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Graphical abstract, Highlights • The mechanisms by which ISL1 and LHX3 specify neuronal cell identity are unknown. • EMSA/SPR data show ISL1 and LHX3 have markedly different DNA-binding behaviours. • SAXS shows ISL1/LHX3:DNA complexes are flexible in nature. • ISL1 binds DNA poorly but appears to modulate the DNA-binding specificity of LHX3., The roles of ISL1 and LHX3 in the development of spinal motor neurons have been well established. Whereas LHX3 triggers differentiation into interneurons, the additional expression of ISL1 in developing neuronal cells is sufficient to redirect their developmental trajectory towards spinal motor neurons. However, the underlying mechanism of this action by these transcription factors is less well understood. Here, we used electrophoretic mobility shift assays (EMSAs) and surface plasmon resonance (SPR) to probe the different DNA-binding behaviours of these two proteins, both alone and in complexes mimicking those found in developing neurons, and found that ISL1 shows markedly different binding properties to LHX3. We used small angle X-ray scattering (SAXS) to structurally characterise DNA-bound species containing ISL1 and LHX3. Taken together, these results have allowed us to develop a model of how these two DNA-binding modules coordinate to regulate gene expression and direct development of spinal motor neurons.

LIM domains are zinc fingers that coordinate two zinc ions and that mediate protein–protein interactions. They are found in arrays of 1–5 LIM domains in a wide variety of proteins inside the cell, and may be accompanied by one or more other types of protein–protein interaction domains and catalytic domains. LIM proteins tend to function by regulating transcriptional events through recruitment of transcription factors (or in the case of LIM-homeodomain proteins by binding directly to DNA through the homeodomain) and/or are involved in remodeling of the cytoskeleton. Many LIM domain proteins have both of these activities and appear to shuttle in and out of the nucleus in response to stimuli, mediating communication between the major compartments of the cell.

The pituitary gland is an organ with a low rate of cell turnover. While differentiated hormone-producing cells can re-enter the cell cycle, most of these cells are not dividing. In the last 7 years, evidence has rapidly accumulated that defines the characteristics of pituitary stem cells or progenitor cells present in rodent embryos, early postnatal pups, and adult pituitaries. In some cases the findings have already been reproduced in humans. Here, we will discuss different approaches used from diverse groups in order to study the pituitary stem cell population. These discoveries are providing a mechanistic understanding of normal organ development and disease pathophysiology. In the future, we expect that understanding the roles of pituitary stem cells will help find alternative therapies for pituitary hormone deficiencies and tumors. Many questions remain unsolved, and some enormous challenges will need to be overcome in order to translate this exciting basic knowledge into therapeutic value. It will be important to further define the steps in the regulation of multi-potent progenitors and understand the mechanisms for guidance to specific cell fates. Some of these aspects will be discussed in this review.

This LIM domain was first described in the LIM homeodomain transcription factor Mec-3 in Caenorhabditis elegans , and named following the identification of two further proteins which share the LIM domain, that is, L (in-11), I (sl1), and M (ec-3). Unlike LIM homeodomain proteins, the LIM domain-only (LMO) proteins lack an obvious DNA-binding element and instead associate with DNA-binding proteins. The LMO family comprises four highly conserved members. Each member of the LIM-only family is involved in transcription regulation controlling normal differentiation processes and in cancer by abnormal expression, in three cases (LMO1, 2, and 3) via chromosomal translocations.

Publisher Summary The nervous system regulates the function of both endocrine and exocrine glands, not only through neurosecretion but also through the autonomic nervous system via cholinergic and noradrenergic pathways. In mice, anterior pituitary development takes place in four distinct stages: pituitary placode formation, the development of a rudimentary Rathke's pouch, the formation of a definitive pouch, and finally the terminal differentiation of various cell types in a temporally and spatially regulated manner. Several signaling molecules and transcription factors that are expressed in the neural ectoderm and not in Rathke's pouch—FGF8, BMP4, and NKX2.1—are thought to play a significant part in normal anterior pituitary development. These signaling molecules can then activate or repress key regulatory genes encoding transcription factors, such as HESX1, LHX3, and LHX4, within the developing Rathke's pouch that are essential for subsequent development of the pituitary. Disorders involving growth hormone (GH) and one or more additional pituitary hormones are caused by mutations in the homeodomain transcription factors that direct embryological development of the anterior pituitary gland.