The LIM Homeodomain Factor Lhx2 Is Required for Hypothalamic Tanycyte Specification and Differentiation

Abstract

Hypothalamic tanycytes, a radial glial-like ependymal cell population that expresses numerous genes selectively enriched in embryonic hypothalamic progenitors and adult neural stem cells, have recently been observed to serve as a source of adult-born neurons in the mammalian brain. The genetic mechanisms that regulate the specification and maintenance of tanycyte identity are unknown, but are critical for understanding how these cells can act as adult neural progenitor cells. We observe that LIM (Lin-11, Isl-1, Mec-3)-homeodomain gene Lhx2 is selectively expressed in hypothalamic progenitor cells and tanycytes. To test the function of Lhx2 in tanycyte development, we used an intersectional genetic strategy to conditionally delete Lhx2 in posteroventral hypothalamic neuroepithelium, both embryonically and postnatally. We observed that tanycyte development was severely disrupted when Lhx2 function was ablated during embryonic development. Lhx2-deficient tanycytes lost expression of tanycyte-specific genes, such as Rax, while also displaying ectopic expression of genes specific to cuboid ependymal cells, such as Rarres2. Ultrastructural analysis revealed that mutant tanycytes exhibited a hybrid identity, retaining radial morphology while becoming multiciliated. In contrast, postnatal loss of function of Lhx2 resulted only in loss of expression of tanycyte-specific genes. Using chromatin immunoprecipitation, we further showed that Lhx2 directly regulated expression of Rax, an essential homeodomain factor for tanycyte development. This study identifies Lhx2 as a key intrinsic regulator of tanycyte differentiation, sustaining Rax-dependent activation of tanycyte-specific genes while also inhibiting expression of ependymal cell-specific genes. These findings provide key insights into the transcriptional regulatory network specifying this still poorly characterized cell type.

Single-Cell RNA-Seq Reveals Hypothalamic Cell Diversity

“…GO analysis of the tanycyte-specific genes identified terms that include signal transduction, GPCR signaling pathway, and modulation of synaptic transmission (Figure S4C), consistent with the known function of tanycytes in transmission of metabolic signals to neurons in regulating homeostasis (Goodman and Hajihosseini, 2015). The tanycyte-enriched genes include Col23a1 , Slc16a2 , Lhx2 , and Ptn (Figures 4C and S4D), some of which have been linked to tanycyte development and function, such as Lhx2 (Salvatierra et al, 2014) and Slc16a2 (Mayerl et al, 2014). To test the potential of these differentially expressed genes to serve as tanycyte- and ependymocyte-specific markers, we examined their expression pattern in mouse brain with the ISH data from Allen Brain Atlas.…”

Superenhancer reprogramming drives a B-cell–epithelial transition and high-risk leukemia

“…Extralineage transcription factors directly repressed by IKAROS and occupying the de novo enhancer network included LMO2, a pioneer factor in iHSC that is associated with hematopoietic stem cell self-renewal, early lineage decisions, and B-cell precursor leukemias (Riddell et al 2014;Chambers and Rabbitts 2015); YAP1 and TEAD (1/2), the nuclear effectors of the Hippo pathway implicated in growth and self-renewal in a variety of nonlymphoid cell types; and LHX2, a pioneer factor in neuronal and skin epithelial stem cells (Rhee et al 2006;Salvatierra et al 2014;Adam et al 2015;Yu et al 2015). Notably, with the exception of LMO2, these extralineage transcription factors are direct targets of EBF1 in IKDN pre-B cells.…”

Essential function of the transcription factor Rax in the early patterning of the mammalian hypothalamus

“…The same authors also used a Six3-Cre transgene to inactivate Rax in the prospective hypothalamus starting at E9.0–E9.5 and observed a reduction in hypothalamic markers at birth, including Pomc 17 . More recently, Salvatierra et al 51 used a Foxd1-Cre transgenic line to eliminate Rax starting at E9.5. Defects in general hypothalamic development were not reported, but the differentiation of tanycytes lining the third ventricle was disturbed 51 .…”