Continuity of spermatogenesis in mammals is underpinned by spermatogenic (also called spermatogonial) stem cells (SSCs) that self-renew and differentiate into sperm that pass on genetic information to the next generation. Despite the fundamental role of SSCs, the mechanisms underlying SSC homeostasis are only partly understood. During homeostasis, the stem cell pool remains constant while differentiating cells are continually produced to replenish the lost differentiated cells. One of the outstanding questions here is how self-renewal and differentiation of SSCs are balanced to achieve a constant self-renewing pool. In this review, we shed light on the regulatory mechanism of SSC homeostasis, with focus on the recently proposed mitogen competition model in a facultative (or open) niche microenvironment.
Meiosis is a crucial process for spermatogenesis and oogenesis. Initiation of meiosis coincides with spermatocyte differentiation and is followed by meiotic prophase, a prolonged G2 phase that ensures the completion of numerous meiosis-specific chromosome events. During meiotic prophase, chromosomes are organized into axis-loop structures, which underlie meiosis-specific events such as meiotic recombination and homolog synapsis. In spermatocytes, meiotic prophase is accompanied by robust alterations of gene expression programs and chromatin status for subsequent sperm production. The mechanisms regulating meiotic initiation and subsequent meiotic prophase programs are enigmatic. Recently, we discovered MEIOSIN (Meiosis initiator), a DNA-binding protein that directs the switch from mitosis to meiosis. This review mainly focuses on how MEIOSIN is involved in meiotic initiation and the meiotic prophase program during spermatogenesis. Further, we discuss the downstream genes activated by MEIOSIN, which are crucial for meiotic prophase-specific events, from the viewpoint of chromosome dynamics and the gene expression program.
Mycoheterotrophic plants can derive carbon from fungi rather than from photosynthesis. Habitat destruction and sensitivity to environmental perturbation may result in the loss of biodiversity including genetic variation of mycoheterotrophic plants. Burmannia nepalensis (Miers) Hook.f. (Burmanniaceae) is a mycoheterotrophic plant with a wide distribution across southern China and southern and eastern Asia. As part of our endeavor to reveal population genetic patterns of mycoheterotrophic plants, fifteen microsatellite loci were developed by RAD (restriction site-associated DNA) sequencing in 89 individuals from four populations of B. nepalensis. A total of 49 alleles were amplified. The number of alleles per locus ranged from two to six with an average of 3.3. The observed and expected heterozygosity per population varied from 0.000 to 1.000 and from 0.000 to 0.722, respectively. A transferability test showed that only one to five loci could be cross-amplified successfully in four other congeneric species of Burmannia. These markers can be used to reveal population genetic diversity in B. nepalensis, and will help to elucidate the evolutionary history and to enhance efforts for conservation of mycoheterotrophic plants.
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