The role of homeobox genes in limb development

Intensive study of the development of the vertebrate limb has led to a conceptual framework for understanding the specification of a limb primordium, the outgrowth of those cells and their organization and differentiation into a functional appendage. During the past few years, a number of homeobox-containing genes have been identified that are likely to play controlling roles in each of these events.     

Molecular mechanisms in the control of limb regeneration: the role of homeobox genes

The Ca2+ sensitivity of cardiac myofibrillar force production can be decreased by acidosis or inorganic phosphate (P(i)) and increased by caffeine. To investigate whether the source of tissue influences the potency of these agents, we compared the actions of acidosis (change of pH from 7.0 to 6.2), P(i) and caffeine (both 20 mM) on force production of skinned cardiac muscles from adult ventricle, adult atrium and neonate ventricle of the rat. Maximum Ca(2+)-activated force was reduced by all three interventions and the responses of the different muscle types to a given intervention were similar. Acidosis reduced myofibrillar Ca2+ sensitivity by 1.09 and 1.04 pCa units in adult ventricle and atrium, respectively, and P(i) reduced it by 0.19 and 0.22 pCa units. However, each effect was only one-third as great in the neonate ventricle, which showed falls of 0.33 pCa units for acidosis and 0.06 for P(i). In contrast, caffeine raised the Ca2+ sensitivity by the same amount (approximately 0.4 pCa units) in all three muscle types. The differential effect between adult and neonate seen with both acidosis and P(i) suggests some similarity in the mechanisms by which these factors decrease Ca2+ sensitivity. In contrast, the equal effects of caffeine on neonate and adult suggests that caffeine acts by a completely different mechanism. The lower pH- and P(i)-sensitivity of the neonatal ventricle can help to explain why neonatal and adult myocardium exhibit differential force responses to ischaemia (or hypoxia alone).     

Expression of homeobox genes shows chelicerate arthropods retain their deutocerebral segment

Expression patterns of six homeobox containing genes in a model chelicerate, the oribatid mite Archegozetes longisetosus, were examined to establish homology of chelicerate and insect head segments and to investigate claims that the chelicerate deutocerebral segment has been reduced or lost. engrailed (en) expression, which has been used to demonstrate the presence of segments in insects, fails to demonstrate a reduced deutocerebral segment. Expression patterns of the chelicerate homologs of the Drosophila genes Antennapedia (Antp), Sex combs reduced (Scr), Deformed (Dfd), proboscipedia (pb), and orthodenticle (otd) confirm direct correspondence of head segments. The chelicerate deutocerebral segment has not been reduced or lost. We make further inferences concerning the evolution of heads and Hox genes in arthropods.     

The PBC domain contains a MEINOX domain: coevolution of Hox and TALE homeobox genes?

The diagnosis of inadequacy of the respiratory apparatus conditioning function (RACFI) necessitates carrying out an appreciable volume of calculations to determine observable and required values for its parameters, together with drawing up a concluding statement according to the existing RACFI classification. The above rapid method permits the 2.5-fold cut in man-power to be streamlined into research on respiratory heat-exchange in patients with cardiopulmonary disorders. The suggested method is recommended for use in therapeutic, pulmonological, cardiological departments and functional-diagnosis units in hospitals.     

PCR-based method for the introduction of mutations in genes cloned and expressed in vaccinia virus

Epidemiological and clinical data are presented on 165 cases of Venezuelan hemorrhagic fever (VHF), a newly emerging viral zoonosis caused by Guanarito virus (of the family Arenaviridae). The disease is endemic in a relatively circumscribed area of central Venezuela. Since its first recognition in 1989, the incidence of VHF has peaked each year between November and January, during the period of major agricultural activity in the region of endemicity. The majority of cases have involved male agricultural workers. Principal symptoms among the patients with VHF included fever, malaise, headache, arthralgia, sore throat, vomiting, abdominal pain, diarrhea, convulsions, and a variety of hemorrhagic manifestations. The majority of patients also had leukopenia and thrombocytopenia. The overall fatality rate among the 165 cases was 33.3%, despite hospitalization and vigorous supportive care.     

