Biomedical subjects

S Merabet

Publications and source records attributed to S Merabet.

3 recordsLinked to original sources

PubMed2000

Distinct hox protein sequences determine specificity in different tissues.

Hox genes encode evolutionarily conserved transcription factors that control the morphological diversification along the anteroposterior (A/P) body axis. Expressed in precise locations in the ectoderm, mesoderm, and endoderm, Hox proteins have distinct regulatory activities in different tissues. How Hox proteins achieve tissue-specific functions and why cells lying at equivalent A/P positions but in different germ layers have distinctive responses to the same Hox protein remains to be determined. Here, we examine this question by identifying parts of Hox proteins necessary for Hox function in different tissues. Available genetic markers allow the regulatory effects of two Hox proteins, Abdominal-A (AbdA) and Ultrabithorax (Ubx), to be distinguished in the Drosophila embryonic epidermis and visceral mesoderm (VM). Chimeric Ubx/AbdA proteins were tested in both tissues and used to identify protein sequences that endow AbdA with a different target gene specificity from Ubx. We found that distinct protein sequences define AbdA, as opposed to Ubx, function in the epidermis vs. the VM. These sequences lie mostly outside the homeodomain (HD), emphasizing the importance of non-HD residues for specific Hox activities. Hox tissue specificity is therefore achieved by sensing distinct Hox protein structures in different tissues.

Animals↗

PubMed1989

Effects of the somatostatin analog BIM 23014 on the secretion of growth hormone, thyrotropin, and digestive peptides in normal men.

BIM 23014 (BIM) is a long-acting octapeptide somatostatin analog. We studied the effects of this analog on the secretion of GH, TSH, and gastroenteropancreatic hormones [secretin, motilin, and pancreatic polypeptide (PP)] in normal men. In the first protocol three BIM doses (125, 250, and 500 micrograms) and vehicle were administered sc in random order at 2000 h to eight normal young men. Plasma GH concentrations decreased during the first part of the night only after the highest dose (P less than 0.05). Plasma secretin levels did not change, while plasma motilin decreased after the 250- and 500-micrograms doses (P = 0.05 and P = 0.02, respectively), and plasma PP decreased after all three doses (P less than 0.05, P less than 0.01, and P less than 0.01, respectively) during the first part of the night. In the second protocol, eight men received BIM, administered by constant sc infusion during the night in a dose of 2 mg/12 h, or vehicle, either alone or in association with a 10 ng/kg.min iv GHRH or vehicle infusion. Nocturnal GH secretion was suppressed by the BIM infusion (P less than 0.001). GH secretion, stimulated by GHRH infusion (P less than 0.001), was reduced by concomitant BIM infusion (P less than 0.001) and was pulsatile during the combined infusions. BIM infusion suppressed the physiological nighttime rise in plasma TSH levels. Plasma motilin and PP levels were reduced by BIM, when administered either alone or in combination with GHRH. We conclude that: 1) BIM is capable of reducing GH secretion when administered sc in a dose of 500 micrograms and of abolishing nocturnal GH secretion when constantly infused at a dose of 2 mg/12 h; 2) BIM, constantly infused, reduces the nocturnal rise in TSH secretion; and 3) motilin and PP secretion are more sensitive than that of GH to BIM, as they are reduced by a lower dose.

Adult↗

PubMed1988

Plasma alpha-subunit levels during the treatment of pituitary adenomas with the somatostatin analog (SMS 201-995).

The effect os SMS 201-995 (Sandostatin), a long-acting somatostatin analog, on different types of pituitary adenomas including alpha-subunit elevation is illustrated in this report. Treatment induced a fall in hCG levels in a woman with a pituitary adenoma producing only alpha-subunit. In 3 acromegalic patients, there was only a partial drop in GH and alpha-hCG. The same effect was observed in a woman with menopausal FSH and LH levels. SMS reduced plasma TSH and alpha-hCG in a case of thyrotropic adenoma. Two patients exhibiting FSH- and alpha-hCG-secreting adenomas did not respond to acute administration of SMS 201-995. More patients have to be treated before a definitive statement can be made on the usefulness of somatostatin analogs in the management of different types of pituitary adenomas.

Adenoma↗