Differential expression of CaMK-II genes during early zebrafish embryogenesis

CaMK-II is a highly conserved Ca(2+)/calmodulin-dependent protein kinase expressed throughout the lifespan of all vertebrates. During early development, CaMK-II regulates cell cycle progression and "non-canonical" Wnt-dependent convergent extension. In the zebrafish, Danio rerio, CaMK-II activity rises within 2 hr after fertilization. At the time of somite formation, zygotic expression from six genes (camk2a1, camk2b1, camk2g1, camk2g2, camk2d1, camk2d2) results in a second phase of increased activity. Zebrafish CaMK-II genes are 92-95% identical to their human counterparts in the non-variable regions. During the first three days of development, alternative splicing yields at least 20 splice variants, many of which are unique. Whole-mount in situ hybridization reveals that camk2g1 comprises the majority of maternal expression. All six genes are expressed strongly in ventral regions at the 18-somite stage. Later, camk2a1 is expressed in anterior somites, heart, and then forebrain. Camk2b1 is expressed in somites, mid- and forebrain, gut, retina, and pectoral fins. Camk2g1 appears strongly along the midline and then in brain, gut, and pectoral fins. Camk2g2 is expressed early in the midbrain and trunk and exhibits the earliest retinal expression. Camk2d1 is elevated early at somite boundaries, then epidermal tissue, while camk2d2 is expressed in discrete anterior locations, steadily increasing along either side of the dorsal midline and then throughout the brain, including the retina. These findings reveal a complex pattern of CaMK-II gene expression consistent with pleiotropic roles during development.

Organization and evolution of multifunctional Ca2+/CaM-dependent protein kinase genes

The "multi-functional" Ca(2+) and calmodulin-dependent protein kinase, type II (CaMK-II) is an evolutionarily conserved protein. It has been found as a single gene in the horseshoe crab, marine sponge, sea urchin, nematode, and fruit fly, whereas most vertebrates possess four genes (alpha, beta, gamma, and delta). Species from fruit flies to humans encode alternative splice variants which are differentially targeted to phosphorylate diverse downstream targets of Ca(2+) signaling. By comparing known CaMK-II protein and nucleotide sequences, we have now provided evidence for the evolutionary relatedness of CaMK-IIs. Parsimony analyses unambiguously indicate that the four vertebrate CaMK-II genes arose via repeated duplications. Nucleotide phylogenies show consistent but moderate support for the placement of the vertebrate delta CaMK-II as the earliest diverging vertebrate gene. delta CaMK-II is the only gene with both central and C-terminal variable domains and has three to four times more intronic sequence than the other three genes. beta and gamma CaMK-II genes show strong sequence similarity and have comparable exon and intron organization and utilization. alpha CaMK-II is absent from amphibians (Xenopus laevis) and has the most restricted tissue specificity in mammals, whereas beta, gamma, and delta CaMK-IIs are expressed in most tissues. All 38 known mammalian CaMK-II splice variants were compiled with their tissue specificity and exon usage. Some of these variants use alternative 5' and 3' donors within a single exon as well as alternative promoters. These findings serve as an important benchmark for future phylogenetic, developmental, or biochemical studies on this important, conserved, and highly regulated gene family.

Molecular and biochemical regulation of early mammalian development

Fertilization initiates a rapid series of changes that restructures the egg into the zygote and initiates the program of early development. These changes in the cell occur while the genetic complement of the egg and sperm are in a highly condensed state and unable to participate in transcription. The egg cytoplasm, formed by the maternal genome, contains the necessary components that mediate the early restructuring of egg into zygote. These changes are mediated by a series of cytoplasmic signal transduction events initiated by the rise in [Ca2+]i caused when the sperm penetrates the egg. The structural changes that the egg undergoes are rapid and result in the extensive remodeling of this specialized cell. Protein kinase C (PKC) and calcium/calmodulin-dependent protein kinase II (CaM KII) are two pivotal signaling agents that mediate several of these rapid modifications in cell structure. Studies indicate the meiotic spindle serves as an architectural element in the egg that acts to colocalize elements from several of the key signaling pathways and may provide a means for these pathways to interact. In mammals, transcription begins earlier than in zygotes from other classes of organisms, starting several hours after fertilization in the male and female pronuclei and continuing in the embryonic nuclei. Studies indicate that nuclei undergo an initial state that is permissive for transcription, and then in Gap 2 of the two-cell embryo, enter a transcriptionally repressive state. These changes have been linked to the times during the cell cycle when the DNA is replicated, and also have been proposed as a requirement for proper initiation of the program of early development.

