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At least 235 records · Page 13Linked to original sources
PubMed1999

Sequence of neuron origin and neocortical laminar fate: relation to cell cycle of origin in the developing murine cerebral wall.

Neurons destined for each region of the neocortex are known to arise approximately in an "inside-to-outside" sequence from a pseudostratified ventricular epithelium (PVE). This sequence is initiated rostrolaterally and propagates caudomedially. Moreover, independently of location in the PVE, the neuronogenetic sequence in mouse is divisible into 11 cell cycles that occur over a 6 d period. Here we use a novel "birth hour" method that identifies small cohorts of neurons born during a single 2 hr period, i.e., 10-20% of a single cell cycle, which corresponds to approximately 1.5% of the 6 d neuronogenetic period. This method shows that neurons arising with the same cycle of the 11 cycle sequence in mouse have common laminar fates even if they arise from widely separated positions on the PVE (neurons of fields 1 and 40) and therefore arise at different embryonic times. Even at this high level of temporal resolution, simultaneously arising cells occupy more than one cortical layer, and there is substantial overlap in the distributions of cells arising with successive cycles. We demonstrate additionally that the laminar representation of cells arising with a given cycle is little if at all modified over the early postnatal interval of histogenetic cell death. We infer from these findings that cell cycle is a neuronogenetic counting mechanism and that this counting mechanism is integral to subsequent processes that determine cortical laminar fate.

Aging↗
PubMedDate not supplied

[Dactylogyrids (Monogenea: Dactylogyridea) with unusual number of the anchors, their origin and phylogenetic significance. Original data].

The haptors Dactylogyrus spp., Anacanthorus sp., Trianchoratus sp. and Schilbetrematoides pseudodactylogyrus are investigated. On the base of the morphology, transfer of the domus, etc. a homology of the hooks in dactylogyrids (s. s.) and the pin-like structures (4 "A") in the haptor of Anacanthorinae and Dactylogyridae sensu Bychowsky et Nagibina, 1978 is demonstrated. The vestiges of the anchors in the haptor of dactylogyrids (s. l.), according to morphological data, correspond to the point of anchor formed during the ontogenesis. In S. pseudodactylogyrus the pins are redescribed as typical vestiges of the anchors.

Animals↗