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B N Nagorcka

Publications and source records attributed to B N Nagorcka.

8 recordsLinked to original sources
PubMed1992

From stripes to spots: prepatterns which can be produced in the skin by a reaction-diffusion system.

A key question in the area of spatial pattern formation in developmental biology is: how do groups of cells in a homogeneous tissue suddenly differentiate along entirely different developmental paths compared to neighbouring cells? Although experiments are now beginning to provide answers to this question, the mechanisms responsible for the development of repeated or periodic structures and spatial patterns, e.g., hair follicles and pigmentation patterns, are still unknown. Theoretical biologists and applied mathematicians have suggested various prepattern mechanisms as the primary cause of repeated or periodic spatial patterns. A class of biochemical reactions referred to here as reaction-diffusion (RD) systems, having the capacity to spontaneously generate stable stationary wavelike spatial patterns (Turing, 1952), has been suggested as a possible prepattern mechanisms, e.g., during hair follicle initiation and development (Nagorcka, 1989), and pigmentation patterns (Murray, 1989). Spatial patterns arising during development of the vertebrate skin are frequently complex. Spatial patterns in the skin can be seen to vary within an individual from one region of the skin to another. One pattern change commonly observed across the skin is from stripes to spots. An RD system is defined which is able to generate different spatial patterns depending on the value of a single parameter. The parameter varied controls the transport of the chemical components of the RD system across the basement membrane separating the epidermis and dermis. The patterns produced range from stripes to an irregular array of spots. Not only are different patterns produced, but a different time sequence of prepatterns is expected to arise in the different skin regions depending on whether the first prepattern in an array of spots or stripes. As a consequence it is possible to account for hair follicle initiation in the hair-bearing regions of the mammalian skin as well as the sequence of events required for the formation of dermatoglyphics in the volar regions.

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PubMed1989

Wavelike isomorphic prepatterns in development.

The patterns generated by these mechanisms are usually wavelike spatial patterns in the distribution of the chemical components and/or physical properties of the organism or tissue being considered. In this paper the range of patterns generated by one of these mechanisms, namely the reaction-diffusion (RD) system (Turing, 1952), is reviewed and its potential to function as a source of isomorphic prepatterns for the regulation of development in a wide range of organisms is illustrated. Examples have been chosen to show the capacity of an RD system to generate a single stationary spatial prepattern, as well as a travelling wavelike spatial prepattern. However, the full potential of an RD system to regulate development stems from its capacity to spontaneously generate a temporal sequence of isomorphic stationary wavelike spatial prepatterns, rather than just a single isomorphic stationary spatial prepattern. To demonstrate this point the examples presented include the morphogenesis of the skin and some of its appendages, as well as the early decisions in the embryogenesis of Drosophila leading to segmentation. The mini-review begins by comparing the concepts of positional information and a temporal sequence of isomorphic prepatterns, which represent two quite different approaches to understanding the spatial and temporal regulation of cellular differentiation.

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PubMed1988

A pattern formation mechanism to control spatial organization in the embryo of Drosophila melanogaster.

It is known that cells are already committed to a particular segment at the cellular blastoderm stage during embryogenesis of Drosophila melanogaster. Recently, several segmentation genes have been observed to be expressed in a sequence of banded spatial patterns in the syncytial blastoderm, prior to the formation of the cellular blastoderm. It is demonstrated in this paper that a two component reaction-diffusion (RD) system with net production functions which are antisymmetric with respect to the uniform steady-state values, is capable of producing a sequence of seven spatial patterns in the syncytial blastoderm. The sequence of patterns obtained exhibit a strong preference for banded or striped patterns. The first pattern is a simple anteroposterior gradient while the second is a gradient in the dorsoventral direction. The next five patterns are a sequence of banded patterns which exhibit frequency doubling, i.e. the number of bands in each pattern tend to be double the number in the previous pattern. The predicted pattern sequence is comparable to that observed in the expression of some segmentation genes. It is suggested that a pattern formation mechanism based on such an RD system may exist in the embryo where it produces a sequence of prepatterns to regulate the expression of various segmentation genes leading ultimately to a segmented embryo. There is sufficient spatial information in the sequence of banded prepatterns for the segments to be unique.

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PubMed1985

Spatial patterns produced by a reaction-diffusion system in primary hair follicles.

This paper is the third in a series examining the role of a reaction-diffusion (RD) system as the principal mechanism providing spatial information for cell differentiation during hair follicle initiation and development and hair fibre formation. A theoretical mechanism is described by which the RD system supplies positional information during hair follicle development. Solutions of the RD system within the primordial follicle are described as well as the sequence of spatial patterns provides the follicle/epidermis boundary conditions required to account for the density and grouping of follicles during initiation. At the same time the spatial patterns are also shown to be capable of providing the positional information which determines various geometrical aspects of follicle development; in particular the development of follicles at an angle to the skin surface and the initiation and location of sweat glands and sebaceous glands on the follicle.

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PubMed1985

The role of a reaction-diffusion system in the initiation of primary hair follicles.

A mechanism based on a reaction-diffusion system is proposed for the initiation of hair follicles in the epidermis during fetal development. It is demonstrated that initiation of primary follicles in a series of waves, within the proposed mechanism, is a consequence of the size and shape dependent properties of the reaction-diffusion system without the need for the propagation of signals through the skin. The observed trio grouping of follicles and variation of primary follicle density per unit skin area during development are also correctly predicted. An explanation, based on the reaction-diffusion system and the variation of its characteristic spatial wavelength with time during development, is suggested for the termination of both primary and secondary follicle initiation as well as follicle neogenesis. The proposed initiation mechanism is basically the same as that used to explain various spatial patterns observed in hair fibre formation (Nagorcka & Mooney, 1982).

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PubMedDate not supplied

Evidence for a reaction-diffusion system as a mechanism controlling mammalian hair growth.

A scheme is outlined for the differentiation of epithelial cells in hair follicle bulbs which requires several spatial pattern properties characteristics of a reaction-diffusion system. Spatial patterns in the reacting and diffusing substances, called morphogens , develop spontaneously depending on the size and shape of the follicle bulb. The patterns correctly predict the cross-sectional shape of several classes of fibres known as awls , auchenes and zigzags found in mice. The spatial patterns also determine the distribution of ortho- and para-cortical cells within the fibre cross-section. In order to explain the observed variation in the morphology of zigzag fibres it is necessary to use the capacity of a reaction-diffusion system to produce spatial patterns with a preferred orientation. Moving the dermal papilla of the hair follicle bulb off-centre causes a homogeneous pattern of morphogens to become unstable and a bilateral pattern to develop with a preferred orientation. This phenomenon forms the basis of a control mechanism for the formation of zigzag fibres.

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