Introduction 
THE annual publication of Research 
in Progress has become one of the 
highlights of the Howard Hughes Medi- 
cal Institute's research activities. By pro- 
viding a synoptic overview of the re- 
search being conducted by the Institute's 
investigators, in essentially nontechnical 
language, it has come to be greatly ap- 
preciated not only by those interested in 
the Institute's activities as a Medical Re- 
search Organization, but by many others 
who view it as an accessible introduction 
to current biomedical research. 
The present volume in this series follows fairly 
closely the pattern that has evolved over the past 
three or four years: it provides a snapshot of the 
status of the Institute's research in early 1991 . As 
in the previous volume, this issue includes a se- 
ries of introductory essays that are intended to 
assist the reader who has had little or no back- 
ground in biology or medicine. These essays are 
not intended to be exhaustive nor simply to repli- 
cate material readily available in most standard 
biology or medical texts; rather they are intended 
to serve as an expanded glossary of terms, defin- 
ing in a general way many of the terms used in the 
individual reports. To emphasize this feature of 
the essays, these technical terms are shown in 
bold type. The essays are based on an initial set of 
drafts prepared for each of the five programmatic 
areas in which the Institute conducts research: 
cell biology and regulation; genetics; immunol- 
ogy; neuroscience; and structural biology. The 
original drafts were kindly prepared by Drs. 
Richard O. Hynes, Philip Leder, Charles A. Jane- 
way, Eric R. Kandel, and Stephen C. Harrison, re- 
spectively. We are grateful to them and to a num- 
ber of their colleagues within the Institute who 
commented on the essays or provided additional in- 
formation and, in some cases, clarified ambiguities 
or corrected errors in the original text. In this year's 
volume the text of the essays has been supple- 
mented by a number of illustrations, derived for the 
most part from general texts or scientific papers that 
are identified in the accompanying legends. We 
hope that these diagrams and photographs will make 
the essays even more useful. 
For readers who wish to know about specific 
research being conducted by HHMI investigators, 
we have provided once again a detailed index. 
The index lists almost every topic or term, from 
ahd-A (a gene that directs the segmental develop- 
ment of the abdomen — first identified in the fruit 
fly Drosophila melanogaster) to the zeppelin 
gene and, in between, the less arcane subjects of 
AIDS, cancer, cystic fibrosis, diabetes, hemo- 
philia, muscular dystrophy, and obesity. Several 
readers have remarked how useful the addition of 
an index has been, and we are grateful once more 
to Diana Witt for preparation of the index. 
As in previous years, the greater part of the vol- 
ume consists of a series of short reports by the 
investigators associated with the Institute during 
the past year. The fact that this volume is appre- 
ciably larger than its predecessor simply reflects 
the increased number of investigators whose 
work is represented, since each is limited to no 
more than two printed pages. The reports submit- 
ted by each investigator have been collated and 
edited by Dr. Claire H. Winestock, Senior Re- 
search Program Administrator; Elizabeth Cowley, 
Copy Editor; William T. Carrigan, Editor/Writer; 
Gail Markley, Manager of Publications; and Kim- 
berly A. Cornejo, Permissions Editor. We are 
grateful to them and to the many investigators 
who have provided us with suitable illustrations 
taken from their ongoing research. Not only do 
the illustrations help to clarify the written text, 
but they also greatly enhance the aesthetic appeal 
of the volume. 
Cell Biology and Regulation Program 
The Cell Biology and Regulation Program is the 
oldest of the Institute's research programs. Origi- 
nally referred to as Metabolic Regulation, which 
reflected the program's roots in clinical studies 
of metabolic and endocrine disorders, the title of 
this program was changed five years ago to reflect 
more accurately its principal theme — the biol- 
ogy of individual cells, the factors that regulate 
their normal growth and distinctive functions, 
and the ways in which cells interact with each 
other. In this sense the program has come to oc- 
cupy a critical position in the Institute's research 
endeavors, and it lies firmly within the main- 
stream of contemporary biological research. 
The human body contains several million mil- 
lion cells of a thousand or more distinct types. 
Research in the field of cell biology seeks to un- 
derstand how these various cells are constructed 
and organized, how they diff^er from one another, 
how they sense and respond to outside influ- 
XXV 
