The isl2a transcription factor regulates pituitary development in zebrafish

ISL LIM homeobox 2, also known as insulin gene enhancer protein ISL-2 ( ), is a transcription factor gene that participates in a wide range of developmental events. However, the role of in the hypothalamus-pituitary-thyroid axis is largely unknown. In the present study, we characterized the expression patterns of and revealed its regulative role during embryogenesis using zebrafish. We used the CRISPR/Cas9 system to successfully establish homozygous -orthologue ( and ) knockout zebrafish. Moreover, we utilized these knockout zebrafish to analyze the pituitary and thyroid phenotypes . For further molecular characterization, hybridization and immunofluorescence were performed. The mutant zebrafish presented with thyroid hypoplasia, reduced whole-body levels of thyroid hormones, increased early mortality, gender imbalance, and morphological retardation during maturity. Additionally, thyrotropes, a pituitary cell type, was notably decreased during development. Importantly, the transcriptional levels of pituitary-thyroid axis hormones-encoding genes, such as , , and , were significantly decreased in mutants. Finally, the thyroid dysplasia in mutant larvae may be attributed to a reduction in proliferation rather than changes in apoptosis. In summary, regulates the transcriptional levels of marker genes in hypothalamus-pituitary-thyroid axis, and knockout causing low thyroid hormone levels in zebrafish. Thus, identified by the present study, is a novel regulator for pituitary cell differentiation in zebrafish, resulting in thyroid gland hypoplasia and phenotypes of hypothyroidism.