The Face of a Frog: Time-Lapse Video Reveals Never-Before-Seen Bioelectric Pattern
Jonathan Wells has already drawn our attention to a recent paper by Vandenberg et al. in the journal Developmental Dynamics. The authors make the startling and innovative discovery that bioelectrical signals are essential for the proper formation of the head and face in frog embryos. Physorg.com reports,
The Tufts biologists found that, before the face of a tadpole develops, bioelectrical signals (ion flux) cause groups of cells to form patterns marked by different membrane voltage and pH levels. When stained with a reporter dye, hyperpolarized (negatively charged) areas shine brightly, while other areas appear darker, creating an "electric face."In the video, you can see for yourself these dynamic patterns of membrane voltage which form the "electric face":
Physorg.com further reports,
First, a wave of hyperpolarization (negative ions) flashed across the entire embryo, coinciding with the emergence of cilia that enable the embryos to move. Next, patterns appeared that matched the imminent shape changes and gene expression domains of the developing face. Bright hyperpolarization marked the folding in of the surface, while both hyperpolarized and depolarized regions overlapped domains of head patterning genes. In the third course, localized regions of hyperpolarization formed, expanded and disappeared, but without disturbing the patterns created during the second stage. At the same time, the spherical embryo began to elongate.
The Tufts team found that disrupting bioelectric signaling by inhibiting ductin (a protein that is part of the machinery that transports hydrogen ions) correlated with craniofacial abnormalities. Some embryos grew two brains rather than one; others had thickened optic nerves or lacked normal nasal or jaw development. Interrupting the ion flux also altered the bioelectric patterns on the embryos' surface and expression of important face patterning mRNAs (messenger RNA that acts as a blueprint for proteins).
You can watch the research team discuss the significance and implications of their work here:
Laura Vandenberg, lead author on the paper, says in the video that "the finding suggests that what we thought about how cells know what to make is incomplete." In the Physorg.com report, she further states,
"Our research shows that the electrical state of a cell is fundamental to development. Bioelectrical signaling appears to regulate a sequence of events, not just one," said Laura Vandenberg. "Developmental biologists are used to thinking of sequences in which a gene produces a protein product that in turn ultimately leads to development of an eye or a mouth. But our work suggests that something else -- a bioelectrical signal -- is required before that can happen."A number of ID proponents have argued in the past that, while DNA provides the information for the specification of proteins, it does not in itself provide the information needed for higher-level organization such as the three-dimensional structure of the embryo. This is controlled and directed, at least in some measure, by information beyond the DNA nucleotide sequence.
The phenomenon of genomic equivalence entails that every cell of a developing embryo (with the exception of T and B lymphocytes) possesses exactly the same DNA sequence. Different cell types are determined by the patterns of gene expression in respective cell types. But cells must receive information concerning their spatial location within the embryo -- so that they "know" to develop into the right kind of cell. This level of organisation cannot be fully determined at the nucleotide sequence level. In fact, many cellular processes which rely on what some have described as "molecular zipcodes" presuppose (rather than determine) a spatial co-ordinate system.
Indeed, previous evidence has suggested that DNA methylation patterns are only applied after patterns of gene expression have already been determined by other mechanisms in the embryo.
Apart from the numerous other problems that plague current understandings of the origin of new genes and protein folds by mutation and selection, if indeed it is the case that higher-level organization is determined independently of the nucleotide sequence, then it appears even more doubtful that mutating DNA alone can be causally sufficient to explain the origin of new body plans.
The failure to explain the origin of animal body plans is a fundamental shortcoming of Darwinian theory, and this problem must be explained by any candidate paradigm that purports to provide a basis for understanding life's origins and evolution.