Purkinje cell compartmentalization in the cerebellum of the spontaneous mutant mouse dreher

The cerebellar morphological phenotype of the spontaneous neurological mutant mouse dreher (Lmx1a ^dr-J ) results from cell fate changes in dorsal midline patterning involving the roof plate and rhombic lip. Positional cloning revealed that the gene Lmx1a, which encodes a LIM homeodomain protein, is mutated in dreher, and is expressed in the developing roof plate and rhombic lip. Loss of Lmx1a causes reduction of the roof plate, an important embryonic signaling center, and abnormal cell fate specification within the embryonic cerebellar rhombic lip. In adult animals, these defects result in variable, medial fusion of the cerebellar vermis and posterior cerebellar vermis hypoplasia. It is unknown whether deleting Lmx1a results in displacement or loss of specific lobules in the vermis. To distinguish between an ectopic and absent vermis, the expression patterns of two Purkinje cell-specific compartmentation antigens, zebrin II/aldolase C and the small heat shock protein HSP25 were analyzed in dreher cerebella. The data reveal that despite the reduction in volume and abnormal foliation of the cerebellum, the transverse zones and parasagittal stripe arrays characteristic of the normal vermis are present in dreher, but may be highly distorted. In dreher mutants with a severe phenotype, zebrin II stripes are fragmented and distributed non-symmetrically about the cerebellar midline. We conclude that although Purkinje cell agenesis or selective Purkinje cell death may contribute to the dreher phenotype, our data suggest that aberrant anlage patterning and granule cell development lead to Purkinje cell ectopia, which ultimately causes abnormal cerebellar architecture in dreher.     

Interspecific Variations of Inner Ear Structure in the Deep‐Sea Fish Family Melamphaidae

Inner ear structures are compared among three major genera of the deep‐sea fish family Melamphaidae (bigscales and ridgeheads). Substantial interspecific variation is found in the saccular otoliths, including the presence of a unique otolithic “spur” in the genera Melamphaes and Poromitra. The variation in the saccular otolith is correlated with an increase in the number of hair bundle orientation groups on the sensory epithelia from the genera Scopelogadus to Poromitra to Melamphaes. The diverse structural variations found in the saccule may reflect the evolutionary history of these species. The sensory hair cell bundles in this family have the most variable shapes yet encountered in fish ears. In the saccule, most of the hair bundles are 15–20 μm high, an exceptional height for fish otolithic end organs. These bundles have large numbers of stereovilli, including some that reach the length of the kinocilium. In the utricle, the striolar region separates into two unusually shaped areas that have not been described in any other vertebrates. The brains in all species have a relatively small olfactory bulb and optic tectum, as well as an enlarged posterior cerebellar region that is likely to be involved in inner ear and lateral line (octavolateral) functions. Data from melamphaids support the hypothesis that specialized anatomical structures are found in the ears of some (if not most) deep‐sea fishes, presumably enhancing their hearing sensitivity. Anat Rec, 296:1064–1082, 2013. © 2013 Wiley Periodicals, Inc.     

Islet1 selectively promotes peripheral axon outgrowth in Rohon‐Beard primary sensory neurons

We isolated a novel zebrafish mutant, lullaby (llb), and showed that the llb locus encodes the zebrafish orthologue of isl1. Rohon‐Beard (RB) primary sensory neurons are multipolar neurons that extend their central axons longitudinally within the spinal cord and also extend their peripheral axons under the skin. In llb embryos, the outgrowth of the peripheral axons of RB neurons was selectively impaired, which correlated with down‐regulation of the expression of dihydropyrimidinase‐like 3 (dpysl3, also known as collapsin response mediator protein 4, crmp4). Antisense morpholino oligonucleotide (AMO)‐mediated knockdown of dpysl3 inhibited the outgrowth of the peripheral axons of RB neurons, and semaphorin 3d (sema3d) AMO enhanced this effect. These data indicate that Dpysl3 is cooperating with Sema3d in the peripheral axon outgrowth, and Isl1 is required for the selective outgrowth of the peripheral axons of RB neurons by maintaining the expression of dpysl3. Developmental Dynamics 240:9–22, 2011. © 2010 Wiley‐Liss, Inc.     

