Competition for Mitogens Regulates Spermatogenic Stem Cell Homeostasis in an Open Niche

In many tissues, homeostasis is maintained by physical contact between stem cells and an anatomically defined niche. However, how stem cell homeostasis is achieved in environments where cells are motile and dispersed among their progeny remains unknown. Using murine spermatogenesis as a model, we find that spermatogenic stem cell density is tightly regulated by the supply of fibroblast growth factors (FGFs) from lymphatic endothelial cells. We propose that stem cell homeostasis is achieved through competition for a limited supply of FGFs. We show that the quantitative dependence of stem cell density on FGF dosage, the biased localization of stem cells toward FGF sources, and stem cell dynamics during regeneration following injury can all be predicted and explained within the framework of a minimal theoretical model based on “mitogen competition.” We propose that this model provides a generic and robust mechanism to support stem cell homeostasis in open, or facultative, niche environments

Anorexia nervosa-associated pancytopenia mimicking idiopathic aplastic anemia: a case report

Abstract Background Patients with anorexia nervosa (AN) often present with pancytopenia. In most cases described in the literature, AN with pancytopenia demonstrates gelatinous marrow transformation (GMT), which is a typical bone marrow feature of malnutrition. Differentiation of AN-associated pancytopenia from other types of pancytopenia, especially idiopathic aplastic anemia (IAA), has not been studied. We encountered a case of pancytopenia in a patient with AN and relatively poor nutritional status, whose hematological findings mimicked those of IAA, specifically fatty bone marrow and absence of GMT. Case presentation The patient was a 32-year-old woman with poorly controlled AN. At 31 years of age, her body mass index (BMI) had fallen from 17.0 kg/m2 to below 13.8 kg/m2. The patient presented with ongoing fatigue and thus was examined by a hematologist. Hematological findings were consistent with IAA: peripheral blood tests revealed pancytopenia, whereas the bone marrow displayed fatty replacement without GMT. Despite the absence of bone marrow features typically seen in malnutrition, the patient’s hematological abnormalities had manifested after a decrease in body weight. Thus, although the bone marrow findings indicated IAA, we considered that the nutritional etiology of pancytopenia could not be thoroughly ruled out. Using nutritional therapy alone, the hematological abnormalities improved as BMI increased to 16.5 kg/m2. The final diagnosis was pancytopenia secondary to malnutrition because pancytopenia and fatty bone marrow improved after implementation of nutritional therapy alone. Conclusions The present case is the first documented case of AN with pancytopenia for which bone marrow examination confirmed fatty marrow without any evidence of GMT. IAA and pancytopenia secondary to malnutrition can present the same clinical findings. This case is significant because it suggests a need to differentiate between malnutrition and IAA

Competition for Mitogens Regulates Spermatogenic Stem Cell Homeostasis in an Open Niche.

In many tissues, homeostasis is maintained by physical contact between stem cells and an anatomically defined niche. However, how stem cell homeostasis is achieved in environments where cells are motile and dispersed among their progeny remains unknown. Using murine spermatogenesis as a model, we find that spermatogenic stem cell density is tightly regulated by the supply of fibroblast growth factors (FGFs) from lymphatic endothelial cells. We propose that stem cell homeostasis is achieved through competition for a limited supply of FGFs. We show that the quantitative dependence of stem cell density on FGF dosage, the biased localization of stem cells toward FGF sources, and stem cell dynamics during regeneration following injury can all be predicted and explained within the framework of a minimal theoretical model based on "mitogen competition." We propose that this model provides a generic and robust mechanism to support stem cell homeostasis in open, or facultative, niche environments.Wellcome Trus