AUTHOR=Manoli Martha , Driever Wolfgang 

TITLE=nkx2.1 and nkx2.4 genes function partially redundant during development of the zebrafish hypothalamus, preoptic region, and pallidum

JOURNAL=Frontiers in Neuroanatomy

VOLUME=8

YEAR=2014

URL=https://www.frontiersin.org/journals/neuroanatomy/articles/10.3389/fnana.2014.00145

DOI=10.3389/fnana.2014.00145

ISSN=1662-5129

ABSTRACT=<p>During ventral forebrain development, orthologs of the homeodomain transcription factor Nkx2.1 control patterning of hypothalamus, preoptic region, and ventral telencephalon. However, the relative contributions of Nkx2.1 and Nkx2.4 to prosencephalon development are poorly understood. Therefore, we analyzed functions of the previously uncharacterized <italic>nkx2.4</italic>-like <italic>zgc:171531</italic> as well as of the presumed <italic>nkx2.1</italic> orthologs <italic>nkx2.1a</italic> and <italic>nkx2.1b</italic> in zebrafish forebrain development. Our results show that <italic>zgc:171531</italic> and <italic>nkx2.1a</italic> display overlapping expression patterns and a high sequence similarity. Together with a high degree of synteny conservation, these findings indicate that both these genes indeed are paralogs of <italic>nkx2.4</italic>. As a result, we name <italic>zgc:171531</italic> now <italic>nkx2.4a</italic>, and changed the name of <italic>nkx2.1a</italic> to <italic>nkx2.4b</italic>, and of <italic>nkx2.1b</italic> to <italic>nkx2.1</italic>. In <italic>nkx2.1, nkx2.4a</italic>, and <italic>nkx2.4b</italic> triple morpholino knockdown (nkx2TKD) embryos we observed a loss of the rostral part of prosomere 3 and its derivative posterior tubercular and hypothalamic structures. Furthermore, there was a loss of rostral and intermediate hypothalamus, while a residual preoptic region still develops. The reduction of the ventral diencephalon was accompanied by a ventral expansion of the dorsally expressed <italic>pax6</italic>, revealing a dorsalization of the basal hypothalamus. Within the telencephalon we observed a loss of pallidal markers, while striatum and pallium are forming. At the neuronal level, nkx2TKD morphants lacked several neurosecretory neuron types, including avp, <italic>crh</italic>, and <italic>pomc</italic> expressing cells in the hypothalamus, but still form <italic>oxt</italic> neurons in the preoptic region. Our data reveals that, while <italic>nkx2.1, nkx2.4a</italic>, and <italic>nkx2.4b</italic> genes act partially redundant in hypothalamic development, <italic>nkx2.1</italic> is specifically involved in the development of rostral ventral forebrain including the pallidum and preoptic regions, whereas <italic>nkx2.4a</italic> and <italic>nkx2.4b</italic> control the intermediate and caudal hypothalamus.</p>