Krüpple-like factors 7 and 6a mRNA expression in adult zebrafish central nervous system

Krüpple-like factors (KLFs) are transcription factors with zinc finger DNA binding domains known to play important roles in brain development and central nervous system (CNS) regeneration. There is little information on KLFs expression in adult vertebrate CNS. In this study, we used in situ hybridization to examine Klf7 mRNA (klf7) and Klf6a mRNA (klf6a) expression in adult zebrafish CNS. Both klfs exhibit wide and similar expression in the zebrafish CNS. Brain areas containing strongly labeled cells include the ventricular regions of the dorsomedial telencephalon, the ventromedial telencephalon, periventricular regions of the thalamus and hypothalamus, torus longitudinalis, stratum periventriculare of the optic tectum, granular regions of the cerebellar body and valvula, and superficial layers of the facial and vagal lobes. In the spinal cord, klf7- and klf6a-expressing cells are found in both the dorsal and ventral horns. Numerous sensory structures (e.g. auditory, lateral line, olfactory and visual) and several motor nuclei (e.g. oculomotor, trigeminal, and vagal motor nuclei) contain klf7- and/or klf6a-expressing cells. Our results may provide useful information for determining these Klfs in maintenance and/or function in adult CNS.

Protocadherin-17 function in Zebrafish retinal development

Cadherin cell adhesion molecules play crucial roles in vertebrate development including the development of the retina. Most studies have focused on examining functions of classic cadherins (e.g. N-cadherin) in retinal development. There is little information on the function of protocadherins in the development of the vertebrate visual system. We previously showed that protocadherin-17 mRNA was expressed in developing zebrafish retina during critical stages of the retinal development. To gain insight into protocadherin-17 function in the formation of the retina, we analyzed eye development and differentiation of retinal cells in zebrafish embryos injected with protocadherin-17 specific antisense morpholino oligonucleotides (MOs). Protocadherin-17 knockdown embryos (pcdh17 morphants) had significantly reduced eyes due mainly to decreased cell proliferation. Differentiation of several retinal cell types (e.g. retinal ganglion cells) was also disrupted in the pcdh17 morphants. Phenotypic rescue was achieved by injection of protocadherin-17 mRNA. Injection of a vivo-protocadherin-17 MO into one eye of embryonic zebrafish resulted in similar eye defects. Our results suggest that protocadherin-17 plays an important role in the normal formation of the zebrafish retina.

Effects of calorie restriction on the zebrafish liver proteome

A proteomic approach was taken to study how fish respond to changes in calorie availability, with the longer-term goal of understanding the evolution of lipid metabolism in vertebrates. Zebrafish (Danio rerio) were fed either high (3 rations/day) or low (1 ration/7 days) calorie diets for 5 weeks and liver proteins extracted for proteomic analyses. Proteins were separated on two-dimensional electrophoresis gels and homologous spots compared between treatments to determine which proteins were up-regulated with high-calorie diet. Fifty-five spots were excised from the gel and analyzed via LC-ESI MS/MS, which resulted in the identification of 69 unique proteins (via multiple peptides). Twenty-nine of these proteins were differentially expressed between treatments. Differentially expressed proteins were mapped to Gene Ontology (GO) terms, and these terms compared to the entire zebrafish GO annotation set by Fisher's exact test. The most significant GO terms associated with high-calorie diet are related to a decrease in oxygen-binding activity in the high-calorie treatment. This response is consistent with a well-characterized response in obese humans, indicating there may be a link between lipid storage and hypoxia sensitivity in vertebrates.

Cadherin-6 function in zebrafish retinal development

Cadherin cell-adhesion molecules play crucial roles in vertebrate development including the development of the visual system. Most studies have focused on examining functions of classical type I cadherins (e.g., cadherin-2) in visual system development. There is little information on the function of classical type II cadherins (e.g., cadherin-6) in the development of the vertebrate visual system. To gain insight into cadherin-6 role in the formation of the retina, we analyzed differentiation of retinal ganglion cells (RGCs), amacrine cells, and photoreceptors in zebrafish embryos injected with cadherin-6 specific antisense morpholino oligonucleotides. Differentiation of the retinal neurons in cadherin-6 knockdown embryos (cdh6 morphants) was analyzed using multiple markers. We found that expression of transcription factors important for retinal development was greatly reduced, and expression of Notch-Delta genes and proneural gene ath5 was altered in the cdh6 morphant retina. The retinal lamination was present in the morphants, although the morphant eyes were significantly smaller than control embryos due mainly to decreased cell proliferation. Differentiation of the RGCs, amacrine cells, and photoreceptors was severely disrupted in the cdh6 morphants due to a significant delay in neural differentiation. Our results suggest that cadherin-6 plays an important role in the normal formation of the zebrafish retina. (c) 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008.