The transcription factor D‐Pax2 regulates crystallin production during eye development in Drosophila melanogaster

The generation of a functioning Drosophila eye requires the coordinated differentiation of multiple cell types and the morphogenesis of eye‐specific structures. Here we show that D‐Pax2 plays a significant role in lens development through regulation of the Crystallin gene and because Crystallin is also expressed in D‐Pax2⁺ cells in the external sensory organs. Loss of D‐Pax2 function leads to loss of Crystallin expression in both eyes and bristles. A 2.3 kilobase (kb) upstream region of the Crystallin gene can drive GFP expression in the eye and is dependent on D‐Pax2. In addition, D‐Pax2 binds to an evolutionarily conserved site in this region that, by itself, is sufficient to drive GFP expression in the eye. However, mutation of this site does not greatly affect the regulatory region's function. The data indicate that D‐Pax2 acts to promote lens development by controlling the production of the major protein component of the lens. Whether this control is direct or indirect remains unresolved. Developmental Dynamics 238:2530–2539, 2009. © 2009 Wiley‐Liss, Inc.     

The role of Zic genes in inner ear development in the mouse: Exploring mutant mouse phenotypes

Background: Murine Zic genes (Zic1–5) are expressed in the dorsal hindbrain and in periotic mesenchyme (POM) adjacent to the developing inner ear. Zic genes are involved in developmental signaling pathways in many organ systems, including the ear, although their exact roles haven't been fully elucidated. This report examines the role of Zic1, Zic2, and Zic4 during inner ear development in mouse mutants in which these Zic genes are affected. Results: Zic1/Zic4 double mutants don't exhibit any apparent defects in inner ear morphology. By contrast, inner ears from Zic2^kd/kd and Zic2^Ku/Ku mutants have severe but variable morphological defects in endolymphatic duct/sac and semicircular canal formation and in cochlear extension in the inner ear. Analysis of otocyst patterning in the Zic2^Ku/Ku mutants by in situ hybridization showed changes in the expression patterns of Gbx2 and Pax2. Conclusions: The experiments provide the first genetic evidence that the Zic genes are required for morphogenesis of the inner ear. Zic2 loss‐of‐function doesn't prevent initial otocyst patterning but leads to molecular abnormalities concomitant with morphogenesis of the endolymphatic duct. Functional hearing deficits often accompany inner ear dysmorphologies, making Zic2 a novel candidate gene for ongoing efforts to identify the genetic basis of human hearing loss. Developmental Dynamics 243:1487–1498, 2014. © 2014 Wiley Periodicals, Inc.     

Ethylnitrosourea‐induced thymus‐defective mutants identify roles of KIAA1440, TRRAP,and SKIV2L2 in teleost organ development

The thymus is an organ where T lymphocytes develop. Thymus development requires interactions of cells derived from three germ layers. However, the molecular mechanisms that control thymus development are not fully understood. To identify the genes that regulate thymus development, we previously carried out a large‐scale screening for ethylnitrosourea‐induced mutagenesis using medaka, Oryzias latipes, and established a panel of recessive thymus‐lacking mutants. Here we report the identification of three genes responsible for these mutations. We found that the mutations in KIAA1440, TRRAP, and SKIV2L2 caused the defects in distinct steps of thymus development. We also found that these genes were widely expressed in many organs and that the mutations in these genes caused defects in the development of various other organs. These results enabled us to identify previously unknown roles of widely expressed genes in medaka organ development. The possible reasons why thymus‐defective teleost mutants could be used to identify widely expressed genes and future strategies to increase the likelihood of identifying genes that specifically regulate thymus development are discussed.     

Mouse ZAR1‐like (XM_359149) colocalizes with mRNA processing components and its dominant‐negative mutant caused two‐cell‐stage embryonic arrest

Maternal effect genes and encoding proteins are necessary for nuclear reprogramming and zygotic genome activation. However, the mechanisms that mediate these functions are largely unknown. Here we identified XM_359149, a Zar1‐like gene that is predominantly expressed in oocytes and zygotes, which we designated Zar1‐like (Zar1l). ZAR1L‐EGFP formed multiple cytoplasmic foci in late two‐cell‐stage embryos. Expression of the ZAR1L C‐terminus induced two‐cell‐stage embryonic arrest, accompanied with abnormal methylation of histone H3K4me2/3 and H3K9me2/3, and marked down‐regulation of a group of chromatin modification factors including Dppa2, Dppa4, and Piwil2. When ectopically expressed in somatic cells, ZAR1L colocalized with P‐body components including EIF2C1(AGO1), EIF2C2(AGO2), DDX6 and LSM14A, and germline‐specific chromatoid body components including PIWIL1, PIWIL2, and LIN28. ZAR1L colocalized with ZAR1 and interacted with human LIN28. Our data suggest that ZAR1L and ZAR1 may comprise a novel family of processing‐body/chromatoid‐body components that potentially function as RNA regulators in early embryos. Developmental Dynamics 239:407–424, 2010. © 2009 Wiley‐Liss, Inc.     

