RESUMEN
The zebrafish is an ideal model for elucidating the cellular and molecular mechanisms that underlie development of the peripheral nervous system. A transgenic line that selectively labels all the sensory circuits would be a valuable tool for such investigations. In this study, we describe such a line: the enhancer trap zebrafish line Tg(SKIV2L2:gfp)(j1775) which expresses green fluorescent protein (gfp) in the peripheral sensory ganglia. We show that this transgene marks all peripheral ganglia and sensory nerves, beginning at the time when the neurons are first extending their processes, but does not label the efferent nerves. The trapped reporter is inserted just upstream of a previously poorly described gene: lhfpl4 on LG6. The expression pattern of this gene by in situ hybridization reveals a different, but overlapping, pattern of expression compared to that of the transgene. This pattern also does not mimic that of the gene (skiv2l2), which provided the promoter element in the construct. These findings indicate that reporter expression is not dictated by an endogenous enhancer element, but instead arises through an unknown mechanism. Regardless, this reporter line should prove to be a valuable tool in the investigation of peripheral nervous system formation in the zebrafish.
Asunto(s)
Elementos de Facilitación Genéticos , Neurogénesis/genética , Sistema Nervioso Periférico/embriología , ARN Helicasas/genética , Células Receptoras Sensoriales/metabolismo , Pez Cebra/embriología , Animales , Animales Modificados Genéticamente , Ganglios/citología , Ganglios/embriología , Ganglios/metabolismo , Genes Reporteros , Proteínas Fluorescentes Verdes/genética , Sistema Nervioso Periférico/citología , Sistema Nervioso Periférico/metabolismo , ARN Helicasas/metabolismo , Células Receptoras Sensoriales/citología , Pez Cebra/genética , Pez Cebra/metabolismoRESUMEN
The two major zona pellucida proteins of the zebrafish chorion, Zp2 and Zp3, are encoded by multicopy genes arranged in tandem arrays on chromosomes 20 and 2, respectively. Expression of these zp genes in zebrafish is oocyte specific, and we report herein that their activity in developing oocytes is dependent on conserved CCAAT box sites in their promoters. A 140-bp region immediately upstream of the transcription initiation site (position 1) of the zp2 genes has been homogenized by gene conversion and contains a single CCAAT box located at -138 that is necessary for promoter activity in oocytes residing in stage I and early stage II ovarian follicles as determined by microinjection of promoter constructs linked to a luciferase reporter gene. The zp3 gene promoters have two inverted CCAAT boxes located in a region of shared homology within the initial 175 nucleotides. Serial deletion of these sites resulted in incremental decreases in luciferase activity. Double-stranded oligonucleotides containing CCAAT box sequences from both genes formed CCAAT box-specific complexes with ovarian follicle extracts in an electrophoretic mobility shift assay. We also found that the expression of the separate zebrafish zp3b gene, more closely related to two oocyte-expressed medaka zpc genes than to the tandemly arrayed zebrafish zp3 genes, is not CCAAT box dependent. The significance that these results have in furthering our understanding of the regulation of zebrafish zp gene evolution and regulation is discussed.