considering the report that the Dub-1 gene expression is controlled by Jak2 (Jaster et al, 1997), which localized in the nucleus at the 1-and 2-cell stages in mouse preimplantation embryos (Ito et al, 2004), the reduced expression of Dub-1 gene in NT embryos may be caused by aberrant signal transduction that controls the gene expression.…”

Kinase activity and subcellular distribution of a chimeric green fluorescent protein-tagged Janus kinase 2

“…These observations are noteworthy because, while various groups employing a variety of approaches to determine the subcellular localization of JAKs have provided apparently conflicting conclusions [16,18,20,21], reports of ubiquitous distribution are rare. To our knowledge, the observation that a single JAK isoform can either be located in or excluded from the nucleus under identical experimental conditions has not been previously reported.…”

“…The current controversy surrounding the subcellular localization of JAKs [16,18,20,21,42,43] arose in part from differences in experimental methodologies (e.g., immunohistochemistry vs. chimeric fluorescent protein expression) and in reagent selection (e.g., different cell lines). There is a reasonable expectation to find evidence for the membrane localization of JAK2, because as one group correctly stated, ''all functional features of JAK proteins point to their involvement in events occurring at the cell surface or at intracellular membranes'' [16].…”

“…Some investigators have provided evidence that yellow fluorescent protein-chimeras containing JAK1, JAK2 or TYK2 are predominantly located at the cellular membrane [16,17]. On the other hand, other groups, whose investigations did not employ fluorescent chimeras, reported a nucleocytoplasmic distribution for JAK2 [18][19][20], while yet other investigators reported that hemagglutinin-tagged JAK2 was distributed in the cytoplasm but excluded from the nucleus [21]. In order to further examine these and other issues surrounding the properties of JAK2's catalytic properties in a cellular context, we sought to develop other approaches to produce the recombinant enzyme in various mammalian cells.…”

Expression of Cytokine Receptors in Pre-implantation Mouse Embryos

“…Recent work has s h o w n t h a t J a k 2 i s e x p r e s s e d i n m o u s e p r eimplantation embryos [1]. Jak2 is a non-receptor tyrosine kinase that mediates various signaling pathways via cytokine receptors [2].…”