Erythroid-specific inhibition of the tal-1 intragenic promoter is due to binding of a repressor to a novel silencer

The basic helix-loop-helix tal-1 gene plays a key role in hematopoiesis, and its expression is tightly controlled through alternative promoters and complex interactions of cis-acting regulatory elements. tal-1 is not expressed in normal T cells, but its transcription is constitutive in a large proportion of human T cell leukemias. We have previously described a downstream initiation of tal-1 transcription specifically associated with a subset of T cell leukemias that leads to the production of NH(2)-truncated TAL-1 proteins. In this study, we characterize the human promoter (promoter IV), embedded within a GC-rich region in exon IV, responsible for this transcriptional activity. The restriction of promoter IV usage is assured by a novel silencer element in the 3'-untranslated region of the human gene that represses its activity in erythroid but not in T cells. The silencer activity is mediated through binding of a tissue-specific nuclear factor to a novel protein recognition motif (designated tal-RE) in the silencer. Mutation of a single residue within the tal-RE abolishes both specific protein binding and silencing activity. Altogether, our results demonstrate that the tal-1 promoter IV is actively repressed in cells of the erythro-megakaryocytic lineage and that this repression is released in leukemic T cells, resulting in the expression of the tal-1 truncated transcript.

[Surgery of post-traumatic ptosis]

Post-traumatic ptosis may be classified as follows: ptosis occurring during lid avulsion, ptosis associated with fractures of the orbital roof and with foreign bodies, post-contusional ptosis, cicatricial ptosis, neurogenic ptosis and post-surgical ptosis. The patient must be thoroughly examined, including examination of the eye-ball, extra-ocular muscles, eyelid and evaluation of upper eyelid levator function and orbital and facial examination. The various surgical methods proposed include levator muscle surgery, aponeurotic surgery, Müller's muscle surgery and frontalis suspension surgery. Surgical indications and choice of surgical method essentially depend on the anatomo-clinical forms. The general rule is to operate under local anesthesia to obtain better control of the muscular function. Some cases are simple to treat such as post-contusional ptosis with good levator function which allows functional surgery with excellent static and dynamic results. Other relatively simple cases with non functional levators may only be treated on a static basis. Last but not least are more difficult cases in which levator function is difficult to evaluate pre-operatively because of severe fibrosis. The aim in such cases is to explore the eyelid by an anterior approach under local anesthesia and to propose either muscular surgery or a frontalis suspension according to the anatomical and functional status of the levator muscle.

[Value of monoclonal antibody study of lymphocyte subpopulations in newborn infants of HIV1 seropositive mothers]

The outcome of infants born to HIV1 seropositive (HIV1+) mothers is still uncertain is spite of current progress in techniques for viral detection. Using the almost elective tropism of HIV1 virus for CD4 lymphocytes and the central role of these cells in the immune regulation, we studied blood lymphocyte populations with 7 monoclonal antibodies during the first month of life in 28 newborns of HIV1 seropositive mothers. Our data are compared to an age-matched population of 35 control infants. According to our results, the coexistence of a low CD8 lymphocyte percentage together with a high CD4/CD8 ratio seems to be correlated with an unfavourable outcome.