Calcium/calmodulin-dependent protein kinase II and calmodulin: regulators of the meiotic spindle in mouse eggs

Elevation of intracellular free calcium causes egg activation by initiating a cascade of interacting signaling pathways that, in unison, act to remodel the cytoplasmic compartment and the nuclear compartment of the egg. We show here that calcium/calmodulin-dependent protein kinase II (CaM kinase II) is tightly associated with the meiotic spindle and that 5 min after egg activation there is a transient, tight association of calmodulin (colocalized with CaM kinase II) on the meiotic spindle. These correlative observations caused us to test whether activation of CaM kinase II mediated the chromosomal transit into an anaphase configuration. We demonstrate that calcium and calmodulin, at physiological levels, along with ATP were capable of driving the spindle (with its associated CaM kinase II) into an anaphase configuration in a permeabilized egg system. The transit into anaphase was dependent on the presence of both calcium and calmodulin and occurred normally when they were present at a ratio of 4 to 1. Peptide and pharmacologic inhibitors of CaM kinase II blocked the transit into anaphase, both in the permeabilized egg system and in living eggs (inhibitors of protein kinase C did not block the transit into anaphase). Using a biochemical approach we confirm that CaM kinase II increases in activity 5 min after egg activation and that a second increase occurs 45 min after activation at the approximate time that the contractile ring of the second polar body is constricting. This corresponds to the approximate time when calmodulin and CaM kinase II colocalize at several points in the activated egg including the region containing midzone microtubules. CaM kinase II appears localized on midzone microtubules as soon as they form and may have a role in specifying the position of the contractile ring of the second polar body.

CaMK-II inhibition reduces cyclin D1 levels and enhances the association of p27kip1 with Cdk2 to cause G1 arrest in NIH 3T3 cells

The calmodulin-dependent protein kinase-II (CaMK-II) inhibitor KN-93 has been shown to reversibly arrest mouse and human cells in the G1 phase of the cell cycle [Tombes, R. M., Westin, E., Grant. S., and Krystal, G. (1995) Cell Growth Differ. 6, 1073-1070; Rasmussen, G., and Rasmussen, C. (1995) Biochem. Cell Biol. 71, 201-207]. The stimulation of Ca(2+)-independent (autonomous) CaMK-II enzymatic activity, a barometer of in situ activated CaMK-II, was prevented by the same KN-93 concentrations that cause G1 phase arrest. KN-93 caused the retinoblastoma protein pRB to become dephosphorylated and the activity of both cdk2 and cdk4, two potential pRb kinases, to decrease. Neither the activity of p42MAP kinase, an early response G1 signaling molecule, nor the phosphorylation status or DNA-binding capability of the transcription factors serum response factor and cAMP responsive element-binding protein was altered during this G1 arrest. The protein levels of cyclin-dependent kinase 2 (cdk2) and cdk4 were unaffected during this G1 arrest and the total cellular levels of the cdk inhibitors p21cip1 and p27kip1 were not increased. Instead, the cdk4 activity decreases resulting from KN-93 were the result of a 75% decrease in cyclin D1 levels. In contrast, cyclin A and E levels were relatively constant. Cdk2 activity decreases were primarily the result of enhanced p27kip1 association with cdk2/cyclin E. All of these phenomena were unaffected by KN-93's inactive analog, KN-92, and were reversible upon KN-93 washout. The kinetics of recovery from cell cycle arrest were similar to those reported for other G1 phase blockers. These results suggest a mechanism by which G1 Ca2+ signals could be linked via calmodulin-dependent phosphorylations to the cell cycle-controlling machinery through cyclins and cdk inhibitors.