Di‐(2‐ethylhexyl) phthalate and bisphenol A exposure impairs mouse primordial follicle assembly in vitro

Bisphenol‐A (BPA) and diethylhexyl phthalate (DEHP) are estrogenic compounds widely used in commercial plastic products. Previous studies have shown that exposure to such compounds have adverse effects on various aspects of mammalian reproduction including folliculogenesis. The objective of this study was to examine the effects of BPA and DEHP exposure on primordial follicle formation. We found that germ cell nest breakdown and primordial follicle assembly were significantly reduced when newborn mouse ovaries were exposed to 10 or 100 μM BPA and DEHP in vitro. Moreover, BPA and DEHP exposure increased the number of TUNEL positive oocytes and the mRNA level of the pro‐apoptotic gene Bax in oocytes. These effects were associated with decreased expression of oocyte specific genes such as LIM homeobox 8 (Lhx8), factor in the germline alpha (Figla), spermatogenesis and oogenesis helix‐loop‐helix (Sohlh2), and newborn ovary homeobox (Nobox). Interestingly, BPA and DEHP exposure also prevented DNA demethylation of CpG sites of the Lhx8 gene in oocytes, a process normally associated with folliculogenesis. Finally, folliculogenesis was severely impaired in BPA and DEHP exposed ovaries after transplantation into the kidney capsules of immunodeficient mice. In conclusion, BPA and DEHP exposures impair mouse primordial follicle assembly in vitro. Environ. Mol. Mutagen. 55:343–353, 2014. © 2014 Wiley Periodicals, Inc.     

Identification and expression patterns of members of the protease‐activated receptor (par) gene family during zebrafish development

Protease‐activated receptors (PARs) play critical roles in hemostasis in vertebrates including zebrafish. However, the zebrafish gene classification appears to be complex, and the expression patterns of par genes are not established. Based on analyses of genomic organization, phylogenetics, protein primary structure, and protein internalization, we report the identification of four zebrafish PARs: par1, par2a, par2b, and par3. This classification differs from one reported previously. We also show that these genes have distinct spatiotemporal expression profiles in embryos and larvae, with par1, par2a, and par2b expressed maternally and ubiquitously during gastrula stages and their expression patterns refined at later stages, and par3 expressed only in 3‐day‐old larvae. Notably, the expression patterns of zebrafish par1 and par2b resemble those of their mammalian counterparts, suggesting that receptor function is conserved among vertebrates. This conservation is supported by our findings that Par1 and Par2b are internalized following exposure to thrombin and trypsin, respectively. Developmental Dynamics, 2011. © 2010 Wiley‐Liss, Inc.     

Foxg1 is required for proper separation and formation of sensory cristae during inner ear development

The vestibular portion of the inner ear, the three semicircular canals and their sensory cristae, is responsible for detecting angular head movements. It was proposed that sensory cristae induce formation of their non‐sensory components, the semicircular canals. Here, we analyzed the inner ears of Foxg1^?/? mouse mutants, which display vestibular defects that are in conflict with the above model. In Foxg1^?/? ears, the lateral canal is present without the lateral ampulla, which houses the lateral crista. Our gene expression analyses indicate that at the time when canal specification is thought to occur, the prospective lateral crista is present, which could have induced lateral canal formation prior to its demise. Our genetic fate‐mapping analyses indicate an improper separation between anterior and lateral cristae in Foxg1^?/? mutants. Our data further suggest that a function of Foxg1 in the inner ear is to restrict sensory fate. Developmental Dynamics 238:2725–2734, 2009. © 2009 Wiley‐Liss, Inc.