Cyclic Expression of Lhx2 Regulates Hair Formation

Hair is important for thermoregulation, physical protection, sensory activity, seasonal camouflage, and social interactions. Hair is generated in hair follicles (HFs) and, following morphogenesis, HFs undergo cyclic phases of active growth (anagen), regression (catagen), and inactivity (telogen) throughout life. The transcriptional regulation of this process is not well understood. We show that the transcription factor Lhx2 is expressed in cells of the outer root sheath and a subpopulation of matrix cells during both morphogenesis and anagen. As the HFs enter telogen, expression becomes undetectable and reappears prior to initiation of anagen in the secondary hair germ. In contrast to previously published results, we find that Lhx2 is primarily expressed by precursor cells outside of the bulge region where the HF stem cells are located. This developmental, stage- and cell-specific expression suggests that Lhx2 regulates the generation and regeneration of hair. In support of this hypothesis, we show that Lhx2 is required for anagen progression and HF morphogenesis. Moreover, transgenic expression of Lhx2 in postnatal HFs is sufficient to induce anagen. Thus, our results reveal an alternative interpretation of Lhx2 function in HFs compared to previously published results, since Lhx2 is periodically expressed, primarily in precursor cells distinct from those in the bulge region, and is an essential positive regulator of hair formation

Lhx2 Is Required for Patterning and Expansion of a Distinct Progenitor Cell Population Committed to Eye Development

Progenitor cells committed to eye development become specified in the prospective forebrain and develop subsequently into the optic vesicle and the optic cup. The optic vesicle induces formation of the lens placode in surface ectoderm from which the lens develops. Numerous transcription factors are involved in this process, including the eye-field transcription factors. However, many of these transcription factors also regulate the patterning of the anterior neural plate and their specific role in eye development is difficult to discern since eye-committed progenitor cells are poorly defined. By using a specific part of the Lhx2 promoter to regulate Cre recombinase expression in transgenic mice we have been able to define a distinct progenitor cell population in the forebrain solely committed to eye development. Conditional inactivation of Lhx2 in these progenitor cells causes an arrest in eye development at the stage when the optic vesicle induces lens placode formation in the surface ectoderm. The eye-committed progenitor cell population is present in the Lhx2−/− embryonic forebrain suggesting that commitment to eye development is Lhx2-independent. However, re-expression of Lhx2 in Lhx2−/− progenitor cells only promotes development of retinal pigment epithelium cells, indicating that Lhx2 promotes the acquisition of the oligopotent fate of these progenitor cells. This approach also allowed us to identify genes that distinguish Lhx2 function in eye development from that in the forebrain. Thus, we have defined a distinct progenitor cell population in the forebrain committed to eye development and identified genes linked to Lhx2's function in the expansion and patterning of these progenitor cells

Stromelysin-3 Is Induced in Mouse Ovarian Follicles Undergoing Hormonally Controlled Apoptosis, but This Metalloproteinase Is Not Required for Follicular Atresia1

International audienceApoptotic processes are often associated with an intense proteolytic remodeling of the extracellular matrix (ECM). Proteolytic degradation of the ECM can also be a signal that induces apoptosis. Here, we have investigated the expression pattern and functional role of the matrix metalloproteinase stromelysin-3 in follicular atresia. Twenty-four hours after the treatment of immature female mice with a low dose of eCG, both apoptosis and the stromelysin-3 mRNA expression were suppressed approximately threefold. However, the initial suppression of apoptosis and stromelysin-3 expression was followed by a time-dependent increase, and 96 h after eCG treatment, the levels were similar to those of untreated control mice. In 15- to 16-day-old juvenile mice, the ovary consisted of relatively undeveloped follicles, and almost no apoptosis and only low stromelysin-3 mRNA expression were observed. However, at the age of 21 days, when several antral follicles were present, a fivefold induction in both apoptosis and stromelysin-3 mRNA expression was detected. For both models, in situ analysis revealed that the expression of stromelysin-3 mRNA was localized to the granulosa cells of atretic follicles. To address the functional role of stromelysin-3 in follicular atresia, stromelysin-3-deficient mice were studied. However, no difference in the pattern of apoptotic DNA fragmentation and no apparent morphological differences were observed when ovaries from wild-type and stromelysin-3-deficient mice were compared. Taken together, our data indicate that stromelysin-3 is induced during follicular atresia, but that this protease is not obligatory for initiation or completion of the atretic process

Reduced mTORC1-signaling in retinal ganglion cells leads to vascular retinopathy

Background: The coordinated wiring of neurons, glia and endothelial cells into neurovascular units is critical for central nervous system development. This is best exemplified in the mammalian retina where interneurons, astrocytes and retinal ganglion cells sculpt their vascular environment to meet the metabolic demands of visual function. Identifying the molecular networks that underlie neurovascular unit formation is an important step towards a deeper understanding of nervous system development and function. Results: Here, we report that cell-to-cell mTORC1-signaling is essential for neurovascular unit formation during mouse retinal development. Using a conditional knockout approach we demonstrate that reduced mTORC1 activity in asymmetrically positioned retinal ganglion cells induces a delay in postnatal vascular network formation in addition to the production of rudimentary and tortuous vessel networks in adult animals. The severity of this vascular phenotype is directly correlated to the degree of mTORC1 down regulation within the neighboring retinal ganglion cell population. Conclusions: This study establishes a cell nonautonomous role for mTORC1-signaling during retinal development. These findings contribute to our current understanding of neurovascular unit formation and demonstrate how ganglion cells actively sculpt their local environment to ensure that the retina is perfused with an appropriate supply of oxygen and nutrients

