ENGRAILED-1 transcription factor has a paracrine neurotrophic activity on adult spinal α-motoneurons.

Several homeoprotein transcription factors transfer between cells and regulate gene expression, protein translation, and chromatin organization in recipient cells. ENGRAILED-1 is one such homeoprotein expressed in spinal V1 interneurons that synapse on α-motoneurons. Neutralizing extracellular ENGRAILED-1 by expressing a secreted single-chain antibody blocks its capture by spinal motoneurons resulting in α-motoneuron loss and limb weakness.

Photoreceptor cKO of OTX2 Enhances OTX2 Intercellular Transfer in the Retina and Causes Photophobia.

In the mature mouse retina, is expressed in both retinal pigmented epithelium (RPE) and photoreceptor (PR) cells, and knock-out (KO) in the RPE alone results in PR degeneration. To study the cell-autonomous function of OTX2 in PRs, we performed PR-specific KO (cKO) in adults. As expected, the protein disappears completely from PR nuclei but is still observed in PR inner and outer segments while its level concomitantly decreases in the RPE, suggesting a transfer of OTX2 from RPE to PRs in response to ablation in PRs.

OTX2 stimulates adult retinal ganglion cell regeneration.

Retinal ganglion cell (RGC) axons provide the only link between the light sensitive and photon transducing neural retina and visual centers of the brain. RGC axon degeneration occurs in a number of blinding diseases and the ability to stimulate axon regeneration from surviving ganglion cells could provide the anatomic substrate for restoration of vision. OTX2 is a homeoprotein transcription factor expressed in the retina and previous studies showed that, in response to stress, exogenous OTX2 increases the in vitro and in vivo survival of RGCs.

OTX2 Non-Cell Autonomous Activity Regulates Inner Retinal Function.

OTX2 is a homeoprotein transcription factor expressed in photoreceptors and bipolar cells in the retina. OTX2, like many other homeoproteins, transfers between cells and exerts non-cell autonomous effects such as promoting the survival of retinal ganglion cells that do not express the protein. Here we used a genetic approach to target extracellular OTX2 in the retina by conditional expression of a secreted single-chain anti-OTX2 antibody.

Homeoprotein Neuroprotection of Embryonic Neuronal Cells.

Most homeoprotein transcription factors have a highly conserved internalization domain used in intercellular transfer. Internalization of homeoproteins ENGRAILED1 or ENGRAILED2 promotes the survival of adult dopaminergic cells, whereas that of OTX2 protects adult retinal ganglion cells. Here we characterize the neuroprotective activity of several homeoproteins in response to HO Protection is observed with ENGRAILED1, ENGRAILED2, OTX2, GBX2, and LHX9 on midbrain and striatal embryonic neurons, whereas cell-permeable c-MYC shows no protective effects.

The Physiology of Homeoprotein Transduction.

The homeoprotein family comprises ~300 transcription factors and was long seen as primarily involved in developmental programs through cell autonomous regulation. However, recent evidence reveals that many of these factors are also expressed in the adult where they exert physiological functions not yet fully deciphered. Furthermore, the DNA-binding domain of most homeoproteins contains two signal sequences allowing their secretion and internalization, thus intercellular transfer.

Engrailed homeoproteins in visual system development.

Engrailed is a homeoprotein transcription factor. This family of transcription factors is characterized by their DNA-binding homeodomain and some members, including Engrailed, can transfer between cells and regulate protein translation in addition to gene transcription. Engrailed is intimately involved in the development of the vertebrate visual system.

Distinct roles of homeoproteins in brain topographic mapping and in neural circuit formation.

The construction of the brain is a highly regulated process, requiring coordination of various cellular and molecular mechanisms that together ensure the stability of the cerebrum architecture and functions. The mature brain is an organ that performs complex computational operations using specific sensory information from the outside world and this requires precise organization within sensory networks and a separation of sensory modalities during development. We review here the role of homeoproteins in the arealization of the brain according to sensorimotor functions, the micropartition of its cytoarchitecture, and the maturation of its sensory circuitry.

Graded Otx2 activities demonstrate dose-sensitive eye and retina phenotypes.

In the human, mutations of OTX2 (Orthodenticle homeobox 2 transcription factor) translate into eye malformations of variable expressivity (even between the two eyes of the same individual) and incomplete penetrance, suggesting the existence of subtle thresholds in OTX2 activity. We have addressed this issue by analyzing retinal structure and function in six mutant mice with graded Otx2 activity: Otx2(+/+), Otx2(+/AA), Otx2(+/GFP), Otx2(AA/AA), Otx2(AA/GFP) and Otx2(GFP/GFP). Null mice (Otx2(GFP/GFP)) fail to develop the head and are embryonic lethal, and compound heterozygous Otx2(AA/GFP) mice show a truncated head and die at birth.

Homeoprotein signaling in development, health, and disease: a shaking of dogmas offers challenges and promises from bench to bed.

Homeoproteins constitute a major class of transcription factors active throughout development and in adulthood. Their membrane transduction properties were discovered over 20 years ago, opening an original field of research in the domain of vector peptides and signal transduction. In early development, homeoprotein transfer participates in tissue patterning, cell/axon guidance, and migration.

Engrailed signaling in axon guidance and neuron survival.

Several homeoproteins can function in a direct cell non-autonomous fashion to control various biological processes. In the developing nervous system, this mode of signaling has been well documented for Engrailed in the guidance of retinal ganglion cell axons and retino-tectal patterning. Engrailed is also a key factor for mesencephalic dopaminergic (mDA) neurons, not only during development but also in the adult.

