Human cytogenetics at Johns Hopkins Hospital, 1959-1962

An account is given of the introduction of human cytogenetics to the Division of Medical Genetics at Johns Hopkins Hospital, and the first 3 years' work of the chromosome diagnostic laboratory that was established at the time. Research on human sex chromosome disorders, including novel discoveries in the Turner and Klinefelter syndromes, is described together with original observations on chromosome behavior at mitosis. It is written in celebration of the centenary of the birth of Victor McKusick, the acknowledged father of Medical Genetics, who established the Division and had the foresight to ensure that it included the investigation of human chromosomes.

snRPN controls the ability of neurons to regenerate axons

BACKGROUND

Retinal ganglion cells (RGCs) of mammals lose the ability to regenerate injured axons during postnatal maturation, but little is known about the underlying molecular mechanisms.

OBJECTIVE

It remains of particular importance to understand the mechanisms of axonal regeneration to develop new therapeutic approaches for nerve injuries.

METHODS

Retinas from newborn to adult monkeys (Callithrix jacchus)1 were obtained immediately after death and cultured in vitro. Growths of axons were monitored using microscopy and time-lapse video cinematography. Immunohistochemistry, Western blotting, qRT-PCR, and genomics were performed to characterize molecules associated with axonal regeneration and growth. A genomic screen was performed by using retinal explants versus native and non-regenerative explants obtained from eye cadavers on the day of birth, and hybridizing the mRNA with cross-reacting cDNA on conventional human microarrays. Followed the genomic screen, siRNA experiments were conducted to identify the functional involvement of identified candidates.

RESULTS

Neuron-specific human ribonucleoprotein N (snRPN) was found to be a potential regulator of impaired axonal regeneration during neuronal maturation in these animals. In particular, up-regulation of snRPN was observed during retinal maturation, coinciding with a decline in regenerative ability. Axon regeneration was reactivated in snRPN-knockout retinal ex vivo explants of adult monkey.

CONCLUSION

These results suggest that coordinated snRPN-driven activities within the neuron-specific ribonucleoprotein complex regulate the regenerative ability of RGCs in primates, thereby highlighting a potential new role for snRPN within neurons and the possibility of novel postinjury therapies.

History and evolution of cytogenetics

The events that have led to the development of cytogenetics as a specialty within the life sciences are described, with special attention to the early history of human cytogenetics. Improvements in the resolution of chromosome analysis has followed closely the introduction of innovative technology. The review provides a brief account of the structure of somatic and meiotic chromosomes, stressing the high conservation of structure in plants and animals, with emphasis on aspects that require further research. The future of molecular cytogenetics is likely to depend on a better knowledge of chromosome structure and function.