Effects of reduced salinities on metamorphosis of a freshwater-tolerant sesarmid crab, Armases roberti: Is upstream migration in the megalopa stage constrained by increasing osmotic stress?

Numerous species of estuarine and freshwater-tolerant crabs show an export strategy, i.e. an early larval downstream transport towards coastal marine waters, later zoeal development at higher salinities, and a return of the last larval stage, the megalopa, into estuaries or rivers. The speed and extent of the upstream migration of the megalopa through strong salinity gradients may be constrained by increasing hypo-osmotic stress. In an experimental laboratory study with Armases roberti, a freshwater-inhabiting sesarmid crab from the Caribbean region, we studied in the megalopa stage (after zoeal rearing at 25) the tolerance of reduced salinities. In the first experiment, the larvae were exposed directly to various constant salinities (125). For the second experiment, they were transferred stepwise to strongly diluted media (within 6 days from 25 to ≤3), simulating differential scenarios of upstream migration into brackish or freshwater habitats. When postmoult megalopae were exposed directly to salinities ≤3, they all died within 24 h. A slightly higher salt concentration (5), however, allowed for considerable survival (46%) through metamorphosis to the first juvenile crab stage. In treatments with continuous exposure to 1015, as well as in a control group (25), survival to metamorphosis was significantly higher (8396%), and the average duration of development was shorter compared to 5 (1213 vs. 16 days). In the second experiment, with stepwise salinity reductions, gradual acclimation to decreasing osmotic pressures permitted a successful development to metamorphosis at ≤3 and even in freshwater (b0.2). This strong physiological adaptability enables the megalopa of A. roberti to cross during its upstream migration, within a short time (6 days), strong osmotic gradients, so that metamorphosis is possible also in freshwater habitats where the conspecific adult crabs live. The speed of migration appears to be limited by physiological constraints related to changes in the capability for osmoregulation occurring during the course of the moulting cycle

Serum of myeloproliferative neoplasms stimulates hematopoietic stem and progenitor cells

<div><p>Background</p><p>Myeloproliferative neoplasms (MPN)—such as polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF)—are typically diseases of the elderly caused by acquired somatic mutations. However, it is largely unknown how the malignant clone interferes with normal hematopoiesis. In this study, we analyzed if serum of MPN patients comprises soluble factors that impact on hematopoietic stem and progenitor cells (HPCs).</p><p>Methods</p><p>CD34⁺ HPCs were cultured in medium supplemented with serum samples of PV, ET, or MF patients, or healthy controls. The impact on proliferation, maintenance of immature hematopoietic surface markers, and colony forming unit (CFU) potential was systematically analyzed. In addition, we compared serum of healthy young (<25 years) and elderly donors (>50 years) to determine how normal aging impacts on the hematopoiesis-supportive function of serum.</p><p>Results</p><p>Serum from MF, PV and ET patients significantly increased proliferation as compared to controls. In addition, serum from MF and ET patients attenuated the loss of a primitive immunophenotype during <i>in vitro</i> culture. The CFU counts were significantly higher if HPCs were cultured with serum of MPN patients as compared to controls. Furthermore, serum of healthy young <i>versus</i> old donors did not evoke significant differences in proliferation or immunophenotype of HPCs, whereas the CFU frequency was significantly increased by serum from elderly patients.</p><p>Conclusion</p><p>Our results indicate that serum derived from patients with MPN comprises activating feedback signals that stimulate the HPCs–and this stimulatory signal may result in a viscous circle that further accelerates development of the disease.</p></div

Moderate association of stimulatory effects of serum with corresponding blood counts.

<p>Mean fluorescence intensities (MFI) were normalized to healthy controls and fold changes were correlated with clinical parameters. (A) Serum taken from patients with low red blood cell (RBC) counts had in tendency higher stimulatory effect on proliferation of HPCs. MFI of residual CFSE staining was normalized by the mean of the healthy control. (B) Proliferation of HPCs was higher in serum with lower platelet counts (PLC). (C) Serum of patients with low RBC counts supported maintenance of CD34 expression better than serum of patients with high RBC counts. (D) White blood counts (WBC) revealed moderate anti-correlation with maintenance of CD133 expression in HPCs upon culture with corresponding serum samples. (E-G) Cytoreductive therapy did not impact on the stimulatory effect of patient serum with regard to (E) proliferation, (F) CD34 expression, and (G) CD133 expression (mean ± standard deviation; n.s. = not significant).</p

Effects of serum from myelofibrosis patients on hematopoietic stem and progenitor cells.

<p>(A) Exemplary histogram to demonstrate higher proliferation of CD34⁺ HPCs in culture medium supplemented with serum of MF patients as compared to serum from healthy controls. After five days, residual staining of carboxyfluorescein succinimidyl ester (CFSE) is lower with MF-serum. Each peak corresponds to one cell division. (B) Mean fluorescence intensity (MFI) of flow cytometric measurements of HPCs that were cultured for 5 days in parallel with 12 MF and 15 control samples. Values were normalized by the mean MFI of healthy controls. (C) Immunophenotypic analysis in relation to the number of cell divisions (according the residual CFSE staining). The numbers provide estimates for cell divisions. (D) CD34⁺ cells were cultured for seven days in parallel with serum-supplements of MF patients (n = 9) or controls (n = 12) and the number of colony forming units (CFUs) was then analyzed. * p<0.05, ** p<0.01, ***p<0.001.</p