Evaluation of mitotic activity in tapetal cells of grapevine (Vitis L.)

The knowledge with reference to the grapevine tapetum has been centered on its anatomy/morphology and hardly anything at all is known about its mitotic activity throughout the microsporogenesis. The aim of this study was to ascertain the mitotic activity in tapetal cells of some grapevines (Vitis L.) broadening knowledge about this tissue and simultaneously corroborating the viability of its use as an alternative tissue for further cytogenetic studies. Young buds of 12 grapevine varieties at different meiotic stages were squashed and tapetal cells a prometaphase/metaphase scored in each meiotic stage. Mitotic activity was observed since the beginning of microsporogenesis, where it was more intense, decreasing toward tetrad. Polyploid tapetal cells arose through endomitosis while the microsporogenesis advanced. Two types of polyploid cells were evidenced, those with two or more individualized diploid chromosome groups and those with only one polyploid group. The percentage of diploid cells and of polyploid cells with two or more individualized diploid groups was higher during the first stage of microsporogenesis, though decreasing and giving way to cells with one large polyploid group as microsporogenesis moved toward tetrad. The nucleolus number was scored at interphase at different stages. Two and four nucleoli prevailed in tapetal cells at all stages except at tetrad where one large nucleolus was seen. The results showed that despite of the squashing technique applied, grapevine tapetum has a substantial amount of cells with mitotic activity with a satisfactory chromosome spreading therefore establishing an interesting alternative and promising tissue for later cytomolecular studies.

Chromosome spreading of the (TTAGGG)n repeats in the Pipa carvalhoi Miranda-Ribeiro, 1937 (Pipidae, Anura) karyotype

Pipidae is a clade of Anura that diverged relatively early from other frogs in the phylogeny of the group. Pipids have a unique combination of morphological features, some of which appear to represent a mix of adaptations to aquatic life and plesiomorphic characters of Anura. The present study describes the karyotype of Pipa carvalhoi Miranda-Ribeiro, 1937, including morphology, heterochromatin distribution, and location of the NOR site. The diploid number of P. carvalhoi is 2n=20, including three metacentric pairs (1, 4, 8), two submetacentric (2 and 7), three subtelocentric (3, 5, 6), and two telocentric pairs (9 and 10). C-banding detected centromeric blocks of heterochromatin in all chromosome pairs and the NOR detected in chromosome pair 9, as confirmed by FISH using the rDNA 28S probe. The telomeric probes indicated the presence of interstitial telomeric sequences (ITSs), primarily in the centromeric region of the chromosomes, frequently associated with heterochromatin, suggesting that these repeats are a significant component of this region. The findings of the present study provide important insights for the understanding of the mechanisms of chromosomal evolution in the genus Pipa, and the diversification of the Pipidae as a whole.

FREE FETAL DNA AS A SCREENING TEST FOR ANEUPLOIDY – DOES IT ADD UP?

The possibility of prenatal screening for genetic disorders was raised as early as the mid-1950s, and with the introduction in 1966 of amniocentesis for sampling fetal material, it became possible to identify pregnancies with trisomy 21 (Down syndrome), the most common prenatal genetic abnormality. The fetal cells in the amniotic fluid could be cultured, then harvested, followed by chromosome spreading on microscope slides. These chromosome spreads, each representing the chromosomes from a single cell nucleus, could be stained, visualised by light microscopy and counted to establish the chromosome number. However, diagnosis of Down syndrome was expensive, and in the early days of amniocentesis, there was an associated risk of miscarriage; most countries therefore recommended this procedure only for women who were identified as having a raised risk of chromosome abnormality. As it is well established that raised maternal age increases the risk of Down syndrome, amniocentesis was first offered only to women above an age cut-off (usually 35). However, although the risk to an individual woman of having a Down syndrome pregnancy is greater in this age group, the majority of Down syndrome babies are born to younger women, due to the preponderance of pregnancies in the younger group.