Engrailed homeoprotein recruits the adenosine A1 receptor to potentiate ephrin A5 function in retinal growth cones.

Engrailed 1 and engrailed 2 homeoprotein transcription factors (collectively Engrailed) display graded expression in the chick optic tectum where they participate in retino-tectal patterning. In vitro, extracellular Engrailed guides retinal ganglion cell (RGC) axons and synergises with ephrin A5 to provoke the collapse of temporal growth cones. In vivo disruption of endogenous extracellular Engrailed leads to misrouting of RGC axons.

Engrailed protects mouse midbrain dopaminergic neurons against mitochondrial complex I insults.

Mice heterozygous for the homeobox gene Engrailed-1 (En1) display progressive loss of mesencephalic dopaminergic (mDA) neurons. We report that exogenous Engrailed-1 and Engrailed-2 (collectively Engrailed) protect mDA neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a mitochondrial complex I toxin used to model Parkinson's disease in animals. Engrailed enhances the translation of nuclearly encoded mRNAs for two key complex I subunits, Ndufs1 and Ndufs3, and increases complex I activity.

Cell non-autonomous functions of homeoproteins in neuroprotection in the brain.

Homeoproteins transcription factors can transfer between cells and play important roles in development. However, some of these homeoproteins are expressed in the adult, but their function is unknown. The loss of mesencephalic dopaminergic (mDA) neurons is the cause of Parkinson's disease.

Otx2 promotes the survival of damaged adult retinal ganglion cells and protects against excitotoxic loss of visual acuity in vivo.

Retinal ganglion cells (RGCs) are the projection neurons from the eye to the brain and their loss results in visual impairment in a number of diseases. Transcription factors with a homeodomain can translocate between cells and, in at least one reported case, can stimulate neuronal survival. Otx2 is a homeoprotein transcription factor expressed in the retina that is taken up by RGCs.

The role of the prion protein in the molecular basis for synaptic plasticity and nervous system development.

The cellular prion protein (PrP(C)) is found prominently at the synapse. However, its role at the nerve termini and elsewhere is unknown. Here we discuss research presented at the 2005 International Institute for Complex Adaptive Matter (I2CAM) first Annual Amyloid Conference that provides insight into the role of synaptic PrP(C).

Developmental changes in cellular prion protein in primate visual cortex.

Cellular prion protein (PrP(c)) is a cell surface glycoprotein highly expressed in neurons, and a protease-resistant conformer of the protein accumulates in the brain parenchyma in prion diseases. In human prion diseases, visual cortex and visual function can be affected. We examined both the levels and the localization of PrP(c) in developing visual cortex of the common marmoset.

Truncated PrP(c) in mammalian brain: interspecies variation and location in membrane rafts.

A key molecular event in prion diseases is the conversion of cellular prion protein (PrP(c)) into an abnormal misfolded conformer (PrP(sc)). The PrP(c) N-terminal domain plays a central role in PrP(c) functions and in prion propagation. Because mammalian PrP(c) is found as a full-length and N-terminally truncated form, we examined the presence and amount of PrP(c) C-terminal fragment in the brain of different species.

The N-terminal cleavage of cellular prion protein in the human brain.

Human brain cellular prion protein (PrP(c)) is cleaved within its highly conserved domain at amino acid 110/111/112. This cleavage generates a highly stable C-terminal fragment (C1). We examined the relative abundance of holo- and truncated PrP(c) in human cerebral cortex and we found important inter-individual variations in the proportion of C1.

Axonal transport of the cellular prion protein is increased during axon regeneration.

The cellular prion protein, PrPc, is a glycosylphosphatidylinositol-anchored cell surface glycoprotein and a protease-resistant conformer of the protein may be the infectious agent in transmissible spongiform encephalopathies. PrPc is localized on growing axons in vitro and along fibre bundles that contain elongating axons in developing and adult brain. To determine whether the growth state of axons influenced the expression and axonal transport of PrPc, we examined changes in the protein following post-traumatic regeneration in the hamster sciatic nerve.

The potential role of tau protein O-glycosylation in Alzheimer's disease.

Single O-linked N-acetylglucosamine (O-GlcNAc) sugar residues can compete with phosphate groups to occupy specific sites on certain nuclear and cytosolic proteins. Here we show that inhibiting cellular kinase activities resulted in changes in protein O-glycosylation levels in heat-stable cytoskeletal protein fractions derived from primary neuronal cells. As increased phosphorylation of the microtubule-associated protein tau is one of the pathological hallmarks of Alzheimer's disease and glycosylation may play an influential role in this process.

Enhanced detection and retrograde axonal transport of PrPc in peripheral nerve.

Neuroinvasion of the CNS during orally acquired transmissible spongiform encephalopathies (TSEs) may involve the transport of the infectious agent from the periphery to the CNS via the peripheral nerves. If this occurs within axons, the mechanism of axonal transport may be fundamental to the process. In studies of peripheral nerve we observed that the cellular prion protein (PrPc) is highly resistant to detergent extraction.

Developmental expression of the cellular prion protein in elongating axons.

PrPc, a sialoglycoprotein present in the normal adult hamster brain, is particularly abundant in plastic brain regions but little is known about the level of expression and the localization of the protein during development. Western blot analysis of whole brain homogenates with mab3F4 show very low levels of the three main molecular weight forms of the protein at birth, in contrast to the strong and wide expression of mRNA transcripts. The PrPc levels increase sharply through P14 and are diminished somewhat in the adult.