Otx/otd homeobox genes specify distinct sensory neuron identities in C. elegans

The mechanisms by which the diverse functional identities of neurons are generated are poorly understood. C. elegans responds to thermal and chemical stimuli using 12 types of sensory neurons. The Otx/otd homolog ttx-1 specifies the identities of the AFD thermosensory neurons. We show here that ceh-36 and ceh-37, the remaining two Otx-like genes in the C. elegans genome, specify the identities of AWC, ASE, and AWB chemosensory neurons, defining a role for this gene family in sensory neuron specification. All C. elegans Otx genes and rat Otx1 can substitute for ceh-37 and ceh-36, but only ceh-37 functionally substitutes for ttx-1. Functional substitution in the AWB neurons is mediated by activation of the same downstream target lim-4 by different Otx genes. Misexpression experiments indicate that although the specific identity adopted upon expression of an Otx gene may be constrained by the cellular context, individual Otx genes preferentially promote distinct neuronal identities.     

A new PCR-based approach to a fast search of a wide spectrum of cry genes from Bacillus thuringiensis strains

A pair of highly degenerated primers was adapted to carry out a single-step PCR-detection of any known and probably unknown cry genes of classes cry1, cry4 and cry9 encoding for 130 kDa protein delta-endotoxins in the natural Bacillus thuringiensis (BT) strains. The Southern hybridization of the product has demonstrated that essentially remote cry-genes like cry1Aa and cry9A (cryIG) could be represented in the single amplificate if they are simultaneously present in the genome of the analyzed strain. Four genes were detected by the proposed scheme in the BT ssp. galleriae 11-67. One of them, gene cry1Ga1 was originally found and cloned using the PCR-amplification product obtained from the genomic DNA of this strain as a probe. The new gene was completely identical to one cloned by B. Lambert (unpublished, EMBL accession number Z22510) and essentially related to cryIM (EMBL accession number Y09326), renamed according to the new nomenclature as cry1Ga2.     

The distirubtion of active genes (globin) and inactive genes (keratin) in fractionated chicken erythroid chromatin

Repeatable fractionation of sheared chromatin from purified populations of chicken erythroid cells has been achieved, based on the Bio-Gel procedure of Janowski et al. ((1972) Karolinska Symp. 5, 112). For reticulocytes, 3-5% of chromatin DNA is excluded from Bio-Gel A-50 m (peak I) and over 90% elutes in the included volume of the column(peak II). Peak I material has a higher protein/DNA ratio than peak II chromatin and the two fractions have melting profiles characteristic of "active" and "inactive" chromatin, respectively. In cells prelabeled with [3H]uridine or [3H]leucine there was very pronounced preferential association of radioactivity with the "active" peak I chromatin. The distribution of "active" (globin) and "inactive" (keratin) gene sequences in the DNA of fractions from peak I and peak II chromatin was determined with complimentary DNA (cDNA) probes to chicken globin mRNA and chicken feather keratin mRNA. While slight enrichment for globin gene sequences was found in peak I (relative to DNA in these fractions), some 80% of the total globin hybrid formed was found in peak II fractions. Experiments with the keratin cDNA probe showed that these genes were equally distributed in both chromatin fractions rather than being confined to the "inactive" peak II material. The hybridization data in particular question the validity of claims for fractionation of chromatin into "active" and "inactive" material.     

The optx2 homeobox gene is expressed in early precursors of the eye and activates retina-specific genes

Vertebrate eye development begins at the gastrula stage, when a region known as the eye field acquires the capacity to generate retina and lens. Optx2, a homeobox gene of the sine oculis-Six family, is selectively expressed in this early eye field and later in the lens placode and optic vesicle. The distal and ventral portion of the optic vesicle are fated to become the retina and optic nerve, whereas the dorsal portion eventually loses its neural characteristics and activates the synthesis of melanin, forming the retinal pigment epithelium. Optx2 expression is turned off in the future pigment epithelium but remains expressed in the proliferating neuroblasts and differentiating cells of the neural retina. When an Optx2-expressing plasmid is transfected into embryonic or mature chicken pigment epithelial cells, these cells adopt a neuronal morphology and express markers characteristic of developing neural retina and photoreceptors. One explanation of these results is that Optx2 functions as a determinant of retinal precursors and that it has induced the transdifferentiation of pigment epithelium into retinal neurons and photoreceptors. We also have isolated optix, a Drosophila gene that is the closest insect homologue of Optx2 and Six3. Optix is expressed during early development of the fly head and eye primordia.