A cross-species approach for the identification of
Drosophila
male sterility genes
Kimihide Ibaraki,
1,†
Mihoko Nakatsuka,
1,†
Takashi Ohsako,
2,†
Masahide Watanabe,
3,†
Yu Miyazaki,
1
Machi Shirakami,
1
Timothy L. Karr,
4
Rikako Sanuki,
3,5
Masatoshi Tomaru,
3,5
and Toshiyuki Takano-Shimizu-Kouno
3,5,
*
1
Applied Biology, Graduate School of Science and Technology, Kyoto Institute of Technology, Kyoto 606-8585, Japan
2
Advanced Technology Center, Kyoto Institute of Technology, Kyoto 606-8585, Japan
3
Department of Drosophila Genomics and Genetic Resources, Advanced Insect Research Promotion Center, Kyoto Institute of Technology, Kyoto 616-8354, Japan
4
Mass Spectroscopy Core Facility, Biodesign Institute, Arizona State University, Tempe, AZ 85257-7205, USA
5
Faculty of Applied Biology, Kyoto Institute of Technology, Kyoto 606-8585, Japan
†
These authors contributed equally to this work.
*Corresponding author: Email: fruitfly@kit.ac.jp
Abstract
Male reproduction encompasses many essential cellular processes and interactions. As a focal point for these events, sperm offer opportu-
nities for advancing our understanding of sexual reproduction at multiple levels during development. Using male sterility genes identified
in human, mouse, and fruit fly databases as a starting point, 103
Drosophila melanogaster
genes were screened for their association with
male sterility by tissue-specific RNAi knockdown and CRISPR/Cas9-mediated mutagenesis. This list included 56 genes associated with
male infertility in the human databases, but not found in the
Drosophila
database, resulting in the discovery of 63 new genes associated
with male fertility in
Drosophila
. The phenotypes identified were categorized into six distinct classes affecting sperm development.
Interestingly, the second largest class (Class VI) caused sterility despite apparently normal testis and sperm morphology suggesting that
these proteins may have functions in the mature sperm following spermatogenesis. We focused on one such gene,
Rack 1
, and found that
it plays an important role in two developmental periods, in early germline cells or germline stem cells and in spermatogenic cells or sperm.
Taken together, many genes are yet to be identified and their role in male reproduction, especially after ejaculation, remains to be eluci-
dated in
Drosophila
, where a wealth of data from human and other model organisms would be useful.
Keywords:
human male infertility; male sterility;
Rack1
; cross-species approach;
Drosophila
Introduction
Like many animals, male reproduction of
Drosophila
encompasses
many different cellular processes such as stem-cell division and
maintenance, spermatogonial mitotic divisions, mitosis-to-meio-
sis transition, mitochondrial transformation, compaction of
sperm chromatin, spermatid elongation, maturation, and storage
(
). Moreover, ejaculated sperm and seminal fluid pro-
teins combine and mix during copulation, travel to the female re-
productive tract, and are stored in the specialized storage organs,
a seminal receptacle, and paired spermathecae. Sperm storage
and utilization are highly efficient processes with approximately
500 sperm in storage (
); the majority (
300) were
used within a week under normal laboratory conditions
(
;
).
Sperm competition is also well documented in
Drosophila
and
many other species (
;
) in cases where sperm from different males are
present (
;
;
). Thus, male reproduction encom-
passes interactions at many different levels including (i) protein,
e.g.
, sperm-by-seminal fluid proteins (
) and
paternal-by-maternal molecular interactions (
);
and (ii) cellular,
e.g.
, sperm-by-egg (
;
;
), stem cell-by-sper-
matogonia (
), niche-by-stem cell
(
;
), and germ cell-by-somatic cyst cell (
); (iii) tissue and organ levels,
e.g.
, sperm-by-fe-
male reproductive tract (
), and sperm-by-
sperm (sperm competition) interactions. As a focal point for these
events, a molecular genetic study of sperm offers unique oppor-
tunities for advancing our understanding of sexual reproduction
at multiple levels during development.
Despite such an important model system, male reproduction
seems to be less studied and less well characterized. An indica-
tion of this comes from a database study of human and model
organisms. The human disease databases, the Online Mendelian
Inheritance in Man (OMIM, https://www.ncbi.nlm.nih.gov/omim
)
and GeneCards (https://www.genecards.org), together with list
more than 1000 genes that are associated with male infertility.
However, many of their orthologs are not found in male infertility
or sterility gene lists extracted from the mouse and fly databases
Received:
April 07, 2021.
Accepted:
May 13, 2021
V
C
The Author(s) 2021. Published by Oxford University Press on behalf of Genetics Society of America.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which
permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
2
G3
, 2021,
11(8),
jkab183
DOI: 10.1093/g3journal/jkab183
Advance Access Publication Date: 29 May 2021
Mutant Screen Report
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