Reduced mTORC1-signalling in retinal progenitor cells leads to visual pathway dysfunction

Development of the vertebrate central nervous system involves the co-ordinated differentiation of progenitor cells and the establishment of functional neural networks. This neurogenic process is driven by both intracellular and extracellular cues that converge on the mammalian target of rapamycin complex 1 (mTORC1). Here we demonstrate that mTORC1-signalling mediates multi-faceted roles during central nervous system development using the mouse retina as a model system. Downregulation of mTORC1-signalling in retinal progenitor cells by conditional ablation of Rptor leads to proliferation deficits and an over-production of retinal ganglion cells during embryonic development. In contrast, reduced mTORC1-signalling in postnatal animals leads to temporal deviations in programmed cell death and the consequent production of asymmetric retinal ganglion cell mosaics and associated loss of axonal termination topographies in the dorsal lateral geniculate nucleus of adult mice. In combination these developmental defects induce visually mediated behavioural deficits. These collective observations demonstrate that mTORC1-signalling mediates critical roles during visual pathway development and function

Dorsal shift in expression of retina-specific eye field transcription factors in the mutant optic vesicle.

<p>(A–E) <i>In situ</i> hybridization analyses on coronal sections of E10.5 optic cups from control embryos (left panels) and <i>Lhx2-Cre:β-catenin^flox/flox</i> mutant embryos (right panels). Arrows indicate the dorsal shift in expression of the retina-specific transcription factors <i>Six3</i>, <i>Six6</i> and <i>Rx</i> in mutant embryos (C–E). Scale bar: 100 µm.</p

Lhx2 Expression Promotes Self-Renewal of a Distinct Multipotential Hematopoietic Progenitor Cell in Embryonic Stem Cell-Derived Embryoid Bodies

The molecular mechanisms regulating the expansion of the hematopoietic system including hematopoietic stem cells (HSCs) in the fetal liver during embryonic development are largely unknown. The LIM-homeobox gene Lhx2 is a candidate regulator of fetal hematopoiesis since it is expressed in the fetal liver and Lhx2 2/2 mice die in utero due to severe anemia. Moreover, expression of Lhx2 in embryonic stem (ES) cell-derived embryoid bodies (EBs) can lead to the generation of HSClike cell lines. To further define the role of this transcription factor in hematopoietic regulation, we generated ES cell lines that enabled tet-inducible expression of Lhx2. Using this approach we observed that Lhx2 expression synergises with specific signalling pathways, resulting in increased frequency of colony forming cells in developing EB cells. The increase in growth factor-responsive progenitor cells directly correlates to the efficiency in generating HSC-like cell lines, suggesting that Lhx2 expression induce self-renewal of a distinct multipotential hematopoietic progenitor cell in EBs. Signalling via the c-kit tyrosine kinase receptor and the gp130 signal transducer by IL-6 is necessary and sufficient for the Lhx2 induced selfrenewal. While inducing self-renewal of multipotential progenitor cells, expression of Lhx2 inhibited proliferation of primitive erythroid precursor cells and interfered with early ES cell commitment, indicating striking lineage specificity of thi

Decreased proliferation and change in physical properties of mutant optic vesicle.

<p>(A) Immunohistochemical analysis for the presence of BrdU-labelled cells in the prospective neural retina on a coronal section of an E10.5 control embryo (left panel) and an <i>Lhx2-Cre:β-catenin^flox/flox</i> embryo (right panel). The part of the prospective neural retina that was analysed for BrdU⁺ cells in the control and mutant embryos are outlined. (B) Immunohistochemical analysis for the presence apoptotic cells as revealed by the presence of activated Casp-3⁺ cells on coronal section of an E10.5 control embryo (left panel) and a <i>Lhx2-Cre:β-catenin^flox/flox</i> embryo (right panel). (C) Immunohistochemical analyses for the presence of phosphorylated myosin light chain 2 (pMLC2) on a coronal section of an E10.5 control embryo. (D) Immunohistochemical analyses for the presence of pMLC2 on a coronal section on an E10.5 <i>Lhx2-Cre:β-catenin^flox/flox</i> embryo. Insets in C and D are a magnification of the areas indicated by the squares. Scale bars: (A, B and C, D) 100 µm.</p

β-catenin is important for maintenance of dorsoventral patterning of the retina.

<p>(A–D) <i>In situ</i> hybridization analyses (A, C, D) and immunohistochemical analysis (B) on coronal sections of E9.5 (ss25–26) optic vesicles from control (left panels) and on <i>Lhx2-Cre:β-catenin^flox/flox</i> embryos (right panels). (E–H) In situ hybridization analyses (E, G, H) and immunohistochemical analysis (F) on coronal sections of E10.5 (ss32–34) optic cups from control (left panels) and <i>Lhx2-Cre:β-catenin^flox/flox</i> embryos (right panels). Black arrow heads in A and E, and white arrow heads in B and F, indicate the boundaries of the area where β-catenin has been inactivated. (I, J) <i>In situ</i> hybridization analyses on coronal sections of E10.5 (ss32–34) optic cups from control (left panel) and <i>Lhx2-Cre:β-catenin^flox/flox</i> embryos (right panels). (K, L) <i>In situ</i> hybridization analyses on coronal sections of an eye from E12.5 control (left panels) and <i>Lhx2-Cre:β-catenin^flox/flox</i> embryos. Dorsal-ventral (D–V) orientation of all panels is indicated in A. Scale bars: (A–E, G–J, F and K, L) 100 µm.</p