Biology Reference
In-Depth Information
CHAPTER
7
Cell Migration in Development:
A Brief Overview
Cell migration takes place at least at some point in the life cycle of almost all animals. For
some, such as coelenterates, it is an important but rather rare event, whereas for others, such
as vertebrates, cell migration is involved in the morphogenesis of most parts of the body. This
chapter will present an overview of the broad types of cell migration that are common in
development: the chapters that follow will examine in detail the cellular mechanisms
involved in their guidance and regulation.
Cell migration of one sort or another is an almost universal attribute of sexual reproduction,
for the obvious reason that two gametes produced in different places, and usually in different
individuals, have to unite. Some organisms, usually ones that are anatomically simple, produce
gametes that are morphologically identical (isogamous) even if they happen to be divided into
two biochemically distinct 'mating types'. In these cases, the gametes share the task of finding
each other. This does not always involve cell migration; in the filamentous alga Spyrogyra,for
example, gametes remain in the organism that produces them and find each other simply by
extending a cell process towards the gametes of an adjacent individual
1
(
Figure 7.1
a). In most
FIGURE 7.1
Mechanisms for bringing gametes together. (a) Union of gametes by extension of cell processes in the
isogametic alga Spyrogyra. The upper conjugation is seen at a late stage, after union of gametes, while the lower one is just
beginning. (b) Amoeboid sperm of the nematode Caenorhabditis elegans, drawn from a phase contrast micrograph.
2
(c)
Spermof the decapod Inacnus, showing actin-rich extensions. (d) Human sperm, showing a single long flagellum. (e) The
pollen tube (p.t.) of a flowering plant, growing towards the ovule (ov); the size of the pollen tube is exaggerated for clarity.
