Switching repulsion to attraction: changing responses to slit during transition in mesoderm migration.

Slit is secreted by cells at the midline of the central nervous system, where it binds to Roundabout (Robo) receptors and functions as a potent repellent. We found that migrating mesodermal cells in vivo respond to Slit as both an attractant and a repellent and that Robo receptors are required for both functions. Mesoderm cells expressing Robo receptors initially migrate away from Slit at the midline. A few hours after migration, these same cells change their behavior and require Robo to extend toward Slit-expressing muscle attachment sites. Thus, Slit functions as a chemoattractant to provide specificity for muscle patterning.

Quantitative analysis of gene function in the Drosophila embryo.

The specific functions of gene products frequently depend on the developmental context in which they are expressed. Thus, studies on gene function will benefit from systems that allow for manipulation of gene expression within model systems where the developmental context is well defined. Here we describe a system that allows for genetically controlled overexpression of any gene of interest under normal physiological conditions in the early Drosophila embryo. This regulated expression is achieved through the use of Drosophila lines that express a maternal mRNA for the yeast transcription factor GAL4. Embryos derived from females that express GAL4 maternally activate GAL4-dependent UAS transgenes at uniform levels throughout the embryo during the blastoderm stage of embryogenesis. The expression levels can be quantitatively manipulated through the use of lines that have different levels of maternal GAL4 activity. Specific phenotypes are produced by expression of a number of different developmental regulators with this system, including genes that normally do not function during Drosophila embryogenesis. Analysis of the response to overexpression of runt provides evidence that this pair-rule segmentation gene has a direct role in repressing transcription of the segment-polarity gene engrailed. The maternal GAL4 system will have applications both for the measurement of gene activity in reverse genetic experiments as well as for the identification of genetic factors that have quantitative effects on gene function in vivo.

Direct activation of Sex-lethal transcription by the Drosophila runt protein.

Runt functions as a transcriptional regulator in multiple developmental pathways in Drosophila melanogaster. Recent evidence indicates that Runt represses the transcription of several downstream target genes in the segmentation pathway. Here we demonstrate that runt also functions to activate transcription. The initial expression of the female-specific sex-determining gene Sex-lethal in the blastoderm embryo requires runt activity. Consistent with a role as a direct activator, Runt shows sequence-specific binding to multiple sites in the Sex-lethal early promoter. Using an in vivo transient assay, we demonstrate that Runt's DNA-binding activity is essential for Sex-lethal activation in vivo. These experiments further reveal that increasing the dosage of runt alone is sufficient for triggering the transcriptional activation of Sex-lethal in males. In addition, a Runt fusion protein, containing a heterologous transcriptional activation domain activates Sex-lethal expression, indicating that this regulation is direct and not via repression of other repressors. Moreover, we demonstrate that a small segment of the Sex-lethal early promoter that contains Runt-binding sites mediates Runt-dependent transcriptional activation in vivo.

Pair-rule gene runt restricts orthodenticle expression to the presumptive head of the Drosophila embryo.

Ectopic expression of the pair-rule gene runt in the anterior end of the Drosophila embryo antagonizes transcriptional activation of the head gap gene orthodenticle (otd) by the anterior morphogen bicoid. Here we investigate the relevance of runt's activity as a repressor of otd in normal Drosophila embryogenesis otd expression is activated in the posterior region of embryos that are mutant for runt. This posterior expression domain of otd depends on the activity of the orphan nuclear receptor protein Tailless. Repression of otd by runt does not require the conserved VVVRPY motif that mediates interaction between Runt and the co-repressor protein Groucho. The observed functional interactions between runt and tailless on otd expression may indicate there are other contexts where members of these two families of transcriptional regulators interact to regulate gene expression during development.

Complex limbal choristomas in linear nevus sebaceous syndrome.

