The kinesin KIF17b and RNA-binding protein TB-RBP transport specific cAMP-responsive element modulator-regulated mRNAs in male germ cells

Abstract

Testis brain RNA-binding protein (TB-RBP), the mouse orthologue of the human protein Translin, is a widely expressed and highly conserved protein with proposed functions in chromosomal translocations, mitotic cell division, and mRNA transport, stabilization, and storage. Targeted inactivation of TB-RBP leads to abnormalities in fertility and behavior. A testis-enriched kinesin KIF17b coimmunoprecipitates with TB-RBP in a RNA-protein complex containing specific cAMP-responsive element modulator (CREM)-regulated mRNAs. The specificity of this interaction is confirmed by in vivo RNA-protein crosslinking and transfections of hippocampal neurons. Combining in situ hybridization and immunohistochemistry at the electron microscope level, a temporally sequential dissociation of KIF17b and TB-RBP from specific mRNAs is detected with TB-RBP release coincident with the time of mRNA translation, indicating a separation of the processes of transport and translation. We conclude that KIF17b serves as a molecular motor component of a TB-RBP-mouse ribonucleoprotein complex transporting a group of specific CREM-regulated mRNAs in mammalian male postmeiotic germ cells. Because KIF17b has been reported to control CREM-dependent transcription in male germ cells by regulating the intracellular location of the transcriptional coactivator activator of CREM in testis, this indicates that one kinesin links the processes of transcription and transport of specific mRNAs in mammalian male germ cells. D uring spermatogenesis, male germ cells undergo massive differentiation and rapid polarization that require transport and specific localization of vesicles, proteins, mRNAs, and organelles. The need to maintain phenotypic equivalence of the X or Y chromosome bearing haploid male germ cells further necessitates the sharing of specific mRNAs through intercellular bridges (1, 2). A number of kinesin and dynein superfamily motor proteins have been proposed to carry out transport processes in the testis (3). The mRNA binding protein TB-RBP, the mouse orthologue of human Translin (4), binds specific mRNAs in postmeiotic germ cells and in neurons, two of the highly polarized cell types in which mRNA transport and localization are essential. In male germ cells TB-RBP transports specific mRNAs intracellularly and intercellularly in a mouse ribonucleoprotein complex containing the Ter ATPase (5). Microtubule reconstitution experiments reveal that specific translationally delayed mRNAs are linked to microtubules through TB-RBP (6). TB-RBP binds brain mRNAs such as ␣-Ca 2ϩ -calmodulin-dependent protein kinase II mRNA and ligatin (7,8) and a number of translationally delayed and X chromosome-encoded mRNAs that are solely expressed in male postmeiotic germ cells (5). In our investigation of the components of the TB-RBP-mRNA complexes involved in mRNA transport, we have identified a kinesin by coimmunoprecipitation and matrix-assisted laser desorption͞ionization-time-offlight (MALDI-TOF) mass spectroscopy. This kinesin, KIF17b, is an isoform of the neuronal...

Expression profiling reveals meiotic male germ cell mRNAs that are translationally up- and down-regulated

“…Messenger RNAs encoding proteins, such as the kinesin, KIF17b, carboxylesterase 3, and CD46 antigen, are in this group. KIF17b serves as a molecular motor component of a Translin (TSN)-RNA complex transporting mRNAs transcribed by cAMP-responsive element modulator tau in haploid spermatids from the nucleus to the cytoplasm and through intercellular bridges (12). Because KIF17b has been reported to regulate the intracellular location of the transcriptional coactivator of cAMP-responsive element modulator tau in male germ cells (21), KIF17b links the processes of transcription and transport of mRNAs in the testis.…”

“…This observation is likely the result of a need for RNA-binding proteins to modulate the translational control and RNA stabilization needed to regulate stage-specific protein synthesis. Interactions between mRNAs and RNA-binding proteins, such as the ELAV (embryonic lethal abnormal visual) proteins (46), CPEB (cytoplasmic polyadenylation element binding protein) (47), and TSN (12) facilitate translational regulation of mRNAs. ELAV proteins have been implicated in the posttranscriptional regulation of growth regulatory mRNAs in the cytoplasm by affecting their stability and translatability (46).…”

“…Some of these mRNAs encoding proteins, such as the protamines, are stored for up to a week as RNPs before being translated (11). To date, most of the known translationally delayed male germ cell mRNAs are first transcribed long after meiosis by the haploid expressed transcription factor cAMP-responsive element modulator tau (12)(13)(14).…”

Translin associated protein X is essential for cellular proliferation

“…Translin and its mouse ortholog, Testis brain RNA-binding protein (TB-RBP), are highly conserved and ubiquitously expressed DNA-and RNA-binding proteins with proposed functions in mitotic cell division [1,2], chromosomal translocations [3][4][5], stabilization, transport, and translational suppression of specific mRNAs [6][7][8]. Mice lacking TB-RBP are viable and when heterozygotes were bred, a normal Mendelian distribution was obtained [2].…”

Neuronal distribution of Spatial in the developing cerebellum and hippocampus and its somatodendritic association with the kinesin motor KIF17

“…Although the role of KIF17b in these structures is still unknown, the function of the kinesin-2 motor KIF17 in other highly organized cytoskeletal structures, such as the cilia and dendrites, has been well established [7][8][9]. Indeed, KIF17 was shown to transport organelles, vesicles, channels, protein complexes and RNA to specific subcellular compartments in neurons [7][8][9][10]. These results raise the possibility that Spatial may also interact with KIF17 during brain development.…”