Lhx2 is a progenitor-intrinsic modulator of Sonic Hedgehog signaling during early retinal neurogenesis.

An important question in organogenesis is how tissue-specific transcription factors interact with signaling pathways. In some cases, transcription factors define the context for how signaling pathways elicit tissue- or cell-specific responses, and in others, they influence signaling through transcriptional regulation of signaling components or accessory factors. We previously showed that during optic vesicle patterning, the Lim-homeodomain transcription factor Lhx2 has a contextual role by linking the Sonic Hedgehog (Shh) pathway to downstream targets without regulating the pathway itself. Here, we show that during early retinal neurogenesis in mice, Lhx2 is a multilevel regulator of Shh signaling. Specifically, Lhx2 acts cell autonomously to control the expression of pathway genes required for efficient activation and maintenance of signaling in retinal progenitor cells. The Shh co-receptors Cdon and Gas1 are candidate direct targets of Lhx2 that mediate pathway activation, whereas Lhx2 directly or indirectly promotes the expression of other pathway components important for activation and sustained signaling. We also provide genetic evidence suggesting that Lhx2 has a contextual role by linking the Shh pathway to downstream targets. Through these interactions, Lhx2 establishes the competence for Shh signaling in retinal progenitors and the context for the pathway to promote early retinal neurogenesis. The temporally distinct interactions between Lhx2 and the Shh pathway in retinal development illustrate how transcription factors and signaling pathways adapt to meet stage-dependent requirements of tissue formation.

Negative Energy Balance Blocks Neural and Behavioral Responses to Acute Stress by "Silencing" Central Glucagon-Like Peptide 1 Signaling in Rats.

Previous reports indicate that caloric restriction attenuates anxiety and other behavioral responses to acute stress, and blunts the ability of stress to increase anterior pituitary release of adrenocorticotropic hormone. Since hindbrain glucagon-like peptide-1 (GLP-1) neurons and noradrenergic prolactin-releasing peptide (PrRP) neurons participate in behavioral and endocrine stress responses, and are sensitive to the metabolic state, we examined whether overnight food deprivation blunts stress-induced recruitment of these neurons and their downstream hypothalamic and limbic forebrain targets. A single overnight fast reduced anxiety-like behavior assessed in the elevated-plus maze and acoustic startle test, including marked attenuation of light-enhanced startle. Acute stress [i.e., 30 min restraint (RES) or 5 min elevated platform exposure] robustly activated c-Fos in GLP-1 and PrRP neurons in fed rats, but not in fasted rats. Fasting also significantly blunted the ability of acute stress to activate c-Fos expression within the anterior ventrolateral bed nucleus of the stria terminalis (vlBST). Acute RES stress suppressed dark-onset food intake in rats that were fed ad libitum, whereas central infusion of a GLP-1 receptor antagonist blocked RES-induced hypophagia, and reduced the ability of RES to activate PrRP and anterior vlBST neurons in ad libitum-fed rats. Thus, an overnight fast "silences" GLP-1 and PrRP neurons, and reduces both anxiety-like and hypophagic responses to acute stress. The partial mimicking of these fasting-induced effects in ad libitum-fed rats after GLP-1 receptor antagonism suggests a potential mechanism by which short-term negative energy balance attenuates neuroendocrine and behavioral responses to acute stress. SIGNIFICANCE STATEMENT: The results from this study reveal a potential central mechanism for the "metabolic tuning" of stress responsiveness. A single overnight fast, which markedly reduces anxiety-like behavior in rats, reduces or blocks the ability of acute stress to activate hindbrain neurons that are immunoreactive for either prolactin-releasing peptide or glucagon-like peptide 1, and attenuates the activation of their stress-sensitive projection targets in the limbic forebrain. In nonfasted rats, central antagonism of glucagon-like peptide 1 receptors partially mimics the effect of an overnight fast by blocking the ability of acute stress to inhibit food intake, and by attenuating stress-induced activation of hindbrain and limbic forebrain neurons. We propose that caloric restriction attenuates behavioral and physiological responses to acute stress by "silencing" central glucagon-like peptide 1 signaling pathways.

Lhx2 balances progenitor maintenance with neurogenic output and promotes competence state progression in the developing retina.

The LIM-Homeodomain transcription factor Lhx2 is an essential organizer of early eye development and is subsequently expressed in retinal progenitor cells (RPCs). To determine its requirement in RPCs, we performed a temporal series of conditional inactivations in mice with the early RPC driver Pax6 α-Cre and the tamoxifen-inducible Hes1(CreERT2) driver. Deletion of Lhx2 caused a significant reduction of the progenitor population and a corresponding increase in neurogenesis. Precursor fate choice correlated with the time of inactivation; early and late inactivation led to the overproduction of retinal ganglion cells (RGCs) and rod photoreceptors, respectively. In each case, however, the overproduction was selective, occurring at the expense of other cell types and indicating a role for Lhx2 in generating cell type diversity. RPCs that persisted in the absence of Lhx2 continued to generate RGC precursors beyond their normal production window, suggesting that Lhx2 facilitates a transition in competence state. These results identify Lhx2 as a key regulator of RPC properties that contribute to the ordered production of multiple cell types during retinal tissue formation.

Risk factors for clinical endometritis in postpartum dairy cattle.

Bacterial contamination of the uterine lumen after parturition occurs in most dairy cattle. The presence of clinical endometritis beyond three weeks post partum depends on the balance between microbes, host immunity, and other environmental or animal factors. The present study tested the hypothesis that clinical endometritis is associated with animal factors, such as retained fetal membranes, assisted calving and twins, as well as fecal contamination of the environment. The association between selected risk factors and the lactational incidence risk of clinical endometritis was examined in 293 animals from four dairy herds. Multivariate analysis was used to identify risk factors and quantify their relative risk (RR) and population attributable fraction (PAF) based on the proportion of cows exposed to each factor. The lactational incidence of clinical endometritis was 27% and significant risk factors for clinical endometritis were retained fetal membranes (RR=3.6), assisted calving (RR=1.7), stillbirth (RR=3.1), vulval angle (RR=1.3), primparity (RR=1.8), and male offspring (RR=1.5) but not the cleanliness of the environment or the animal. The highest PAF was associated with male offspring (0.6) so the use of sexed semen has the greatest potential to reduce the incidence of clinical endometritis. The dominant association between retained fetal membranes and clinical endometritis was supported by an expert panel of clinicians. The risk factors for clinical endometritis appear to be associated with trauma of the female genital tract and disruption of the physical barriers to infection rather than fecal contamination.