Editor's note: Science Scan is a round-up of recently published biotechnology-related research.
Fish are smooth, sleek, streamlined creatures, purpose-designed for swimming. No limbs or external genitalia clutter their hydrodynamic form.
Humans have arms and legs, fingers and toes, essential for moving on land and grasping and manipulating objects, from stone tools to computer keyboards. And the male of the species possesses a cylindrical, erectile genital member, ideal for deep impregnation of the female with sperm.
These apical — endpoint — protuberances are common to all mammals and birds, bespeaking, say evolutionists, their transition from an aquatic to a terrestrial life- style.
For them to acquire these bumps on the smooth log required the emergence of genes dedicated to apical morphogenesis during embryogenesis. Human babies born without digits or external genitalia reflect mutations in one or more of those genes.
"The 39 'master control' Hox genes regulate embryonic development in vertebrates," observed medical geneticist Jeffrey Innis, "by coordinating the activity of other genes — turning them on and off at precise times and locations as the embryo develops."
Innis is an assistant professor of medical genetics at the University of Michigan Medical School, in Ann Arbor.
Last month, he reported to the American Society for Human Genetics meeting in Baltimore that an experimental mutation in one Hox gene, Hoxad-13, caused abnormal limb and genital development in mice. One such mutation, inherited over six generations by a Michigan family, gave Innis the clue linking evolutionary and embryological development in mice and humans.
He is co-author, with biologist Denis Duboule, of the University of Geneva, Switzerland, of a brief communication in the current issue of Nature, dated Nov. 6, 1997. It bears the tantalizing headline: "Of fingers, toes and penises."
The Swiss-American team raised compound mutant mice carrying various deletions in a Hox gene complex, resulting in partial or complete absence of embryonic buds that preform toes and feet. "This progressive reduction in genital bud size with reductions in Hox gene dose," their paper reports, "was accompanied by proportional reductions in digit size." It went on to note: "Mild anatomic defects in these two structures also occur in the human hand-foot-genital syndrome, which involves a mutation within Hoxad-13."
The team's transgenic mouse embryos lacking this gene died in utero with "complete absence of external genitalia."
They also noted, as evidence of water-to-land evolution, that "in fish, which lack digits and external genitalia, posterior Hox genes are expressed in areas from which these structures emerged (the cloacal region and paired fins)." They added: "Related phylogenetic histories between digits and the penis/clitoris thus seem plausible, and may reflect combined adaptive or preadaptive solutions to the transition toward a terrestrial environment . . . necessary for efficient locomotion and internal fertilization."
A Nature press summary of this article concluded: "It suggests that those rude jokes about the predictive value of shoe sizes could have some basis in fact." In other words, Hox is nature's way of giving mankind the finger.
Recently Discovered Egyptian Mummy With TB Beats Previously Found Peruvian Mummy By 1,000 Years
A male Egyptian who lived between 3,000 and 3,500 years ago died, in his 30s, with pulmonary tuberculosis.
A team of German archeologists from the University of Munich reported this highly post-mortem diagnosis in the current issue of The Lancet, dated Nov. 8, 1997. The brief item is headed "Molecular evidence for tuberculosis in an ancient Egyptian mummy."
It pointed out that "the molecular diagnosis of tuberculosis in historic specimens has thus far only been successful in a Peruvian mummy dating to about 1,000-1,300 A.D., [See BioWorld Today, Mar. 15, 1994, p. 1], and has not been reported before in an Egyptian mummy."
The expedition excavated the mummified remains at the tombs of the nobles in Thebes-West, Upper Egypt, and "under sterile conditions" removed previously undisturbed tissues from its lungs and adjacent chest areas.
They extracted DNA for PCR amplification of mycobacterial DNA and recovered a surface antigen expressed in Mycobacterium species. When sequenced, this confirmed M. tuberculosis as the cause of pulmonary and bone pathology in their long-dead "patient."
The report concluded that "a carefully controlled analysis of ancient Egyptian mummies may provide new insights in infectious diseases of ancient individuals and populations."
Discovery Of Receptor That Binds Nicotine In Brain Elucidates Addiction, Epilepsy, Alzheimer's Disease
What's an addictive alkaloid like nicotine doing docked to a neurotransmitter receptor in the human brain? Acetylcholine (Ach) is the usual activator of this nicotinic cholinergic receptor, so-called because it naturally binds and responds to nicotine.
This counter-intuitive neuronal encounter takes place in the hippocampus, a brain region thought to be critical in learning and memory.
Scientists at the National Institute of Environmental Health Sciences (NIEHS), in Research Triangle Park, N.C., report finding this receptor in the Nov. 1, 1997 issue of the British Journal of Physiology (v. 504.3, 603-610). Their paper bears the title: "Functional nicotinic Ach receptors on interneurons in the rat hippocampus."
The article's senior author, NIEHS neuroscientist Jerrel Yakel, observed that the identification of this receptor in the hippocampus may have relevance to nicotine addiction, to a rare form of epilepsy, and to enhancement of memory in some Alzheimer's disease patients. "It may also be important," he added, "in other diseases, such as depression or Parkinson's." *