Monosomy of the X chromosome owing to divergence between the sex chromosomes leads to dosage compensation mechanisms to restore balanced expression between the X and the autosomes In Drosophila melanogaster, upregulation of the male X leads to dosage compensation It has been hypothesized that mammals likewise upregulate their active X chromosome Together with X inactivation, this mechanism would maintain balanced expression between the X chromosome and autosomes and between the sexes Here, we show that doubling of the global expression level of the X chromosome leads to dosage compensation in somatic tissues from several mammalian species X-linked genes are highly expressed in brain tissues, consistent with a role in cognitive functions Furthermore, the X chromosome is expressed but not upregulated in spermatids and secondary oocytes, preserving balanced expression of the genome in these haploid cells Upon fertilization, upregulation of the active X must occur to achieve the observed dosage compensation in early embryos

Dosage compensation of the active X chromosome in mammals.

The spermatogonial stem cell initiates and maintains spermatogenesis in the testis. To perform this role, the stem cell must self replicate as well as produce daughter cells that can expand and differentiate to form spermatozoa. Despite the central importance of the spermatogonial stem cell to male reproduction, little is known about its morphological or biochemical characteristics. This results, in part, from the fact that spermatogonial stem cells are an extremely rare cell population in the testis, and techniques for their enrichment are just beginning to be established. In this investigation, we used a multiparameter selection strategy, combining the in vivo cryptorchid testis model with in vitro fluorescence-activated cell sorting analysis. Cryptorchid testis cells were fractionated by fluorescence-activated cell sorting analysis based on light-scattering properties and expression of the cell surface molecules α6-integrin, αv-integrin, and the c-kit receptor. Two important observations emerged from these analyses. First, spermatogonial stem cells from the adult cryptorchid testis express little or no c-kit. Second, the most effective enrichment strategy, in this study, selected cells with low side scatter light-scattering properties, positive staining for α6-integrin, and negative or low αv-integrin expression, and resulted in a 166-fold enrichment of spermatogonial stem cells. Identification of these characteristics will allow further purification of these valuable cells and facilitate the investigation of molecular mechanisms governing spermatogonial stem cell self renewal and hierarchical differentiation.

https://www.pnas.org/content/pnas/97/15/8346.full.pdf

Spermatogonial stem cell enrichment by multiparameter selection of mouse testis cells.

Regulation of Early Wave of Germ Cell Apoptosis and Spermatogenesis by Deubiquitinating Enzyme CYLD

Sertoli cells--immunological sentinels of spermatogenesis.

The autosomal gene DAZL is a member of a family of genes (DAZL, DAZ, BOULE), all of which contain a consensus RNA binding domain and are expressed in germ cells. Adult male and female mice null for Dazl lack gametes. In order to define more precisely the developmental stages in germ cells that require Dazl expression, the patterns of germ cell loss in immature male and female wild-type (+/+, WT) and Dazl ‐/‐ (DazlKO) mice were analysed. In females, loss of germ cells occurred during fetal life and was coincident with progression of cells through meiotic prophase. In males, testes were recovered from WT and DazlKO males obtained before and during the first wave of spermatogenesis (days 2‐19). Mitotically active germ cells were present up to and including day 19. Functional differentiation of spermatogonia associated with detection of c-kit positive cells did not depend upon expression of Dazl. RBMY-positive cells (A, intermediate, B spermatogonia, zygotene and preleptotene spermatocytes) were reduced in DazlKO compared with WT testes. Staining of cell squashes from day 19 testes with anti-‐ H2AX and anti-SCP3 antibodies showed that germ cells from DazlKO males were unable to progress beyond the leptotenestageofmeioticprophaseI.Itwasconcludedthat in the absence of Dazl, germ cells can complete mitosis, and embark on functional differentiation but that, in both sexes, progression through meiotic prophase requires this RNA binding protein.

/pdf/absence-of-mdazl-produces-a-final-block-on-germ-cell-3wnc3be6eb.pdf

Absence of mDazl produces a final block on germ cell development at meiosis

Analysis of the biochemical events and the genes expressed at various postnatal developmental stages in the testis of mammals is of great importance for understanding spermatogenesis in general and meiosis in particular. A prerequisite for such an analysis is the characterization of a detailed developmental schedule of the postnatal testis. In this study we used four-parameter flow cytometry analysis to determine a detailed testicular developmental schedule in rats as compared to mice. A dot plot of forward-scatter/side-scatter of testicular cell suspensions from mature animals revealed 7 distinct subpopulations within the testis. These, when analyzed by fluorescence parameters, were divided into 4 levels of fluorescence: cells containing 4d DNA, 2d DNA, and 2 levels of haploid cells. Observing the acquisition pattern of these subpopulations during postnatal development, we were able to suggest the following developmental schedule for the rat. At postnatal Days 6-7, the testis contains somatic cells and spermatogonia cells only. By Days 13-14, leptotene spermatocytes appear; by Days 17-18, zygotene spermatocytes are present; by Days 19-20 and Days 22-23, early and late pachytene spermatocytes, respectively, are seen. Haploid round spermatids first appear at Days 24-25 and elongating spermatids by Days 30-31; by Day 36, elongated spermatozoa can be found.

/pdf/developmental-schedule-of-the-postnatal-rat-testis-51u798a43h.pdf

Mira Malkov

Papers

Developmental Schedule of the Postnatal Rat Testis Determined by Flow Cytometry