Abstract
Simultaneous determinations of DNA content in cell nuclei and condensed chromatin bodies formed by heterochromatized regions of sex chromosomes (gonosomal chromatin bodies, GCB) have been performed in two trophoblast cell populations of the East-European field vole Microtus rossiaemeridionalis: in the proliferative population of trophoblast cells of the junctional zone of placenta and in the secondary giant trophoblast cells. One or two GCBs have been observed in trophoblast cell nuclei of all embryos studied (perhaps both male and female). In the proliferative trophoblast cell population characterized by low ploidy levels (2–16c) and in the highly polyploid population of secondary giant trophoblast cells (32–256c) the total DNA content in GCB increased proportionally to the ploidy level. In individual GCBs the DNA content also rose proportionally to the ploidy level in nuclei both with one and with two GCBs in both trophoblast cell populations. Some increase in percentage of nuclei with 2–3 GCBs was shown in nuclei of the placenta junctional zone; this may be accounted for by genome multiplication via uncompleted mitoses. In nuclei of the secondary giant trophoblast cells (16–256c) the number of GCBs did not exceed 2, and the fraction of nuclei with two GCBs did not increase, which suggests the polytene nature of sex chromosomes in these cells. In all classes of ploidy the DNA content in trophoblast cell nuclei with the single GCB was lower than in nuclei with two and more GCBs. This can indicate that the single GCB in many cases does not derive from fusion of two GCBs. The measurements in individual GCBs suggest that different heterochromatized regions of the X- and Y-chromosome may contribute in GCB formation.
Highlights
Study of genome multiplication in various trophoblast cell populations is of great importance for elucidating different mechanisms of genome reproduction responsible for performance by the trophoblast cells of their specific functions
In this aspect our data resemble results of studying interphase nuclei of M. agrestis both in embryonal cells and in definite tissues of adult females and males [9,13,18,19]. In nuclei of both male and female there were most often observed two large compact heterochromatin bodies seen as heteropicnotic areas of X- and Y-chromosomes when the cells entered mitosis
(page number not for citation purposes) http://www.RBEj.com/content/1/1/32. Both sexes in M. rossiaemeridionalis and M. agrestis seems to be due to peculiarities of the structural heterochromatin of the vole sex chromosomes [35,36]; this affects considerably the character of inactivation of X-chromosome in these animals [16,17]
Summary
Study of genome multiplication in various trophoblast cell populations is of great importance for elucidating different mechanisms of genome reproduction responsible for performance by the trophoblast cells of their specific functions. Reproductive Biology and Endocrinology 2003, 1 http://www.RBEj.com/content/1/1/32 of trophoblast cells, various chromosomal markers can be used One of such markers is one of two X-chromosomes, which in female individuals is genetically inactive; this provides for a dose compensation of X-linked genes in somatic cells of female (XX) and male (XY) individuals [1]. In some vole species, large condensed chromatin clumps resembling sex chromatin (Barr body) are revealed in cells both of female and male individuals [8,18,19], presumably due to a significant degree of heterochromatization of both sex chromosomes
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