Published papers

Neuronal precursor cells generated by stem cells in the subventricular zone (SVZ) migrate and differentiate into mature interneurons in the olfactory bulb (OB). The mechanisms responsible for the dynamic morphological changes in cells during this process are largely unknown. Wnt/planar cell polarity (PCP) signaling regulates various developmental events, including neuronal migration and neurite formation. Here, we studied the function of two components of the PCP pathway, Dishevelled2 and Van Gogh like-2, in the newborn neurons in the postnatal mouse OB. Electroporation- or lentivirus-mediated introduction of vectors carrying a knockdown or dominant-negative construct of these genes into the SVZ altered the distribution and dendrite formation of newborn neurons in the OB, suggesting that PCP signaling is involved in regulating the maturation of new neurons in the OB. © AlphaMed Press.

Motile cilia generate constant fluid flow over epithelial tissue, and thereby influence diverse physiological processes. Such functions of ciliated cells depend on the planar polarity of the cilia and on their basal bodies being oriented in the downstream direction of fluid flow. Recently, another type of basal body planar polarity, characterized by the anterior localization of the basal bodies in individual cells, was reported in the multiciliated ependymal cells that line the surface of brain ventricles. However, little is known about the cellular and molecular mechanisms by which this polarity is established. Here, we report in mice that basal bodies move in the apical cell membrane during differentiation to accumulate in the anterior region of ependymal cells. The planar cell polarity signaling pathway influences basal body orientation, but not their anterior migration, in the neonatal brain. Moreover, we show by pharmacological and genetic studies that non-muscle myosin II is a key regulator of this distribution of basal bodies. This study demonstrates that the orientation and distribution of basal bodies occur by distinct mechanisms.

We previously cloned and characterized the Drosophila gene, tincar (tinc), which encodes a novel protein with eight putative transmembrane domains. Here, we have studied the expression pattern and functions of tinc during developmental processes. Tinc mRNA is expressed in the central and peripheral nervous systems, and midgut during embryogenesis. In the third-instar larval eye disc, tinc mRNA is strongly expressed in all the differentiating ommatidial cells within and in the vicinity of the morphogenetic furrow. Loss-of-function analysis using the RNA-interference method revealed severe defects of eye morphogenesis during the late developmental stages. Our results suggested that tinc may have an indispensable role in the normal differentiation of ommatidial cells. © Springer-Verlag 2005.

We cloned and characterized the Drosophila gene, tincar (tinc), which encodes a novel protein with eight putative transmembrane domains. The tinc mRNA was expressed specifically in four of the six pairs of cardioblasts in each segment, in a pattern identical to that of tinman (tin), a homeobox gene required for the specification of the dorsal vessel. In the non-Tin-expressing pairs of cardioblasts, tinc transcription seemed to be repressed by Seven-up. © 2003 Elsevier Science Ireland Ltd. All rights reserved.

We have examined the roles played by the Drosophila neural RNA-binding protein Musashi (MSI) in eye development. MSI expression was observed in the nuclei of all photoreceptor cells (R1-R8). Although a msi loss-of-function mutation resulted in only weak abnormalities in photoreceptor differentiation, we found that the msi eye phenotype was significantly enhanced in a seven in absentia (sina) background. sina is known to be involved in the degradation of the Tramtrack (TTK) protein, leading to the specification of the R7 fate. We demonstrated that MSI also functions to regulate TTK expression. The sina msi mutants showed significantly high ectopic expression of TTK69 and failure in the determination of the R1, R6, and R7 fates. Other photoreceptor cells also failed to differentiate with abnormalities occurring late in the differentiation process. These results suggest that MSI and SINA function redundantly to downregulate TTK in developing photoreceptor cells. Copyright (C) 1999 Elsevier Science Ireland Ltd.

The Ral GTPase is activated by RalGDS, which is one of the effector proteins for Ras. Previous studies have suggested that Ral might function to regulate the cytoskeleton; however, its in vivo function is unknown. We have identified a Drosophila homologue of Ral that is widely expressed during embryogenesis and imaginal disc development. Two mutant Drosophila Ral (DRal) proteins, DRal(G20V) and DRal(S25N), were generated and analyzed for nucleotide binding and GTPase activity. The biochemical analyses demonstrated that DRal(G20V) and DRal(S25N) act as constitutively active and dominant negative mutants, respectively. Overexpression of the wild-type DRal did not cause any visible phenotype, whereas DRal(G20V) and DRal(S25N) mutants caused defects in the development of various tissues including the cuticular surface, which is covered by parallel arrays of polarized structures such as hairs and sensory bristles. The dominant negative DRal protein caused defects in the development of hairs and bristles. These phenotypes were genetically suppressed by loss of function mutations of hemipterous and basket, encoding Drosophila Jun NH2-terminal kinase kinase (JNKK) and Jun NH2-terminal kinase (JNK), respectively. Expression of the constitutively active DRal protein caused defects in the process of dorsal closure during embryogenesis and inhibited the phosphorylation of JNK in cultured S2 cells. These results indicate that DRal regulates developmental cell shape changes through the JNK pathway.

The small GTP-binding protein Ral is activated by RalGDS, one of the effector molecules for Ras. Active Ral binds to a GTPase activating protein for CDC42 and Rac. Although previous studies suggest a role for Ral in the regulation of CDC42 and Rac, which are involved in arranging the cytoskeleton, its in in vivo function is largely unknown. To examine the effect of overexpressing Ral on development, transgenic Drosophila were generated that overexpress wild-type or mutated Ral during eye development. While wild-type Ral caused no developmental defects, expression of a constitutively activated protein resulted in a rough eye phenotype. Activated Rat did not affect cell fate determination in the larval eye discs but caused severe disruption of the ommatidial organization later in pupal development. Phalloidin staining showed that activated Ral perturbed the cytoskeletal structure and cell shape changes during pupal development. This phenotype is similar to that caused by RhoA overexpression. In addition, the phenotype was synergistically enhanced by the coexpression of RhoA. These results suggest that Ral functions to control the cytoskeletal structure required for cell shape changes during Drosophila development.