Inactivation by ammonia of the photosynthetic reduction of nitrate in Nostoc muscorum particles.

Ammonia, as well as other uncouplers of photophosphorylation, strongly inhibit the photosynthetic reduction of nitrate by particles of the blue-green alga Nostoc muscorum. The enzyme responsible for nitrate reduction, nitrate reductase, can be reversibly inactivated by reduction in a ferredoxin-dependent reaction. Nitrate protects against this inactivation, and molecular oxygen restores the original activity.     

Continuous loss of oocytes throughout meiotic prophase in the normal mouse ovary

The number of germ cells reaches the maximum just prior to entry into meiosis, yet decreases dramatically by a few days after birth in the female mouse, rat, and human. Previous studies have reported a major loss at the pachytene stage of meiotic prophase during fetal development, leading to the hypothesis that chromosomal pairing abnormalities may be a signal for oocyte death. However, the identification as well as the quantification of germ cells in these studies have been questioned. A recent study using Mouse Vasa Homologue (MVH) as a germ cell marker reached a contradictory conclusion claiming that oocyte loss occurs in the mouse only after birth. In the present study, we established a new method to quantify murine germ cells by using Germ Cell Nuclear Antigen-1 (GCNA-1) as a germ cell marker. Comparison of GCNA-1 and MVH immunolabeling revealed that the two markers identify the same population of germ cells. However, nuclear labeling of GCNA-1 was better suited for counting germ cells in histological sections as well as for double labeling with the antibody against synaptonemal complex (SC) proteins in chromosome spreading preparations. The latter experiment demonstrated that the majority of GCNA-1-labeled cells entered and progressed through meiotic prophase during fetal development. The number of GCNA-1-positive cells in the ovary was estimated by counting the labeled cells retained in chromosome spreading preparations and also in histological sections by using the ratio estimation method. Both methods demonstrated a continuous decline in the number of GCNA-1-labeled cells during fetal development when the oocytes progress through meiotic prophase. These observations suggest that multiple causes are responsible for oocyte elimination.     

Accumulation of piRNAs in the chromatoid bodies purified by a novel isolation protocol

Haploid male germ cells are featured by an intriguing cytoplasmic cloud-like structure that has been named as chromatoid body (CB) on the basis of its staining properties and appearance under a microscope. Notwithstanding its early discovery in the late 19th century, the function of the CB is still largely obscure. Emerging evidence suggests a role for the CB and other similar RNA-containing granules, such as germ plasm in lower organism and processing bodies in somatic cells, in the control and organization of RNA processing and/or storage. Despite the increasing scientific demand, the lack of CB purification protocols has still been the main obstacle in the functional characterization of this structure. We have successfully isolated CBs from mouse testis by a novel immunoaffinity purification procedure and validated by several different methods that pure CB fractions are obtained. Analysis of the CB RNA content reveals enrichment of PIWI-interacting RNAs (piRNAs), further emphasizing the role of CB as the RNA processing body.