Developmental Biology Quotes

“A quite rare but nevertheless important event before gastrulation in mammalian embryos, including humans, is the splitting of the embryo into two, and identical twins can then develop. This shows the remarkable ability of the early embryo to regulate and develop normally when half the normal size, just like the Driesch experiment. It also makes clear that the early embryo should not be thought of as a human being as it can still develop into two people.”
― Lewis Wolpert, Developmental Biology: A Very Short Introduction

“How is left–right established? Vertebrates are bilaterally symmetric about the midline of the body for many structures, such as eyes, ears, and limbs, but most internal organs are asymmetric. In mice and humans, for example, the heart is on the left side, the right lung has more lobes than the left, the stomach and spleen lie towards the left, and the bulk of the liver is towards the right. This handedness of organs is remarkably consistent, but there are rare individuals, about one in 10,000 in humans, who have the condition known as situs inversus, a complete mirror-image reversal of handedness. Such people are generally asymptomatic, even though all their organs are reversed.”
― Lewis Wolpert, Developmental Biology: A Very Short Introduction

“Finally, we can contemplate the evolution of our understanding of developmental biology. Progress has been impressive but due to the complexity of cells with all their proteins and other molecules interacting, there is still much to be learned. It is likely that in the next 50 years, given the genes and structure of a fertilized egg, it will be possible to reliably compute the details of that organism’s development and just what the adult would be.”
― Lewis Wolpert, Developmental Biology: A Very Short Introduction

“Future motor neurons are located ventrally, and form the ventral roots of the spinal cord. The neurons of the sensory nervous system develop from neural crest cells. The dorso-ventral organization of the spinal cord is produced by Sonic hedgehog protein signals from ventral regions such as the notochord. Sonic hedgehog forms a gradient of activity from ventral to dorsal in the neural tube, and acts as the ventral patterning positional signal. As well as being organized along the dorso-ventral axis, neurons at different positions along the antero-posterior axis of the spinal cord become specified to serve different functions. The antero-posterior specification of neuronal function in the spinal cord was dramatically illustrated some 40 years ago by experiments in which a section of the spinal cord that would normally innervate wing muscles was transplanted from one chick embryo into the region that normally serves the legs of another embryo. Chicks developing from the grafted embryos spontaneously activated both legs together, as though they were trying to flap their wings, rather than activating each leg alternately as if walking. These studies showed that motor neurons generated at a given antero-posterior level in the spinal cord had intrinsic properties characteristic of that position. The spinal cord becomes demarcated into different regions along the antero-posterior axis by combinations of expressed Hox genes. A typical vertebrate limb contains more than 50 muscle groups with which neurons must connect in a precise pattern. Individual neurons express particular combinations of Hox genes, which determine which muscle they will innervate. So all together, expression of genes resulting from dorso-ventral position together with those resulting from antero-posterior position confers a virtually unique identity on functionally distinct sets of neurons in the spinal cord.”
― Lewis Wolpert, Developmental Biology: A Very Short Introduction

“Neurons are formed in the proliferative zone of the vertebrate neural tube from multipotent neural stem cells, which give rise to many different types of neurons and to glia. For many years it was thought that no new neurons could be generated in the adult mammalian brain, but the production of new neurons has been demonstrated as a normal occurrence in the adult mammalian brain, and neural stem cells have been identified in adult mammals that can generate neurons.”
― Lewis Wolpert, Developmental Biology: A Very Short Introduction

“In humans, about 1 in 100 live-born infants has some congenital heart malformation, while in utero, heart malformation leading to death of the embryo occurs in between 5 and 10% of conceptions.”
― Lewis Wolpert, Developmental Biology: A Very Short Introduction

“All the information for embryonic development is contained within the fertilized egg. So how is this information interpreted to give rise to an embryo? Does the DNA contain a full description of the organism to which it will give rise; is it a blueprint for the organism? The answer is no. Instead, the fertilized egg contains a program of instructions for making the organism—a generative program—that determines where and when different proteins are synthesized and thus controls how cells behave. A descriptive program such as a blueprint or a plan describes an object in some detail, whereas a generative program describes how to make an object. For the same object, the programs are very different. Consider origami, the art of paper folding. By folding a piece of paper in various directions it is quite easy to make a paper hat or a bird from a single sheet. To describe in any detail the final form simply by marking regions on the flat piece of paper is really very difficult, and not of much help in explaining how to achieve it. Much more useful and easier to formulate are instructions on how to fold the paper. The reason for this is that simple instructions about folding have complex spatial consequences. In development, gene action similarly sets in motion a sequence of events that can bring about profound changes in the embryo. One can thus think of the genetic information in the fertilized egg as equivalent to the folding instructions in origami; both contain a generative program for making a particular structure.”
― Lewis Wolpert, Developmental Biology: A Very Short Introduction