Impaired fetal erythrocytes' filterability: relationship with cell size, membrane fluidity, and membrane lipid composition.

The lipid composition of erythrocytes (red blood cells [RBCs]) plays a significant role in determining certain membrane biophysical properties. We have found that fetal RBCs showed a dramatically low filterability compared with adult RBCs and questioned whether this could be a consequence of their membrane lipid composition. We therefore studied fetal RBCs at two different gestational ages, neonatal RBCs and adult RBCs. Biophysical parameters were studied using two different techniques, filterability and membrane fluidity. The latter was measured by fluorescence polarization using three different probes. The membrane lipid composition was examined by measuring cholesterol and phospholipids. After extraction of the phospholipids, followed by high performance thin-layer chromatography, the fatty acids in the phospholipid subfractions were analyzed by gas-liquid chromatography. The fetal RBCs' filterability was found to be correlated with both the larger size and the higher hemoglobin content of the cells, but there was no correlation between RBC filterability and fluidity or membrane lipid composition. In adult RBCs, compared with neonatal RBCs, the slight increase of unsaturated fatty acids in phosphatidylcholine and phosphatidylethanolamine should have increased the membrane fluidity. However, in RBCs, no change was observed in the fluidity parameters measured by fluorescence polarization.

Myosin content and distribution in human neonatal erythrocytes are different from adult erythrocytes.

Neonatal erythrocytes (N-RBC) are different from adult erythrocytes (A-RBC). N-RBC are larger, less deformable, and undergo enhanced spontaneous and drug-induced endocytosis. The reticulocyte population of N-RBC is also different, consisting primarily of the youngest (R1) reticulocytes that are motile and capable of receptor-mediated endocytosis. Processes such as motility could require a contractile system. Myosin, a contractile protein, was identified in both A-RBC and N-RBC. We proposed to compare myosin content and distribution in A-RBC and N-RBC by immunofluorescence and enzyme-linked immunosorbent assay (ELISA) using a monospecific polyclonal rabbit antimyosin. There was bright immunofluorescence on 44% of N-RBC with some heterogeneity contrasting with a barely detectable fluorescence on A-RBC. ELISA measurements showed that A-RBC had 4,315 myosin copies/RBC, whereas N-RBC had 10,855 copies/RBC (or 2.5 times as much). ELISA measurements of white ghosts showed that A-ghosts contained 1,250 copies of myosin/RBC (29% of total) whereas N-ghosts contained 3.4 times as much at 4,320 copies/RBC (39% of total). Therefore, N-RBC not only have more myosin, but the amount that is membrane-associated is disproportionately increased. It is proposed that such differences in amount and distribution of myosin could account for some of the unusual properties of neonatal RBC indicated.

Spontaneous endocytosis in human neonatal and adult red blood cells: comparison to drug-induced endocytosis and to receptor-mediated endocytosis.

Neonatal RBC contain many more spontaneous endocytic vacuoles than do adult RBC. It is not known if this difference is a result of an increase in production of vacuoles in the neonatal RBC (as is the case in drug-induced endocytosis), or is the result of a less effective neonatal macrophagic "pitting" process. Using an in vitro model of spontaneous endocytosis, we compared the rate and quantity of vacuoles and the shape of cord and adult RBC containing pits, visible by interference contrast microscopy (Nomarski method). The mechanism of the spontaneous endocytosis was explored using different inhibitors: sodium vanadate an inhibitor of ATPases, sodium fluoride which inhibits the generation of ATP and sodium cyanide a potent inhibitor of oxidative phosphorylation. We then compared spontaneous endocytosis with two other forms of RBC endocytosis: drug-induced endocytosis and receptor-mediated endocytosis. Spontaneous endocytosis is in fact increased in neonatal RBC initially but the increase in number of RBC containing pits after 144 hr of incubation is almost the same in adult RBC and neonatal RBC. Comparing spontaneous endocytosis with drug-induced endocytosis, it appears that their mechanisms are different in that spontaneous endocytosis is not preceded by stomatocytic shape change and is not inhibited by sodium vanadate or sodium fluoride as is the case for drug-induced endocytosis. Spontaneous endocytosis is different than transferrin receptor-mediated endocytosis because it occurs in many RBC, not only in the motile R1 reticulocytes and is not inhibited by sodium cyanide as is receptor-mediated endocytosis. Thus spontaneous endocytosis appears to be different than drug-induced endocytosis and transferrin receptor-mediated endocytosis. The increase in spontaneous endocytosis in cord RBC seen in vivo is probably a consequence of an immaturity of the neonatal macrophage pitting process.

[Partial trisomy 14q II.--Partial trisomy 14q due to a maternal t(12; 14) (q24.4; q21)]. / Trisomie 14q partielle. II.--Trisomie 14q partielle par translocation maternelle t(12; 14) (q24.4; q21)

The phenotype of an 18-month-old male infant trisomic for the proximal portion of the long arm of chromosome 14 was reported and compared with that of previously reported cases. For the identification of the resulting syndrome, the most consistent features are psychomotor and growth retardation, and an oval, dysmorphic facies which includes a distinctive form of the mouth and a prominent nose. The trisomy in the child reported here is due to a familial translocation transmitted by the mother and present in at least three generations: t(12;14)(q24.4;q21). The 12q duplication in the child's genome is minimal and does not seem to have contributed to his phenotype.