Diversification of the expression patterns and developmental functions of the dishevelled gene family during chordate evolution

Dishevelled (Dvl) proteins are key transducers of Wnt signaling encoded by members of a multi‐gene family in vertebrates. We report here the divergent, tissue‐specific expression patterns for all three Dvl genes in Xenopus embryos, which contrast dramatically with their expression patterns in mice. Moreover, we find that the expression patterns of Dvl genes in the chick diverge significantly from those of Xenopus. In addition, in hemichordates, an outgroup to chordates, we find that the one Dvl gene is dynamically expressed in a tissue‐specific manner. Using knockdowns, we find that Dvl1 and Dvl2 are required for early neural crest specification and for somite segmentation in Xenopus. Most strikingly, we report a novel role for Dvl3 in the maintenance of gene expression in muscle and in the development of the Xenopus sclerotome. These data demonstrate that the expression patterns and developmental functions of specific Dvl genes have diverged significantly during chordate evolution. Developmental Dynamics 238:2044–2057, 2009. © 2009 Wiley‐Liss, Inc.     

Cis‐regulatory mechanisms of gene expression in an olfactory neuron type in Caenorhabditis elegans

The generation of cellular diversity is dependent on the precise spatiotemporal regulation of gene expression by both cis‐ and trans‐acting mechanisms. The developmental principles regulating expression of specific gene subsets in individual cell types are not fully understood. Here we define the cis‐regulatory mechanisms driving expression of cell‐selective and broadly expressed genes in vivo in the AWB olfactory neuron subtype in C. elegans. We identify an element that is necessary to drive expression of neuron‐selective chemoreceptor genes in the AWB neurons, and show that this element functions in a context‐dependent manner. We find that the expression of broadly expressed sensory neuronal genes in the AWB neurons is regulated by diverse cis‐ and trans‐regulatory mechanisms that act partly in parallel to the pathways governing expression of AWB‐selective genes. We further demonstrate that cis‐acting mechanisms driving gene expression in the AWB neurons appear to have diverged in related nematode species. Our results provide insights into the cis‐regulatory logic driving cell‐specific gene expression, and suggest that variations in this logic contribute to the generation of functional diversity. Developmental Dynamics 238:3080–3092, 2009. © 2009 Wiley‐Liss, Inc.     

Sequence and expression of the zebrafish alpha‐actinin gene family reveals conservation and diversification among vertebrates

alpha‐actinins are actin microfilament crosslinking proteins. Vertebrate actinins fall into two classes: the broadly‐expressed actinins 1 and 4 (actn1 and actn4) and muscle‐specific actinins, actn2 and actn3. Members of this family have numerous roles, including regulation of cell adhesion, cell differentiation, directed cell motility, intracellular signaling, and stabilization of f‐actin at the sarcomeric Z‐line in muscle. Here we identify five zebrafish actinin genes including two paralogs of ACTN3. We describe the temporal and spatial expression patterns of these genes through embryonic development. All zebrafish actinin genes have unique expression profiles, indicating specialization of each gene. In particular, the muscle actinins display preferential expression in different domains of axial, pharyngeal, and cranial musculature. There is no identified avian actn3 and approximately 16% of humans are null for ACTN3. Duplication of actn3 in the zebrafish indicates that variation in actn3 expression may promote physiological diversity in muscle function among vertebrates. Developmental Dynamics 238:2936–2947, 2009. © 2009 Wiley‐Liss, Inc.     

Neural stem cell self‐renewal requires the Mrj co‐chaperone

The Mrj co‐chaperone is expressed throughout the mouse conceptus, yet its requirement for placental development has prohibited a full understanding of its embryonic function. Here, we show that Mrj^?/? embryos exhibit neural tube defects independent of the placenta phenotype, including exencephaly and thin‐walled neural tubes. Molecular analyses revealed fewer proliferating cells and a down‐regulation of early neural progenitor (Pax6, Olig2, Hes5) and neuronal (Nscl2, SCG10) cell markers in Mrj^?/? neuroepithelial cells. Furthermore, Mrj^?/? neurospheres are significantly smaller and form fewer secondary neurospheres indicating that Mrj is necessary for self‐renewal of neural stem cells. However, the molecular function of Mrj in this context remains elusive because Mrj does not colocalize with Bmi‐1, a self‐renewal protein. Furthermore, unlike in Mrj^?/? placentas, intermediate filament‐containing aggregates do not accumulate in Mrj^?/? neuroepithelium, ruling out nestin as a substrate for Mrj. Regardless, Mrj plays an important role in neural stem cell self‐renewal. Developmental Dynamics 238:2564–2574, 2009. © 2009 Wiley‐Liss, Inc.     

Whole‐exome sequencing suggests multiallelic inheritance for childhood‐onset Ménière's disease

The genetic background of Ménière's disease (MD) was studied in one patient with childhood‐onset MD and his grandfather affected with middle age–onset MD. Whole‐exome sequencing was performed and the data were compared to 76 exomes from unrelated subjects without MD. Thirteen rare inner ear expressed variants with pathogenic estimations were observed in the case of childhood‐onset MD. These variants were in genes involved in the formation of cell membranes or the cytoskeleton and in genes participating in cell death or gene‐regulation pathways. His grandfather shared two of the variants: p.Y273N in HMX2 and p.L229F in TMEM55B. HMX2 p.Y273N was considered the more likely candidate for MD, as the gene is known to affect both hearing and vestibular function. The variant in the HMX2 gene may affect inner ear development and structural integrity and thus might predispose to the onset of MD. As there was a significant difference in onset between the patients, an accumulation of defects in several pathways is probably responsible for the exceptionally early onset of the disease, and the genetic etiology of childhood‐onset MD is most likely multifactorial. This is the first molecular genetic study of childhood‐onset MD.