OBJECTIVE: This study aimed to describe the clinical and histopathologic findings in four patients with complex limbal choristomas associated with linear nevus sebaceous syndrome (LNSS), a rare disorder including nevus sebaceous, seizures, and mental retardation, and often accompanied by ocular anomalies. DESIGN: Small observational case series. METHODS: A retrospective review of the clinical and histopathologic records of four patients. RESULTS: Each of four patients had complex limbal choristomas in the setting of clinical and histopathologic LNSS. The limbal choristomas were multiple in three patients and bilateral in two patients. Most choristomas involved the superotemporal limbus (6 of 10), although nasal (3 of 10) and inferior (1 of 10) limbal tumors also were present. Three patients had significant corneal astigmatism or involvement of the central cornea requiring surgical removal of their choristomas, one accompanied by a lamellar keratoplasty and another accompanied by two consecutive penetrating keratoplasties. Each graft eventually vascularized, reducing vision. One patient's vision was limited by amblyopia and another by occipital cortical dysgenesis with visual impairment. Histopathologic examination of the excised choristomas showed foci of lacrimal gland (3 of 4 patients), adipose tissue (3 of 4), neural tissue (1 of 4), cartilage (1 of 4), lymphoid follicles (1 of 4), skin adnexal tissue (1 of 4), and smooth muscle (1 of 4). Other associated ocular findings included an eyelid mass (1 of 4), colobomas of the eyelid (3 of 4), colobomas of the choroid and retina (2 of 4), nonparalytic strabismus (2 of 4), scleral ectasia (1 of 4), partial oculomotor palsy with ptosis and anisocoria (1 of 4), microphthalmia (1 of 4), hypertelorism (1 of 4), and cortical visual impairment (1 of 4). CONCLUSIONS: Complex limbal choristomas, although rare, can occur in the setting of LNSS and can be associated with multiple ocular and systemic abnormalities. Visual prognosis appears poor in most cases despite aggressive management.

Corneal allograft rejection after multiple blood transfusions.

We treated two patients with corneal allograft rejections, both of which occurred within a few weeks after administration of multiple blood transfusions. In the first case, a patient with a graft that had been previously clear for 11 years developed severe endothelial rejection six weeks after transfusion of ten units of packed red blood cells. In the second case, a graft that had been clear for 14 months irreversibly rejected two weeks after transfusion of six units of packed red blood cells. These cases suggest that multiple blood transfusions may be a risk factor for corneal allograft rejection.

The triple procedure: cataract extraction in a different setting.

This article compares and contrasts ordinary cataract extraction, including lens implantation, with cataract extraction and lens implantation in eyes also undergoing penetrating keratoplasty. Variations in cataract extraction technique which are necessary when a keratoplasty is added are described, and differences in an important complication which occurs in both settings, cystoid macular edema, are evaluated.

Penetrating keratoplasty combined with extracapsular cataract extraction.

In my previous prospective study of 132 eyes, the incidence of clinically significant cystoid macular edema was 42% in aphakic penetrating keratoplasty, 33% in combined keratoplasty and cataract extraction with vitrectomy, and only 4% in combined keratoplasty and cataract extraction without vitrectomy. In the present study we added 26 aphakic and 11 pseudophakic keratoplasties and 17 procedures combining keratoplasty with extracapsular cataract extraction. Grafts were clear in 94% of patients, and 43% had visual acuity of 20/40 or better. Clinically significant cystoid macular edema occurred in 35% of aphakic and 27% of pseudophakic keratoplasties. Cystoid macular edema did not occur in combined keratoplasty and extracapsular cataract extraction.

Acute effects of dexamethasone on intraocular pressure in glaucoma.

The effects of 3 mg orally administered dexamethasone on the intraocular pressure (IOP) were examined in four patients with primary open-angle glaucoma hospitalized for this study. Plasma-free glucocorticoid activity was measured by a radioreceptor assay. Diurnal rhythms of IOP and plasma-free glucocorticoid activity were detected prior to administration of dexamethasone. The plasma-free glucocorticoid activity rose two- to threefold in the 30-min period following steroid administration and then declined throughout the rest of the day. IOP was approximately 2 mmHg higher in the 0-4-hr period and approximately 5.5 mmHg higher in the 4-8-hr period following the pharmacologic doses of dexamethasone compared with similar periods on control days. The increase in the IOP was highly significant (P less than 0.006) in the latter time period. These findings suggest that the glucocorticoids may have a greater role in regulating IOP than generally has been appreciated.