Quantification of Muscle Satellite Stem Cell Divisions by High-Content Analysis

High-content screening is commonly performed on 2D cultured cells, which is high throughput but has low biological relevance. In contrast, single myofiber culture assay preserves the satellite cell niche between the basal lamina and sarcolemma and consequently has high biological relevance but is low throughput. We describe here a high-content screening method that utilizes single myofiber culture that addresses the caveats of both techniques. Our method utilizes the transgenic reporter allele Myf5-Cre:R26R-eYFP to differentiate stem and committed cells within a dividing couplet that can be quantified by high-content throughput immunodetection and bioinformatic analysis.

Intestinal stem cell response to injury: lessons from Drosophila

Many adult tissues and organs are maintained by resident stem cells that are activated in response to injury but the mechanisms that regulate stem cell activity during regeneration are still poorly understood. An emerging system to study such problem is the Drosophila adult midgut. Recent studies have identified both intrinsic factors and extrinsic niche signals that control the proliferation, self-renewal, and lineage differentiation of Drosophila adult intestinal stem cells (ISCs). These findings set up the stage to interrogate how niche signals are regulated and how they are integrated with cell-intrinsic factors to control ISC activity during normal homeostasis and regeneration. Here we review the current understanding of the mechanisms that control ISC self-renewal, proliferation, and lineage differentiation in Drosophila adult midgut with a focus on the niche signaling network that governs ISC activity in response to injury.

The role of cell location and spatial gradients in the evolutionary dynamics of colon and intestinal crypts

BACKGROUND

Colon and intestinal crypts serve as an important model system for adult stem cell proliferation and differentiation. We develop a spatial stochastic model to study the rate of somatic evolution in a normal crypt, focusing on the production of two-hit mutants that inactivate a tumor suppressor gene. We investigate the effect of cell division pattern along the crypt on mutant production, assuming that the division rate of each cell depends on its location.

RESULTS

We find that higher probability of division at the bottom of the crypt, where the stem cells are located, leads to a higher rate of double-hit mutant production. The optimal case for delaying mutations occurs when most of the cell divisions happen at the top of the crypt. We further consider an optimization problem where the "evolutionary" penalty for double-hit mutant generation is complemented with a "functional" penalty that assures that fully differentiated cells at the top of the crypt cannot divide.

CONCLUSION

The trade-off between the two types of objectives leads to the selection of an intermediate division pattern, where the cells in the middle of the crypt divide with the highest rate. This matches the pattern of cell divisions obtained experimentally in murine crypts.

REVIEWERS

This article was reviewed by David Axelrod (nominated by an Editorial Board member, Marek Kimmel), Yang Kuang and Anna Marciniak-Czochra. For the full reviews, please go to the Reviewers' comments section.

Nek11 regulates asymmetric cell division during mouse oocyte meiotic maturation

Nek11, a member of the never in mitosis gene A (NIMA) family, is activated in somatic cells associated with G1/S or G2/M arrest. However, its function in meiosis is unknown. In this research, the expression, localization and functions of NEK11 in the mouse oocyte meiotic maturation were examined. Western blotting indicated that NEK11S was the major NEK11 protein in mouse oocyte. MYC-tagged Nek11 mRNA microinjection and immunofluorescent staining showed that NEK11 was localized to the meiotic spindles at MI and MII stage. Knockdown of Nek11 by microinjection of siRNA did not affect germinal vesicle breakdown (GVBD) and the first polar body extrusion, but caused formation of 2-cell-like eggs. These results demonstrate that Nek11 regulates asymmetric cell division during oocyte meiotic maturation.

Division of shape-standardized tobacco cells reveals a limit to the occurrence of single-criterion-based selection of the plane of symmetric division

The plane of symmetric plant cell division tends to be selected so that the new cross-wall halving the cell volume has the least possible area, and several cases of such selection are best represented by a recently formulated model which promotes the view that the strength of the least area tendency is the only criterion for selecting the plane. To test this model, the present study examined the divisions of two types of shape-standardized tobacco BY-2 cell, oblate-spheroidal (os) cells prepared from protoplasts and spheri-cylindrical (sc) cells with unusual double-wall structures prepared from plasmolyzed cells. Measurements of cell shape parameters and division angles revealed that both cell types most frequently divide nearly along their short axes. While os cells did not exhibit any other division angle bias, sc cell division was characterized by another bias which made the frequency of longitudinal divisions secondarily high. The geometry of sc cells barely allows the longitudinal cross-walls to have locally minimum areas. Nevertheless, a comparison of detected and hypothetical standard divisions indicates that the frequency of longitudinal sc cell division can be significantly higher than that predicted when the longitudinal cross-walls are assumed to have locally minimum areas smaller than their original areas. These results suggest that, even in isolated plant cell types, the strength of the least area tendency is not the only criterion for selecting the division plane. The possibility that there is another basic, though often hidden, criterion is discussed.