{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T15:52:06Z","timestamp":1753890726098,"version":"3.41.2"},"reference-count":43,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2023,2,7]],"date-time":"2023-02-07T00:00:00Z","timestamp":1675728000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Endocrinol."],"abstract":"<jats:sec><jats:title>Background<\/jats:title><jats:p>ISL LIM homeobox 2, also known as insulin gene enhancer protein ISL-2 (<jats:italic>ISL2<\/jats:italic>), is a transcription factor gene that participates in a wide range of developmental events. However, the role of <jats:italic>ISL2<\/jats:italic> in the hypothalamus-pituitary-thyroid axis is largely unknown. In the present study, we characterized the expression patterns of <jats:italic>ISL2<\/jats:italic> and revealed its regulative role during embryogenesis using zebrafish.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>We used the CRISPR\/Cas9 system to successfully establish homozygous <jats:italic>ISL2<\/jats:italic>-orthologue (<jats:italic>isl2a<\/jats:italic> and <jats:italic>isl2b<\/jats:italic>) knockout zebrafish. Moreover, we utilized these knockout zebrafish to analyze the pituitary and thyroid phenotypes <jats:italic>in vivo<\/jats:italic>. For further molecular characterization, <jats:italic>in situ<\/jats:italic> hybridization and immunofluorescence were performed.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>The <jats:italic>isl2a<\/jats:italic> 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 <jats:italic>tshba<\/jats:italic>, <jats:italic>cga<\/jats:italic>, and <jats:italic>tg<\/jats:italic>, were significantly decreased in <jats:italic>isl2a<\/jats:italic> mutants. Finally, the thyroid dysplasia in <jats:italic>isl2a<\/jats:italic> mutant larvae may be attributed to a reduction in proliferation rather than changes in apoptosis.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>In summary, <jats:italic>isl2a<\/jats:italic> regulates the transcriptional levels of marker genes in hypothalamus-pituitary-thyroid axis, and <jats:italic>isl2a<\/jats:italic> knockout causing low thyroid hormone levels in zebrafish. Thus, <jats:italic>isl2a<\/jats:italic> identified by the present study, is a novel regulator for pituitary cell differentiation in zebrafish, resulting in thyroid gland hypoplasia and phenotypes of hypothyroidism.<\/jats:p><\/jats:sec>","DOI":"10.3389\/fendo.2023.920548","type":"journal-article","created":{"date-parts":[[2023,2,7]],"date-time":"2023-02-07T06:18:56Z","timestamp":1675750736000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":4,"title":["The isl2a transcription factor regulates pituitary development in 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