Developmental expression of Cyclin H and Cdk7 in zebrafish: the essential role of Cyclin H during early embryo development

Abstract

Cyclin-dependent kinase 7 (Cdk7) is the catalytic subunit of the metazoan Cdk-activating kinase (CAK). Activation of Cdk7 requires its association with a regulatory subunit, Cyclin H. Although the Cdk7/Cyclin H complex has been implicated in the regulation of RNA polymerase in several species, the precise function of their orthologs in zebrafish has not been fully elucidated. In this study, we isolated from zebrafish blastula embryos two cDNAs encoding the orthologs of human Cyclin H and Cdk7, and examined the role of Cdk7/Cyclin H in zebrafish embryogenesis. Sequence analysis showed that the zebrafish Cyclin H and Cdk7 cDNAs encode proteins with 65% and 86% identity to the respective human orthologs. RT-PCR and whole-mount in situ hybridization analyses of their expression in unfertilized eggs, embryos and organs of adult fish suggested that Cyclin H and Cdk7 messages are maternally loaded. Our data also showed that their transcripts were detected throughout development. Distribution of Cyclin H transcripts was found to be ubiquitous during early stages of development and become restricted to the anterior neural tube, brain, eyes, procreate tissues, liver and heart by 5 days post-fertilization. Expression of a dominant-negative form of Cyclin H delayed the onset of zygotic transcription in the early embryo, resulting in apoptosis at 5 hours post-fertilization and leading to sever defects in tissues normally exhibiting high levels of Cyclin H expression. These results implicate Cyclin H in the regulation of the transcriptional machinery during midblastula transition and suggest that it is an essential gene in early zebrafish larval development.

Knockdown of Cyclin-dependent Kinase 10 (cdk10) Gene Impairs Neural Progenitor Survival via Modulation of raf1a Gene Expression

“…Scale bars, 100 m. Ctrl, control. expressed in the brain, eye, and heart (14). The expression of cdkl1, which is another cdc2-related protein kinase, is restricted to the floor plate, pronephric ducts, and hypochord at 12 HPF (18).…”

“…Reduced expression of ngn1, emx1, and wnt1 in cdk10 morphants was evident. Expression of a dominant negative form of cyclin H, which decreases cdk7 activities, results in apoptosis in the early stage of zebrafish embryos (14). Previous reports demonstrated the down-regulation of zebrafish cdk5 by using siRNA, which leads to apoptosis in the brain and a subsequent reduction in the number of primary sensory neurons in the trigeminal ganglion (15,31).…”

“…The progressively restricted pattern of cdk10 expression was similar to that of other cdk and cdk-related genes in zebrafish. The cdk7/cyclin H and cdkl1 genes are ubiquitously distributed before gastrulation (14,18). At 24 HPF and thereafter, cdk7 and cyclin H are primarily FIGURE 10.…”

“…Zebrafish cyclin H/cdk7 is ubiquitously expressed throughout all examined stages and tissues (14). Abrogation of cyclin H expression results in defective development and apoptosis (14). Previous reports revealed that zebrafish cdk5 is ubiquitously and abundantly expressed in the brain and the eyes (15).…”

“…To date, the role of CDKs in zebrafish development remains poorly understood. Zebrafish cyclin H/cdk7 is ubiquitously expressed throughout all examined stages and tissues (14). Abrogation of cyclin H expression results in defective development and apoptosis (14).…”