The zebrafish eya1 gene and its expression pattern during embryogenesis

Abstract

The eyes absent-like genes encode a group of putative transcriptional coactivators with a sole representative in Drosophila and several members in mammals. Haploinsufficiency of the human EYA1 gene results in branchio-oto-renal syndrome characterized by developmental anomalies of the branchial arches, the three compartments of the ear and the kidney. As a first step towards a functional analysis of this gene in lower vertebrates, we isolated its zebrafish homologue, eya1, and studied its expression pattern during embryogenesis. The eya1 cDNA predicts a protein with 84.7% identity with the human homologue. Transcripts are first detected at the tailbud stage in presumptive cranial placodal precursor cells. Thereafter, eya1 expression continues in anterior pituitary, olfactory, otic, and lateral line placodes. Aside from these placodal sites of expression, eya1 transcripts were observed in the somites, developing pectoral fins, and branchial arches. No expression was found in pronephros or Wolffian duct of the zebrafish renal system. Within the developing ear, eya1 expression becomes confined to the ventral part of the otic vesicle from where the acoustic ganglion precursor cells arise and the sensory patches differentiate. In the lateral line, eya1 is expressed in the placodes, ganglia, migrating primordia, and receptive organs at all developmental stages, including both the differentiating hair and supporting cells. Taken together, these results indicate a remarkable similarity in both the structure and expression pattern of eya1 between higher and lower vertebrates, suggesting that the function of this gene has been conserved throughout vertebrate evolution.

Origin and Early Development of the Posterior Lateral Line System of Zebrafish

“…The existence of a "pan-placodal field" from which all cranial placodes would originate has been comprehensively reviewed (Baker and Bronner-Fraser, 2001), and its relevance for amphibian PLL development has been authoritatively assessed by Schlosser (2002). Placodal markers such as dlx, eya1, or six4 genes (Akimenko et al, 1994;Sahly et al, 1999;Kobayashi et al, 2000) are expressed in a horseshoe-shaped region that would correspond to this panplacodal field. Their expression starts around 10 hpf, suggesting that retinoic acid signaling is required for PLL development before the onset of pan-placodal gene expression.…”

“…This region is supposed to define a preplacodal domain that is later subdivided into distinct placodes (for review, see Baker and Bronner-Fraser, 2001;Schlosser, 2006). The expression of both eya1 and six1 is later confined to some placodes, including lateral line placodes (Sahly et al, 1999;Bessarab et al, 2004;Schlosser, 2006).…”

Initial specification of the epibranchial placode in zebrafish embryos depends on the fibroblast growth factor signal

“…Several genes have been reported to show expression in the cranial sensory placode during segmentation, such as dlx3 (Akimenko et al, 1994), eya1 (Sahly et al, 1999), and six4.1 (Kobayashi et al, 2000). However, their expression domains are larger than that of sox3 at the one-somite stage, and they likely also represent the presumptive common cranial sensory placode that generates the nasal, lens, and otic placodes (Streit, 2004).…”

Development of the zebrafish inner ear

“…Although eya1 is a preplacodal marker (Sahly et al, 1999), the earliest defects seen in the ear are at otic vesicle stages. These defects include an increase in cell death, and abnormal neurogenesis (Kozlowski et al, manuscript in preparation; see the Neurogenesis and Formation of the Statoacoustic Ganglion section).…”

“…The expression pattern of eya1 mRNA has been described in detail in the zebrafish (Sahly et al, 1999). At noi/noi embryos; n ϭ 18; range, 9 -15; (d) noi/noi embryos injected with pax2.2-MO; n ϭ 14; range, 2-4.…”